Update (8/28/22):
I wrote an abstract of this hypothesis and posted it to Academia:
https://www.academia.edu/96574784/Nanotyrannus_is_Dryptosaurus_An_Abstract
Update (1/25/23):
I wrote a paper on the baby T. rex tooth UCMP 119853, and the baby cf. Dryptosaurus aquilinguis tooth UCMP 124406:
https://www.academia.edu/96575022/A_Baby_Tyrannosaurus_rex_Premaxillary_or_First_Maxillary_Tooth
Update (8/11/23):
I wrote a description of the baby T. rex specimen BHI 6439:
https://www.academia.edu/105502160/A_Description_of_the_Baby_T_rex_Specimen_BHI_6439
Update (10/24/23-1/16/24):
Longrich and Saitta (2024) said that Nanotyrannus was a tyrannosauroid, just like Dryptosaurus:
https://www.mdpi.com/2813-6284/2/1/1
2023 Preprint:
https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs
Nanotyrannus (Jurassic Fight Club):
I have been flip-flopping between my opinions on Nanotyrannus as of late. I wanted to keep it as a juvenile T. rex, but then I wanted to give the genus a chance by studying its bones. Not too long ago, I fell back into my original opinion that Nanotyrannus is just a juvenile T. rex. However, some clues came to light that made me rethink my original stance. These clues have been hiding in plane sight the whole time, and one of them was in the most unlikeliest of places.
My History with Nanotyrannus:
Growing up, I've known about Nanotyrannus but I didn't know too much about it. I saw it as being a separate genus from T. rex for the most part, thanks to Jurassic Fight Club. Later on, I saw another documentary, called The Mystery Dinosaur, that talked about the discovery of BMRP 2002.4.1 ("Jane"). There were two teams of scientists: One said that "Jane" was a Nanotyrannus, and the other said a juvenile T. rex. The team that favored the juvenile T. rex hypothesis won, and "Jane" was categorized as a juvenile T. rex. I was oblivious to Nanotyrannus for a long time, and I didn't care about what it was. All I knew was that it was a tyrannosauroid, however which way you'd look at it.
Now, after some years have passed by and I've grown up, I've started examining dinosaur fossils on my own (mainly theropoda). I've even started to categorize them with my very own system. I decided to check out Nanotyrannus for myself a little while ago, and I can honestly say that Nanotyrannus has thrown a monkey wrench into my categorizing system for theropoda! It has led me to a radical new conclusion on how I categorize tyrannosauroid genera, but I have learned a lot.
This has been a rather exhaustive journey, so I've come to this conclusion: Whether or not
Nanotyrannus is a juvenile T. rex, I don't care. I think we should, at least, feel free to investigate any topic in paleontology to see if we can come to an answer on our own. I'm still investigating this topic, but as of right now, I'm split. I'm going to study T. rex ontogeny later on, and as of right now, all
Nanotyrannus specimens seem to fall within Dryptosaurus' growth curve and not T. rex's. Granted, some private specimens help to prove this, so I know that this is not going to help sway a lot of people. My opinion on this may change in the future, but I want to come to this conclusion on my own without being pressured into choose a side.
Now, enjoy the post!
Nanotyrannus in full view (Jurassic Fight Club):
What is Nanotyrannus?
Let's take a look at how Nanotyrannus came to be named. Gilmore (1946) named "Gorgosaurus lancencsis" based on the skull, CMNH 7541 (p. 2). Then, Bakker et al., (1988) changed the name to Nanotyrannus lancensis (p. 2). In between 1946 and 1988, Russell (1970) says that Gorgosaurus is actually Albertosaurus (p. 4). CMNH 7541 was then changed to "Albertosaurus lancensis" (Carpenter, 1992, pp. 258-260). Interestingly, there were two names given to this one specimen. However, Carpenter (1992) started to shake things up when he said that CMNH had features similar to T. rex, and that it was not fully grown. This led him to suggest that CMNH was a juvenile T. rex (p. 260). Now here comes the shot that was heard around the world! Carr (1999) also concluded that CMNH 7541 was a juvenile T. rex (pp. 508-509). In 2020, Carr gave an age of 8 for the specimen (Carr, 2020, Figure 2 and 12). Erickson et al., (2006) originally gave this age (Supplementary Materials, p. 13). Despite being an immature individual, some scientists still call CMNH 7541 Nanotyrannus (Currie, 2003, pp. 223-225) (Currie et al., 2003, pp. 229) (Larson, 2013, "Abstract") (Dalman et al., 2018, p. 135 Figure 15), but most scientists call Nanotyrannus a juvenile T. rex (Yun, 2015) (Woodward et al., 2020, "Abstract," "Implications for the Nanotyrannus hypothesis") (Carr, 2020, Figures 2 and 12).
CMNH 7541's Skull (Dalman et al., 2018, p. 135 Figure 15):
That was just the holotype. Now, let's talk about BMRP 2002.4.1. This specimen, also known as "Jane," was considered to be a second specimen of Nanotyrannus (Larson, 2013, "Abstract"). However, the majority of scientists put "Jane" as a juvenile T. rex (Yun, 2015) (Woodward et al., 2020, "Abstract," "Implications for the Nanotyrannus hypothesis") (Carr, 2020, Figures 2 and 12). An age of 11-13 years was given to "Jane" (Erickson et al., 2006, Supplementary Materials, p. 13) (Woodward et al., 2020, "Abstract," "Implications for the Nanotyrannus hypothesis") (Carr, 2020, Figure 2 and 12).
BMRP 2002.4.1's ("Jane's") Skeleton (Hope Babowice, 2017):
My original title for this post was "Evidence of a Subadult Nanotyrannus!?," which was based on a specimen that was discussed in a conference paper by Griffin (2014). In his paper, Griffin states that this specimen of Nanotyrannus (nicknamed “Zuri” on SWAU) shows signs of being older than a juvenile. After examining cross-sections of the specimen’s ribs, pubis, and tibia, there are signs of extensive Haversian remodeling, "longitudinal vascularization and decrease in vascularization in subperiosteal zones," and "a shift from woven to parallel-fibered bone matrix in outer growth zones." There was no sign of a external fundamental system (EFS), which signifies that the specimen has stopped growing (Stated in Stein et al., 2010, Discussion: Potential Problems: Lack of EFS), but what was present in "Zuri's" bones signified that it is not a juvenile. Griffin says that this proves that Nanotyrannus is a valid taxon (Abstract).
Griffin (2014)'s Abstract:
Nanotyrannus "Zuri's' cross-sections showing Haversian remodeling, secondary remodeled bone, and other features described above (Griffin, 2014, Figures 3-6):
"Zuri's" Rib (SWAU, HRS08467):
I’ve never heard of Haversian remodeling before this, so I went on an extensive search to find out what it is. As mentioned above, Haversian remodeling does signify that the individual is either close to maturity, or is mature and even old. This is seen in apes (Lad, 2018, p. 14 Abstract), humans (Nyssen-Behets et al., 1997, Abstract), and a new titanosaur from Bulgaria (Nikolov et al., 2020). In fact, Haversian remodeling was used to help validate another pygmy dinosaur: Magyarosaurus, a dwarf titanosaur (Stein et al., 2010). It seems that Haversian remodeling might help prove that “Zuri” is a subadult Nanotyrannus. EFS was not found in “Zuri,” or Magyarosaurus, but Stein et al., (2010) said that Haversian remodeling could have gotten rid of any evidence of an EFS barrier being present (Discussion: Potential Problems: Lack of EFS). This is interesting because the Magyarosaurus specimens were around 12-14 years old (Results: Histologic Ontogenetic Stages in the M. dacus Sample, para. 1). Haversian remodeling can also remove growth rings (LAGs) from cross-sections of bones (Griffin et al., 2014, Abstract). Griffin (2014) says that “Zuri” was 12-13 when it died, but more than likely it was 13 based on the number of growth rings seen in a section of its pubis (Figure 3). This is the same age as “Jane” (Carr, 2020, Figure 12).
However, after talking to Professor Holtz, I've realized that no EFS period means that the specimen is young:
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Conversation with Dr. Griffin (10/11/21):
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1. BMRP 2006.4.4 ("Petey"):
Woodward et al., (2020) gave this specimen an age of 15 (Results, para. 4; Discussion: Ontogenetic age, para. 1-3), based on a cross-section of its femur. Carr (2020) considers this specimen to be a subadult, and a female (Figure 12 Number 7). Professor Holtz also said that "Petey" was a subadult (Photo provided by Luke Skywalker Jedi Knight 27):
I was able to find a couple of pictures of "Petey's" manual unguals (hand claws) from Peter Larson's Twitter account. LACM 23845, a 14-16-year old specimen of T. rex (Erickson et al., 2006, Supplementary Materials, p. 13) (Carr, 2020, Figure 12 Number 8), has manual bones that are the same size as juvenile
Gorgosaurus' (Molnar, 1980, pp. 105-106), and are "quite short relative to hind limb" (Olshevsky, 1995, p. 4). The claw, although incomplete, would still seem to have been smaller than "Petey's." (Los Angeles Natural History Museum). Another young T. rex specimen, UCRC-PV1 (or UCRC PV1), has both manual unguals that are extremely short compared to "Petey's." Larson also says that UCRC is a subadult (Photo from Peter Larson's Twitter account). I also received this picture from Sebastian Dalman.
"Petey's" (white), and T. rex ("Sue" on top left, "Darwin" on top right), claw casts (Pete Larson's Twitter account):
Recently, in an abstract from Jevnikar et al., (2021) (SVP abstract) (p. 151), "Petey" falls outside of T. rex's growth curve:
2. BHI 6437 ("Bloody Mary"):
BHI 6437, also known as the "Dueling Dinosaurs tyrannosauroid" (Raphael Rosen, 2014). No papers on this specimen have been published yet, so there's not too much to say about it. Larson said that the name of the specimen is BHI 6437 on Twitter.
BHI 6437/"Dueling Dinosaurs tyrannosauroid" Specimen (Bonhams):
BHI 6437 was stated by Carr, on his blog, to be a subadult (to my surprise) (Tyrannosauroidea central: Tyrannoethics: The naturalist T. rex and the and the T. rex list of shame, updated, 2015):
Nanotyrannus BHI 6437 (bottom) and T. rex "Wyrex" arm bones (Alexander Jack Lund's Twitter post). Original drawing is by GetAwayTrike (Holtz, pers. comm.):
Professor Holtz saying that "Bloody Mary's" arm is complete, and he explains what the above drawing originally meant (Photos provided by Luke Skywalker Jedi Knight 27):
Now that we got that controversy cleared up, I must say that, on a first glance, BHI 6437's manual unguals are larger than T. rex's, but I'll discuss that down below. My question is that, if we have two possible subadult specimens of Nanotyrannus, then why are they called juvenile T. rex specimens? I remember learning that juvenile dinosaurs looked different from the adults, and for a long time I accepted that as an answer. However, I now realized that that explanation may work for some dinosaurs, but not all of them.
Gilmore (1946) (PP. 2, 7, 16, and 21):
https://repository.si.edu/bitstream/handle/10088/22800/SMC_106_Gilmore_1946_13_1-19.pdf?sequence=1&isAllowed=y
Bakker et al., (1988) (PP. 2, 8-9 Table 1):
https://zenodo.org/record/1037529#.X9Ai5CVOmEf
Russell (1970) (PP. 4, 5, 7, 13-14, 15-16, and 17):
https://www.biodiversitylibrary.org/page/36032001#page/26/mode/1up
Carpenter (1992) (PP. 254-256, 258-260):
https://www.researchgate.net/profile/Kenneth_Carpenter3/publication/314988830_Tyrannosaurids_Dinosauria_of_Asia_and_North_America/links/58c8026ea6fdcca657f63102/Tyrannosaurids-Dinosauria-of-Asia-and-North-America.pdf?origin=publication_detail
Link 2:
https://www.researchgate.net/publication/314988830_Tyrannosaurids_Dinosauria_of_Asia_and_North_America
Carr (1999) (PP. 508-509, pg. 514 and 516 Table 2):
https://zenodo.org/record/3372241#.X7K6PyVOmEc
Link 2:
https://core.ac.uk/download/pdf/227005733.pdf
Carr (2020) (Figures 2 and 12):
https://peerj.com/articles/9192/
Erickson et al., (2006) (Supplementary Materials) (PP. 13-14):
http://science.sciencemag.org/content/sci/suppl/2006/07/11/313.5784.213.DC1/Erickson.SOM.pdf
Currie (2003) (Pg. 223-225):
https://www.app.pan.pl/archive/published/app48/app48-191.pdf
Currie et al., (2003) (Pg. 229):
https://www.researchgate.net/publication/40662064_Skull_structure_and_evolution_in_tyrannosaurid_dinosaurs
Larson (2013) ("Abstract"):
https://www.researchgate.net/publication/289687970_The_case_for_Nanotyrannus
Dalman et al., (2018) (Pg. 135 Figure 15):
https://www.researchgate.net/publication/328676947_TYRANNOSAURID_TEETH_FROM_THE_UPPER_CRETACEOUS_CAMPANIAN_TWO_MEDICINE_FORMATION_OF_MONTANA
Yun (2015) (Pg. 5):
https://www.researchgate.net/publication/308710995_Evidence_points_out_that_Nanotyrannus_is_a_juvenile_Tyrannosaurus_rex
Woodward et al., (2020) ("Abstract," "Implications for the Nanotyrannus hypothesis"):
https://advances.sciencemag.org/content/6/1/eaax6250
Abstract:
https://www.semanticscholar.org/paper/Using-Osteohistology-to-Determine-the-Taxonomic-of-Griffin/149cadc7cd0f9aa4b55d77810a818ab59b040417
Full:
https://digitalcommons.cedarville.edu/cgi/viewcontent.cgi?article=1136&context=research_scholarship_symposium
Pubis (HRS01514):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS01514
Rib (HRS08467):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08467
Tibia (HRS08421):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08421
CMNH 7541 Skull:
Dalman et al., (2018) (Pg. 135 Figure 15 D):
https://www.researchgate.net/publication/328676947_TYRANNOSAURID_TEETH_FROM_THE_UPPER_CRETACEOUS_CAMPANIAN_TWO_MEDICINE_FORMATION_OF_MONTANA
BMRP ("Jane") Skeleton:
Hope Babowice (2017):
https://www.dailyherald.com/submitted/20170619/t-rex-was-the-king-of-chomp
https://www.bonhams.com/auctions/21076/lot/1032/
Photo:
BHI 6437 Specimen Name:
Larson's Twitter:
https://mobile.twitter.com/PeteLarsonTrex/status/762721220701847552
Ages of Subadult Nanotyrannus Specimens:
"Petey":
Jevnikar et al., (2021) (SVP, 2021 abstract):
https://vertpaleo.org/wp-content/uploads/2021/10/SVP_2021_VirtualBook_final.pdf
Carr (2020) (Figure 12 Number 7):
https://peerj.com/articles/9192/
Woodward et al., (2020) ("Abstract," "Implications for the Nanotyrannus hypothesis"):
https://advances.sciencemag.org/content/6/1/eaax6250
BHI 6437:
Carr, Thomas. Tyrannosauroidea central. Tyrannoethics: The naturalist T. rex and the and the T. rex list of shame, updated. 2015:
https://tyrannosauroideacentral.blogspot.com/2015/02/tyrannoethics-4-naturalis-t-rex-t-rex.html
Unguals:
T. rex and Nanotyrannus Unguals from Peter Larson's Twitter post:
"Petey's" Manual Unguals:
https://mobile.twitter.com/PeteLarsonTrex/status/973337486528274432
"Petey's" Manual Ungual 2:
https://twitter.com/PeteLarsonTrex/status/770673307729457152
Drawing of BHI 6437's arm:
Fran Vidakovic's Twitter post:
https://twitter.com/Goji1999/status/1212775954667450373
BHI 6437's arm:
Pantuso (2019):
Pic:
https://images.app.goo.gl/JkCKufmnA9w5pTEH9
Article:
https://www.theguardian.com/science/2019/jul/17/montana-fossilized-dueling-dinosaurs-skeletons-dino-cowboy
Actual juvenile T. rex specimens not similar to Nanotyrannus?
My cohort Luke Skywalker Jedi Knight 27 showed me pics from Twitter concerning Paleontologist Michael Deak arguing with Dr. Carr about Carr pretending not to know about an actual juvenile T. rex specimen. I later found out that this specimen was BHI 6439. I saw the messages on Twitter myself. I talked to Dalman about it, and he believes that Carr is lying about not seeing the specimen too. I actually got into contact with Deak himself, and he says that he knows eyewitnesses who remember seeing Carr check out BHI 6439, and Carr was dumbfounded by what he saw. Interesting...
If this is true, then in all honesty, there are juvenile T. rex specimens that are morphologically distinct from Nanotyrannus. Other juvenile T. rex specimens are either privately owned ("Baby Bob"), or haven't been described yet (UCRC-PV 1; Larson says it's a subadult but I might disagree). With this in mind, I know now why most tyrannosauroid Paleontologist place Nanotyrannus into T. rex. You cannot compare the Nanotyrannus specimens to other specimens that are privately owned, or haven't been described in a paper, because you cannot fact-check what someone says about a particular specimen. Someone needs to describe the actual juvenile specimens of T. rex and compare them to the Nanotyrannus specimens!
Well, since I am able to obtain some information regarding those specimens, I decided to check them out for myself and compare them to Nanotyrannus.
Exploring Possible Nanotyrannus' Traits.
Here's a list of traits that I have been told that Nanotyrannus possesses, and ones that I've observed myself. The ones that I think are the most important are marked with an asterisk ("*") next to them.
**1. Bone count in the skeleton:
Cervicals: 7-8.
Gastralia: 14 (at best).
Chevrons/Haemal arches: 13 (visible).
BHI 6437's gastralia (Bonhams, Dueling Dinosaurs):
Another pic (Photo given to me by Luke Skywalker Jedi Knight 27):
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As for the cervicals and caudals, I had to use the replica of the specimen. It's also from Bonham's website, but I found close ups of the vertebrae from news articles.
"Dueling Dinosaurs" replica (Bonhams, Dueling Dinosaurs):
Replica from Pantuso (2019):
Caudals:
Part 1 (Number 1-7):
Chevrons:
Count: 13 (visible) (Chevrons are on the bottom of the caudal vertebrae. The 7th one is covered up by the ceratopsian's tail, but the tip is showing).
Cervicals: 8 (at best).
Caudal count:
Part 1: Numbers 1-6:
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BHI 6437's ACUTAL caudals from a BHI YouTube video:
Pic 1: 6 caudals that seem to be from the anterior:
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Now, here's an interesting piece of info. that I learned about Dryptosaurus' caudals: Brusatte et al., (2011) described Dryptosaurus' caudals towards the distal to the end (middle of the tail to the tip) are elongated (p. 18). This is seen in the pics of BHI 6437's tail, specifically in pics 2-4. Cope (1869) said that the Dryptosaurus holotype would have had about 25 caudals in its tail (p. 102):
%20on%20dryptosaurus'%20caudal%20vertebrae%20(p.%20102).png)
Both "Jane" and BHI 6437 seem to have a similar caudal, and chevron, count. I have some pictures of "Jane's" skeleton, which I think come from Dr. Carr's blog but I'm still looking for the links to some of them. The caudals definitely came from his blog.
Chevrons/Haemal arches (Tyrannosauroidea central, The Jane Diaries, Entry #25) (Check Brochu, 2003, pp. 76-80):
Gastrula (Tyrannosauroidea central, The Jane Diaries, Entry #21) (Check Brochu, 2003, p. 83):
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1. FMNH PR 2081 ("Sue"):
Dorsals: 12 (11 + 12 = 23 presacral vertebrae) (pp. 60-61, Figures 57-58).
Dorsal ribs: 10 (p. 74).
Caudal: 40-45 (36 were preserved, and 47 are in the reconstruction) (pp. 49 and 90).
Chevrons or Haemal Arches: 27 (preserved) (p. 90).
Cervical: 9 (Osborn, 1917, p. 765).
Dorsal: 14 (Osborn, 1917, p. 765).
Sacrum: 5 (Osborn, 1906, p. 289).
3. AMNH 5027:
Cervical: 11 (Carpenter, 1991, p. 144 Figure 10.4) (Brochu, 2003, p. 48).
Thoracic/Dorsal: 12 (11 + 12 = 23 total presacral vertebrae) (Osborn, 1917, p. 765).
Sacral: 5 (Osborn, 1917, p. 763).
4. BHI 3033 ("Stan"):
Neal Larson (2008a; in Larson and Carpenter, 2008) (P. 21):
Cervicals: 9.
Dorsals: 14.
Sacrals: 5.
5. MOR 555/USNM 555000:
Cervicals: 9 (Brochu, 2003, p. 48; "11" is for AMNH 5027).
6. BMNH R7994 (Originally 5866):
Cervicals: 11 (Osborn, 1906, pp. 282, 287-288) (Carpenter, 1991, p. 144 Figure 10.4, A).
Dorsals: 12 (12-23; 11 + 12 = 23 presacral vertebrae) (Osborn, 1906, p. 282, 287-288) (Osborn, 1917, p. 765).
Extra notes:
1. Pre-sacral (cervicals to dorsals) for T. rex in total: 23 (Osborn, 1917, p. 765).
2. Transition from cervical to dorsal for AMNH 5027 and MOR 555/USNM 555000: Cervical 9 or 11 (Brochu, 2003, p. 48).
Total bone count:
T. rex:
*Cervicals: 11 (at most).
Dorsals: 14 (at most).
Pre-sacral vertebrae (cervical to dorsal): 23
Dorsal Ribs: 11.
Gastrula: 18.
Sacrum: 5.
*Caudal: 40-45 (maybe 47?).
*Chevrons/Haemal Arches: 27 (preserved in "Sue").
Note: Asterisks indicate what bone count is different from Nanotyrannus'.
Nanotyrannus:
Cervicals: 8.
Caudals: Up to about 25 or so, like Dryptosaurus.
Chevrons/Haemal arches: 17.
T. rex has about 3 more cervical, about 20 more (or so) caudal vertebrae, and 10 more chevrons/haemal arches, than Nanotyrannus. The caudal count is the same in Nanotyrannus and Dryptosaurus. The caudal vertebrae count is very telling. Maleev (1955b) stated that the juvenile Tarbosaurus specimen PIN 552-2 has 40-45 caudal vertebrae (p. 4), just like the larger specimen PIN 552-1 (Maleev, 1974, pp. 13 and 29). This means that juvenile tyrannosaurs, in particular tyrannosaurine, didn't increase in caudal count during ontogeny. Using Tarbosaurus as an example, juvenile T. rex specimens would have likely had a similar caudal count to the adults.
Maleev (1955b) on juvenile Tarbosaurus specimen PIN 552-2's caudal vertebrae count (p. 4):
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Tarbosaurus specimen PIN 552-1 cauldal count from Maleev (1974):
P. 13:
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P. 29:
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Tarbosaurus:
1. PIN 552-1:
Cervical: 9 (Maleev, 1974, p. 26).
Dorsal Ribs: 11 (Maleev, 1974, pp. 31).
Sacral: 5 (Maleev, 1974, p. 28).
Caudal: 35-45 or *40-45 (Maleev, 1974, pp. 12 and 29) (Brochu, 2003, p. 90).
2. PIN 552-2 (Juvenile):
Caudal: 40-45 (Maleev, 1955b, p. 4).
Daspletosaurus:
1. NMC 8506:
Cervical: 10 (Russell, 1970, p. 26).
Dorsal: 13 (Russell, 1970, p. 26).
Dorsal ribs: 12 (Russell, 1970, p. 25).
Caudal: 37+ (Most are reconstructed, and end of tail is not complete) (Russell, 1970, pp. 15-16).
Gorgosaurus:
1. Holotype:
Cervical: 7 (preserved), but maybe 9 in total (Lambe, 1917, p. 22); 10 (Russell, 1970, p. 23).
Dorsal: 22 (Lambe, 1917, p. 23).
Ribs: 11 (Lambe, 1917, p. 37).
Gastralia: 17 (preserved), but 19 were used in reconstruction (Brochu, 2003, p. 91).
Sacrum: 5 (Lambe, 1917, p. 27).
Caudal: 31 (preserved), but estimated to have 36 when complete (Lambe, 1917, p. 28).
Total:
Cervicals: 9 or 10.
Dorsals: 22.
Ribs: 11.
Gastralia: 17. Maybe 19.
Sacrum: 5.
Caudal: 36.
As for Nanotyrannus being an albertosaurine, Gorgosaurus has 3 (maybe 5) more gastralia, and 11 more caudal vertebrae, than Nanotyrannus, which is more of an incentive for me not to place it in the albertosaurine. Bone count doesn't seem to increase or decrease during ontogeny, as indicated by the juvenile and older specimens of Tarbosaurus. Since Dryptosaurus' tail morphology is distinctive from T. rex's, but similar to BHI 6437's and probably "Jane's," perhaps this would place Nanotyrannus as a juvenile, and maybe even subadult, Dryptosaurus?
Skull:
**2. Deep maxillary strut with the maxillary fenestra closer to the antorbital fenestra.
Nanotyrannus has a deep, and wide, maxillary strut on the maxilla (Dalman and Lucas, 2018, GSA
Abstract). Simply put, the inside of maxilla has a ridge, and the interior of the ridge, the antorbital fossa (Hurum and Sabath, 2003, Figure 4), is deep/concave. The maxillary fenestra (small hole) is located inside the antorbital fossa. For Nanotyrannus, the fenestra is positioned further into the antorbital fossa, closer to the antorbital fenestra (the largest hole in the maxilla). This is present in CMNH 7541 (Dalman et al., 2018, Figure 15 D), "Jane" (Peterson, 2019, Figure 6), "Zuri" (SWAU, HRS08438), and BHI 6347 (Bonhams, Dueling dinosaurs). This also appears to be true in Appalachiosaurus (Carr et al., 2005, p. 124), and Jinbeisaurus (Wu et al., 2019, pp. 3-4).
T. rex’s maxillary strut is not as deep when it is young, but it grows larger during ontogeny (Dalman and Lucas, 2018, GSA Abstract). This is seen in the young juvenile specimen RSM P2347 (pers. obs. the pic from Holtz's Twitter page), and the 26-year old CM 9380 (Hendrickx and Mateus, 2014, Figure 2 A-B) (Carr, 2020, Figure 16 Number 25). The maxillary fenestra is positioned closer to the beginning of the maxillary strut, unlike in Nanotyrannus, Appalachiosaurus, or Jinbeisaurus. Megaraptor seems to have a deep maxillary strut, but its maxillary fenestra is closer to the beginning of the strut (Porfiri et al., 2014, p. 41 Figure 5).
Delcourt (2017), using Carr (1999) as a source, said that a small maxilla belonging to Daspletosaurus was a subadult because it has a maxillary fenestra far away from the antorbital fenestra because of its age (Abstract). This likely means that when the specimen was younger, the maxillary fenestra was closer to the antorbital fenestra and changed positions when it grew older. However, this is not seen in Daspletosaurus horneri. Three specimens in different ontological stages had the maxillary fenestra closer to the maxillary strut than the antorbital fossa (Carr et al., 2017, Figures 1 and 3). It seems that Daspletosaurus' maxillary fenestra was in the same position as Tarbosaurus' and Tyrannosaurus'.
Voris (2018) studied the ontogeny of Gorgosaurus. On pp. 80 and 83, we can see that the maxillary fenestra stayed closer to the antorbital fossa rather than the maxillary strut. This is seen in baby, juvenile, subadult, and adult specimens. This leads me to believe that Daspletosaurus' maxillary fenestra probably stayed closer to the maxillary strut rather than change positions during ontogeny, similar to T. rex's. Nanotyrannus' maxillary fenestra probably didn't change position either, especially since we have RSM P2347.1.
Albertosaurus' maxillary fenestra was in the same position as Gorgosaurus' (Paleofile, "Albertosaurus") (Bell and Currie, 2014, Figure 2), and a juvenile specimen has its maxillary fenestra in the same position as well (Currie, 2003, p. 195 Figure 3). It doesn't seem that the maxillary fenestra changed locations during ontogeny in Albertosaurus or Gorgosaurus.
Baby Tarbosaurus specimen MPC-D 107/7's maxillary fenestra was closer to the maxillary strut (Tsuihiji et al., 2011, pp. 499 and 505), and the larger specimen ZPAL MgD-I/4's maxillary fenestra is in the same position (Hurum and Sabath, 2003, p. 165 Figure 1). Currie (2003) also shows this in three Tarbosaurus specimens of different ages (p. 195 Figure 3). It seems that Tarbosaurus' maxillary fenestra stayed close to the maxillary strut throughout its lifetime. This is stated in Tsuihiji et al., (2011) (p. 11). This is also seen in baby T. rex specimens shown below.
Yun (2015) said that young tyrannosaurs had small maxillary fenestrae, and he used Currie (2003) as a source (p. 4). Currie (2003) does say this on p. 195, but he also stated on that same page that the maxillary fenestra does not change position in Gorgosaurus' antorbital fossa. Also, as I will show below, Currie (2003) does not actually show a change in size (from small to large) in the maxillary fenestra. As I've already shown above, maxillary fenestrae differs in size for different genera, but they stay either large or small throughout the animals' lives. Also, as stated before, Tsuihiji et al., (2011) said that the maxillary fenestra doesn't change shape (small to large).
Alioramus altai's maxillary fenestra is closer to the antorbital fenestra as well, but interestingly, the fenestra is pretty large for a tyrannosauroid (Brusatte et al., 2009, p. 17262 Figure 1). Still, based on its location inside the antorbital fossa, this is definitely a tyrannosauroid characteristic rather than a tyrannosaurinae one.
There are a couple of exceptions to this rule. For the tyrannosauroids, Qiazhousaurus (or Alioramus sinensis) has a large maxillary fenestra near the maxillary strut rather than the antorbital fenestra (Lu et al., 2014, Figure 1). One Alioramus remotus skull from Bonhams shows the maxillary fenestra closer to the strut. Alioramus' maxillary fenestra may have been placed in different positions in individual specimens or species, but it was still large regardless. As for the tyrannosaurinae, both Lythronax and Teratophoneus have small maxillary fenestrae located near the antorbital fenestrae, but Lythronax has a premaxillary fenestra which made the maxillary fenestra farther back in position (Loewen et al., 2013, Figures 2 and 3; 6). This can also be seen in T. rex specimen "Sue's" maxilla (Brochu, 2003, p. 11 Figure 3; p. 16 Figure 8). Lythronax and Teratophoneus have lighter maxillary struts compared to Qiazhousaurus (Alioramus sinesis), which seems to be a classic tyrannosaurine trait. Tarbosaurus also has this (Hurum and Sabath, 2003, Figure 4).
In conclusion, the maxillary fenestrae in T. rex's, Tarbosaurus', and Daspletosaurus', antorbital fossa stayed near the maxillary strut, contra Nanotyrannus', Appalachiosaurus', Jinbeisaurus', Gorgosaurus', and Albertosaurus' maxillary fenestrae being near the antorbital fossa. Larson (2013) says that the maxillary fenestra for Nanotyrannus stayed in the center of the antorbital fossa (p. 26). The maxillary fenestra also doesn't change shape during ontogeny.
Baby T. rex RSM P2347.1's Maxilla (Holtz's Twitter page) (Scale bar is 10 cm):
Large maxillary fenestra right on the maxillary strut/antorbital fossa.
14-year old juvenile T. rex "Tinker" skull (Christies):
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T. rex "Duffy" (subadult or juvenile) skull (right side) (BHIGR):
Subadult T. rex specimen TMM 41436-1's maxilla (Wick, 2014, Figure 1) (Scale bar is 10 cm):
Adult T. rex CM 9380 (26 years old) maxilla (Hendrickx and Mateus, 2014, Figure 2) (Scale bar is 5 cm):
Maxilla pic. from Michael Deak's Twitter post:
Notice how the maxillary fenestra is closer to the maxillary strut/antorbital fossa, just like in the baby, and juvenile, T. rex specimens listed above.
Baby Tarbosaurus specimen MPC-D 107/7's skull (Tsuihiji et al., 2011, pp. 499):
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Maxilla (Tsuihiji et al., 2011, p. 505):
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Growth stage of Tarbosaurus (Credit goes to Ville Sinkkonen. Photo was presented by Holtz on 2/16/21):
Notice that the maxillary fenestra stays near the antorbital fossa all throughout ontogeny.
Daspletosaurus horneri holotype skull (Carr et al., 2017, Figure 1 A) (Scale bar is 10 cm):
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Daspletosaurus horneri growth stage (Carr et al., 2017, Figure 3):
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Maxillary fenestra stays near the maxillary strut/antorbital fossa throughout ontogeny, just like T. rex's and Tarbosaurus'.
Nanotyrannus CMNH 7541's Skull (Dalman et al., 2018, p. 135 Figure 15):
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BHI 6437's (Subadult) Skull (Bonhams, Dueling dinosaurs):
Appalachiosaurus' maxilla (Carr et al., 2005, p. 124):
Jinbeisaurus' maxilla (Wu et al., 2019, p. 4 Figure 3 A-D):
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Gorgosaurus' ontogeny chart (Voris, 2018, p. 80):
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Multiple Gorgosaurus maxillas from different ontogenetic stages (Voris et al., 2022, Figure 3):
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Albertosaurus skulls from Paleofile:
NMC 5600 (Holotype):
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In all five of these genera, the maxillary fenestra is farther away from the maxillary strut and closer to the antorbital fenestra.
Maxillary fenestrae positions in several tyrannosaurid genera (Currie, 2003, p. 195 Figure 3):
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Megaraptor's maxilla (Porfiri et al., 2014, p. 41 Figure 5):
Megaraptor has a deep maxillary strut, but the maxillary fenestra is closer to the beginning of the strut.
Alioramus altai Holotype Skull (Brusatte et al., 2009, pg. 17262 Figure 1):
Alioramus (or Qianzhousaurus) sinensis Holotype Skull (Lu et al., 2014, Figure 1):
The maxillary strut is deep, but the maxillary fenestra is close to the maxillary strut.
Larger Alioramus remotus skull (Bonhams):
Right side:
Left side:
Lythronax's maxilla (Loewen et al., 2013, Figure 2):
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Teratophoneus' maxilla (Loewen et al., 2013, Figure 3):
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This individual was a subadult too (Loewen et al., 2013, Results). Just like Lythronax, the maxillary strut is light, but the maxillary fenestra is small and closer to the antorbital fossa.
**3. Maxillary strut tips down, and triangular, at the front of the maxilla.
The maxillary strut, at the front, dips down, forming a triangular-shaped body near the beginning of the maxilla. This can be seen in all Nanotyrannus specimens with a maxilla. This can also be seen in Gorgosaurus, Albertosaurus, Jinbeisaurus, and Alioramus. T. rex and Tarbosaurus did not have this feature in their struts. In fact, their struts are so straight that you could draw a straight line through it and cut it in half. The front of the struts in those two species are also circular.
Nanotyrannus CMNH 7541's Skull (Dalman et al., 2018, p. 135 Figure 15):
"Jane's" Maxilla (Peterson, 2019, Figure 6) (Scale bars are 10 cm):
BHI 6437's (Subadult) Skull (Bonhams, Dueling dinosaurs):
Juvenile (A) and adult (B) Gorgosaurus maxillae (Voris, 2018, p. 83):
Multiple Gorgosaurus maxillas from different ontogenetic stages (Voris et al., 2022, Figure 3):
Albertosaurus skulls from Paleofile:
NMC 5600 (Holotype):
NMC 5601 (Paratype):
RTMP 1981.10.1:
Albertosaurus specimen TMP 1989.17.53's maxilla (Bell and Currie, 2014, Figure 2):
Jinbeisaurus' maxilla (Wu et al., 2019, p. 4 Figure 3 A-D):
Alioramus altai Holotype Skull (Brusatte et al., 2009, pg. 17262 Figure 1):
Alioramus (or Qianzhousaurus) sinensis Holotype Skull (Lu et al., 2014, Figure 1):
The triangular-shaped, and down-sloping, beginning of the maxillary strut seems to stay the same throughout Gorgosaurus' ontogeny, and is present in the baby Alioramus altai's, and the supposed adult Qiazhousaurus/Alioramus sinensis', maxillary struts as well. This is not an ontogenetic change.
Baby T. rex RSM P2347.1's Maxilla (Holtz's Twitter page) (Scale bar is 10 cm):
14-year old juvenile T. rex "Tinker" skull (Christies):
T. rex "Duffy" (subadult or juvenile) skull (right side) (BHIGR):
Subadult T. rex specimen TMM 41436-1's maxilla (Wick, 2014, Figure 1) (Scale bar is 10 cm):
Adult T. rex CM 9380 (26 years old) maxilla (Hendrickx and Mateus, 2014, Figure 2) (Scale bar is 5 cm):
Maxilla pic. from Michael Deak's Twitter post:
Baby Tarbosaurus specimen MPC-D 107/7's skull (Tsuihiji et al., 2011, pp. 499):
Maxilla (Tsuihiji et al., 2011, p. 505):
Larger Tarbosaurus Specimen ZPAL MgD-I/4 Skull (Hurum and Sabath, 2003, p. 165 Figure 1):
For both genera, the beginning of the maxillary strut stays oval in shape near the front of the maxilla. It also stays straight.
**3. Small maxillary fenestra.
Nanotyrannus has a small maxillary fenestra (small hole) inside of the maxillary strut. This is present in CMNH 7541 (Dalman et al., 2018, Figure 15 D), "Jane" (Peterson, 2019, Figure 6), "Zuri" (SWAU), and BHI 6437 (Bonhams, Dueling dinosaurs). Gorgosaurus (Voris, 2018, p. 83) (voris et al., 2022, Figure 3) and Appalachiosaurus has this too (Carr et al., 2005, p. 124). Megaraptor also shares this characteristic (Porfiri et al., 2014, p. 41 Figure 5), and Jinbeisaurus (Wu et al., 2019, p. 4).
T. rex’s fenestra is large throughout its lifetime, as seen in RSM P2347.1's (RSM photo from Holtz's
Twitter page), BHI 3033's ("Stan") (18 years old) (Hendrickx and Mateus, 2014, Figure 2 C), and CM 9380 (26 years old) (Hendrickx and Mateus, 2014, Figure 2 A-B).
Juvenile T. rex RSM P2347.1's Maxilla (Holtz's Twitter page) (Scale bar is 10 cm):
14-year old juvenile T. rex "Tinker" skull (Christies):
T. rex CM 9380 (26 years old) maxilla (Hendrickx and Mateus, 2014, Figure 2) (Scale bar is 5 cm):
Maxilla pic. from Michael Deak's Twitter post:
Nanotyrannus CMNH 7541's Skull (Dalman et al., 2018, p. 135 Figure 15):
BHI 6437's (Subadult) Skull (Bonhams, Dueling dinosaurs):
Juvenile (A) and adult (B) Gorgosaurus maxillae (Voris, 2018, p. 83):
Appalachiosaurus' maxilla (Carr et al., 2005, p. 124):
Jinbeisaurus' maxilla (Wu et al., 2019, p. 4 Figure 3 A-D):
Juvenile Megaraptor's maxilla (Porfiri et al., 2014, p. 41 Figure 5):
Lacrimal is shaped like Gorgosaurus' (Voris, 2018, p. 86) and Appalachiosaurus' (Carr et al., 2005, p. 122). This is seen in "Jane" (Larson, 2013, p. 29 Figure 2.10), "Zuri" (SWAU, HRS08496), and a private specimen from the FossilForum. Dalman told me that he believes that Nanotyrannus is an albertosaurinae (pers. comm.), and the lacrimal kind of goes in that direction. However, Nanotyrannus' lacrimal is also similar to Appalachiosaurus too.
Baby Tarbosaurus specimen MCP 107/7's lacrimal was shaped like Nanotyrannus' (Tsuihiji et al., 2011, p. 13). Juvenile specimen MCP-107/14's lacrimal (Figure 8 E) may have a lacrimal with a horn on it. One specimen, GIN 100/66, has a lacrimal shaped like Nanotyrannus' and a horn is on it (Currie, 2003, p. 200) (Yun, 2015, p. 4).
Nanotyrannus "Zuri's" lacrimal (13 years old) (SWAU, HRS08496):
T. rex "Baby Bob" skull fragments (FossilForum):
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T. rex RSM P.2990.1's (13-15 years old) lacrimal (Holtz's Twitter page):
Baby Tarbosaurus specimen MCP 107/7's lacrimal (Tsuihiji et al., 2011, p. 10 Figure 8 E):
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Juvenile Tarbosaurus specimen MCP-107/14's lacrimal (Tsuihiji et al., 2011, p. 10 Figure 8 F):
T. rex "Stan's" (18 years old) (A), Gorgosaurus' (B), Nanotyrannus "Jane's" (C), lacrimals (Larson, 2013, p. 30 Figure 2.10):
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Appalachiosaurus' lacrimal (Carr et al., 2005, p. 122) ("Pneumatic recess of the lacrimal" is the large hole, and it is comparable in morphology to "Jane's," as shown above):
Nanotyrannus BHI 6437's skull (Bonhams, Dueling dinosaurs):
Nanotyrannus skull from Fossil Forum:
**5. Wide interior pneumatopore inside the lacrimal.
However, baby Tarbosaurus specimen MCP 107/7's lacrimal has a somewhat large pneumatopore in it (Tsuihiji et al., 2011, Figure 8 E). However, the juvenile individual MCP 107/14's is skinny, as in the adults (Figure 8 F). It could be speculated that T. rex's lacrimal pneumatopore went through a similar change when it went from being a baby to a juvenile. We already see something akin to this in RSM P.2990.1.
Nanotyrannus "Zuri's" lacrimal (13 years old) (SWAU, HRS08496):
T. rex RSM P.2990.1's (13-15 years old) lacrimal (Holtz's Twitter page):
Baby Tarbosaurus specimen MCP 107/7's lacrimal (Tsuihiji et al., 2011, p. 10 Figure 8 E):
T. rex "Stan's" (18 years old) (A), Gorgosaurus' (B), Nanotyrannus "Jane's" (C), lacrimals (Larson, 2013, p. 30 Figure 2.10):
Appalachiosaurus' lacrimal (Carr et al., 2005, p. 122) ("Pneumatic recess of the lacrimal" is the large hole, and it is comparable in morphology to "Jane's," as shown above):
Nanotyrannus BHI 6437's skull (Bonhams, Dueling dinosaurs):
Nanotyrannus skull from Fossil Forum:
6. Multiple large rugose bumps on lacrimal.
Lacrimal has rugose bumps on the dorsal (top). This is seen in "Jane" (Larson, 2013, p. 29 Figure 2.10), and "Zuri" (SWAU, HRS08496). It also seems to be present in BHI 6437 (Bonhams, Dueling dinosaurs). Gorgosaurus has this too (Larson, 2013, p. 30 Figure 2.10). Juvenile T. rex specimens don't seem to have this (RSM photo from Holtz's Twitter page) (Olshevsky, 1995, p. 3) (Carr and Williamson, 2004, p. 500 Figure 10) (Larson, 2013, p. 29 Figure 2.10; p. 47 Figure 2.21). A large Tarbosaurus specimen does have rugose lacrimals, but they're not as large as Nanotyrannus' or Gorgosaurus' (Hurum and Sabath, 2003, p. 170 Figure B).
Nanotyrannus "Zuri's" lacrimal (13 years old) (SWAU, HRS08496):
T. rex RSM P.2990.1's (13-15 years old) lacrimal (Holtz's Twitter page):
Baby Tarbosaurus specimen MCP 107/7's lacrimal (Tsuihiji et al., 2011, p. 10 Figure 8 E):
Juvenile T. bataar specimen MCP-107/7's lacrimal (Tsuihiji et al., 2011, p. 10 Figure 8 F):
Nanotyrannus BHI 6437's skull (Bonhams, Dueling dinosaurs):
Nanotyrannus skull from Fossil Forum:
7. Multiple pneumatopores (holes) in lacrimal.
Possibly two-four pneumatopores (small holes) are inside the lacrimal (excluding the hole always featured in the lacrimal). This is seen in "Jane" (Larson, 2013, p. 47 Figure 2.21), "Zuri" (SWAU, HRS08496), and BHI 6437 (Bonhams, Dueling dinosaurs). This is not seen in T. rex specimens RSM P.2990.1 (photo from Holtz's Twitter account), or "Stan" (Larson, 2013, p. 47 Figure 2.21).
"Jane's" and "Stan's" lacrimals (Larson, 2013, p. 47 Figure 2.21):
Admittedly, these multiple pneuatopores could be juvenile characteristics, since "Zuri" and "Jane" are only 13 years old. For now, I do not see this as being an autapomorphy.
**8. Premaxillary tooth morphology:
It seems that T. rex's premaxillary tooth morphology stayed the same throughout its lifetime. In Stein (2021), there is a T. rex tooth that is identical to subadult, and adult, T. rex premaxillary teeth (Stein, 2021, p. 39 Figure 17, B). However, the specimen, TD-13-251, is small. It seems that the specimen could be a baby or a juvenile. Next to it, Stein shows a Nanotyrannus premaxillary tooth, TD-13-247, that is almost the same size as TD-13-251. This could be a baby or juvenile Nanotyrannus specimen.
Baby or juvenile T. rex premaxillary tooth TD-13-251 (Stein, 2021, p. 39 Figure 17, B):
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Nanotyrannus specimen LACM 28471 first and second maxillary teeth (Molnar, 1978, p. 76 Figure 5, A and C):
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UCMP 124406 tooth ("Aublysodon") (Carpenter, 1982, p. 128 Figure 7):
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T. rex's premaxillary teeth also lack a vertical/lingual/posterior ridge that runs down the middle of the tooth on the rear of it (Dalman et al., 2018, p. 134). One tyrannosauroid premaxillary tooth from Zanno et al., (2015) has this same feature, along with the ridges on the posterior end of the tooth that reach the base (pp. 132 and 134, Figure 2, G). The authors assigned the tooth to T. rex, but I'll assign it to Nanotyrannus. this ridge also seems to be visible in UCMP 124406, so it seems that Nanotyrannus had the posterior ridge on its premaxillary teeth, unlike T. rex. Gorgosaurus also has this ridge on the posterior side of its premaxillary teeth, and it's on the juvenile and adult specimens (Voris et al., 2022, Systematic Paleontology, Description of Juvenile Gorgosaurus Skulls, Dentition, para. 2). Seems that the lingual/posterior ridge doesn't disappear during ontogeny.
Baby Nanotyrannus premaxillary tooth FMNH PR 2902 (Zanno et al., 2015, p. 134 Figure 2, G). Scale bar is 1 mm:
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Gorgosaurus' lingual/posterior ridge on its teeth (Voris et al., 2022, Systematic Paleontology, Description of Juvenile Gorgosaurus Skulls, Dentition, para. 2):
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Some tyrannosauroid premaxillary teeth, YPM VPPU 023387 and 023475, from Dalman et al., (2018), have the groove on them as well, while one tooth, YPM VPPU 023469, doesn't and matches the morphology of T. rex's premaxillary teeth (p. 128 Figure 3; p. 134). This is interesting because, not only do we have some evidence that points to T. rex being in the Campanian-aged Two Medicine Formation (p. 126), but Nanotyrannus' premaxillary teeth matches another tyrannosauroid that are different from T. rex's.
**9. First maxillary tooth.
First maxillary tooth is incisiform (small and shaped like a premaxillary tooth), D-shaped in cross-section, and are either lacking, or have no, serrations. If there are any serrations, they are located on the sides of the tooth connected to ridges. This is something that Gorgosaurus had, but not T. rex (Larson, 2013, pp. 33-35) (Larson's Twitter post) (Bakker et al., 1988, p. 24) (Molnar, 1978, p. 77). The Dryptosaurus holotype, Alioramus altai, and Jinbeisaurus, also have an incisiform first maxillary tooth (Brusatte et al., 2011, p. 9) (Cope, 1869, pp. 100-101) (Carpenter et al., 1997, p. 562) (Wu et al., 2019, p. 9). The fact that Dryptosaurus has this means that tooth morphology doesn't always change during ontogeny, since the Dryptosaurus holotype is presumed to be an adult (Brusatte et al., 2011, p. 15). If Nanotyrannus is a Dryptosaurus, then the first maxillary tooth would have stayed incisiform.
Gorgosaurus had incisiform premaxillary, and first maxillary, teeth throughout its lifetime and they never changed form during ontogeny (Voris et al., 2022, Systematic Paleontology, Description of Juvenile Gorgosaurus Skulls, Dentition, para. 2):
Baby Tarbosaurus specimen MCP 107/7's first maxillary tooth is serrated (Tsuihiji et al., 2011, p. 17). Tsuihiji et al. do not mention the specimen's tooth as being incisiform.
There is a baby tyrannosaur tooth, UCMP 119853, from either the Hell Creek or Lance Formation, that is ascribed to being a first maxillary tooth, is serrated, and is wide and robust (Carpenter, 1982, pp. 128 Figure 5 and 130). This could only come from a baby T. rex, especially since it resembles Tarbosaurus' more than Nanotyrannus'. Carpenter does mention that this tooth resembles an incisiform nature, but Bakker et al., (1988) (p. 24) and Larson (2013) (p. 34) say that T. rex and Tarbosaurus do not have an incisiform first maxillary tooth.
To make sure that UCMP 119853 was a first maxillary tooth, I read Smith (2005). Smith said that the first maxillary tooth has serrations on the sides of it, is larger than the premaxillary teeth, and has an oval-shaped base (pp. 872 and 875). It has one of the largest crowns (length, I assume), having almost the same length as the fourth tooth in the dentary (p. 872). The fourth dentary tooth is the largest tooth in the dentary (p. 876). As for the location of the serrations, the fourth dentary tooth has them on the anterior (front) and posterior (back) views of it, unlike in the first maxillary tooth. "Stan's" fourth dentary tooth varies slightly, with the serrations towards the bottom of the tooth appearing on the sides (pp. 875-877; p. 879 Figure 13 D, F-G; p. 880 Figure 14 A). This to me supports UCMP 119853 as being a first maxillary tooth. Having a D-shaped cross section may also support this too (Carpenter, 1984, p. 130). Tarbosaurus' first maxillary tooth is the same as T. rex's (Smith, 2005, p. 872).
Samman et al., (2005) said that the first two maxillary, and dentary, teeth in tyrannosaurs are more rounded in cross-section, and are either incisiform or sub-incisiform (p. 762). It seems that Carpenter may be right about the first maxillary tooth being slightly incisiform. Samman et al. also said that T. rex's mesial (anterior/front) serrations on its maxillary teeth do not reach the base of the tooth (pp. 762 and 768). This is also seen on UCMP 119853 in Figure 5 A in Carpenter (1982).
Interestingly, Carr and Williamson (2004) said that young juvenile T. rex specimens had no serrations ("nondenticulation") on the first maxillary tooth (p. 517) (Tsuihiji et al., 2011, p. 513). This is because he used the tyrannosauroid specimen LACM 23871. This specimen also had a small incisiform first maxillary tooth, just like "Jane" (p. 489). Larson (2013) placed this specimen in the genus Nanotyrannus (pp. 17, 21, 33-34). Larson also said that "Jane" had serrations on the first maxillary tooth (Larson's Twitter post), but they are lacking (Larson, 2013, pp. 33-35). If Carr and Williamson (2004) are correct in saying that LACM 23841 didn't have serrations on the first maxillary tooth, then Nanotyrannus did not have, or had very few, serrations on its first maxillary tooth. However, we can clearly see many serrations on UCMP 119853.
Tyrannosaur tooth (ascribed to T. rex in this post based on comparison with Tarbosaurus) from either Hell Creek or Lance Formation (Carpenter, 1982):
P. 128 Figure 5 (A is side view and B is the posterior (back) view). scale bar is 2 mm:
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Subadult T. rex "Stan's" 4th premaxillary and 1st maxillary teeth (Smith, 2005, p. 875 Figure 8 F-G; both are side views) (Arrows indicate serrations):
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P. 872:
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Nanotyrannus (D), T. rex (A and C), and Gorgosaurus' (B), first maxillary teeth (Larson, 2013, p. 35 Figure 2.14):
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Subadult T. rex specimen "Stan's" premaxillary teeth (numbers 1 and 3) (Smith, 2005, p. 870 Figure 3 B, both in lingual/posterior views):
Dalman told me that there is a new tyrannosaur from the Fruitland Formation that has incisiform teeth as well (pers. comm.):
Update (5/31/22): I found something very interesting. Carr (2020) said that the first two maxillary teeth are incisiform, and the first two dentary teeth are "subconical" (p. 48, Bite force and maturity: Tooth morphology). Alioramus' first two maxillary teeth are also incisiform (Brusatte et al., 2012, p. 24). Seems that Nanotyrannus has more in common with Alioramus the more I research this genus.
*10. Shape of the cross-sections of the teeth.
Bakker et al., (1988) showed cross-sections of the maxillary teeth in Nanotyrannus. They didn't belong to the holotype specimen, but they matched the maxillary teeth in the holotype so the authors ascribed the teeth to Nanotyrannus (p. p. 22 Figure 12; p. 24). The first tooth has a mainly oval-shaped cross-section, but with a triangle-shaped edge on each side of the tooth. The second tooth has a cross-section with pinched sides, with the front being rounded and the rear being triangular.
Nanotyrannus lancensis maxillary teeth (Bakker et al., 1988, p. 22 Figure 12) Scale bar is 2 cm:
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When it comes to T. rex, its maxillary teeth seems to be more wide and circular-shaped, with the rear being somewhat triangular in shape. This is the case with a juvenile T. rex tooth that I was graciously offered to by Stein (pers. comm.).
Juvenile T. rex maxillary tooth TD-15-022 (Stein, pers. comm., 5/9/22):
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Nanotyrannus also has oval-shaped cross-sections, but also the triangle-shaped endings as seen in Bakker et al., (1988). These endings are not seen in the oval cross-sections of Dakotaraptor's tooth. I would make that a characteristic to help identify, and separate, Dakotaraptor's teeth from Nanotyrannus'. It may not completely resolve the identification problem, but I think it could be a start though.
As for Dryptosaurus, I was able to find two cross-sections of its teeth in Brownstein (2018):
NJSM 13095 (Brownstein, 2018, Figure 2, 13):
NJSM 16601, (Brownstein, 2018, Figure 2, 5):
NJSM 13095's cross-section is oval-shaped with apparent triangle-shaped endings, albeit the anterior ending doesn't seem to be preserved. The morphology does seem to indicate that it might have been there.
NJSM 16601's cross-section seems to be pinched, which is more visible in the interior of the tooth. The anterior, while not preserved entirely, seems to have been triangular in shape as well. So far, these teeth match Nanotyrannus' in morphology.
Brochu (2003) said that the Nanotyrannus holotype specimen CMNH 7541 has "circular" cross-sections (p. 3). Both Cope (1869) and Brusatte et al., (2011) said that Dryptosaurus' alveoli and teeth are oval in shape (Cope, 1869, p. 101) (Brusatte et al., 2011, p. 12). However, Dryptosaurus' maxillary teeth were also ziphodont and labiolingually-compressed (Brusatte et al., 2011, p. 8). Carr (2020) said that Nanotyrannus also had "ziphiform" teeth (p. 48, Bite force and maturity: Tooth morphology). Seems that, if Nanotyrannus was Dryptosaurus, the teeth would have stayed ziphodont throughout the genus' lifetime.
Nanotyrannus tooth cross section (Dino Death Match):
Update (10/1/22):
Both Professor Holtz and Sebastian Dalman confirmed that UCMP 119853 was a first maxillary tooth!
**11. Tooth loss or increase?
Long story short: Tyrannosauroids DID NOT lose teeth during ontogeny. I wrote a post on this subject here:
https://psdinosaurs.blogspot.com/2022/05/tyrannosauroids-did-not-lose-teeth.html
Here's what I originally wrote on the topic for this post:
Nanotyrannus' maxilla has 15-16 teeth (Bakker et al., 1988, p. 9; Figure 3) (Larson, 2013, p. 37).
Specimen BHI 6437 ("Bloody Mary") might have 17 (personal observation). The dentary has 16-17 teeth. Carr has stated that T. rex lost teeth during ontogeny (1999) (2020), but interestingly, Currie (2003) and Tsuihiji et al., (2011) said that tooth loss does not occur in ontogeny (Currie, 2003, p. 196 Figure 5; p. 224) (Tsuihiji et al., 2011, Abstract; pp. 18-19). Tsuihiji et al. came to this conclusion after studying a baby, and adult, Tarbosaurus specimens (Tsuihiji et al., 2011, Abstract; pp. 18-19). Deak and McKenzie (2016) say that there are 12 teeth in 4-year old juvenile T. rex specimen "Baby Bob's" dentary, like an adult's (slide. 11). Dalman stated this too (pers. comm.):
Dalman also told me that Daspletosaurus did not lose teeth with age. He based this on a bone bed he and his team are digging up in the Two Medicine Formation, and there are multiple individuals of various sizes and ages. Little, to no, tooth loss have been reported, especially in the dentary:
Here's a list of T. rex specimens with their ages and tooth counts:
1. RSM P2347.1:
Age: Unknown. Maybe 4 or younger.
Maxilla: Teeth were not found, but reconstruction shows that 13 can fit.
RSM P2347.1's maxilla and reconstructed skull (Jack Milligan's Twitter page):
2. "Baby Bob":
Age: 4.
Dentary tooth count: 12.
Source: Deak and McKenzie (2016) (slide 12), Dalman (pers. comm.), Michael Deak's Twitter post.
"Baby Bob" Dentary (Deak and McKenzie, 2016, slide 12):
"Baby Bob's" age (Michael Deak's Twitter post):
Age: 13 (estimated) (dentary and tooth row is the same size as "Jane's").
Dentary tooth count: 13.
Sources: Dalman (pers. comm.), Peter Larson's Twitter page.
Note: Dalman says that the dentary is the same size as "Jane's," with the same dentary tooth row length. This could mean that it is the same age, and even size, as "Jane," as hinted at by Sebastian Dalman (pers. comm.).
Sources: Sebastian Dalman (personal communication), Peter Larson's Twitter page.
Nanotyrannus "Jane's" (top) and baby T. rex specimen BHI 6439's (bottom's) dentaries (interior) (photo from Peter Larson's Twitter page):
Note: Lingual bar covers the first two teeth/alveoli on BHI 6439's dentary, and in T. rex overall. "Jane's" only covers the first alveoli (Dalman, pers. comm.) (Dalman and Lucas, 2016, p. 23).
Top view (pic. provided by Dalman):
Dentary length (pic. given to me from Dalman):
Age: 14.
Maxilla (Left): 11.
Dentary: 12-13:
-Right dentary pic. from Sebastian Dalman: 12 teeth.
-Left dentary (Skull cast pic. from Sebastian Dalman): 13.
Sources: Erickson et al., (2006) (Supplementary Materials, p. 13), Sebastian Dalman (pers. comm.).
-Others: (Prehistoric Planet Store, Tinker the Juvenile Tyrannosaurus rex, skull) (Wyoming Dinosaur Ranch), (Angelfire).
"Tinker's" Dentary (photo belongs to Dalman) (Measuring tape is presumably in inches):
5. BHI 3033 ("Stan"):
Age: 18.
Maxillary tooth count: 11.
Dentary tooth count: 13.
Sources: Erickson et al., (2006) (Supplementary Materials, p. 13), Hendrickx and Mateus (2014) (Figure 2 C), Dalman and Lucas (2016) (p. 25), Larson (2013) (p. 37).
"Stan's" dentary (Dalman and Lucas, 2016, p. 25):
Note: Lingual bar covers the first two alveoli/teeth, just like in BHI 6439's dentary, but not in "Jane's."
7. CM 79057 ("Samson") and PARC-TD-11-094/FDM-xx?:
Ages:
-"Samson": 23.
-PARC-TD-11-094/FDM-xx?: Estimated to be an adult.
Maxilla:
-"Samson": 13.
-PARC: Unknown.
Dentaries (Both): 15.
Sources: Erickson et al., (2006) (Supplementary Materials, p. 14), Deak and McKenzie (2016) (slide 13), Stein (2021) (p. 36).
"Samson" dentary and tooth count (Deak and McKenzie, 2016, slide 9; from Horner, 2011):
Note: First two alveoli are covered by the lingual bar (A).
Stein's statement on the dentary having 14-15 tooth positions (Stein, 2021, p. 36):
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It seems that T. rex's tooth count either stays constant, or increases in number, throughout its lifetime. There doesn't seem to be any need, during T. rex's ontogeny, in which it needed to grow more, and then lose, teeth. Dalman told me this as well:
1. "Cassi":
Age: Unknown, but dentary size suggests that it's a baby/juvenile.
Dentary:
-Length: About 30 cm.
-Tooth Count: 16-17 (first tooth may be small).
Age: Unknown, but probably 4 since its dentary is 22 inches. This is the same as "Baby Bob's."
Tooth Count: Unknown.
Dino Lab Inc. specimen (photos provided by Luke Skywalker Jedi Knight 27):
Maxilla:
3. CMNH 7541:
Age: 7.
Dentary: 16.
Sources: Witmer and Ridgely (2010a) (pp. 76 and 78), Deak and McKenzie (2016) (slide 12).
CMNH 7541's dentary and tooth count (Deak and McKenzie, 2016, slide 12) (from Witmer and Ridgely, 2010a, pp. 76 and 78):
Dentary:
Sources: Griffin (2014) (Abstract), Woodward (pers. comm.), Dalman (pers. comm.), SWAU (HRS08486).
"Zuri's" dentary (SWAU, HRS08486) (16 alveoli in total):
4. BMRP 2002.4.1 ("Jane"):
Age: 13.
Maxilla: 15-16.
Dentary: 17.
Source: Larson (2013) (Abstract; p. 37 Table 2.3 C), Horner (2011), Deak and McKenzie (2016) (slide 9), Burnham et al., (2016) (Abstract).
"Jane's" dentary and tooth count (Deak and McKenzie, 2016, slide 9) (from Horner, 2011):
Maxilla: 17 or 18 (pers. obs.) (16-18 have been estimated).
Sources: Tyrannosauroidea central: Tyrannoethics: The naturalist T. rex and the and the T. rex list of shame, updated (2015), personal observation, Rosen (2014), Bonhams: Mortal combat: The Carnivore.
BHI 6437's maxilla (Dino Death Match, 1:12):
Currie (2003) graphed the maxillary tooth row length and compared the tooth count of multiple tyrannosauroid genera (p. 196 Figure 5).
Tyrannosaurid Tooth Count Chart (Currie, 2003, p. 196 Figure 5):
Currie (2011) reiterated his findings from his 2003 paper. There was no sign of tooth loss in tyrannosaurs based on the size of the individual (Abstract):
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To me, this is possibly the second most important trait that differentiates T. rex from Nanotyrannus. T. rex's, Tarbosaurus', Zhuchengtyrannus, Daspletosaurus', and Lythronax's, lingual bars cover the first two alveoli (Dalman and Lucas, 2017, pp. 23-24) (Dalman and Lucas, 2018) (Dalman, pers. comm.). We don't see this in "Jane's," or "Zuri's," dentaries. Juvenile T. rex specimen BHI 6439 clearly shows its groove covering its first two alveoli, compared to "Jane's" which only covers the first alveoli (Peter Larson's Twitter post) (Dalman and Lucas, 2017, pp. 23-24) (Dalman and Lucas, 2018) (Dalman, pers. comm.). This is also seen in Appalachiosaurus (Pillion, 2021), and Gorgosaurus specimen TMP 1994.143.1 (Currie, 2003, p. 218 Figure 33) (Voris et al., 2019, Figure 1 B). Both of these specimens are young too. The Appalachiosaurus specimen is a subadult (Carr et al., 2005, pp. 119-121), and the Gorgosaurus specimen is a juvenile (Voris et al., 2019). However, one adult specimen of Gorgosaurus also has this trait (Dalman and Lucas, 2017p. 17 Figure 1 B). It seems that basal tyrannosauroids have this trait, but tyrannosaurine do not (Loewen et al., 2013, Figure 6).
Currie (2003) (P. 218 Figure 33):
Adult Gorgosaurus dentary (Dalman and Lucas, 2017p. 17 Figure 1 B) ("lb" and "aslb" are the lingual bar and anterior lingual bar):
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It is also interesting to note that Jinbeisaurus is placed phylogenetically close to Dryptosaurus, and other more primitive tyrannosauroids than to the tyrannosaurids and tyrannosaurine. Dr. Carr was also a part of that paper.
Jinbeisaurus' phylogenetic tree (Wu et al., 2019, Figure 8):
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Nanotyrannus "Jane's" (top) and baby T. rex specimen BHI 6439's (bottom's) dentaries (interior) (photo from Peter Larson's Twitter page):
Note: Lingual bar covers the first two teeth/alveoli on BHI 6439's dentary, and in T. rex overall. "Jane's" only covers the first alveoli (Dalman, pers. comm.) (Dalman and Lucas, 2016, p. 23).
"Jane's" lingual bar (Dalman and Lucas, 2017, p. 24 Figure 9, B'):
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Baby T. rex specimen "Baby Bob" dentary (Photo sent to me by Luke Skywalker Jedi Knight 27):
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Subadult T. rex "Stan's" dentary (Dalman and Lucas, 2016, p. 25):
Note: Lingual bar covers the first two alveoli/teeth, just like in BHI 6439's dentary, but not in "Jane's."
*11. Skinny dentary:
Brusatte et al., (2009) state that Alioramus has a "shallow dentary" (Description and Comparisons, para. 6). I'm guessing that this means that Alioramus' dentary is skinny. When compared to baby T. rex specimen BHI 6439, Nanotyrannus specimen "Jane' and BHI 6437 have extremely skinny dentaries.
Alioramus altai Holotype Skull (Brusatte et al., 2009, pg. 17262 Figure 1):
Nanotyrannus "Jane's" (top) and baby T. rex specimen BHI 6439's (bottom's) dentaries (interior) (photo from Peter Larson's Twitter page):
Nanotyrannus BHI 6437's skull (Bonhams, Dueling dinosaurs):
BHI 6437's dentary is extremely skinny, and shaped a lot like Alioramus'.
The fragment of Dryptosaurus' dentary show that could have been very skinny as well (Brusatte et al., 2011, p. 11 Figure 4):
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Pneumatic foramen (small hole) on the quadrujugal that is not present on T. rex’s (Tsuihiji et al., 2011, p. 19) (Larson, 2013, p. 45 Figure 2.19). Tsuihiji et al. also says that this is not present in Tarbosaurus (both young and old), nor in tyrannosaurids in general (p. 19). Daspletosaurus horneri does have this (Carr et al., 2017, Diagnosis, para. 2). Interestingly, Daspletosaurus horneri has 17 teeth in its dentary as well. I wonder if there is a close relationship between it and Nanotyrannus? Mainly, this pneumatic foramen is not present on T. rex.
Update (10/13-17/21):
Sebastain Dalman says that Daspletosaurus horneri does not have this foramen. It's the result of damaged bone surface (personal communication). Also, he told me that "Zuri" does not have this trait. This might be a result of ontogeny, but I'll have to look this up later. Therefore, T. rex, T. bataar, and Daspletosaurus horneri, did not have this trait. It seems to be an autapomorphic trait for Nanotyrannus, albeit maybe for the younger individuals, but this is inconclusive:
Of course, this could be a sign the foramen being a juvenile trait when "Zuri" grew into an adult T. rex. However, this doesn't change the fact that "Jane," another 13-year old Nanotyrannus, does have this foramen. Maybe individual variation could account for this?
As far as I'm concerned, "Zuri" not having the foramen on its quadrajugal signifies either the individual being of a slightly older status than "Jane," or is a result of individual variation.
"Jane's" (left) and "Stan's" quadrujugals (Larson, 2013, p. 29 Figure 2.9):
I will conclude that this is a juvenile characteristic.
14. Endocast is shaped differently from T. rex's.
I've noted before in my "What IF: Are Nanotyrannus and Alioramus Juvenile Tyrannosaurus?" that the endocast of Nanotyrannus is shaped differently from T. rex's, but Dr. Holtz says that the brain of theropods changed throughout ontogeny. I even found a paper saying that birds' brains change throughout ontogeny too, and since birds are dinosaurs, then Nanotyrannus' brain should have changed shape as it matured into a full-grown T. rex. But to be fair, Brusatte et al., (2009) used Alioramus' endocast to support it as being a separate genus from Tarbosaurus. I declared that Alioramus' endocast could not support it as a separate genus because it was a juvenile, and its endocast would have changed as it matured, presumably, into an adult Tarbosaurus. If we're going to be fair, then we need to keep Nanotyrannus' endocast in mind when debating whether or not it is a valid genus. We can't support one thing being valid, and be bias towards another being invalid. Professor Holtz also said that Nanotyrannus' brain became damaged when its skull got squished during preservation, but we'll get to that in a minute.
I'm a little hesitant in saying this because the argument that Nanotyrannus' endocast was damaged during preservation, and that it would turn into looking like a normal T. rex's when it matured, sounds very convincing. I used this logic before for Alioramus' endocast, which admittedly, looks very similar to Tarbosaurus'. However, people use Alioramus' higher tooth count, nasal bumps, jugal horn, and other traits on the skull, for example, to separate it from Tarbosaurus. Even if Nanotyrannus' endocast would change as it matured, does it mean that its endocast was damaged during preservation? I originally thought so, but Deak and McKenzie (2016) might've counteracted this argument with the T. rex specimen "Sue." Her skull was squished during preservation, but Deak and McKenzie say that "Sue's" endocast looks identical to other T. rex specimens whose skulls were not damaged during preservation (slide 6). I forgot that "Sue's" skull was crushed. If its brain still preserved its original shape after its skull was deformed, then I can't say for certain that Nanotyrannus' endocast was damaged when the skull was crushed during preservation. Once again, I think the same excuses given to Alioramus can be given to Nanotyrannus, even if we dismiss the endocast: Higher tooth count with the first maxillary tooth being an incisiform like Gorgosaurus' that is not seen in other juvenile T. rex specimens, a wide "T"-shaped lacrimal with three pneumatic foramen (holes) inside it not seen in juvenile/subadult T. rex specimens, a deep maxillary strut not present in juvenile T. rex specimens, a pneumatopore (hole) on the quadrujugal not seen in T. rex, etc.
T. rex "Sue's" crushed skull and endocast (right) compared to a normal T. rex skull and endocast (Deak and McKenzie, 2016, slide 6):
T. rex "Sue's" crushed skull (Brochu, 2003, p. 15):
T. rex (Left) and Nanotyrannus (Right) Endocasts (Dino Death Match, 29:20):
Kawabe et al., (2015) says that chicken brains change shape during ontogeny, and this seems to have happened for dinosaurs ("Abstract;" "Discussion: Implications for paleontology," para. 1). So until we get more juvenile T. rex, and Nanotyrannus, endocasts scanned, I will not include the endocast morphology as an autapomorphy.
I forgot about this though: Here's an endocast from a juvenile T. rex (Dinosaurs: Inside and Out: S1E3: "The Killer Elite," 14:14):
Neal Larson is the one that said that this is a juvenile T. rex's endocast. However, on the Prehistoric Store's website, I found another T. rex endocast that looks identical to it. However, it's described as being an adult endocast.
Adult T. rex endocast from Prehistoric Store:
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This can go in two directions: Firstly, this is the same endocast from the documentary and it belongs to an adult T. rex. On the other hand, this means that a juvenile T. rex's endocasts resembles more like the adults' rather than Nanotyrannus'.
Extremely rugose nasals usually occur in more mature T. rex specimens, as seen in the adult specimen "Scotty" (Persons IV et al., 2019, p. 659):
Note: Notice that Appalachiosaurus' bumps are the same size as "Zuri's."
Alioramus altai's (Brusatte et al., 2012, p. 25 Figure 10 D) (Scale bar is 5 cm):
Alioramus remotus Holotype Skull (Paleofile, Alioramus):
Alioramus (or Qianzhousaurus) sinensis holotype skull (mature individual) (Lu et al., 2014, Figure 1):
T. rex has two "horns," called lacrimal processes, on the end of the nasals (Hurum and Sabbath, 2003, p. 169 Figure 5 B). These processes fuse the nasals to the lacrimals. Nanotyrannus specimen "Zuri" has the best preserved nasals that I can find for Nanotyrannus. As far as I can tell, there doesn't seem to be any lacrimal processes on either side of its nasals (SWAU, HRS08423). However, after talking to Sebastian Dalman about this, he said that both "Jane" and "Zuri" had lacrimal processes on their nasals (pers. comm.). "Jane's" nasals have been reconstructed with lacrimal processes (Carr, 2020, Supplementary Information, Figure 7), but admittedly this becomes less apparent in Figure 10. He reconstructed CMNH 7541 without the processes (Figure 6). Supposedly, the processes appear as the animal grows older (Figure 7). After inspecting the nasal and lacrimal bones of "Jane" myself, there does appear to be a notch for the nasal's lacrimal processes at the beginning of the lacrimal (Todd Johnson's Facebook posts). BHI 6437's rear end of its nasals are crunched, so it's hard to tell if it had the lacrimal processes. Since "Jane" and "Zuri" had the lacrimal processes, it seem more than likely that BH 6437 had them as well.
Interestingly, Gorgosaurus had the lacrimal processes on its nasals throughout its lifetime (Voris, 2018, p. 80). This leads me to believe that Nanotyrannus had lacrimal processes throughout its lifetime as well and not just when it grew older during ontogeny, contra Carr (2020). Interestingly, Tarbosaurus, a tyrannosaurinae closely related to T. rex, does not (Hurum and Sabath, 2003, p. 169 Figure 5). Bistahieversor had these as well (Carr et al., 2010, p. 2 Figure 1, A). Bistahieversor had the lingual bar covering the first alveoli on the interior side of its dentary (Dalman and Lucas, 2017, pp. 23 and 24 Figure 9, A), and the maxillary fenestra was closer to the antorbital fenestra rather than the maxillary strut (Carr et al., 2010, p. 2 Figure 1), so this would make it a basal tyrannosauroid or tyrannosaurid. It seems that the presence, or absence, of the lacrimal processes vary in the genera of the tyrannosauroidea.
Tarbosaurus (A3) and Tyrannosaurus (B) nasals (Hurum and Sabath, 2003, p. 169 Figure 5):
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Nanotyrannus "Zuri" nasals (SWAU, HRS08423) (Side/Lateral view):
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Nanotyrannus and Appalachiosaurus have lacrimal processes/articular surfaces for the lacrimals.
Appalachiosaurus' nasals (Carr et al., 2005, p. 122):
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Baby Tarbosaurus specimen MPC-D 107/7's nasals (Tsuihiji et al., 2011, p. 3 Figure 2):
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Alioramus altai's nasals (Brusatte et al., 2012, p. 25 Figure 10):
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Gorgosaurus' ontogeny chart (Voris, 2018, p. 80):
Juvenile Gorgosaurus specimen TMP 2009.12.14's skull drawing (Voris, 2018, p. 81 Figure 3.3). Scale bar is 5 cm. Lacrimal process is present here:
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Juvenile Gorgosaurus specimen TMP 94.143.01 skull drawing with lacrimal processes (p. 80):
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**17. Nanotyrannus' skull width:
It has been said that Nanotyrannus' skull width is large, which would make it consistent in being a juvenile T. rex (Currie, 2003, p. 223) (Longrich et al., 2010, p. 4). However, after checking this out for myself, it seems that Nanotyrannus' skull is not that wide, even compared to a juvenile Albertosaurus specimen with a smaller skull.
In Peterson et al., (2009), I measured a cast of "Jane's" skull and got a width of 36 cm (at best), with a top/dorsal-view skull length of 80.5 cm (at best) (p. 782 Figure 3). Compared to other tyrannosaurs, like the juvenile Albertosaurus that I mentioned, catalogued as CMN 5601 (Tanke and Currie, 2010, pp. 1199 and 1201 Figure 2) (Check Lambe, 1904, pp. 26 and 28), it has a skull width/"breadth" of 41.2 cm with a skull length of 61 cm (Lambe, 1904, p. 12). The left side of CMN 5601's snout, the maxilla, has folded over, but the posterior end of the skull is in good condition (Lambe, 1904, pp. 7 and 26), and the overall condition of the skull seems good enough (Tanke and Currie, 2010, p. 1199), so I don't think that the posterior end experienced any crushing, or some other force, that was exerted onto it to alter its width. Teratophoneus' skull width is about 25-30 cm, and Lythronax has a skull width of over 50 cm (Loewen et al., 2013, Figures 2 and 3). Russell (1970) gave a skull width of 42.5 cm ("across the quadratojugals"), and a skull length of 104 cm, for the Daspletosaurus holotype (p. 25).
Lythronax would make a great contender for being a second species of Tyrannosaurus. As for Nanotyrannus, its skull width is closer to Teratophoneus', Albertosaurus', and Daspltosaurus', rather than T. rex's and Lythronax's. Currie (2003) gives a width of 21 cm ("across the postorbitals"), and a skull a length of 60 cm, for the Nanotyrannus holotype specimen CMNH 7541's skull (p. 223). This is still smaller for the juvenile Albertosaurus', Teratophoneus', and Daspletosaurus', skull's width. I estimate that an adult Nanotyrannus specimen would have a skull width of about 40 or so cm.
Nanotyrannus "Jane" (Peterson et al., 2009, p. 782 Figure 3). Scale bar is 10 cm:
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Teratophoneus' skull (Loewen et al., 2013, Figure 30. Scale bars are 10 cm, but 50 cm for N):
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Black (2010) had an interview with Tyler Keillor, a paleo-artist, and he stated that "Jane" had a skull similar to Appalachiosaurus, Dryptosaurus' limited skull bones seem to have been similar to Appalachiosaurus' skull as well, and that "Jane's" bones were similar in size to Dryptosaurus'. Keillor then stated that he used "Jane's" head to help recreate Dryptosaurus' skull:
Photo of "Jane's" and "Sue's" humeri (Holtz's Twitter post):
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Nanotyrannus BHI 6437 (bottom) and T. rex "Wyrex" arm bones (Alexander Jack Lund's Twitter post). Original drawing is by GetAwayTrike (Holtz, pers. comm.):
(Russell, 1970, p. 34 Plate 4) (Scale bar is 5 cm):
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Nanotyrannus and Dryptosaurus. Lambe (1917) gives a length of 32.4 cm for the humerus, 15.6 cm for the radius, and 18.0 cm for the ulna (pp. 51-52).
T. rex specimen MOR 555/USNM 555000 (40 feet/12.2 meters) does have a relatively complete arm and scapula. It was shown in the dinosaur show Paleoworld: "The Legendary T. rex" (scale bar is 21 cm):
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Twitter page) (SWAU, HRS15001) (MOR FaceBook's page). LACM 23845, a juvenile/subadult at 14-16 years of age, has small arms (Paul, 1988, pp. 334 and 336) (Olshevsky, 1995, p. 4), or match the proportions of Albertosaurus (probably meaning Gorgosaurus) (Molnar, 1980, p. 106). This can also be seen in UCRC-PV 1. My measurement of UCRC's phalanx 1-1 is 6.8 cm. There is a smaller Tarbosaurus specimen (humerus is 27.1 cm long, and the femur is 101.1 cm long) that has a 5.4-cm long phalanx 1-1 (Brusatte et al., 2011, p. 47 Table 3). Therefore, T. rex had short arms when it was young just like Tarbosaurus did, and the giant hand bones of Nanotyrannus seems to be a significant autopomorphy.
Nanotyrannus hand claw (Stein, 2021, p. 43):
Note: "Zuri's" deformed manus claw is in the second row, number four from the top. Sebastian Dalman also gave me the same picture. That Nanotyrannus hand on the far right is larger than any of the other T. rex hands in the pic.
Nanotyrannus "Zuri's" (13 years old) Hand Claw (SWAU, HRS15001) (side view) (Recorded length is 10.8 cm from SWAU):
LACM 23845's manual ungual (hand) claw (top view) (Los Angeles Natural History Museum):
Side view:
Update (10/27/21):
Carr and Williamson (2004) (p. 511), and Dalman (pers. comm.), said that the claw is a pes (foot) claw.
Carr and Williamson (2004) on LACM 23845's pes ungual/claw (p. 511):
Dalman on LACM 23845's pes ungual (10/27/21):
UCRC-PV1 now has the most complete T. rex arm ever found. From what I also know, MOR 980 is the second best one (pic shown below from MOR's facebook page). However, regarding the arm bones of LACM that we do have, the left ulna and metacarpal, it has been stated that the arms are small (Paul, 1988, pp. 334 and 336) (Olshevsky, 1995, p. 4), or match the proportions of Albertosaurus (probably meaning Gorgosaurus) (Molnar, 1980, p. 106). Nanotyrannus, Dryptosaurus, and Megaraptor, had long arms. LACM, and UCRC, show that T. rex's arms grew during ontogeny.
FMNH 2081's ("Sue's") hand was not recovered with the skeleton (Brochu, 2003, pp. 100 and 103), and Dr. Holtz told me this as well (pers. comm.), so that this with a grain of salt:
Brochu (2003) on "Sue's" supposed wrist and manual ungual:
P. 100:
P. 103:
Instead, I will be using other specimens:
Juvenile T. rex UCRC-PV1's arm (Peter Larson's Twitter page):
Manual ungual 2 claw (Fran Vidakovic's Twitter post):
Description of specimen by Larson on his Twitter account:
Larson and Carpenter (2008) wrote about the specimen. Catalogued as UCRC PV1, it was discovered in 1950, and excavated by Paul Sereno and his team in 2001. The specimen is in the University of Chicago. Sereno is quoted as saying that the specimen has both complete forelimbs (p. 41):
Adult T. rex MOR 980 (MOR FaceBook's page) (Dark colors indicate the real bones):
Re: [dinosaur] The Dueling tyrannosaurid is not, repeat is not, Tyrannosaurus), but when I asked Dalman about this, he said that we need more Dryptosaurus bones first (pers. comm.). I'll keep all of this in mind, but as I've noted before in this post, Nanotyrannus shares a lot of traits similar to Dryptosaurus' and Appalachiosaurus'. I think Nanotyrannus may be a primitive tyrannosauroid related to Dryptosaurus and Appalachiosaurus, or it even might be Dryptosaurus. However, I do not think it is a tyrannosaurine, or even a tyrannosaurid.
Left to right: manual phalanx 1-1 bones of Gorgosaurus, Nanotyrannus BHI 6437, T. rex specimens MOR 980, and subadult (16 years old) TCM 2001.90.1 ("Bucky") (Peter Larson's Twitter post):
According to Brusatte et al., (2011), Dryptosaurus' manual phalanx 1-1 is long (14.8 cm as preserved, but 16.0 estimated when complete) (p. 20 Table 2), just like BHI 6437's. A manual ungual is 17.6 cm long, but it's unknown as to which hand this claw belonged to (p. 21). Based on a comparison with "Petey," this ungual/claw could be the claw from the second finger. In addition to. a small humerus, Dryptosaurus also has a large hand (Brusatte et al., 2011, Abstract). This is seen in "Jane" and BHI 6437.
Dryptosaurus' hand bones (Brusatte et al., 2011, p. 22 Figure 12):
UCRC-PV 1's Hand (Fran Vidakovic's Twitter post). Scale bar is 10 cm:
P. 56:
I found a pic of an T. rex specimen's manual phalanx 1-1 and its ungual compared to a Nanotyrannus' manual ungual 1. The T. rex specimen, "Victoria," was a subadult at 40 feet in length, and between 18-25 years old (Strickland, 2019, para. 4-5). This specimen was the same size as "Stan," so I imagine it was 18 years old when it died.
T. rex "Victoria" age (Strickland, 2019, para. 4):
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The humerus of T. rex also show that the arms grew during ontogeny. Check out my post here:
https://psdinosaurs.blogspot.com/2019/08/size-calculations-for-tyrannosaurus-rex.html
Update (2/2/23):
In a 2015 SVP abstract, Dr. Carr said that "Jane" had a long humerus compared to other tyrannosaurids specimens that were of the same age. This, along with the T. rex specimens UCRC-PV 1, TCM 2001.90.1, MOR 555/USNM 555000, and MOR 980 show that the "Nanotyrannus" specimens had longer arms than T. rex, just like the Dryptosaurus holotype (EurekAlert, 2015, para. 15/last para.):
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*21. Tibia is longer than, or the same size as, the femur.
This is just like Alioramus (Qiazhousaurus) sinensis'. A. sinensis' femur is 70 cm long, but its tibia is 76 cm long (Lu et al., 2014, Supplementary Materials, p. 9):
Raptorex tibia being longer than its femur (Brusatte et al., 2011, p. 30):
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Carpenter et al., (1997) gave Dryptosaurus a femur length of 77 cm, and a tibia length of 77.5 cm (p. 568 Table 3):
Peter Larson gave a length of 73 cm for BHI 6437's femur on Twitter. Using this, I extrapolated a length of 84.8 cm for the tibia.
Larson giving a length of 73 cm for BHI 6437's femur (Twitter post):
73 - 72 = 1.
1/72*100 = 1.4% increase.
83.6 cm + 1.4% = 84.8 cm.
1. A femur that's 65.7 cm long and a tibia that's 72 cm long.
2. Or, has a femur that's 73 cm long and a tibia that's possibly 84.8 cm long.
77.4 - 72 = 5.4.
5.4/72*100 = 7.5% increase.
83.6 cm + 7.5% = 89.9 cm.
Juvenile T. rex specimen LACM 23845 has a femur and a tibia length that are exactly the same (82.5 cm) (Persons and Currie, 2016, p. 6):
T. rex specimens USNM 6183's (17 years old), and CM 9380 (AMNH 973)'s, femur and tibia lengths (Gilmore, 1920, p. 122):
T. rex specimen "Baby Bob," a 4-year old specimen (Deak and McKenzie, 2016, slide 12), has a femur that is 64.5 cm long, and its tibia is 65 cm (Peter Larson's Twitter post).
T. rex "Baby Bob's" Femur and Tibia (Peter Larson's Twitter post):
This is not good if Nanotyrannus was a juvenile T. rex. I also did two charts for Tarbosaurus and Alioramus:
Skull and femur lengths:
Update (5/3/22): Carpenter et al., (1997) stated that Dryptosaurus aquilunguis' femur and tibia were the same length, with the femur being 77 cm long and the tibia 77.5 cm (p. 568 Table 3). Brusatte et al., (2011) said the femur was longer than the tibia (p. 20 Table 2; p. 30). I measured the two bones myself in Brusatte et al., (2011), and I got a length of 81 cm (at best) for both bones (pp. 27 and 31, Figures 15 and 18, A). This gave me an idea: Perhaps the femora of the Nanotyrannus specimens grew to be the same length as their tibiae?
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So, what's going on here? Professor Holtz told me last year that Nanotyrannus' tibia is longer than its femur because of its young age (pers. comm.), but the Dryptosaurus holotype and Appalachiosaurus are adult and subadult individuals and their femora and tibiae are either the same length or the tibia is longer than the femur. Qiazhousaurus is suppose to be an adult individual, yet its tibia is longer than its femur. The Guanlong specimen used in Persons IV and Currie (2016), IVPP V14531, the holotype, seems to have been an adult individual as well, being 12 years in age and reached its adult length (Xu et al., 2006, pp. 715-716).
Guanlong holotype IVPP V14531 is mature (Xu et al., 2006, p. 715):
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Update (6/19/22): I decided to measure the Dryptosaurus holotype's femur and tibia in Carpenter et al., (1997), and I was able to get 77 cm (at best) for the femur and 81 cm for the tibia (Figure 8). Seems that the tibia in the Dryptosaurus holotype could have been longer than the femur after all, as in the Nanotyrannus specimens. If we add 4 cm to the result I got for the tibia in Brusatte et al., (2011), then the tibia would be 85 cm long compared to a 81-cm femur.
Femur and tibia from Carpenter et al., (1997) (p. 568, Figure 8). The scale bar is 5 cm, but if I went with that the results for both bones would be in the 40-cm mark, and I don't think that's correct. I went with 10 cm, and I got results closer to what the authors of the paper got in Table 3:
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I could not find a picture of "Jane's" complete femur. The femur is fragmentary, as shown in Woodward et al., (2020) (Supplementary Materials, p. 9 Figure S2 A). Therefore, I have to go with Larson (2013)'s, and Persons and Currie (2016)'s lengths for the femur, which is 72 cm.
"Baby Bob's" Skull and femur length (Detrich Fossil Co's Twitter post):
Femur and Tibia (Peter Larson's Twitter post):
These are the top characteristics that I've chosen that separate Nanotyrannus from T. rex:
1. Nanotyrannus has 8 cervicals. T. rex has 11 (max.), 3 more than Nanotyrannus. Daspletosaurus has 10, Tarbosaurus has 9, and Gorgosaurus has 9 or 10.
2. Nanotyrannus' caudal vertebrae count is 25, the same as Dryptosaurus', and not 40-45 (maybe 47) as in T. rex's and Tarbosaurus', or 36 as in Gorgosaurus'. They are also extremely elongated towards the middle to the end of the tail, just like Dryptosaurus'.
3. Nanotyrannus had 17 chevrons/haemal arches in its tail. T. rex had 27 (as preserved in "Sue"), indicating that T. rex had at least 10 more chevrons/haemal arches than Nanotyrannus.
4. Overall skull morphology of Nanotyrannus, Appalachiosaurus, and Dryptosaurus are similar.
5. The nasals of Nanotyrannus, Appalachiosaurus, and especially Alioramus, are rugose to very rugose in nature, even though they range from babies to subadults. This is interesting since a 14-year old juvenile T. rex specimen, LACM 23845, has very low rugosities on its nasals.
6. Nanotyrannus, Appalachiosaurus, Jinbeisaurus, and probably Megaraptor, have a deep maxillary strut throughout their ontogenies, and the maxillary fenestra is closer to the antorbital fossa. T. rex's maxillary strut grew during ontogeny, and the maxillary fenestra was closer to the beginning of the strut. Same goes for Tarbosaurus and Daspletosaurus. The maxillary fenestra in Megaraptor was also closer to the maxillary strut. The position of the maxillary fenestra doesn't change.
7. The maxillary strut for Nanotyrannus tips down, and is triangular in shape, near the beginning of the maxilla. This is also seen in Gorgosaurus throughout its ontogeny, Jinbeisaurus, Alioramus altai and Qiazhousaurus/Alioramus sinensis, and Albertosaurus. T. rex's and Tarbosaurus' maxillary strut are circular, and straight, at the beginning of the maxilla. The different forms of the maxillary struts for all genera named stay the same throughout ontogeny.
8. Nanotyrannus, Appalachiosaurus, Jinbeisaurus, and Megaraptor have a small maxillary fenestrae. T. rex and Tarbosaurus have a large maxillary fenestrae. The morphology of the maxillary fenestra (from small to large) doesn't occur in ontogeny.
9. The premaxillary teeth of Nanotyrannus matches Gorgosaurus', and other Campanian-aged North American tyrannosauroids, in having a distal/ventral/posterior groove on the rear end of the teeth, and having the ridges on the posterior end of the teeth, side-to-side. The ridges either have very few, or no, serrations. T. rex's premaxillary teeth lack the posterior ridge, and the ridges are on the lateral sides of the tooth.
10. Nanotyrannus, Dryptosaurus, Gorgosaurus, Jinebisaurus, and Alioramus all have the first maxillary tooth as an incisiform. Nanotyrannus' is also not serrated, or is very lightly serrated. Both of these features are not seen in T. rex or Tarbosaurus. Gorgosaurus had this morphology for its first maxillary tooth throughout its lifespan, and three nanotyrannus specimens had this as well. It's more than likely that Nanotyrannus' first maxillary tooth is a definitive trait that separates it from T. rex.
11. Cross-sections of Nanotyrannus' and Dryptosaurus' teeth are similar, having pinched sides, are oval or labiolingually-compressed, and have triangle-shaped tips on each end.
12. Nanotyrannus' and Gorgosaurus' lacrimals are very rugose, while T. rex's and Tarbosaurus' are either smooth or low in rugosity.
13. Nanotyrannus', Appalachiosaurus,' and Gorgosaurus' lacrimals have a large and wide pneumatopore inside it, while Tarbosaurus' lacrimals have a somewhat large pneumatopore in the lacrimal when it's a baby, but it gets skinnier as the species turns into a juvenile. A juvenile T. rex lacrimal shows that it also had a small pneumatopore in it, indicating that T. rex's lacrimal pneumatopore probably went through similar changes when the species went from being a baby to a juvenile.
14. Lingual bar covers the first alveoli in the interior side of Nanotyrannus' dentary, as well as Appalachiosaurus' and Gorgosaurus'. This seems to be a basal tyrannosauroid trait. T. rex's, Daspletosaurus', Tarbosaurus', and Lythronax's, covers the first two alveoli. This doesn't change during ontogeny.
15. The skull widths of Nanotyrannus, Teratophoneus', Albertosaurus', and Daspletosaurus', are closer to one another than the large ones of T. rex's and Lythronax's.
16. Nanotyrannus' humerus is either the same size as, or smaller than, the radius and ulna. This is not seen in T. rex, Daspletosaurus, or Albertosaurus.
17. The morphology of Nanotyrannus' humerus is similar to Dryptosaurus', and not T. rex's or
Daspletosaurus'. Both Nanotyrannus and Dryptosaurus have bumps on the tops of their humeri, which is not seen in T. rex's.
18. Nanotyrannus' manual phalanx 1-1 is identical to Dryptosaurus', and is twice as long, or more, as T. rex's, Tarbosaurus', and even Gorgosaurus'. T. rex's hands were small in general but they grew during ontogeny. This is seen in the juvenile LACM 23845, and the presumed subadult UCRC-PV 1. The manual phalanx 1-1 grew during ontogeny. This is seen in the juvenile specimen LACM 23845, the presumed subadult (more than likely juvenile) specimen UCRC-PV 1, the subadult specimen "Bucky," and the adult specimen MOR 980.
19. Nanotyrannus' and Megaraptor's manual unguals are longer than T. rex's, Daspletosaurus', and Albertosaurus'. In fact, the first manual ungual of Nanotyrannus is the same size as the entire first finger of a 18-year old T. rex.
20. Nanotyrannus' tibia is longer than the femur. This could just be a juvenile characteristic, even compared to Dryptosaurus, but this is also present in Alioramus (Qiazhousaurus) sinensis and Guanlong, which are both said to be a mature individuals. This could be a synapomorphy between Nanotyrannus,
Alioramus/Qiazhousaurus), and Guanlong. T. rex's tibia is either the same length, or is barely any longer, than its femur during its younger years. This is seen in multiple young T. rex individuals. Dryptosaurus' femur and tibia are either the same length, or the tibia is longer than the femur. Either both bones were 81 cm long, or the femur was 81 cm long and the tibia was 84 cm long (my measurements). Other sources have given the tibia a longer length than its femur. Other tyrannosauroids have tibiae the same length as, or longer than, their femora as well, suggesting that this could be a tyrannosauroid characteristic.
21. Nanotyrannus' (probably), and Alioramus', skulls were longer than their femurs. Or, following Dryptosaurus' femur and tibia lengths, it is possible that Nanotyrannus' femur and tibia lengths would be identical. Baby, and juvenile, T. rex specimens "Baby Bob" and LACM 23845 had skulls shorter than their femurs. In fact, LACM 23845's skull was the same size as its fibula. Only when T. rex became a subadult did the skull grow larger than its femur, as seen in USNM 6183.
22. Baby and juvenile T. rex specimens are twice as large as juvenile and subadult Nanotyrannus specimens, and an adult Dryptosaurus specimen. The Nanotyrannus specimens fit inside
Dryptosaurus' growth curve, but they are far below T. rex's growth curve. This suggests that the
Nanotyrannus specimens are probably juvenile and subadult Dryptosaurus specimens, rather than being juvenile T. rex specimens.
Laramidia and Appalachia reconnected?
We seem to have some interesting leads that show us that Nanotyrannus could be either a relative of Dryptosaurus, or even is Dryptosaurus. Gates et al., (2012) (Figure 1), Fiorillo and Tykosi (2014) (Results and Discussion: Laramidian Geographic Provincialism, para. 1), Bell and Currie (2014) (Figure 4), and Druckenmiller et al., (2021) (Figure 1A), all say that Laramidia and Appalachia reconnected during the late Maastrichtian, due to the Western Interior Sea receding. I think Dryptosaurus was more widespread than we currently believe. Blakey (2014) shows that Appalachia and Laramidia reconnected 70.8 Ma, and the Western Interior Sea basically receded considerably around 68-67 Ma (pp. 35-39).
Map of North America 66 Ma (Bell and Currie, 2014, Figure 4) ("n" means number of specimens found):
Map of North America Campanian-Maastrichtian (Druckenmiller et al., 2021, Figure 1) (Notice how Appalachia and Laramidia reconnected at the bottom):
Dryptosaurus holotype was "mature or nearing maturity" (p. 5), and the Nanotyrannus specimens have similarities to Dryptosaurus (and both Dryptosaurus and Nanotyrannus share similarities to
Appalachiosaurus, as is explained below), so why wouldn't Dryptosaurus be the adult Nanotyrannus? However, I would call all Nanotyrannus specimens juvenile Dryptosaurus specimens!
Dryptosaurus was named first, Laramidia and Appalachia reconnected in the late Maastrichtian, and both genera share similar traits, so as far as I'm concerned, Nanotyrannus is a juvenile Dryptosaurus. However, based on the tibia length, Nanotyrannus lancesis might be Dryptosaurus (?)lancensis, but that's not entirely clear to me yet. Still, I'm lumping Nanotyrannus into Dryptosaurus.
Location of the Specimens.
I don't entirely recall where or when I was told this, but I think Professor Holtz told me that Nanotyrannus was always found in locations where adult T. rex were found. Naturally, this would lead to lumping the young Nanotyrannus specimens into the genus Tyrannosaurus. However, if Nanotyrannus is actually Dryptosaurus, then this would solve the issue. Dryptosaurus aquilunguis was found in the new Egypt Formation, which is in New Jersey (Brusatte et al., 2011, p. 5) and in Appalachia. T. rex was in Laramidia. Check the map from Bell and Currie (2014) (Figure 4). Since the Dryptosaurus holotype is located farther away from where T. rex specimens are usually discovered, and it possessed many characteristics that the Nanotyrannus specimens had so we can place Nanotyrannus into the genus Dryptosaurus, then we can say that Dryptosaurus had a wider range/geography than T. rex did. This would make Nanotyrannus a separate genus from T. rex. This technique was used in order to keep Torosaurus as a separate genus from Triceratops (Deak and McKenzie, 2016, slide 7) (Longrich and Field, 2012, Figure 2).
Coexisting taxa?
Dryptosaurus aquilunguis and T. rex were found in different formations in different regions of North America, but one way we could tell if the fauna from the two locations interacted with each other is to see if the formations had similar taxa. I will be using the New Egypt Formation and the Hell Creek Formation to start out with. The New Egypt Formation had the marine reptile Mosasaurus hoffmani in it, with two skulls recovered from the formation (Gallagher et al., 2012, p. 147). A mosasaur skeleton was recovered from the Hell Creek Formation, but it could belong to either Mosasaurus or Prognathodon (Van Vranken and Boyd, 2021, Abstract; p. 5).
In Hell Creek, a couple of sources have stated that lambeosaurinae hadrosaur fossils have been discovered there (Sullivan et al., 2011, p. 405) (Rolleri et al., 2020, pp. 284-285; in SVP, 2020). A lambeosaur specimen was also found in the Naashoibito Member (Sullivan et al., 2011). This is interesting because a tyrannosaur tooth identical to Nanotyrannus' maxillary teeth was also discovered from the same member (see below). In the New Egypt Formation, a possible lambeosaur fossil was described in 2020 (Brownstein and Bissel, 2020, Abstract; Discussion, para. 3-4). Brownstein and Bissel hypothesize that dinosaurs during the Maastrichtian of North America could have travelled across the continent, and they use a ceratopsian tooth from the similarly-aged Owl Creek Formation, located in Mississippi (Appalachia), to help their case (Discussion, para. 4) (Farke and Phillips, 2017, Abstract). Ceratopsians were also found in the Hell Creek Formation, but I don't have to tell you that. A lambeosaur called Latirhinus was found in Mexico, and lived during the late Campanian (Serrano-Branas and Prieto-Marquez, 2022) (Luis V. Rey Blog, 1/30/22).
Rolleri et al., (2020) abstract (SVP, 2020):
P. 284:
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1. The Western Interior Seaway either disappeared or shrunk around the late Cretaceous.
2. Dinosaurs from both Laramidia and Appalachia were able to coexist.
3. If Dryptosaurus was able to migrate into Laramidia, and Nanotyrannus shared more traits with it than T. rex, then Nanotyrannus is Dryptosaurus.
Concluding Remarks:
(DML.CMNH.Org, Re: [dinosaur] The Dueling tyrannosaurid is not, repeat is not, Tyrannosaurus). I originally thought that Nanotyrannus was probably an albertosaurine, like Dalman thinks (pers. comm.), but Dr. Holtz on Twitter said that there wasn't any evidence for that. Dalman disagrees. And here I am, saying that Nanotyrannus is Dryptosaurus... All I'm doing is following the evidence. Isn't that what science is all about?
Update (5/15/22):
I've found a new specimen that I think belongs to Dryptosaurus:
A baby tyrannosauroid tooth from the Naashoibito Member of New Mexico, catalogued as NMMNH P-32567 (Williamson and Brusatte, 2014, p. 9 Figure 4, T-Y), matches very well with the maxillary teeth of Dryptosaurus lancensis specimen CMNH 7541, and other maxillary teeth ascribed to the species (Bakker et al., 1988, p. 22 Figure 12; p. 24). In particular, the cross-section of NMMNH P-32567 is pinched on the sides, and the anterior side is round while the posterior side is pointed (Williamson and Brusatte, 2014, p. 9 Figure 4, W), which is seen in the maxillary teeth of D. lancensis (Bakker et al., 1988, p. 22 Figure 12). Another trait of NMMNH P-32567 is that the serrations on the front/mesial view reach the base of the tooth (Williamson and Brusatte, 2014, p. 9 Figure 4, Y). This is typical of D. lancensis (Bakker et al., 1988, p. 22 Figure 12; p. 24), but not T. rex (Samman et al., 2005, pp. 762 and 768) (Carpenter, 1982, p. 128 Figure 5, A; p. 130).
Bistahieversor's lingual bar on the interior side of its dentary covers the first alveoli, just like D. lancensis' (Dalman and Lucas, 2016, pp. 23-24), but T. rex's lingual bar covers the first two alveoli (pp. 23-24). D. lancensis and Bistahieversor seem to share similar traits in their teeth and dentaries that T. rex does not share. The lingual bar covering the first two alveoli on the interior side of the dentary seems to be present in the more derived (advanced) tyrannosaurine, like T. rex, Lythronas, Daspletosaurus, Zhuchengtyrannus, and Tarbosaurus (pp. 23-24). I've explained in my "Nanotyrannus is Dryptosaurus" post that the lingual bar doesn't change positions during ontogeny. The traits in the teeth and dentaries of Bistahieversor and D. lancensis support the hypothesis that D. lancensis is a more basal member of the tyrannosauridea, and Bistahieversor seems to be the same.
On 10/13/21, I got into contact with paleontologist Sebastian G. Dalman, and he is studying the tyrannosaurid specimens from New Mexico. He told me that Nanotyrannus specimens haven't been found in New Mexico, so the bones belong to a brand new species of tyrannosaurid with blade-like teeth. This is also true for the specimen SMP VP-2352 from Jasinski et al., (2011), which I talk about below:
Baby tyrannosaur teeth from New Mexico (Williamson and Brusatte, 2014, p. 9 Figure 4) Scale bars are 1 mm:
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https://psdinosaurs.blogspot.com/2021/08/a-possible-tyrannosauroids-that.html
Update (5/27/22):
After careful consideration, I've come to the conclusion that there are very few differences, if any, between Dryptosaurus lancensis and aquilunguis. Since the D. aquilunguis holotype is a presumed adult specimen, I will place the D. lancensis specimens into D. aquilunguis. My reasonings includes the following:
1. North America was not separated into two continents (Laramidia and Appalachia) anymore, so Dryptosaurus going through allopatric speciation due to environmental separation doesn't seem likely. All of the specimens would have lived in the same place.
2. D. aquilunguis and lancensis coexisted at the same time in the late Maastrichtian (70-66 Ma).
3. Having D. lancensis turn into aquilunguis would settle the search for an adult specimen for D. lancensis, since the D. aquilunguis specimen is considered to be an adult.
4. There is very little distinction between D. aquilunguis and lancensis. All specimens have:
-An incisiform first maxillary tooth.
-Ziphodont teeth.
-About 25 or so caudal vertebrae, with the middle to posterior caudals being more elongate than an adult T. rex's. T. rex also has more caudal vertebrae (40+) than the Dryptosaurus specimens.
-Similar, if not identical, humeri morphology.
-A very elongated manual phalanx 1-1 that is longer than all other tyrannosauroids, including Gorgosaurus'. This was listed as being as distinctive Dryptosaurus trait.
-Large manual unguals that are longer than T. rex's.
-The femur and tibia are either the same length (Carpenter et al., 1997) (my numbers), or the tibia is longer than the femur (Persons IV and Currie (2016), in the D. aquilunguis specimen. This is seen in the "Nanotyrannus" specimens, and other basal tyrannosauroid genera like Guanlong, Dilong, and Yutyrannus.
In conclusion, I will place D. lancensis into D. aquilunguis. This settles two major problems in my eyes: Firstly, we have more Dryptosaurus aquilunguis specimens to study, rather than just the fragmentary holotype. Second, we have a definitive adult specimen for the previously-named "Nanotyrannus" specimens. Of course, the tyrannosaur specimens from New Mexico and Mexico could also be potential adult specimens, especially the New Mexico tooth described above.
Update (2/8/24):
Longrich and Saitta (2024) briefly described another juvenile specimen of T. rex. The specimen, catalogued as UCMP V84133, is a "small right frontal" from the Hell Creek Formation. The estimated body length of the animal would have been about 4 meters in length (p. 43). Two phylogenetic analyses place it within derived tyrannosaurine (p. 44).
Description of UCMP V84133 part 1 (p. 43):
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Description part 2 (p. 44):
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UCMP V84133 (Figure 29):
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Comparison with "Nanotyrannus'" frontals (Figure 30) and phylogenetic analyses (Figure 31):
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On 1/4/24, Professor Holtz said that the Nanotyrannus frontal bones (catalogued as DDM 334.1) could "*potentially*" be from an adult Nanotyrannus:
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Special thanks to Luke Skywalker Jedi Knight 27 for the photo of the tweet.
It seems that we might have an adult specimen of Nanotyrannus/Dryptosaurus lancensis after all!
Also, after going back and forth, I've decided to place the Nanotyrannus specimens under the name Nanotyrannus/Dryptosaurus lancensis. My reasoning is that I've become more open to the idea that Nanotyrannus could be its own genus, but there is enough physical similarities between it and Dryptosaurus to place it under the latter genus name. Not to mention, North America became a single continent again at the end of the Maastrichtian. Therefore, Dryptosaurus migrating from the Eastern part of North America (Appalachia) to the Western part (Laramidia) could've led to either the spreading of D. aquilunguis, or to two species of Dryptosaurus: D. aquilunguis and D. lancensis.
Link:
Holtz's Tweet (1/4/24):
https://x.com/tomholtzpaleo/status/1742968130995945476?s=61&t=DgZNoZU2b-DFLtG5TI6cbQ
Abstract:
https://www.semanticscholar.org/paper/Using-Osteohistology-to-Determine-the-Taxonomic-of-Griffin/149cadc7cd0f9aa4b55d77810a818ab59b040417
Full:
https://digitalcommons.cedarville.edu/cgi/viewcontent.cgi?article=1136&context=research_scholarship_symposium
Pubis (HRS01514):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS01514
Rib (HRS08467):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08467
Tibia (HRS08421):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08421
Maxilla (HRS08438):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08438
Lacrimal (HRS08496):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08496
Ungual (Hand) Claw (HRS15001):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS15001
Quadrujugal (HRS08440):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08440
Dentary (HRS08486):
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08486
Nasals (HRS08423)
https://fossil.swau.edu/link/Public/Browse/Specimen/HRS08423
SWAU's Dinosaur Science Museum Link:https://www.swau.edu/dinomuseum
Haversian Remodeling:
Lad (2018):
https://ufdc.ufl.edu/UFE0054010/00001
Nyssen-Behets et al., (1997):
https://pubmed.ncbi.nlm.nih.gov/9386983/
Nikolov et al., (2020):
https://palaeo-electronica.org/content/2020/2940-bulgarian-titanosaur
Stein et al., (2010):
https://www.pnas.org/content/107/20/9258
Nanotyrannus Traits:
Dalman et al., (2018):
https://www.researchgate.net/figure/Tyrannosaurid-skulls-with-closed-jaws-A-Albertosaurus-sarcophagus-TMP-850980001-B_fig10_328676947
Dalman and Lucas (2018) (GSA Abstract):
https://gsa.confex.com/gsa/2018RM/webprogram/Paper313788.html
V2:
https://www.researchgate.net/publication/325803282_MAXILLARY_AND_DENTARY_MORPHOLOGY_DISTINGUISHES_THE_LATE_CRETACEOUS_TYRANNOSAURID_DINOSAUR_NANOTYRANNUS_LANCENSIS_AS_A_VALID_TAXON_AND_NOT_A_JUVENILE_OF_TYRANNOSAURUS_REX
Larson (2013) (PP. 15-53):
https://www.geokniga.org/bookfiles/geokniga-tyrannosaurid-paleobiology.pdf
Stein (2021):
http://www.thefossilforum.com/applications/core/interface/file/attachment.php?id=755388
Nanotyrannus and T. rex Hand Bones from Larson's Twitter:
https://twitter.com/PeteLarsonTrex/status/1388947864869429248/photo/1
T. rex MOR 980's hand bones from MOR's FaceBook page:
https://www.facebook.com/mormsu/photos/happy-fossilfriday-on-july-4-1997-the-bones-of-montanas-t-rex-mor-980-were-found/10157755904625458/
Deak and McKenzie (2016) (Slide 6):
Dalman and Lucas (2017) (pp. 23-24):
https://www.dinosaur.pref.fukui.jp/archive/memoir/memoir016-017.pdf
Carr et al., (2017):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5372470/#!po=16.1111
13-15-year old T. rex RSM P.2990.1:
Holtz's Twitter:
https://mobile.twitter.com/TomHoltzPaleo/status/1308744116365295617
Carr (2020):
https://peerj.com/articles/9192/
T. rex CM 9380 maxillary pics:
Hendrickx and Mateus (2014) (Figure 2):
https://www.researchgate.net/figure/Left-maxillae-of-Tyrannosaurus-rex-in-A-B-lateral-view-CMNH-9380-reversed-and-C_fig2_260561984
Michael Deak's Twitter post:
https://twitter.com/deak_michael/status/1109059921755205638
T. rex "Baby Bob's" age:
Deak and McKenzie (2016) (Slide 12):
https://www.researchgate.net/publication/309340780_HYPOTHETICAL_DIVERGENT_EVOLUTION_OF_TWO_APEX_PREDATORS_FROM_THE_HELL_CREEK_FORMATION_NANOTYRANNUS_LANCENSIS_AND_TYRANNOSAURUS_REX
Michael Deak's Twitter post:
https://twitter.com/deak_michael/status/1075732456412774401
Age of other T. rex specimens:
Erickson et al., (2004):
http://webpages.math.luc.edu/~ebalderama/bayes_resources/mt/nature02699.pdf
Erickson et al., (2006):
Supplementary Materials (P. 13):
https://science.sciencemag.org/content/sci/suppl/2006/07/11/313.5784.213.DC1/Erickson.SOM.pdf
Carr (2020):
https://peerj.com/articles/9192/
T. rex LACM 23845 (14 years old):
Molnar (1980):
https://www.jstor.org/stable/1304167
Paul (1988):
https://archive.org/details/g.s.paul1988predatorydinosaursoftheworld/page/n338/mode/1up
Olshevsky (1995):
https://zenodo.org/record/1038228#.YT875SUpCEe
Carr and Williamson (2004):
Link 1:
https://www.academia.edu/2291683/Diversity_of_late_Maastrichtian_Tyrannosauridae_Dinosauria_Theropoda_from_western_North_America
Link 2:
https://academic.oup.com/zoolinnean/article/142/4/479/2632290
Los Angeles Natural History Museum:
Juvenile T. rex finger bones from Don Glut's website:
Don Glut's Dinosaurs:
https://donglutsdinosaurs.com/tyrannosaurus-rex-claw-2/
Nanotyrannus ("Bloody Mary") complete arm:
Pantuso (2019):
theguardian.com/science/2019/jul/17/montana-fossilized-dueling-dinosaurs-skeletons-dino-cowboy
Gregory S. Paul on Nanotyrannus possibly being Related to Dryptosaurus:
(DML.CMNH.Org. Re: [dinosaur] The Dueling tyrannosaurid is not, repeat is not, Tyrannosaurus):
http://dml.cmnh.org/2020Dec/msg00005.html
Link 2:
http://dml.cmnh.org/2020Nov/msg00137.html
Juvenile Nanotyrannus specimen from Dino Lab Inc.:
Maxilla and Dentaries:
https://www.instagram.com/p/CTU8Uowlx-2/?utm_medium=copy_link
Maxilla:
https://www.instagram.com/p/CSdKGvoF1lc/?utm_medium=copy_link
Alioramus (Qiazhousaurus) sinensis:
Lu et al., (2014):
https://www.nature.com/articles/ncomms4788
Supplementary Information:
https://static-content.springer.com/esm/art%3A10.1038%2Fncomms4788/MediaObjects/41467_2014_BFncomms4788_MOESM253_ESM.pdf
Nanotyrannus "Jane's" skull from Brusatte et al., (2010):
Brusatte et al., (2010):
https://www.researchgate.net/publication/46288434_Tyrannosaur_Paleobiology_New_Research_on_Ancient_Exemplar_Organisms
T. rex USNM 6183's Femur and Tibia Lengths:
Gilmore (1920) (P. 122):
https://www.biodiversitylibrary.org/item/125786#page/140/mode/1up
Appalachiosaurus:
Carr et al., (2005): https://www.researchgate.net/publication/233904673_A_New_Genus_And_Species_Of_Tyrannosauroid_From_The_Late_CretaceousMiddle_Campanian_Demopolis_Formation_Of_Alabama
Alioramus altai:
Brusatte et al., (2012) (P. 25 Figure 10):
http://digitallibrary.amnh.org/bitstream/handle/2246/6162/B366.pdf?sequence=1&isAllowed=y
Alioramus remotus:
Paleofile. Alioramus:
http://www.paleofile.com/Dinosaurs/Theropods/Alioramus.asp
T. rex "Baby Bob's" Femur and Tibia pic:
https://mobile.twitter.com/PeteLarsonTrex/status/1226656066177523717
Deak and McKenzie (2016) (Slide 12):
https://www.researchgate.net/publication/309340780_HYPOTHETICAL_DIVERGENT_EVOLUTION_OF_TWO_APEX_PREDATORS_FROM_THE_HELL_CREEK_FORMATION_NANOTYRANNUS_LANCENSIS_AND_TYRANNOSAURUS_REX
T. rex nasal rugosities:
Molnar (1980) (P. 103):
https://www.jstor.org/stable/1304167
Persons IV et al., (2019) (P. 659 or P. 8):
https://anatomypubs.onlinelibrary.wiley.com/doi/am-pdf/10.1002/ar.24118
Link 2:
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24118?tracking_action=preview_click&r3_referer=wol&show_checkout=1
Link 3:
https://www.gbif.org/species/159236947
Abstract:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.24118
"Jane" has a skull similar to Appalachiosaurus':
Black (2010):
https://www.smithsonianmag.com/science-nature/bringing-a-dryptosaurus-back-to-life-66488736/
T. rex manual phalanx 1-1 sizes:
Persons IV et al., (2019):
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24118?tracking_action=preview_click&r3_referer=wol&show_checkout=1
Abstract:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.24118
Version 2:
https://www.gbif.org/species/159236947
Woodward et al., (2020) (Supplementary Materials):
https://www.science.org/action/downloadSupplement?doi=10.1126%2Fsciadv.aax6250&file=aax6250_sm.pdf
Megaraptor:
Novas et al., (2016):
https://www.researchgate.net/publication/305642021_Phylogenetic_relationships_of_the_Cretaceous_Gondwanan_theropods_Megaraptor_and_Australovenator_The_evidence_afforded_by_their_manual_anatomy
Porfiri et al., (2014):
https://www.sciencedirect.com/science/article/abs/pii/S0195667114000755
Teeth:
Premaxillary teeth and cross-sections:
Nanotyrannus:
Stein (pers. comm.).
Molnar (1978):
https://www.jstor.org/stable/1303791
Carpenter (1982):
Bakker et al., (1988):
https://zenodo.org/record/1037529#.YmuXSyUpCEe
Larson (2013):
https://www.geokniga.org/bookfiles/geokniga-tyrannosaurid-paleobiology.pdf
Zanno et al., (2015):
https://www.app.pan.pl/archive/published/app60/app20120145.pdf
Stein (2021):
http://www.thefossilforum.com/applications/core/interface/file/attachment.php?id=755388
V2:
https://www.aaps-journal.org/pdf/JPS.C.2021.0001.pdf
T. rex:
Stein (pers. comm.).
Stein (2021):
http://www.thefossilforum.com/applications/core/interface/file/attachment.php?id=755388
V2:
https://www.aaps-journal.org/pdf/JPS.C.2021.0001.pdf
Kawabe and Hattori (2021) (Abstract):
https://www.tandfonline.com/doi/full/10.1080/08912963.2021.1965137
Randall (2021):
https://www.dailymail.co.uk/sciencetech/article-9919241/Fossils-T-rex-complex-nerve-sensors-tips-jaws-study-finds.html
Dalman et al., (2018):
Dryptosaurus:
Brownstein (2018) (Figure 2):
Appalachiosaurus:
The Charleston Museum: Appalachiosaurus, Dinosaur tooth:
https://www.charlestonmuseum.org/research/collection/appalachiosaurus-dinosaur-tooth/43F18566-9D86-48F6-AF1C-578440369203
Gorgosaurus:
Voris et al., (2022):
https://www.tandfonline.com/doi/full/10.1080/02724634.2021.2041651
Actual Baby T. rex first maxillary tooth:
Carpenter (1982):
Samman et al., (2005):
https://www.app.pan.pl/archive/published/app50/app50-757.pdf
Nanotyrannus' first maxillary tooth description:
Larson (2013):
https://www.geokniga.org/bookfiles/geokniga-tyrannosaurid-paleobiology.pdf
Larson's Twitter post:
https://mobile.twitter.com/PeteLarsonTrex/status/1217195208921747463?cxt=HHwWjsC0of6lrOQhAAAA
Carr and Williamson (2004):
Link 2:
https://academic.oup.com/zoolinnean/article/142/4/479/2632290
Molnar (1978):
https://www.jstor.org/stable/1303791
Adult T. rex maxillary teeth:
Smith (2005) (P. 875 Figure 8 F-G):
Alioramus maxillary teeth:
Brusatte et al., (2012):
http://digitallibrary.amnh.org/bitstream/handle/2246/6162/B366.pdf?sequence=1&isAllowed=y
PaleoAdventures T. rex and Nanotyrannus hand claws:
T. rex:
https://virtualdinosaurmuseum.org/FieldRecord_t_view_fn_TD-13-047_rid_72.html
Nanotyrannus:
Stein (2021):
http://www.thefossilforum.com/applications/core/interface/file/attachment.php?id=755388
PaleoAdventures:
https://virtualdinosaurmuseum.org/FieldRecord_t_view_fn_TD-11-121_rid_82.html
Appalachiosaurus dentary:
Image:
Website:
Pillion (2021);
https://www.al.com/news/2021/11/in-search-of-appalachiosaurus-t-rexs-alabama-cousin.html
Juvenile Gorgosaurus dentary:
Currie (2003):
https://www.app.pan.pl/archive/published/app48/app48-191.pdf
Voris et al., (2019):
https://www.researchgate.net/figure/Skull-reconstruction-of-TMP-19941431-Digital-rendering-of-skull-based-on-CT-data-in_fig1_337602721
Dueling Dinosaurs:
Bonhams. Dueling Dinosaurs:
https://www.bonhams.com/auctions/21076/lot/1032/
Pantuso (2019):
Pic:
https://images.app.goo.gl/JkCKufmnA9w5pTEH9
Article:
https://www.theguardian.com/science/2019/jul/17/montana-fossilized-dueling-dinosaurs-skeletons-dino-cowboy
Dueling Dinosaurs website drawing/computer image of the skeletons
Pic:
https://images.app.goo.gl/rcrwMHmWTZtgrWph8
Website:
https://duelingdinosaurs.org/
BHI video:
Dryptosaurus caudals:
Cope (1869) (P. 102):
https://www.biodiversitylibrary.org/page/39852079#page/108/mode/1up
Brusatte et al., (2011) (PP. 16-18):
https://digitallibrary.amnh.org/bitstream/handle/2246/6117/N3717.pdf?sequence=1&isAllowed=y
"Jane's" bones:
The Theropod Database. Tyrannosaurus rex:
https://www.theropoddatabase.com/Tyrannosauroidea.html#Tyrannosaurusrex
Tyrannosauroidea central:
The Jane Diaries, Entry #21:
https://tyrannosauroideacentral.blogspot.com/search?q=jane+diaries+%2321
The Jane Diaries, Entry #25:
https://tyrannosauroideacentral.blogspot.com/2014/12/the-jane-diaries-entry-25.html?m=0
The Jane Diaries, Entry #1:
https://tyrannosauroideacentral.blogspot.com/2014/10/the-jane-diaries-entry-1.html?m=1
The Jane Diaries, Entry #4:
https://tyrannosauroideacentral.blogspot.com/2014/10/the-jane-diaries-entry-4.html?m=1
T. rex's bone count:
Brochu (2003):
Osborn (1906):
Osborn (1917):
Carpenter (1991):
https://www.researchgate.net/publication/295458205_Variation_in_Tyrannosaurus_rex
Neal Larson (2008a):
Figure 1.1:
https://zenodo.org/record/3750269#.Yoo2AyUpCEc
Figure 1.27:
https://zenodo.org/record/3750321#.Yoj1jiUpCEc
Paper:
V1:
https://zenodo.org/record/3750267#.Yoj2MSUpCEd
V2:
V3:
https://zenodo.org/record/3808759#.YokK4yUpCEc
BHIGR:
http://www.bhigr.com/store/product.php?productid=511&cat=2&page=1
-Link 2 (pdf):
http://www.bhigr.com/store/product.php?productid=46&cat=2&page=1
Gorgosaurus' bone count:
Lambe (1917):
https://ia800804.us.archive.org/19/items/b29809940/b29809940.pdf
Russell (1970):
https://www.biodiversitylibrary.org/page/36032001#page/26/mode/1up
Brochu (2003):
Maleev (1955b):
https://paleoglot.org/files/Maleev_55b.pdf
Maleev (1974):
https://paleoglot.org/files/Maleev_74.pdf
Brochu (2003):
Daspletosaurus' bone count:
Russell (1970):
https://www.biodiversitylibrary.org/page/36032001#page/26/mode/1up
Jinbeisaurus paper:
Wu et al., (2019):
Endocast change during ontogeny:
Kawabe et al., (2015):
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0129939
North America during Late Maastrichtian:
Gates et al., (2012) (Figure 1):
https://www.researchgate.net/figure/Paleogeographic-maps-of-North-America-during-the-A-late-Campanian-75-Ma-and-B-late_fig6_230639253
Fiorillo and Tykosi (2014) (Results and Discussion: Laramidian Geographic Provincialism, para. 1):
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091287
Bell and Currie (2014) (Figure 4):
https://www.semanticscholar.org/paper/Albertosaurus-(Dinosauria%3A-Theropoda)-material-from-Bell-Currie/904ec35df857d1c6f22cf6a178de25a037bb30f3/figure/3
Blakey (2014):
https://www.searchanddiscovery.com/documents/2014/30392blakey/ndx_blakey
Druckenmiller et al., (2021):
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00739-9
T. rex UCRC-PV 1:
Photo of T. rex UCRC-PV1's Arm:
https://mobile.twitter.com/PeteLarsonTrex/status/973346519423246336
Larson and Carpenter (2008) (P. 41):
https://books.google.com/books/about/Tyrannosaurus_Rex_the_Tyrant_King.html?id=5WH9RnfKco4C&printsec=frontcover&newbks=1&newbks_redir=0&source=gb_mobile_entity#v=onepage&q=ucrc%20pv1&f=false
Lacrimals:
Nanotyrannus:
1. BHI 6437 ("Bloody Mary"):
Photo:
https://images.app.goo.gl/J9aHKG3BQTyegNyZ9
Bonhams. Dueling Dinosaurs:
https://www.bonhams.com/auctions/21076/lot/1032/
T. rex:
1. RSM P.2990.1:
Holtz's Twitter:
https://mobile.twitter.com/TomHoltzPaleo/status/1308744116365295617
Carr (2020):
https://peerj.com/articles/9192/
2. LACM 23845:
Olshevsky (1995):
https://zenodo.org/record/1038228#.YT875SUpCEe
Tarbosaurus/Tyrannosaurus bataar:
1. MCP-107/7:
Tsuihiji et al., (2011):
https://www.researchgate.net/publication/232865497_Cranial_Osteology_of_a_Juvenile_Specimen_of_Tarbosaurus_bataar_Theropoda_Tyrannosauridae_from_the_Nemegt_Formation_Upper_Cretaceous_of_Bugin_Tsav_Mongolia
Other Tyrannosauroid Arms:
Mallon et al., (2019):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7079176/
Russell (1970) (P. 9):
https://www.biodiversitylibrary.org/page/36032001#page/27/mode/1up
Nanotyrannus BHI 6437 and T. rex "Wyrex" arm drawings:
Pic.:
https://images.app.goo.gl/u6Yu2BCwe49kavod8
Alexander Jack Lund's Twitter post:
https://twitter.com/Nannotyrannus/status/972591409592225792
Nanotyrannus BHI 6437's manual phalanx 1-1 bone from Peter Larson's Twitter post:
Pic.:
https://images.app.goo.gl/xDcRsxwf8bMu9BLj7
Twitter:
https://twitter.com/PeteLarsonTrex/status/1214576760718794753
T. rex manual 1-1 phalanx sizes:
Persons IV et al., (2019):
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24118?tracking_action=preview_click&r3_referer=wol&show_checkout=1
Abstract:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.24118
Version 2:
https://www.gbif.org/species/159236947
Larson and BHI 6437's femur length:
Larson's Twitter:
https://mobile.twitter.com/PeteLarsonTrex/status/1214957069884887041
Nanotyrannus Femur and Tibia Sizes:
Woodland et al., (2020):
https://advances.sciencemag.org/content/6/1/eaax6250
Dryptosaurus links:
Brusatte et al., (2011):
https://digitallibrary.amnh.org/bitstream/handle/2246/6117/N3717.pdf?sequence=1&isAllowed=y
Carpenter et al., (1997):
https://www.jstor.org/stable/4523837
Maxillary fenestrae and strut links:
Delcourt (2017):
Carr et al., (2017):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5372470/
Voris (2018):
https://prism.ucalgary.ca/bitstream/handle/1880/109240/ucalgary_2018_voris_jared.pdf?sequence=1&isAllowed=y
Voris et al., (2022):
https://www.tandfonline.com/doi/full/10.1080/02724634.2021.2041651
Paleofile. "Albertosaurus":
http://www.paleofile.com/Dinosaurs/Theropods/Albertosaurus.asp
Bell and Currie (2014) (Figure 2):
https://www.researchgate.net/figure/Albertosaurus-sarcophagus-left-maxilla-TMP-19891753-in-A-B-lateral-and-C-D_fig2_277476642
Tsuihiji et al., (2011):
Figure 6 (Tooth count):
https://www.researchgate.net/figure/Dental-morphology-of-a-juvenile-Tarbosaurus-bataar-MPC-D-107-7-A-numbers-of-alveoli_fig6_232865497
Paper:
https://people.ohio.edu/witmerl/Downloads/2011_Tsuihiji_et_al._Tarbosaurus_juvenile_skull_PROOF.pdf
V2:
https://www.researchgate.net/publication/232865497_Cranial_Osteology_of_a_Juvenile_Specimen_of_Tarbosaurus_bataar_Theropoda_Tyrannosauridae_from_the_Nemegt_Formation_Upper_Cretaceous_of_Bugin_Tsav_Mongolia
Hurum and Sabath (2003):
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.738.4318&rep=rep1&type=pdf
Currie (2003):
https://www.app.pan.pl/archive/published/app48/app48-191.pdf
Yun (2015) (p. 4):
Tooth count in other theropod genera:
Mortimer, Mickey. The Theropod Database Blog. "Validity of Nanotyrannus." 2013. "#X," para. 2, "#7":
http://theropoddatabase.blogspot.com/2013/09/validity-of-nanotyrannus.html?m=1
Larson (2013) (Full) (Start at p. 15):
https://www.geokniga.org/bookfiles/geokniga-tyrannosaurid-paleobiology.pdf
"Baby Bob" skull pic from FossilForum:
Image:
https://images.app.goo.gl/bkcNXKVNCkuFi3d88
Link:
http://www.thefossilforum.com/index.php?/topic/61245-bob-the-baby-t-rex/
"Tinker" skull:
Christies:
https://www.christies.com/lot/lot-5989561
LACM 23845's arms being small:
Molnar (1980):
https://www.jstor.org/stable/1304167
Paul (1988) (pp. 333 and 334):
https://archive.org/details/g.s.paul1988predatorydinosaursoftheworld/page/n338/mode/1up
Olshevsky (1995):
https://zenodo.org/record/1038228#.YT875SUpCEe
"Baby Bob's" skull and femur length:
Detrich Fossil Co Twitter post:
https://mobile.twitter.com/kingfossil/status/1121904029095866370
"Nanotyrannus" skull from Fossil Forum:
V1:
http://www.thefossilforum.com/index.php?/topic/57402-my-jurassic-park-hell-creeklance-theropods/page/2/&tab=comments#comment-653993
V2:
http://www.thefossilforum.com/index.php?/topic/55855-is-nanotyrannus-a-separate-species-or-is-it-a-juvenile-t-rex/page/4/&tab=comments#comment-649656
Full discussion (V1):
http://www.thefossilforum.com/index.php?/topic/57402-my-jurassic-park-hell-creeklance-theropods/
T. rex "Duffy" skull links from BHIGR:
Link 1 (Poster):
http://www.bhigr.com/store/product.php?productid=632
Link 2 (Right side of skull):
http://www.bhigr.com/store/product.php?productid=55
Link 3 (Left side of skull):
http://www.bhigr.com/store/product.php?productid=614
Lythronax and Teratophoneus:
Loewen et al., (2013):
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079420
Adult T. rex endocast from Prehistoric Store:
Prehistoric Store:
http://www.prehistoricstore.com/item.php?item=186
Alioramus skulls:
Brusatte et al., (2009):
https://www.pnas.org/content/106/41/17261
Bonhams:
Bonhams. "Rare Tyrannosaurid Skull-Tyrant Lizard from the Age of Dinosaurs":
https://www.bonhams.com/auctions/17502/lot/1159/
Juvenile T. rex TMM 41436-1:
Wick (2014) (Brief history and referral, para. 2):
Figure 1:
https://images.app.goo.gl/5s863Z7Q9niWnQsC7
Paper:
https://www.sciencedirect.com/science/article/abs/pii/S0195667114000500
Carr (2020) (pp. 59 and 93):
https://peerj.com/articles/9192/
"Jane's" and "Sue's" humeri:
Holtz's Twitter post:
https://twitter.com/TomHoltzPaleo/status/1367247262124929026?s=20
Gorgosaurus' arms:
Lambe (1914):https://www.biodiversitylibrary.org/page/5739477#page/20/mode/1up
Lambe (1917):https://ia800804.us.archive.org/19/items/b29809940/b29809940.pdf
Currie on no sign of tooth loss during ontogeny:
Currie (2011):
https://www.researchgate.net/publication/40662060_Allometric_growth_in_tyrannosaurids_Dinosauria_Theropoda_from_the_Upper_Cretaceous_of_North_America_and_Asia
18-year old T. rex "Victoria":
Strickland (2019):
https://www.cnn.com/2019/09/12/world/victoria-t-rex-fossil-scn/index.html
Pangea Fossils Facebook post:
https://m.facebook.com/Pangeafossils/photos/a.248323211899474/4610872618977823/?type=3&source=54&ref=page_internal
NMMNH P-32567:
Williamson and Brusatte (2014):
https://www.researchgate.net/publication/261443973_Small_Theropod_Teeth_from_the_Late_Cretaceous_of_the_San_Juan_Basin_Northwestern_New_Mexico_and_Their_Implications_for_Understanding_Latest_Cretaceous_Dinosaur_Evolution
Bakker et al., (1988):
https://zenodo.org/record/1037529#.YiYc4yVOmEc
Samman et al., (2005):
https://www.app.pan.pl/archive/published/app50/app50-757.pdf
Carpenter (1982):
https://www.researchgate.net/publication/281039198_Baby_dinosaurs_from_the_Late_Cretaceous_Lance_and_Hell_Creek_Formations_and_a_description_of_a_new_species_of_theropod
SMP VP-1113:
Lucas and Sullivan (2000):
https://www.researchgate.net/publication/296486576_Stratigraphy_and_vertebrate_biostratigraphy_across_the_Cretaceous-Tertiary_Boundary_Betonnie_Tsosie_Wash_San_Juan_Basin_New_Mexico
Sullivan et al., (2005):
https://www.researchgate.net/publication/266228740_Dinosaurs_pollen_and_the_Cretaceous-Tertiary_boundary_in_the_San_Juan_Basin_New_Mexico
V2:
https://nmgs.nmt.edu/publications/guidebooks/downloads/56/56_p0395_p0407.pdf
Gilmore (1920):
https://www.biodiversitylibrary.org/item/125786#page/140/mode/1up
Lambe (1917):
https://ia800804.us.archive.org/19/items/b29809940/b29809940.pdf
Mortimer, Mickey. Theropod Database. "Alamotyrannus":
https://theropoddatabase.com/Tyrannosauroidea.html#Alamotyrannusbrinkmani
Skull Width:
Currie (2003):
https://www.app.pan.pl/archive/published/app48/app48-191.pdf
Longrich et al., (2010):
https://www.researchgate.net/publication/47545561_Cannibalism_in_Tyrannosaurus_rex
Peterson et al., (2009):
https://www.researchgate.net/publication/250083005_Face_biting_on_a_juvenile_tyrannosaurid_and_behavioral_implications
Loewen et al., (2013):
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079420
V2:
Lambe (1904):
https://archive.org/details/LambeL.M.1904.OnDryptosaurusIncrassatuscopeFromTheEdmonton/page/n38/mode/1up?view=theater
Russell (1970):
https://www.biodiversitylibrary.org/page/36032001#page/15/mode/1up
IRGNM-211:
Lucas et al., (1995):
https://play.google.com/store/books/details/C%C3%A9sar_Jacques_Ayala_Studies_on_the_Mesozoic_of_Son?id=QxdHAwAAQBAJ
Lambe (1917) (P. 67 Figure 43, A):
https://ia800804.us.archive.org/19/items/b29809940/b29809940.pdf
Carr et al., (2005) (P. 135, Figure 16, K):
https://www.researchgate.net/publication/233904673_A_New_Genus_And_Species_Of_Tyrannosauroid_From_The_Late_CretaceousMiddle_Campanian_Demopolis_Formation_Of_Alabam
Mallon et al., (2019):
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24199
Brusatte et al., (2011) (PP. 7 and 17):
https://digitallibrary.amnh.org/bitstream/handle/2246/6117/N3717.pdf?sequence=1&isAllowed=y
Brochu (2003):
https://www.researchgate.net/profile/Christopher-Brochu/publication/249022959_Osteology_of_Tyrannosaurus_rex_Insights_from_a_Nearly_Complete_Skeleton_and_High-Resolution_Computed_Tomographic_Analysis_of_the_Skull/links/58b08cb6aca2725b5413d94c/Osteology-of-Tyrannosaurus-rex-Insights-from-a-Nearly-Complete-Skeleton-and-High-Resolution-Computed-Tomographic-Analysis-of-the-Skull.pdf?origin=publication_detail
LACM Collections:
LACM 23845:
https://collections.nhm.org/dinosaur-institute/Display.php?irn=2059998&QueryPage=%2Fdinosaur-institute%2F&BackRef=ResultsList.php
LACM 150167 ("Thomas"):
https://collections.nhm.org/dinosaur-institute/Display.php?irn=1941562&QueryPage=%2Fdinosaur-institute%2F&BackRef=ResultsList.php
Serrano-Branas et al., (2014):
https://www.academia.edu/6608485/Tyrannosaurid_teeth_from_the_Lomas_Coloradas_Formation_Cabullona_Group_Upper_Cretaceous_Sonora_México
Lacrimal Processes:
Dalman (pers. comm.).
Hurum and Sabath (2003):
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.738.4318&rep=rep1&type=pdf
Carr (2020):
https://peerj.com/articles/9192/
Figure 6 (CMNH 7541):
https://dfzljdn9uc3pi.cloudfront.net/2020/9192/1/Figure_S1.png
Figure 7 ("Jane"):
https://dfzljdn9uc3pi.cloudfront.net/2020/9192/1/Figure_S2.png
Figure 10 ("Jane" [Top/dorsal view]):
https://dfzljdn9uc3pi.cloudfront.net/2020/9192/1/Figure_S5.png
Todd Johnson Facebook posts:
Link 1
https://m.facebook.com/photo.php?fbid=1959485944118685&id=100001718944180&set=p.1959485944118685&source=47&__tn__=R-R
Link 2:
Link 3:
Voris (2018):
Carr et al., (2010):
V1:
https://bioone.org/journalArticle/Download?fullDOI=10.1080%2F02724630903413032
V2:
https://bioone.org/journals/Journal-of-Vertebrate-Paleontology/volume-30/issue-1/02724630903413032/iBistahieversor-sealeyi-i-gen-et-sp-nov-a-New-Tyrannosauroid/10.1080/02724630903413032.full
Tyrannosauroidea femora and tibiae sizes:
Persons IV and Currie (2016):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728391/#!po=0.632911
Xu et al., (2006):
http://lesdinos.free.fr/Ty160.pdf
Locations of Dryptosaurus and T. rex:
Deak and McKenzie (2016):
Longrich and Field (2012):
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0032623
Coexisting Taxa from New Egypt and Hell Creek Formations:
Gallagher et al., (2012):
https://geology.rutgers.edu/images/stories/faculty/miller_kenneth_g/kgmpdf/12-Gallagher.GeolFrance.pdf
Van Vranken and Boyd (2021):
V2:
https://escholarship.org/content/qt8v08w2d6/qt8v08w2d6_noSplash_d355beed52f7ab721a6a0b9ed4c5e057.pdf
Sullivan et al., (2011):
https://www.researchgate.net/publication/266459570_The_first_lambeosaurin_Dinosauria_Hadrosauridae_Lambeosaurinae_from_the_Upper_Cretaceous_Ojo_Alamo_Formation_Naashoibito_Member_San_Juan_Basin_New_Mexico
Rolleri et al., (2020) (pp. 284-285) (SVP, 2020):
https://vertpaleo.org/wp-content/uploads/2021/03/SVP_2020_Program-Abstracts-Volume-FINAL-for-Publishing-1.27.2021.pdf
Brownstein and Bissel (2020):
https://www.cambridge.org/core/journals/journal-of-paleontology/article/an-elongate-hadrosaurid-forelimb-with-biological-traces-informs-the-biogeography-of-the-lambeosaurinae/3AADDB876793B4A99950C56D74CE2CD8
Farke and Phillip (2017):
https://peerj.com/articles/3342/
(Serrano-Branas and Prieto-Marquez, 2022):
https://luisvrey.files.wordpress.com/2022/01/serrano-branas-and-prieto-marquez-2021-taphonomy-latirhinus.pdf
Luis V. Rey's blog on the paper (1/30/22):
