(News) Longrich and Saitta (2024) Says "Nanotyrannus" was a Basal Tyrannosauroid!

So for a couple of years now, I have stated that "Nanotyrannus" was actually the genus Dryptosaurus, or a sister taxon to Dryptosaurus and the two genera form a clade within tyrannosauroidea. Looks like my perseverance has paid off! 

I have been alerted that professional paleontologist Nicholas Longrich (or Nick Longrich) wrote a message on Facebook on October 18. He is uploading a preprint to BioRXiv about "Nanotyrannus." In his message, he states that there are 77 characteristics that separate "Nanotyrannus" from T. rex, that the specimens show signs of slow maturity instead of rapid growth associated with T. rex, and that "Nanotyrannus" is a tyrannosauroid and not a tyrannosaurinae like T. rex! 

Longrich's message from Facebook:
Pic 1:

Pic 2:

Pic 3:

Link:
https://m.facebook.com/story.php?story_fbid=pfbid02LVfzbMwkXg7feHtuCP78YhwqzfipLjLjfDCbj3gibcVhCS6JhGTSCYXmazNtrNHol&id=556574124

I'll be waiting for his preprint "with great interest."

Here's my own work on "Nanotyrannus" for comparison:

Blogposts:
"Nanotyrannus" is Dryptosaurus:

https://psdinosaurs.blogspot.com/2021/08/evidence-of-subadult-nanotyrannus.html

Size Calculations of Dryptosaurus:

https://psdinosaurs.blogspot.com/2022/06/size-calculations-for-dryptosaurus.html

My Academia papers:

"Nanotyrannus" is Dryptosaurus: An Abstract:

https://www.academia.edu/96574784/Nanotyrannus_is_Dryptosaurus_An_Abstract

A Baby Tyrannosaurus rex Premaxillary, or First Maxillary, Tooth:

https://www.academia.edu/96575022/A_Baby_Tyrannosaurus_rex_Premaxillary_or_First_Maxillary_Tooth

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): 
The preprint is here (Longrich and Saitta, 2023):

https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs

V2:

https://www.researchgate.net/publication/374913485_Taxonomic_status_of_Nanotyrannus_lancensis_Dinosauria_Tyrannosauroidea_-_a_distinct_taxon_of_small-bodied_tyrannosaur

Review:
1. Highlights:
1.) First off, the authors said that tyrannosauroids reached peak diversity in the late Cretaceous, which means that there is ample opportunity for more than one tyrannosaur genus to coexist in one place. The best examples are Gorgosaurus and Daspletosaurus in North America, and Tarbosaurus (or Tyrannosaurus bataar) and Alioramus (pp. 7-8; p. 9 Table 3). They also raise the question as to how likely it would be for only one genus of large predator to reign uncontested in its environment, saying that having two genera of tyrannosaurs in the same environment is more than likely to occur (p. 10).

2.) Second, no other specimens fill in the morphological gaps between the "Nanotyrannus," and T. rex, specimens (pp. 10 and 15; p. 15 Figure 3).

3.) The authors then go on to state 77 morphological differences between the "Nanotyrannus" and T. rex specimens (pp. 10-14). Some of the traits have been mentioned elsewhere in other publications (p. 10). I will say that the authors mentioned the lingual bar (p. 13), but they didn't state that it covers the first alveoli in "Nanotyrannus" and the first two in T. rex. The authors said that the bar is "deep posteriorly" in "Nanotyrannus," but is "narrow and tapered relative to the anterior of the toothrow" in T. rex (p. 13). 

The placement of the lingual bar near the anterior of the dentary is a huge trait to help identify tyrannosauroid and tyrannosaurid, or tyrannosaurinae, taxa. I've stated this on the blog many times, and in my paper that described BHI 6439, but I'll reiterate it here: the lingual bar covers the first alveoli in basal tyrannosauroids and tyrannosaurids, but it covers the first two in tyrannosaurinae. This was first mentioned in Dalman and Lucas (2017). The lingual bar covers the first alveoli in "Nanotyrannus," but the first two alveoli in T. rex. This is seen in BHI 6439 (a baby T. rex specimen) and FMNH PR 2081 (an adult T. rex specimen).

Figure 5 from my "A Description of the Baby T. rex Specimen BHI 6439" paper: T. rex dentaries in medial views. 5A: BHI 6439. 5B: FMNH PR 2081 from Brochu (2003) (p. 42 Figure 41). 5C: BMNH R7994 from Dalman and Lucas (2017) (p. 24 Figure 10). 5D: RSM P2523.8 from Persons IV et al., (2019) (p. 668 Figure 18B). Numbers indicate the position of the first three teeth in the dentary. The teeth in the dentary of RSM P2523.8 were numbered by the authors of Persons IV et al., (2019). Green arrows indicate the lingual bar covering the first two teeth/alveoli. The red arrows show that the lingual bar drops at the third alveolus/tooth. The position of the lingual bar doesn’t change during ontogeny. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, “idp” is the interdentary plate, and “dp” are the dental plates.

All in all, the characteristics in the "Nanotyrannus" specimens do not appear as juvenile characteristics of T. rex. Using other tyrannosaur taxa, like Tarbosaurus/Tyrannosaurus bataar, baby and juvenile tyrannosaurs have characteristics seen in mature individuals. Although some characteristics in "Nanotyrannus" could potentially be juvenile in nature, a comparison with juvenile 

Tarbosaurus/Tyrannosaurus bataar, and Gorgosaurus, specimens, demonstrate that they do not undergo massive transformations during ontogeny like T. rex supposedly would. Thus, the growth series provided by Carr (2020) is incorrect (pp. 15-16). 

I have also stated that the teeth, and dentary, characteristics of T. rex did not change during ontogeny either. The baby T. rex premaxillary tooth UCMP 119853 had an identical morphology to the premaxillary teeth seen in the adults (carina on the labial and lingual sides, and being serrated). It was also distinct from the "Nanotyrannus" premaxillary teeth (two carinae on the distal side of the tooth, unserrated, and a distal ventral ridge in the middle of the tooth).

Figure 11 from my "A Baby Tyrannosaurus rex Premaxillary, or First Maxillary, Tooth" paper. 11A is UCMP 119853 (T. rex premaxillary tooth, 8 mm), and 11B is UCMP 124406 

(cf. Dryptosaurus/"Nanotyrannus" premaxillary tooth, 6.6 mm). UCMP 119853’s carina is on the lateral (labial and lingual) sides (green arrows) that are serrated, and lacks a vertical ridge on the posterior/distal end of the crown. UCMP 124406 has distal carinae (red arrows) that lack serrations, and a distal vertical ridge (purple arrows) on the distal end of the crown:

The larger baby T. rex specimen, BHI 6439, had 13 teeth in its dentary, and the lingual bar covered the first two alveoli. This is seen in adult specimens as well. "Nanotyrannus" had 16-17 teeth in its dentary, with the lingual bar covering the first alveoli only. This is seen in BMRP 2002.4.1 ("Jane") (and "Zuri," but I haven't used that specimen yet. I will in the future). 

Figure 9 from my "A Description of the Baby T. rex Specimen BHI 6439" paper: Close-ups of cf. Dryptosaurus specimen BMRP 2002.4.1 and T. rex specimen BHI 6439 (reversed). In 9A, the green arrow indicates that the lingual bar covers the first alveolus only. The red arrows show that the lingual bar drops at the second alveolus, and past the third one. In 9B, the green arrows show that the lingual bar covers the first alveoli and second tooth. The red alveoli shows that the lingual bar drops at the third tooth. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, and “idp” is the interdentary plate.

Therefore, young T. rex specimens didn't go through a rapid transformation as proposed by Carr (2020) (tooth loss during ontogeny, tooth morphology transformation, etc.). 

4.) Larson (2013) noted that BMRP 2002.4.1 ("Jane") had skeletal fusion in some of its bone, meaning that it was nearing maturity (pp. 17-21). Longrich and Saitta said that "not all skeletal fusions are associated with maturity," the axial, scapulacoracoid, and pelvis, fusions seen in BMRP 2002.4.1 ("Jane") signify that that specimen was reaching maturity (p. 17). 

5.) Rugosities on BMRP 2002.4.1 ("Jane"), KU 155809, and the SWAU specimen ("Zuri"), signify that these specimens were reaching maturity. There is "relatively weakly developed rugosity" on the juvenile T. rex specimen LACM 23845 (a 14-year old individual [Erickson et al., 2004]) (p. 18; p. 29 Table 5).

6.) The lack of an EFS (External Fundamental System) rules out that BMRP 2002.4.1 ("Jane") and BMRP 2006.4.4 ("Petey") are old adults, "but does not rule out the possibility that these animals are young adults, approaching full size." The T. rex specimen "Sue" weighed 7,930 kg before getting the EFS, but weighed only 8,223 kg when she got the EFS and then died. The animal only gained "around 300 kg." The EFS only appears when a specimen reaches full maturity, thus BMRP 2002.4.1 ("Jane") and BMRP 2006.4.4 ("Petey") were probably young adults (p. 18). Although no specimen has an EFS, a "Nanotyrannus" specimen can be found someday having one. It should be noted that only one specimen of Daspletosaurus, Albertosaurus, and T. rex, have an EFS (p. 29). Thus, more specimens need to be found.

7.) The fact that BMRP 2002.4.1 ("Jane") and BMRP 2006.4.4 ("Petey") "show low growth rates" due to the "narrow spacing of LAGs," and not "exceeding 800 kg/yr," means that these were not rapidly-growing juvenile T. rex specimens. In fact, the "Nanotyrannus" specimens didn't exhibit growth rates "exceeding 150 kg/yr for the last few years of life." Juvenile T. rex specimens "are predicted to have very high maximal growth rates as they approach 1000 kg/yr." This can be estimated from "Sue" as well. Thus, the hypothesis that BMRP 2002.4.1 ("Jane") and BMRP 2006.4.4 ("Petey") were juvenile T. rex specimens is incorrect (p. 19; p. 21 Figure 5). The growth curves for the two "Nanotyrannus" specimens do not match with the growth curves of T. rex (p. 24 Figure 7). The estimated adult body mass for BMRP 2002.4.1 ("Jane") is about 1250-1600 kg, while BMRP 2006.4.4 ("Petey") is 700-1100 kg (p. 28).

*8.) This is the best part to me. The authors did a phylogenetic analysis of "Nanotyrannus," and found it as a basal tyrannosauroid! It is not a tyrannosaurid, nor a tyrannosaurinae. This is alongside Dryptosaurus, 

Appalachiosaurus, and Alioramus (pp. 26-27). I've been saying this four about two years now! Although the authors did not say that "Nanotyrannus" is the genus Dryptosaurus, they still say that "Nanotyrannus" is a basal tyrannosauroid alongside Dryptosaurus. I have also stated this. That works for me too! I'm still going to say that "Nanotyrannus" is either cf. Dryptosaurus aquilunguis, or that "Nanotyrannus" and Dryptosaurus are sister taxa within tyrannosauroidea. 

Figure 9 (phylogenetic chart) from Longrich and Saitta (2023) (p. 27):
Figure 9A:

Figure 9B:

In both charts from Figure 9, "Nanotyrannus" is situated outside of tyannosauridae.

2. Problems:
1.) I will say that there are a couple of problems that I had with the paper. First, I am surprised that there weren't any figures of the bones aside from the skull of CMNH 7541. 

2.) The authors state that only one juvenile T. rex has been discovered, which is LACM 23845 (pp. 18, 26, and 29). There are actually many baby and juvenile T. rex specimens that do not exhibit "Nanotyrannus" traits. Here's my own growth series for T. rex:

*UCMP 119853: 7 feet (2.1 meters):

*BHI 6439: 23 feet (7.0 meters):

LACM 23845: 24 feet (7.3 meters) (14 years old).
*UCRC-PV 1: 26 feet (8.0 meters);

TCM 2001.90.1 ("Bucky"): 35 feet (10.8 meters) (16 years old).
BHI 3033 ("Stan"): 40 feet (12.2 meters) (18 years old).
CM 9380: 42 feet (12.9 meters) (22 years old).
FMNH 2081 ("Sue"): 45 feet (13.6 meters) (28-33 years old).

The three specimens with asterisks next to them are specimens that are smaller in, or are comparable in, size to the "Nanotyrannus" specimens "Jane" and "Petey." LACM 23845 is only 14 years old while BMRP 2006.4.4 ("Petey") is 15 (Woodward et al., 2020). In fact, UCMP 119853 is smaller than other more complete "Nanotyrannus" specimens, which means that it was younger as well. There are other juvenile T. rex specimens as well, like TCM 2001.90.1 ("Bucky") which is 16 years old.

In the middle:
1.) This next remark is not really a problem, nor is it really a highlight. The authors say that some of the "Nanotyrannus" specimens ("Dueling Dinosaurs," and LACM 28471) might actually be a third genus of tyrannosauroid: Stygivenator (pp. 29-30). I'm not entirely against that idea, but to keep things simple for now, I'm going to keep the "Nanotyrannus" specimens as either cf. Dryptosaurus aquilunguis or "Nanotyrannus lancensis." Heck, Dryptosaurus lancensis might even work.

1st Conclusion:
In summation, Longrich and Saitta (2023) confirm the majority of my hypothesis that "Nanotyrannus" is a basal tyrannosauroid, not a tyrannosaurid or tyrannosaurinae. T. rex doesn't go through a major transformation during ontogeny, and that two tyrannosauroids coexisted in North America during the late Maastrichtian. 

Other sources used:
Larson (2013):
https://www.researchgate.net/publication/289687970_The_case_for_Nanotyrannus
Woodward et al., (2020):
https://advances.sciencemag.org/content/6/1/eaax6250

Update (1/3/24):
Longrich's and Saitta's paper has been officially published:

https://www.mdpi.com/2813-6284/2/1/1

They have figures, and more data, in the paper. Of particular note are:

1.) They stated that "Nanotyrannus'" lingual bar on the medial side of the dentary covers the first alveolus, while T. rex's lingual bar covers the first two alveoli (Figure 12):

Dalman and Lucas (20170 noted this first, and I have stated this as well. You can see this clearly in the young T. rex specimen BHI 6439. 

2.) No amniote (any animal that has an egg during its embryonic stage of life) has their hands shrink, or reabsorbed, during ontogeny (p. 31):

They also posted a figure of the manual unguals (Figure 21):

3.) Another juvenile specimen of T. rex was listed by the authors. In the preprint, the authors listed LACM 23845 as the only conclusive juvenile specimen of T. rex. The new specimen, 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):

Description part 2 (p. 44):

UCMP V84133 (Figure 29):

Comparison with "Nanotyrannus'" frontals (Figure 30) and phylogenetic analyses (Figure 31):

On 1/4/24, Professor Holtz said that the Nanotyrannus frontal bones (catalogued as DDM 334.1) could "*potentially*" be from an adult Nanotyrannus:

Special thanks to Luke Skywalker Jedi Knight 27 for the photo of the tweet.

Link:

Holtz's Tweet (1/4/24):

https://x.com/tomholtzpaleo/status/1742968130995945476?s=61&t=DgZNoZU2b-DFLtG5TI6cbQ

4.) "Nanotyrannus" is still a basal tyrannosauroid (p. 46). Figures 33 and 34A shows 
"Nanotyrannus" alongside Dryptosaurus, Appalachiosaurus, Alioramus, and other basal tyrannosauroidea taxa (p. 47 Figure 32; p. 49 Figure 34A).

Nanotyrannus is a basal tyrannosauroid (p. 46):

Figure 33B:

Figure 34A:

2nd Conclusion:
As I have been saying for almost three years now, "Nanotyrannus" is a basal tyrannosauroid. I'm still certain that it is either Dryptosaurus (as D. aquilunguis or even D. lancensis), or it is a sister taxon to Dryptosaurus. I will be writing more about that in the future. Always keep an open mind and do your own research, ladies and gentlemen!

A Description of the Baby T. rex Specimen BHI 6439 (2023)

Written on 7/3/23

Link:
https://www.academia.edu/105502160/A_Description_of_the_Baby_T_rex_Specimen_BHI_6439

                                    A Description of the Baby T. rex Specimen BHI 6439

                                                                    Abstract:

The T. rex specimen BHI 6439 has been stated, and referenced, as being a young individual that differs from the cf. Dryptosaurus (or “Nanotyrannus”) specimens. Thus, showing that young T. rex specimens differed from the latter genus. However, to this author’s knowledge, there isn’t a description of the specimen yet. Only DePalma et al., (2013) referenced it. Therefore, this author decided to (as best as they could) give a description of the specimen. BHI 6439 is a semi-complete dentary that is 54.5 cm long, has 13 alveoli with teeth that are ziphodont yet robust, a tooth row that is 33 cm long, and a lingual bar that covers the first two dentary alveoli/teeth on the medial side of the bone. Using the tooth row length, the specimen would’ve been about 23 feet (7.0 meters) in length. The specimen shares all of the characteristics seen in older T. rex specimens. The specimen differs from the cf. Dryptosaurus specimen BMRP 2002.4.1 (“Jane”) in having 17 teeth that have an extreme ziphodont morphology than the teeth of BHI 6439, and a lingual bar that covers the first alveolus on the medial side instead of the first two. BMRP 2002.4.1 is about the same size as BHI 6439 at 22 feet (6.7 meters), yet differs in dentary characteristics. The latter specimen, along with the smaller T. rex specimen UCMP 119853 (2.1 meters), demonstrate that young T. rex specimens did not differ in dentary and tooth morphologies from the adults. Thus, the “Nanotyrannus” specimens belong to another genus.

Figures:

Figure 1: BHI 6439 in lateral view. Figure 1A displays the specimen as is. Figure 1B displays the terminology. The numbers above the teeth display their positions in the dentary. The white arrow locates the foramina. The blue arrow demonstrates the chin/inflection point. The numbers above the teeth display their positions in the dentary. Photo belongs to Hiroshi Kato. 

Figure 2: BHI 6439 in medial view. Figure 2A displays the specimen as is. Figure 2B displays the terminology. The numbers above the teeth display their positions in the dentary. The white arrows indicate the first and last visible dentary plates. The green arrows indicate the first alveolus, and the second tooth, are covered by the lingual bar. The red arrow indicates that the third tooth is not covered by the lingual bar. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, and “idp” is the interdentary plate. Photo belongs to Peter Larson. 

Figure 3: BHI 6439 in dorsal view. Figure 3A displays the specimen as is. Figure 3B displays the terminology. The numbers above the teeth display their positions in the dentary. The white arrow points towards the 5th tooth. Blue arrows indicate the carina on the teeth. Photo belongs to Hiroshi Kato.

Figure 4: T. rex specimens FMNH PR 2081 (4A) and BHI 6439 (4B) in lateral view. White arrows point towards the foramina. The blue arrows point to the inflection points. Photo of FMNH PR 2081 comes from Brochu (2003) (p. 41 Figure 40).

Figure 5: T. rex dentaries in medial views. 5A: BHI 6439. 5B: FMNH PR 2081 from Brochu (2003) (p. 42 Figure 41). 5C: BMNH R7994 from Dalman and Lucas (2017) (p. 24 Figure 10). 5D: RSM P2523.8 from Persons IV et al., (2019) (p. 668 Figure 18B). Numbers indicate the position of the first three teeth in the dentary. The teeth in the dentary of RSM P2523.8 were numbered by the authors of Persons IV et al., (2019). Green arrows indicate the lingual bar covering the first two teeth/alveoli. The red arrows show that the lingual bar drops at the third alveolus/tooth. The position of the lingual bar doesn’t change during ontogeny. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, “idp” is the interdentary plate, and “dp” are the dental plates.

Figure 6: Comparison between cf. Dryptosaurus specimen BMRP 2002.4.1 and T. rex specimen BHI 6439 in dorsal view. 6A is the original photo. 6B is a close up, showing the 17th alveoli for BMRP 2002.4.1 and the 13th alveoli for BHI 6439. Despite having a close tooth row length, BHI 6439 has fewer teeth than BMRP 2002.4.1. This demonstrates that young T. rex individuals would’ve had a tooth count similar to the adults. The teeth in the T. rex specimen are also more robust, while the teeth in the cf. Dryptosaurus specimen shows an extreme ziphodont morphology. Photo belongs to Hiroshi Kato.

Figure 7: Dentary of cf. Dryptosaurus specimen BMRP 2002.4.1 in dorsal view. 6A is the original photo. 6B shows the number of teeth. 6C is the tooth count of BHI 6439 (also in dorsal view). Tooth row length for BMRP 2002.4.1 is 31.5 cm. The tooth row length for BHI 6439 is 33 cm. Photo belongs to Hiroshi Kato.

Figure 8: cf. Dryptosaurus specimen BMRP 2002.4.1 dentary from Dalman and Lucas (2017) (p. 24 Figure 9B and B’). 8A is the whole dentary. 8B is a close-up of the anterior tip. Numbers indicate the position of the teeth. Green arrows show that the lingual bar covers the first alveolus only. Red arrows show that the lingual bar drops at the second alveolus, and continues past the third alveolus. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, and “idp” is the interdentary plate.

Figure 9: Close-ups of cf. Dryptosaurus specimen BMRP 2002.4.1 and T. rex specimen BHI 6439 (reversed). In 9A, the green arrow indicates that the lingual bar covers the first alveolus only. The red arrows show that the lingual bar drops at the second alveolus, and past the third one. In 9B, the green arrows show that the lingual bar covers the first alveoli and second tooth. The red alveoli shows that the lingual bar drops at the third tooth. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, and “idp” is the interdentary plate.

Figure 10: Close-ups of the anterior tips of basal tyrannosauroidea and tyrannosauridae dentaries in medial views. Figures belong to Dalman and Lucas (2017). 10A is cf. Dryptosaurus specimen BMRP 2002.4.1 (p. 24 Figure 9B’). 10B is the Alioramus altai holotype IGM 100/1844 (p. 23 Figure 6B) (reversed). 10C is Gorgosaurus specimen FPDM-V8062 (p. 19 Figure 2B). 10D is Albertosaurus specimen TMP 1999.50.40 (p. 21 Figure 3B) (reversed). 10E is Bistahieversor specimen NMMNH P-27469 (p. 29 Figure 9A’). The numbers indicate the placement of the teeth/alveoli. The green arrows indicate that the first alveolus is covered by the lingual bar only. The red arrows indicate that the second and third alveoli are not covered by the lingual bar.

Figure 11: Skull and mandible bones of Appalachiosaurus holotype RMM 6670 compared to cf. Dryptosaurus specimen BMRP 2002.4.1. Photo of Appalachiosaurus belongs to Joe Songer. 11A shows the photo as is. 11B shows a close-up of the anterior tip of the dentary of Appalachiosaurus in medial view (rotated). 11C shows the anterior portion of the dentary of BMRP 2002.4.1 in medial view. Numbers indicate the position of the teeth/alveoli. Green arrows indicate that the lingual bar covers the first alveolus only. The red arrows indicate that the lingual bar drops past the second, third, and fourth alveoli. All basal tyrannosauroids and tyrannosaurids share this characteristic.

Figure 12: Close-ups of the anterior tip of the dentaries derived tyrannosaurinae taxa in medial views. Figures belong to Dalman and Lucas (2017), and Fiorillo and Tykoski (2014). 12A is Daspletosaurus torosus specimen TMP 2001.36.1 (Dalman and Lucas, 2017, p. 24 Figure 10A’). 12B is T. bataar specimen ZPAL MgD-I/5 (p. 24 Figure 10C’). 12C is Nanuqsaurus holotype DMNH 21461 from Fiorillo and Tykoski (2014) (Figure 3) (reversed). 12D is Lythronax (or T. argestes?) holotype UMNH VP 20200 (Dalman and Lucas, 2017, p. 24 Figure 10B’). 12E is Zhuchengtyrannus (or T. magnus?) holotype ZCDM V0031 (p. 24 Figure 10E’). 12F is T. rex specimen BMNH R7994 (p. 24 Figure 10D’). Numbers represent the tooth/alveoli placement. Nanuqsaurus’ alveoli were numbered by the authors of Fiorillo and Tykoski (2014). Green arrows indicate that the lingual bar covers the first two alveoli/teeth. Red arrows indicate that the lingual bar drops at the third tooth/alveolus. Unlike the basal tyrannosauroids and tyrannosaurids in Figure 11, all derived tyrannosaurinae here have the lingual bar covering the first two alveoli.

Figure 13: Photos of an adult and baby T. rex specimen dentaries. 13A is a figure of the dentary of the adult T. rex specimen NMMNH P-3698 from Larson (2008) (p. 41 Figure 1.24) (called UMNH 110000 in the paper). 13B is a close-up of the anterior tip of the dentary in medial view. 13C is BHI 6439. Numbers indicate the position of the alveoli/teeth. Green arrows demonstrate that the lingual bar covers the first two alveoli. The red arrows show that the lingual bar drops at the third tooth/alveolus, and continues past the fourth tooth/alveolus. This characteristic is seen in other T. rex specimens (see Figure 5), and other derived tyrannnosaurinae taxa (Figure 10).

Figure 14: Daspletosaurus dentaries in medial views. 14A is an X-ray reconstruction of the dentary of the cf. D. horneri hatchling MOR 268 in medial view from Funston et al., (2021) (Figure 7). 14B is a close-up of the anterior portion of the dentary in medial view. 14C is the anterior portion of the dentary of the D. torosus specimen TMP 2001.36.1. Numbers indicate the position of the teeth/alveoli. The green arrows indicate that the lingual bar covers the first two alveoli/teeth. The red arrows indicate that the lingual bar drops past the third alveolus. The position of the lingual bar stays the same in different species of the same genus, regardless of age.

Figure 15: Sketch of the two different dentary morphologies seen within tyrannosauroidea in medial views. 15A is the basal tyrannosauroidea and tyrannosauridae dentary morphology, with the lingual bar covering the first alveolus only. This sketch was based on BMRP 2002.4.1. 15B is the derived tyrannosaurinae dentary morphology, with the lingual bar covering the first two alveoli. This sketch was based on BHI 6439. Numbers represent the amount of alveoli the lingual bar covers. Abbreviations: “lb” is the lingual bar, “mg” is the Meckelian groove, and “idp” is the interdentary plate. Sketch belongs to this author.

Tables:

Table 1: Position of the lingual bar within multiple genera of tyrannosauroidea. Basal tyrannosauroidea and tyrannosauridae taxa have the lingual bar covering the first alveoli only. Derived tyrannosaurinae genera have the lingual bar covering the first two alveoli.

Table 2: A comparison between the dentaries of T. rex specimen BHI 6439, and cf. Dryptosaurus aquilunguis specimen BMRP 2002.4.1. BHI 6439 has 13 teeth that are robust in morphology, and a lingual bar covering the first two alveoli/teeth on the medial side of the dentary. BMRP 2002.4.1 has 17 teeth that have an extreme ziphodont morphology, and a lingual bar that covers the first alveoli on the medial side of the bone. Both specimens have a close body size (6.7 to 7.0 meters), yet the two dentaries show major differences in morphology. The morphology of the dentary for BMRP 2002.4.1 is closer to basal tyrannosauroidea and tyrannosauridae genera, while BHI 6439 matches the morphology of derived tyrannosaurinae taxa.

Saurophaganax is a Carcharodontosaurid: An Abstract (2023)

Written on 5/12/23.

Link:
https://www.academia.edu/101770036/Saurophaganax_is_a_Carcharodontosaurid_An_Abstract

                                  Saurophaganax is a Carcharodontosaurid: An Abstract

Saurophaganax maximus is a carnivorous theropod from the late Jurassic of North America. In the past, the genus has either been listed as a basal allosaurid that was a sister taxon to Allosaurus, or as a species of Allosaurus called Allosaurus maximus. This author proposes a different classification: Saurophaganax was a carcharodontosaurid, and was probably the first member of the clade to inhabit North America. The fossils were found in Quarry 1 in Oklahoma, but were not excavated at once or by professionals. With all due respect to the original excavators, to be as thorough as possible, this author decided to examine every bone individually to see if they belonged to a basal allosaurid or a carcharodontosaurid. OMNH 01135, an atlas, is morphologically similar to Tyrannotitan/Giganotosaurus chubutensis, exhibiting a “V-shaped” morphology. In comparison, the atlas of Allosaurus is linear in profile. The holotype specimen of Saurophaganax, OMNH 01123, is a mid-dorsal neural arch that has two horizontal laminae projecting off of it. This is not documented in Allosaurus. The overall morphology of OMNH 01123 is similar to Tyrannotitan/Giganotosaurus chubutensis’ first dorsal vertebra. Tyrannotitan/Giganotosaurus chubutensis also had an accessory lamina on its second and third dorsal vertebrae. Lusovenator had a lamina on the prezygapophysis on the second caudal vertebra, and a lateral lamina on the mid-posterior caudal vertebrae. Veterupristisaurus exhibited two “V-shaped” spinoprezygapophyseal laminae that are connected to the prezygapophysis, and two short laminae that are connected to the spinoprezygapophyseal laminae, on its caudal vertebrae. Laminae like these are typically not seen in other carnivorous theropod clades, but in carcharodontosaurids they had a wide range of forms and placements on the vertebral column. The mid to distal caudal chevrons (OMNH 01685) are morphologically similar to Acrocanthosaurus’, Meraxes’, and Lusovenator’s, but not Allosaurus’. The ilium (OMNH 01338) resembles Concavenators’, Meraxes’, and Acrocanthosaurus’. The tibia (OMNH 01370) looked similar to Acrocanthosaurus’. OMNH 01708/0112, a femur, had a head pointing upwards and a shaft that was bowed/convex laterally, as seen in many carcharodontosaurid taxa. This is not present in Allosaurus’ femur. OMNH 01425, a partial right pubis, is closer in form to Mapusaurus/Giganotosaurus roseae’s than to Allosaurus’. Previously, this author assigned a partial left pubis (OMNH 01707), and a left pes (OMNH 01708), to possibly belonging to Allosaurus. However, these bones could belong to either Allosaurus or a carcharodontosaurid. Tyrannotitan exhibited a similar morphology in its pubis to OMNH 01707. Therefore, both OMNH 01425 and OMNH 01707 can be assigned to a carcharodontosaurid. OMNH 01708 has a similar morphology to both Lusovenator’s and Meraxes’, with the fourth metatarsal being concave. Currently, a giant humerus (OMNH 01935), and a manual ungual (OMNH 780), don’t seem to exhibit carcharodontosaurid traits so far. They appear characteristically similar to Allosaurus, so they could belong to Allosaurus or to a carcharodontosaurid. This author will keep both possibilities open. In summation, Saurophaganax exhibits numerous skeletal features that could place it within the carcharodontosaurid clade.