Thursday, April 3, 2025

What did Spinosaurus Look Like Part 2: Bipedalism?

Introduction:
Hello! Welcome to part 2 of my "What did Spinosaurus Look Like?" series. I originally focused on the arms of Spinosaurus in this post, but it eventually grew to be about Spinosaurus potentially being a biped. In this post, we will focus on the arms, weight, and hip bones of the animal in order to see if it was truly a biped.

Link:
Part 1: The Limbs and Center of Mass:
https://psdinosaurs.blogspot.com/2023/03/what-did-spinosaurus-look-like-part-1.html

1.) Did Spinosaurus have short arms?
Originally, I came to the conclusion that Spinosaurus would've been a quadruped. This was due to the fact that Spinosaurus had long arms but short claws that were not robust, trace fossils of theropod arm and hand marks, and I kept getting a large center of mass for the animal. However, I noticed a pattern regarding a spinosauroid manual ungual from Ibrahim et al., (2020a) and the reconstructed Spinosaurus arm from DinoLab a few years back. It led me to a new possibility: Spinosaurus probably had short arms! If Spinosaurus was bipedal, then this is probably the best hypothesis to make it so.

I've learned over time to let go of my biases in order to get to the truth of a particular matter. It's been a gradual process with Spinosaurus, but it's better late than never. Let's suppose that Spinosaurus wasn't a quadruped. Let's agree that Spinosaurus' arms weren't capable of supporting its weight. Suppose that it's center of mass was shorter than its femoral length, allowing it to be a biped. These conclusions came from Sereno et al., (2022). However, we're also going to add Ibrahim et al., (2020a) and the reconstructed arm from DinoLab into the equation. Sereno et al., (2022) showed that about 90% of the arm for the reconstructed skeleton is a composite (then again, the whole skeleton is a composite). Only one phalange, and one manual ungual, came from the neotype. The phalange belongs on the second finger (Sereno et al., 2022) (Fabbri et al., 2022). The manual ungual is on the third digit, and it is very small (Fabbri et al., 2022). The phalange is elongated and skinny (Sereno et al., 2022) (Fabbri et al., 2022), just like the phalanges on the reconstructed arm from DinoLab. So far, so good! I also noted that, in my original post announcement about the DinoLab arm, I stated that the arm looked smaller than the arms on the reconstructed skeleton made by Ibrahim, Sereno, and co. It should be noted that the metacarpals (not shown), phalanges, and the radius and ulna (they are partially complete), are real material. The humerus is a "cast"/"articulated." There is also some criticism towards the third finger being way too long, but it's not conclusive. This comes from DinoLab on their Facebook post, and Paleontologist Roberto Diaz Sibaja from Facebook as well. Terry from DinoLab said that some paleontologists have verified the bones (that are real) to be conclusive (Facebook), so we seem to be on the right path here. I will also ignore the radius from Goo (2022) for now. 

DinoLab Spinosaurus arm (Facebook, 2021):

Compare the claws to the spinosauroid claw (NMC 41820) from Ibrahim et al., (2020a) (Figure 111A-B):
Full figure. Scale bar is 5 cm:
Description of NMC 41820 (Ibrahim et al., 2020a, Theropoda: Manual ungual morphotype 1):
Information on Spinosaurus arm from DinoLab (Facebook, 2021):
Another pic of the DinoLab arm (The Zone @91-3, 2021):
Pics of DinoLab arm from Twitter-X (2020):
First:
Second (Notice that the arm looks smaller here):
Spinosaurus' skeletal design by Sereno et al., (2022) (Figure 1). The neotype's bones are blue. The phalange in D is not from the neotype though. It's from the first digit, not the second. Scale bar for D is 3 cm:
Spinosaurus skeleton from Fabbri et al., (2022) (Figure 1). The red bones are from the neotype:
Close up of the hand. You can see phalange 2-1, and manual ungual 3, in red:
The claws on the hand look small in Fabbri et al., (2022) as well, which might lend support to Spinosaurus having small manual unguals.

If we compare the presumed unguals of Spinosaurus to Baryonyx/Suchomimus walkeri, for example, then we can see a huge difference. Baryonyx's thumb claw, or manual ungual 1, is 31.0 cm (310 mm) long 
(Charig and Miller, 1997, p. 46):
Baryonyx's manual ungual 1 (p. 47 Figure 35):
The ungual from Ibrahim et al., (2020a) is about 5 cm, or slightly longer (Theropoda: Manual ungual morphotype 1). The presumed manual ungual from the T. rex specimen FMNH PR 2081 ("Sue") is about the same size, albeit more of the tip is missing (Brochu, 2003, p. 101 Figure 87) (Scale bar is 5 cm): 
The carcharodontosaurid Meraxes has all three manual unguals preserved, and most of its forearm. All three manual unguals are smaller than 10 cm, with the first ungual (the largest one) barely reaching 10 cm (Canale et al., 2022, Figure 1J) (Scale bar is 10 cm): 
Full figure. Notice how small the arm is compared to the animal's body (Scale bar under tail is 1 meter. All other scale bars are 10 cm):
Spinosaurus' presumed manual ungual is basically the same size as T. rex's, and Meraxes'! Baryonyx's claws were large, and robust, enough for dexterity. Spinosaurus' are not. In fact, the hand bones attributed to Spinosaurus in Sereno et al., (2022) (Figure 1) are similar in morphology to a baryonychinae than to a spinosaurid. This might suggest that there was a baryonychinae (Sigilmassasaurus?) coexisting with Spinosaurus. I will keep in mind that the ungual from Ibrahim et al., (2020a) could belong to any digit on the manus, so other claws could've been bigger, or smaller, than NMC 41820. Comparing it to the arm from Dino Lab, the ungual could belong to the first digit. The third ungual is more recurved than the first two, so NMC 41820 could belong to the first or second digit. The overall morphology of NMC 41820 matches the first ungual, so I'll place NMC 41820 as the thumb claw for now.

So in total, we have a Spinosaurus arm that consists of a (probable) small and stocky radius and ulna, slender manual phalanges, and small manual unguals that were not large and recurved as typically seen in the other spinosauroids like the baryonychinae. The humerus is unknown, but we can speculate that it was probably smaller than the one from DinoLab and shaped more akin to a baryonychinae. Taking all of this into account, one could speculate that Spinosaurus' arms were probably shorter than typically reconstructed. I would imagine that Spinosaurus could've taken the tyrannosaurid and carcharodontosaurid route: Evolve larger skulls that replaced the necessity to have long arms. In return, the forelimbs would be reduced in size. 

This is, by no means, the final say in the matter. There is something strange with the arms of Spinosaurus, which leads me to believe that they were probably not very useful to the animal in life. There are other factors that still go against a strictly bipedal Spinosaurus (see part 1 of this series). Until more bones are discovered (hopefully from the neotype specimen), I'll say that Spinosaurus could've been quadrupedal IF it had long arms. I can't see Spinosaurus dragging is arms across the ground while being bipedal. If it had short arms, then I will say that Spinosaurus was bipedal. 

Links:
Ibrahim et al., (2020a):
https://zookeys.pensoft.net/article/47517/element/7/0/deltadromeus/
DinoLab:
1.) Instagram (Gramho):
https://gramho.com/media/2535465340537444071
2.) Facebook:
https://m.facebook.com/dinolabinc/posts/our-spinosaurus-arm-is-still-on-display-we-arent-sure-how-much-longer-we-are-goi/885524165571071/
3.) Twitter-X:
https://mobile.twitter.com/DinoLab_Inc/status/1322305140020269058
4.) The Zone @91-3:
-Photo:
https://images.app.goo.gl/FYeo7rjhQr6cPLja7
-Website:
https://www.thezone.fm/2020/09/02/geekout-dino-lab-spino-arm/
Sereno et al., (2022):
https://www.biorxiv.org/content/10.1101/2022.05.25.493395v1.full
Fabbri et al., (2022):
https://www.nature.com/articles/s41586-022-04528-0.epdf?sharing_token=rxUUwyZxDWQ24dJfwtIw89RgN0jAjWel9jnR3ZoTv0NEFj8DFZa3bazFWKdXldNTvT8T3daJQzYMUbPXaqso6c2KKBgthBeOpsV72_JOZHeSlOxZzzE9wUggHYItKT5ASyn5r0hTiRPfCQi_Cfe9RPf0tvCNFd3T4QXE2UU4r7wR-SYYL4_TSvBiBpniofeQoStgnv6yWzzkL81Gcy2g6hKT9nO8ozsufeY9DwX1VK-Vsw94pFBHTtBWnm2-q0bJ33Xx2cPSUh5t7T-nx3NDvtkT9MSkWBYPTw7aqWM5FRs%3D&tracking_referrer=www.sciencenews.org
Mr. Sibaja (Palaeos):
1.) Facebook Post:
https://m.facebook.com/PalaeosPag/photos/a.157631294723661/1059058504580931
2.) Blog:
https://palaeos-blog.blogspot.com/?m=0
Charig and Miller (1997) (PP. 46-47):
https://www.biodiversitylibrary.org/page/36949178#page/201/mode/1up
Brochu (2003) (P. 101 Figure 87):
https://www.researchgate.net/publication/249022959_Osteology_of_Tyrannosaurus_rex_Insights_from_a_Nearly_Complete_Skeleton_and_High-Resolution_Computed_Tomographic_Analysis_of_the_Skull
Canale et al., (2022):
https://www.cell.com/current-biology/fulltext/S0960-9822(22)00860-0
-Link 2:
https://www.sciencedirect.com/science/article/abs/pii/S0960982222008600

2.) Given up?
The more I tried to make Spinosaurus bipedal, the more problems I keep running into. My main goal was to make the arms shorter, and the legs longer. I used Suchomimus to try and do that because it's the only spinosauroid that has arm material that I can find, and so far it's not working. The arms for 
Spinosaurus seem to be longer than Suchomimus' a little bit, and the legs are extremely short compared to Suchomimus'. I also tried to do the same thing with Baryonyx, and that didn't work either. This, along with the information from my first post in this series, makes me think that Spinosaurus is still a quadrupedal. At the very least, that's the best hypothesis that seems to be working so far. We NEED to have the arm bones of this animal. That's the only way we can find a definitive answer. If I find another way to make Spinosaurus a biped, then I'll post it here. For now, I'll have to go with Spinosaurus as a quadruped. I will say this about the manual unguals: They seem to be shorter, and less robust, than the baryonychinae manual unguals.

3.) I might've found a way!
I think I've found a way!

I should note that my plan requires the Baryonyx finger to be the second digit of the manus. Charig and Miller (1997) said that the digit could be the second or third one (p. 47), so if it's the third finger then my math will not work. If it is the second finger, then we can hypothesize the length of the arm of the Spinosaurus neotype. 

The Spinosaurus neotype has the manual phalanx 2-1 preserved. It's 17.5 cm long (Ibrahim et al., 2014, Supplementary Materials, p. 33). Baryonyx's manus also preserves a relatively complete finger (the tip of the ungual is missing though), but it's unknown if it's the second or third digit. I will assume, for the sake of this experiment, that it's the second finger. The probable manual phalanx 2-1 bone is 13.2 cm long (Charig and Miller, 1997, p. 47). I'm going to use these two bones to speculate the length of the 
Spinosaurus' neotype's arm and hand.

Math:
Spinosaurus neotype FSAC-KK 11888:
Manual phalanx 2-1: 17.5 cm (Ibrahim et al., 2014, Supplementary Materials, p. 33).
Femur: 62.5 cm (Ibrahim et al., 2020b, Supplementary Materials: Date File 2, Body dimensions, body mass, body segment masses, and whole body center of mass, p. 1).
Tibia: 66.8 cm (Ibrahim et al., 2014, Supplementary Materials, p. 33).

Baryonyx:

Probable manual phalanx 2-1: 13.2 cm.

Humerus: 46.3 cm.

Radius: 22.5 cm.
Probable manual phalanx 2-2: 9.1 cm.
Source: Charig and Miller (1997) (pp. 43, 45, and 47). 


Manual phalanx 2-1:

17.5 - 13.2 = 4.3.

4.3/13.2*100 = 32.6% increase.


Spinosaurus neotype arm bones estimates:

Humerus: 46.3 cm + 32.6% = 61.4 cm.

Radius: 22.5 cm + 32.6% = 29.8 cm.
Maual phalanx 2-2: 9.1 cm + 32.6% = 12.1 cm.


Complete arm length: 

1.) Humerus + radius = 91.2 cm (61.4 + 29.8).

2.) Humerus + radius + manual phalanx 2-1 = 108.7 cm.

3.) Humerus + radius + manual phalanx 2-1 + manual phalanx 2-2 = 120.8 cm.
4.) Humerus + radius + manual phalanx 2-1 + manual phalanx 2-2 (120.8) + hypothetical manual ungual from Ibrahim et al., (2020a) (8.8 cm; 9.4 cm at whole? [Measured and estimated by me]) = 129.6 to 130.2 cm.


Leg length:

1.) Femur (62.5) + tibia (66.8) = 129.3 cm.

2.) Femur + tibia + metatarsal 1 (10.5 cm [Ibrahim et al., 2014, Supplementary Materials, p. 34]) = 139.8 cm.
3.) Femur + tibia + metatarsal 1 + pedal phalanx 1-1 (11.5 cm [Ibrahim et al., 2014, Supplementary Materials, p. 34]) = 151.3 cm.


Percentage of arm compared to leg:

*1.) Humerus + radius - femur + tibia:

129.3 - 91.2 = 38.1.

38.1/129.3*100 = 29.5% decrease.

100% - 29.5% = 70.5% of the leg.

*2.) Humerus + radius + manual phalanx 2-1 - femur + tibia + metatarsal 1: 

139.8 - 108.7 = 31.1.

31.1/139.8*100 = 22.3% decrease.

100% - 22.3% = 77.8% of the leg.

3.) Humerus + radius + manual phalanx 2-1 + manual phalanx 2-2 - femur + tibia + metatarsal 1:

139.8 - 120.8 = 19.

19/139.8*100 = 13.6% decrease.

100% - 13.6% = 86.4% of the leg.

5.) Humerus + radius + manual phalanx 2-1 + manual phalanx 2-2 + possible manual ungual - femur + tibia + metatarsal 1 + pedal phalanx 1-1:

151.3 - 129.6 cm = 21.7.
21.7/151.3*100 = 14.3% decrease.
100% - 14.3% = 85.7% of the leg.

Or:
151.3 - 130.2 cm = 21.1.
21.1/151.3*100 = 14% decrease.
100% - 14% = 86% of the leg.


Hypothetically speaking, the arm of the Spinosaurus neotype would be about 70.5-86.4% of the leg (at best). 

Links:
Charig and Miller (1997):
https://www.biodiversitylibrary.org/page/36949178#page/201/mode/1up
Ibrahim et al., (2014):
https://www.researchgate.net/publication/265553416_Semiaquatic_adaptations_in_a_giant_predatory_dinosaur
-Supplementary Materials:
http://science.sciencemag.org/content/suppl/2014/09/10/science.1258750.DC1/Ibrahim.SM.pdf

Ibrahim et al., (2020b):


4.) Another complete Spinosaurus arm!?
I don't know how I missed this, but someone on Reddit, called Super-Masterpiece-34, posted a picture of another complete Spinosaurus arm. It's a private specimen though, but it reveals what I said about the arm from Dino Lab: The humerus would've been shorter! The third finger is also shorter than the second one, contrary to the third digit of the Dino Lab arm. The manual unguals are the same as the ones in the Dino Lab, Ibrahim et al., (2020a), and Fabbri et al., (2022), which means that Spinosaurus' manual unguals are shorter than the baryonychinae's. 

Photo of the private Spinosaurus arm (Reddit, Super-Masterpiece-34, May surprise many people):

Notice that the third finger is smaller than the first two fingers. Perhaps the Dino Lab arm is missing a phalanx in the middle finger, or one of the bones is in the wrong position, etc. The humerus seems to be about the same size as the radius and ulna. It also looks kind of similar to the Dino Lab humerus. It looks smaller than the Dino Lab humerus, so maybe it's authentic? From what I can guess, the arm would've been about 2/3 of the length of the man in the photo. We can also see this in a photo of the Dino Lab arm with paleontologist Dr. Philip Currie:

The arm, with a proper humerus, would've been about 2/3 the size of Dr. Currie, and probably the lady in the photo as well. Here's another picture of the arm with the same lady present:
This suggests to me that Spinosaurus' arms were smaller than a fully-grown adult human. It's definitely smaller than the reconstructed arm in the 2014 skeleton.

Arms of the reconstructed 2014 Spinosaurus skeleton (Kenneth Chang, 2014):

The arms of the reconstructed skeleton are the same size, if not a little longer, than the man in the photo. This is not the case with the Dino Lab, and the private, Spinosaurus arms. I also noticed that Sereno et al., (2022) stated that the arms of their Spinosaurus model are shorter than the model used by Ibrahim et al., (2020b) (Figure 9):

Description of figure:
So, if the arms of Spinosaurus were smaller than previously stated, then perhaps this means that it was bipedal after all? Perhaps the center of mass (CoM) is really towards the pelvis instead of the stomach. There is the problem of body mass. In my first post of this series, that seemed to be a constant bother regarding a fully bipedal Spinosaurus. Spinosaurus had to have been about 2-3 tons or so in order for the femur to support the animal's eight. If that's true, then the animal still would've been a quadruped. Still, Spinosaurus bones have been found inland (Sereno et al., 2022, Figure 7A), so the animal had to have been able to traverse across the land somehow. 

I'll say this: Based on what I've found so far, my math tells me that the arms of the Spinosaurus neotype would've been about 70.5-86.4% of the leg length at best. I made a small drawing using a scale bar from Lucas et al., (2005) (Figure 1), and there is a small gap between the hands and the ground. This gap is represented by the arrow:
The gap is not as large as I would've liked, so I don't know if it's definitive proof of a bipedal Spinosaurus. Perhaps it's enough for the animal to be bipedal without its hands brushing against the ground? Maybe. As for the weight of the animal, if it turns out that Spinosaurus was too heavy to support its weight just by its femur/legs alone, then it was a quadruped. It's best to have an open mind. I really want paleontologists to find the rest of the bones in the neotype's arms. My answer: It could've been either-or. 

Links:
Reddit. Super-Masterpiece-34. May surprise many people:

https://www.reddit.com/r/Dinosaurs/comments/15ocfp3/may_surprise_many_people/

Kenneth Chang (2014):
https://www.nytimes.com/2014/09/12/science/a-nomads-find-helps-solve-the-mystery-of-the-spinosaurus.html
Photo:
https://images.app.goo.gl/19ScuGkueXHXFEFB9

Sereno et al., (2022a):

https://elifesciences.org/articles/80092
Lucas et al., (2005) (Figure 1):

https://www.researchgate.net/figure/Skeleton-of-New-Mexicos-official-state-fossil-Coelophysis-bauri-after-Paul-1993_fig1_255459322

5.) Suchomimus to the rescue?
Just when I thought I ran out of ideas, I find another way!

I went back to Suchomimus, and Suchomimus' manual phalanx 1-1 does make Spinosaurus' arms smaller. Granted, I had to take a few things into account:

1.) Suchomimus' and Spinosaurus' manual phalanxes from Sereno et al., (2022) aren't from the neotype, or Suchomimus holotype. They're separate specimens. 
2.) However, Sereno et al. used them to finish skeletal diagrams of Spinosaurus and Suchomimus. I will assume that the manual phalanxes were scaled to size with the rest of the skeletons. 


The Spinosaurus manual phalanx 1-1 used is UCRC PV8, and the Suchomimus manual phalanx 1-1 used is MNBH GAD503. They are "D" and "H" in Sereno et al., (2022).

Figure 1 (Sereno et al., 2022) (Scale bars for D and H are 3 cm):

Spinosaurus' manual ungual 1-1:
Suchomimus' manual ungual 1-1:
Manual phalanx 1-1:
-Suchomimus (MNBH GAD503 [NOT holotype]): 14.4 cm (at best) (Measured myself).
-Spinosaurus (UCRC PV8): 14.6 cm (Measured myself).

Sereno et al., (1998) for Sucho holotype (MNBH GAD500):

Humerus: 56.0 cm.
Radius: 25.5 cm.
Femur: 107.5 cm.
Tibia; 94.5 cm.

Spino neotype:
Femur: 62.5 cm (Ibrahim et al., 2022b).
Tibia: 66.8 cm (Ibrahim et al., 2014, Supp. Mat.).

1.) Arm length:
14.6 - 14.4 = 0.2.
0.2/14.4*100 = 1.4% increase.
Humerus:
56 cm + 1.4% = 56.8 cm.
Radius:
25.5 cm + 1.4% = 25.9 cm.
Spino:
-Humerus + radius: 56.8 cm + 25.9 cm = 82.7 cm.
-Humerus + radius + manual phalanx 1-1: 56.8 cm + 25.9 cm + 14.6 cm = 97.3 cm.
-Humerus + radius + manual phalanx 1-1 + possible manual ungual (incomp.): 56.8 cm + 25.9 cm + 14.6 cm + 8.8 cm = 106.1 cm.
-Humerus + radius + manual phalanx 1-1 + possible manual ungual (poss. comp. length): 56.8 cm + 25.9 cm + 14.6 cm + 9.4 cm = 106.7 cm.

Hypothetical Spinosaurus arm length: 106.1 to 106.7 cm.
Hypothetical Spinosaurus leg height: 151.3 cm.

This is smaller than the 129.6- to 130.2-cm length I obtained using Baryonyx. I also added this length to my previous diagram ("S" is for Suchomimus, and "B" is for Baryonyx):

Perhaps, this could help support a bipedal, and a smaller-armed, Spinosaurus. Still have to shrink Spinosaurus' weight down, and I still want the arm bones for the Spinosaurus neotype discovered.

Links
Sereno et al., (1998):

Sereno et al., (2022):
https://www.biorxiv.org/content/10.1101/2022.05.25.493395v1.full

6.) Too much weight to carry?
Well, I might've hit another roadblock... Possibly two of them. I found Myhrvold et al., (2022), and another figure of UCRC PV8. This time, the scale bare is 5 cm instead of 3 cm as in Sereno et al., (2022). I decided to remeasure the specimen.

UCRC PV8 from Myhrvold et al., (2022) (Figure 1d):

Length: 28.4 cm (at best).

Using Suchomimus manual phalanx 1-1 from Sereno et al., (2022):

28.4 - 14.4 = 14.
14/14.4*100 = 97.2% increase.

If Suchomimus' manual phalanx 1-1 was actually 23 cm (at best), and UCRC's manual phalanx 1-1 was 24.5 cm (at best) (Both were remeasured on 4/21/25 in Sereno et al., 2022. I assumed that the scale bars for both bones were 5 cm instead of 3 cm):

24.5 - 23 = 1.5.
1.5/23*100 = 6.5% increase.
56 cm + 6.5% = 59.64 cm for UCRC's humerus.

Using the 28.4-cm estimate for UCRC:

28.4 - 23 = 5.4.
5.4/23*100 = 23.5% increase.
56 cm + 23.5% = 69.16 cm for UCRC's humerus.

Now, after re-reading Sereno et al., (2022) and Myhrvold et al., (2022), it is stated that UCRC PV8 is 28 cm long. The authors scaled up UCRC PV8 to the length of the largest Spinosaurus specimen, MSMN V4047. UCRC PV8 was 20% smaller than MSNM V4047. Using UCRC and Irritator/Angaturama's manual phalanx 1-1, they estimated that MSNM's manual phalanx 1-1 was 35 cm long (Sereno et al., 2022, Table 1). If I upscaled Suchomimus' humerus using the 97.2% increase I obtained from UCRC, then we get a length of 110.4 cm for the humerus. This would just be for UCRC PV8's hypothetical humerus. I wasn't satisfied with this, so I went back to Sereno et al., (2022) and remeasured both manual phalanxes again. I assumed that the scale bars for both bones were 5 cm instead of 3 in order to see if I could make Suchomimus' manual phalanx longer. I got 23 cm (at best) for Suchomimus, and 24.5 cm (at best) for UCRC PV8. This would've made UCRC's humerus 6.5% larger than Suchomimus', resulting in a humerus length of 59.64 cm for UCRC's humerus. Since UCRC's manual phalanx is actually 28.4 cm long, this would result in a 23.5% increase. UCRC's humerus would be 69.16 cm long. The humerus is still growing. If MSNM's manual phalanx 1-1 was an estimated 35 cm, then the humerus would've been even longer for the largest adult Spinosaurus specimen. No matter what I do, the arms of Spinosaurus keep growing longer... The arm length I obtained for the neotype specimen, using Baryonyx, is probably more accurate than the numbers I obtained using Sereno et al., (2022). The Spinosaurus neotype, FSAC-KK 11888, doesn't have a preserved manual phalanx 1-1, so I cannot do any comparisons.


There's one last move that I could do in order to estimate the probable length of the FSAC's humerus. I can use the femur lengths of Suchomimus, and FSAC, to guess a humerus and radius length for FSAC.

FSAC's femur length: 62.5 cm.
Suchomimus' femur length: 107.5 cm.

107.5 - 62.5 = 45.
45/107.5*100 = 41.9% decrease.
56 cm - 41.9% = 32.5 cm for the hypothetical humerus.
25.5 cm - 41.9% = 14.8 cm for the hypothetical radius.

Arm lengths for FSAC:
32.5 cm + 14.8 cm = 47.3 cm.
Leg lengths:

62.5 cm + 66.8 = 129.3 cm.

As much as these measurements would be satisfactory for a bipedal Spinosaurus, I have to remember that we have the manual phalanx 2-1 for FSAC. As shown above, using Baryonyx's possible manual phalanx 2-1 because the Suchomimus holotype doesn't have the manual phalanx 2-1 preserved (sheesh!), we get a humerus length of 61.4 cm for FSAC. Perhaps Spinosaurus had long hands, but a short upper and lower arm? Either way, no matter what I do, the arms of Spinosaurus are suggested to have been very long. This leads me to suggest that Spinosaurus had long arms and hands, but short manual unguals.

Not only are Spinosaurus' arms getting longer, but the weight of the animal seems to be a big hinderance for a purely bipedal Spinosaurus. In Persons IV et al., (2019), Spinosaurus' femoral length is 83 cm. The weight of the animal is 1,645 kg (1.81 tons) (p. 670 Table 2):

This is the estimated hypothetical femoral length for the specimen MSNM V4047. How can a 14-meter long animal weigh only 1.8 tons!? Persons IV et al. couldn't comprehend this either. They used the "minimum femoral cross-section area (MCF)" method from Campione et al., (2014) to calculate the weight of MSNM, and they obtained a weight of 1,645 kg for the specimen. They stated that the weight of the animal, and "the cross-sectional strength" of the femur because Spinosaurus has a closed medullary cavity, must've been greater (pp. 665-666). They also suggested that Spinosaurus being a quadruped or semi-quadrupedal, as suggested by Ibrahim et al., (2014), could've helped in the distribution of the expected greater weight of Spinosaurus, especially if Spinosaurus' femur couldn't hold its weight by itself. This is due to Ibrahim et al. stating that Spinosaurus' legs were "reduced in all dimensions relative to its body mass." Thus, obtaining an accurate body mass estimate for Spinosaurus is tricky (pp. 666-667). 

This is interesting because paleo-artist/paleontologist Hank Sharpe on Twitter-X also used Campione et al., (2014) to estimate the weight of Spinosaurus, and came to the same conclusions. He said that Spinosaurus' femur wasn't large enough to support its weight (Sharpe, 2023, "Think Spinosaurus' legs look kinda wimpy for its size?..."). Sharpe also stated that Spinosaurus having a femur with a thick cross-section wouldn't help its femur to support its weight either (YouTube, EDGE Science, Y'all Were Right. Spinosaurus May Have Just Been Too Big To Walk. Spino Saga, 9:54-11:09).

Hank Sharpe's femoral circumference ("femoral estimate"), and body weight ("volumetric estimate"), estimates of Spinosaurus. Spinosaurus' femur (dot inside the green bar) wasn't strong enough to support its estimated body weight from Sereno et al., (2022) (dot above the green bar with Spinosaurus silhouette). Graph came from Campione et al., (2014). Photo taken from EDGE Science's video (9:06):

Larramendi et al., (2020) also stated that Spinosaurus' legs weren't capable of holding its weight alone (3. Results and Analysis 3.2.9 Nonavian avepod theropod dinosaurs para. 2). Even paleontologist Dr. Witton, who supports the strictly bipedal posture for Spinosaurus, said that Spinosaurus' legs wouldn't be able to carry an animal that was over four tons, and the animal's legs would have to be straight and not bend in order to support itself as a biped. If Spinosaurus was in a vertical posture, as proposed by paleontologist Dr. Cau in 2014-2015, and didn't bend its legs, then it could support itself. In any other posture, Witton said that Spinosaurus' legs wouldn't be able to support its weight (Spinosaurus 2020: thoughts for artists: Posture and balance, para. 2-3). All that I'm getting here is that Spinosaurus' legs weren't capable of supporting its weight as a 14-meter theropod. This beast should've been up to about 10 tons or so. Sereno et al., (2022) said that an adult Spinosaurus was 14 meters long and weighed 7,400 kg (8.2 tons) (Conclusions, number 1 and 5), so I cannot imagine a 80-cm long femur supporting a 14-meter creature that weighed 8 tons.


Interestingly, according to Sereno et al., (2022), Ibrahim et al., (2020b) said that an adult Spinosaurus had a CoM as of about 95.7-108.9 m (Table 9):

This is very close to the results I got in part 1 of this series, albeit that was for the neotype specimen which was not an adult yet. It seems that Spinosaurus' CoM grows as its body grows, and it is still longer than the femoral length of the animal.


So in the end, what do we know?

1.) We need the rest of FSAC's forelimb bones to be excavated.
2.) Based on what we do have, Spinosaurus' arm bones suggest that the animal had long arms and short manual unguals. The arms seem to have been as long as the animal's legs.
3.) If I use the femoral lengths of FSAC and the Suchomimus holotype, we get relatively small arms. However, this contradicts the very long manual phalanx 2-1 that FSAC has. UCRC PV8 also has a very long manual phalanx 1-1, correlating with the trend that Spinosaurus had long hands and possibly long forelimbs in general. Either Spinosaurus had short arms with long hands, or using the femoral lengths of Spinosaurus and Suchomimus do not yield accurate results for a hypothetical arm length for Spinosaurus.  
3.) The weight estimates of Spinosaurus do not correlate with the size, and width, of its femur. An adult Spinosaurus was 14 meters and 8 tons, but it has been noted that its femur couldn't hold an animal that weighed that much. This suggests that Spinosaurus was too heavy to walk as a biped after all. 
4.) The center of mass (CoM) of Spinosaurus seems to have grown as the animal's body grew. The CoM is still longer than the femoral length of the animal.

For now, I have to stick with a quadrupedal Spinosaurus. The hands of the Dino Lab, and private, specimens do look long and sturdy enough to have given some support for Spinosaurus while it walked. Albeit, the belly-sliding hypothesis for Spinosaurus could potentially work as well. I'm not leaving any stone unturned. 

Links:
Myhrvold et al., (2022):

https://www.biorxiv.org/content/10.1101/2022.04.13.487781v1.full.pdf
Sereno et al., (2022):
https://www.biorxiv.org/content/10.1101/2022.05.25.493395v1.full
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
-V2:

https://anatomypubs.onlinelibrary.wiley.com/doi/am-pdf/10.1002/ar.24118

-V3:
https://www.gbif.org/species/159236947
-Abstract:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.24118

Sharpe (2023) ("Think Spinosaurus' legs look kinda wimpy for its size?..."):

https://twitter.com/Paleoartologist/status/1622728136403337216
YouTube. EDGE Science. Y'all Were Right. Spinosaurus May Have Just Been Too Big To Walk. Spino Saga:

https://youtu.be/Nfmz3WM84c8?feature=shared

Larramendi et al., (2020):

https://anatomypubs.onlinelibrary.wiley.com/doi/abs/10.1002/ar.24574

Witton (2020):

7.) Spinosaurus and the Pangolin?
I remember that, back around 2014-2016, some people thought that Spinosaurus would've walked like a pangolin. Not wanting to leave any stone unturned, I started researching pangolin walking gaits. The majority of pangolins genera are quadrupedal (Gaudin et al., 2020 and Wu et al., 2020; in Challender et al., 2020, pp. 35, 60, 81-82, 98, and 190), but there is one genus that is bipedal: The Temminck's pangolin (Smutsia temminckii) (Gaudin et al., 2020 and Wu et al., 2020; in Challender et al., 2020, pp. 35 and 190). According to Swart (2013), the Temminck's pangolin have small forelimbs, but its hind limbs are "shorter and stockier than the hindlimbs." This doesn't stop them from being bipedal. Looks like we have a winner. Spinosaurus could've walked like a Temminck's pangolin, right? Well, according to Swart, this animal is mainly bipedal since it is more terrestrial than other pangolins, but it still uses its "knuckles and the tip of the tail" to touch the ground "to maintain balance." Most importantly, "The pelvis is more vertical than in other pangolin species, emphasizing the greater use of the hindlimbs for bearing weight," (in Kingdom and Hoffmann, 2013, Vol. 5 p. 400). Spinosaurus' pelvis/ilium isn't vertical. It's horizontal. Not to mention, even the Temminck's pangolin uses its forelimbs (and tail) to help support itself while walking.

The Chinese pangolin (Manis pentadactyla) is quadrupedal, but it can also be bipedal as well (Wu et al., 2020; in Challender et al., 2020, p. 60). However, I saw what the ilium of this pangolin looked like. The ilium is extremely vertical. You can see this in a photo from Pappas (2012). A better view is seen in a photo from the Museum of Osteology's Facebook profile.

Chinese pangolin's (Manis pentadactyla) vertical ilium from the Museum of Osteology's Facebook page (June 8, 2020):
Full skeleton. Skulls below the skeleton belong to other species of pangolin:
Once again, we're back at square one for Spinosaurus. 

Links:
Challender et al., (2020):

https://books.google.com/books?id=zey_DwAAQBAJ&pg=PA98&dq=Pangolin+walk&hl=en&newbks=1&newbks_redir=0&source=gb_mobile_search&sa=X&ved=2ahUKEwjUtc-Er_-NAxUjFVkFHeJ0MiMQ6AF6BAgLEAM#v=onepage&q=Pangolin%20walk&f=false
Swart (2013; in Kingdom and Hoffmann, 2013) (Vol. 5 p. 400):

https://books.google.com/books?id=BkvrDwAAQBAJ&pg=PA400&dq=Temminck%E2%80%99s+pangolin+short+forelimbs&hl=en&newbks=1&newbks_redir=0&source=gb_mobile_search&sa=X&ved=2ahUKEwj65OSes_-NAxUnmIkEHTVYAHwQ6AF6BAgHEAM#v=onepage&q=Temminck%E2%80%99s%20pangolin%20short%20forelimbs&f=false 
Pappas (2012):
-V1:

https://www.livescience.com/22700-termite-digging-mammal-discovered.html

-V2:

https://www.nbcnews.com/id/wbna48804056

Museum of Osteology's Facebook post (June 8, 2020):
https://www.facebook.com/photo.php?fbid=3001597486559916&id=142744599111900&set=a.558676410852048

-Photo:
https://images.app.goo.gl/QSUJSfmkuLSH95fN9


8.) Spinosaurus and Deinocheirus?
I thought that Deinocheirus would've been a good example of bipedalism for Spinosaurus. Deinocheirus has a large hump that resembles a mini-sail, so maybe it would be a good template for a bipedal Spinosaurus. Unfortunately, this is not the case. Deinocheirus has a vertically-shaped/"hypertrophied" ilium designed to "support the animal's great weight" (Lee et al., 2014, p. 1 Figure 1; p. 3), and a femur that's longer than the tibia (p. 3). 

Deinocheirus skeletons (Lee et al., 2014, p. 1 Figure 1). Scale bar is 1 meter:

MPC-D 100/127's ilium (Figure 3j):
Reconstructed ilium (Figure 1):
Spinosaurus has neither of these characteristics. We can see this in the design from Fabbri et al., (2022) (Figure 1):
We also see the actual bone in the documentary Bigger than T. rex (Nova):
So, it looks like we're back with a quadrupedal or belly-sliding Spinosaurus. 

Link:
Lee et al., (2014):

https://www.academia.edu/11176967/Resolving_the_long_standing_enigmas_of_a_giant_ornithomimosaur_Deinocheirus_mirificus

-Abstract:
https://www.nature.com/articles/nature13874
Fabbri et al., (2022):
https://www.nature.com/articles/s41586-022-04528-0.epdf?sharing_token=rxUUwyZxDWQ24dJfwtIw89RgN0jAjWel9jnR3ZoTv0NEFj8DFZa3bazFWKdXldNTvT8T3daJQzYMUbPXaqso6c2KKBgthBeOpsV72_JOZHeSlOxZzzE9wUggHYItKT5ASyn5r0hTiRPfCQi_Cfe9RPf0tvCNFd3T4QXE2UU4r7wR-SYYL4_TSvBiBpniofeQoStgnv6yWzzkL81Gcy2g6hKT9nO8ozsufeY9DwX1VK-Vsw94pFBHTtBWnm2-q0bJ33Xx2cPSUh5t7T-nx3NDvtkT9MSkWBYPTw7aqWM5FRs%3D&tracking_referrer=www.sciencenews.org

9.) Using the equation from Campione et al., (2014):
I finally found a way to use the equation from Campione et al., (2014). This was the equation that Persons IV et al., (2019), and Hank Sharpe in 2022, used to estimate the body weight of Spinosaurus aegyptiacus. Now, they got a mass estimate of 1,645 kg (1.81 tons) or 1.3 tons. Let's see if I can get the same results.

Here is the equation. It's called "equation 7" (Campione et al., 2014, Mathematical details):

Now, the correct way to solve this equation was shown in a video I saw from the YouTuber Vividen (YouTube, Vividen, The Paleontological Size Guide: Calculate Dinosaur Size Yourself, 4:35):

Note: "Campione et al. 2017" is actually Campione et al., (2014).


I had to readjust myself to the basics of logarithms, but it seems that you use the Quotient Property to solve this. Since the equation involves subtraction, we have to divide in order to get our answer (Chili Math, Proofs of Logarithm Properties):

We have to use the "femoral circumference" of a specimen in the equation. Now, using Persons IV et al., (2019), an adult Spinosaurus has a femoral circumference of 320 mm (or 32.0 cm) (p. 670 Table 2). There are no circumference measurements given in my other sources, so I'll go with 320 mm.  


Steps:

1.) Femoral circumference^2.754/10^0.683 = number (Note: Use "xy"/"x^y" on calculator to get exponent).

2.) Number/1000 = answer in kg.

Math:
320^2.754 = 7,928,354.131247174
10^0.683 = 4.819477976251273
7,928,354.131247174/4.819477976251273 = 1,645,064.915809424
1,645,064.915809424/1000 = 1,645.064915809424 or 1,645.1 kg (1.813 tons).

I got the exact same result as Persons IV et al. 


Links:
Campione et al., (2014):
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12226

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
-V2:

https://anatomypubs.onlinelibrary.wiley.com/doi/am-pdf/10.1002/ar.24118

-V3:
https://www.gbif.org/species/159236947
-Abstract:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ar.24118
YouTube. Vividen. The Paleontological Size Guide: Calculate Dinosaur Size Yourself. 4:35 and 4:49:
https://www.youtube.com/watch?v=uJK_NRs6Fnc

Chili Math. Proof of Logarithm Properties:

https://www.chilimath.com/lessons/advanced-algebra/proofs-of-logarithm-properties/


Conclusion:
I have tried everything, but the femur of Spinosaurus cannot hold over 1.8 tons. I'll have to stick with the belly-sliding hypothesis for now.


Update (4/28/26):
I'm not sure if this is authentic or not, but I think I found another Spinosaurus arm. On an Instagram post made by dream.fossils, they said that they found a lower arm of Spinosaurus. What is interesting about the arm is that the manual digit 3, and the manual unguals, match those of the DinoLab arm. The manual unguals also match the arm from Reddit, and the manual ungual from Ibrahim et al., (2020a). 


Picture of Spinosaurus arm (dream.fossils):
We now have, possibly, two Spinosaurus arms with long third digits. If Spinosaurus had a long third finger, I wonder what the purpose for it was? How flexible was it? Could it support any weight? 

I also found a Dinopedia discussion page that said that this specimen was a real fossil (Fandom, Dinopedia, HUGE NEWS! ...As promised: Another giant 13-14 meters Spinosaurus specimen in private hands). Also, I found a video on the PNSO's Facebook profile that was uploaded in 2022. The person in the video said that, during that time, people online were hypothesizing that Spinosaurus had a long third finger that might've acted as a "fin-like structure" (Facebook, PNSO, Essien the Spinosaurus 3: The Forelimbs). I don't remember hearing, or seeing, that idea floating around the internet back in 2022! Could Spinosaurus' hand acted like a fin, better yet a flipper? Where the hands webbed? More questions that need to be answered!

If, and I do mean if, this specimen is authentic, then this adds extra weight to the hypothesis that Spinosaurus had different hands compared to other spinosaurids. I hope Ibrahim, and his team, excavate the arms of the Spinosaurus neotype so we can have conclusive Spinosaurus arms.

Links:
Instagram. dream.fossils:

https://www.instagram.com/p/DPGhGafD1Nd/?img_index=1

-V2:

https://www.instagram.com/p/DPGhGafD1Nd/
Fandom. Dinopedia. HUGE NEWS! ...As promised: Another giant 13-14 meters Spinosaurus specimen in private hands:

https://dinopedia.fandom.com/f/p/4400000000000144128
Facebook. PNSO. Essien the Spinosaurus 3: The Forelimbs:

https://www.facebook.com/pnso.us/videos/essien-the-spinosaurus-3-the-forelimb-learn-to-draw-dinosaurs-with-zhao-chuang/1233529810713691/


Update (5/19/26):
So, I thought that I found another analog as to what a possible bipedal Spinosaurus might've been. I thought that the penguin, primarily the emperor penguin, would've been the answer. The emperor penguin has a short femur, a long tibia and fibula, and short metatarsals. This matches the hindlimb of Spinosaurus. The animal has an overall long body, yet it is bipedal. Some prehistoric penguins also had this body design, as shown below.

Penguin skeletons (The first two are extinct; extant emperor penguin is the last one) by Dr. Giovanardi (University of Cambridge Christ's College, 2023):

I would imagine a bipedal Spinosaurus with its body being vertical, and its tail touching the ground. Most of the weight of the animal should be put on the base of its tail, so the hind limbs could be able to support the animal for the most part in a bipedal posture. Spinosaurus' arm wouldn't be in close proximity with the ground  Problem solved, right? Well, not really. The ilium (top) in the penguin is small, and the ischium (bottom) is longer and wider. According to Agarwal V.K. (2017), Neognathae, the superorder of birds that "includes modern birds," have a "ilium and ischium" that "are united" (p. 362). According to the University of California Museum of Paleontology (UCMP), Penguins are neognaths (Introduction to Neognathae). The fused pelvic area, along with the synsacrum (Stanchak et al., 2020), probably helps the Emperor penguin (and neognathae in general) to stand upright. Then again, Davenport and Bels (2023) said that the emperor penguin could use its forelimbs to traverse across snow on land. The forelimbs would move the snow during their "power strokes." This is their quadrupedal form of locomotion (Abstract). Spinosaurus' ilium and ischium are not fused, and Spinosaurus' ischium is short and skinny. 

Maybe I'm thinking too hard about this? Perhaps Spinosaurus was bipedal, and I'm just refusing to see it? The math doesn't support strict bipedalism, and the pelvic bones don't match a strictly bipedal animal; let alone a bipedal animal with such a weird body design. I am definitely conflicted about this. My go-to posture for Spinosaurus is a belly-slider that pushed itself forward by its hind limbs. The lower arm might've helped as well. I want to make sure that I'm not being pushed by bias towards one mode of transportation only. If Spinosaurus was bipedal, then my new penguin-mode is my best bet. If not, I'm stuck with the belly-sliding mode. In fact, I hypothesize that Spinosaurus could've used its lower arms in a power stroke motion across the ground, especially mud, like the emperor penguin does across the snow.


Links:

Agarwal V.K. (2017) (P. 362): 

https://www.google.com/books/edition/Zoology_for_Degree_Students_For_B_Sc_Hon/6UV_EAAAQBAJ?hl=en&gbpv=1&dq=emperor+penguin+ilium+bone&pg=PA362&printsec=frontcover
University of California Museum of Paleontology. Introduction to Neognathae:

https://ucmp.berkeley.edu/diapsids/birds/neognathae.html

University of Cambridge Christ's College (2023):

https://www.christs.cam.ac.uk/news/super-sized-penguin-fossil-identified
-Pic:

https://share.google/cY5MuyqCge6dTXZZm

Davenport and Bels (2023):

https://ui.adsabs.harvard.edu/abs/2023JNatH..57.1972D/abstract
-V2:

https://www.tandfonline.com/doi/full/10.1080/00222933.2023.2282623

Stanchak et al., (2020):

https://pmc.ncbi.nlm.nih.gov/articles/PMC7751001/

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Thursday, February 27, 2025

(Biography) The Determination of Louis R. Purnell Jr.

It's the end of February, a.k.a Black History Month. I wanted to take a brief moment to discuss the career of a man who, honestly, helped to reinvigorate my passion for prehistory. Long story short, late 2021-2023 were very challenging years for me and I kind of lost some of my passion for paleontology. However, in late 2023, I found strength in the story of Louis Purnell Jr. Now that I'm moving on with my life, and I regained my passion for paleontology, I wanted to write this post to discuss Mr. Purnell's career at the Smithsonian Museum of Natural History. 

Louis R. Purnell Jr. as Curator of the National Air and Space Museum (1980s) (The Smithsonian Institution Archives):

According to the Smithsonian Institution Archives, "Louis R. Purnell Jr. was born in 1920" in "Maryland's Eastern Shore," (Smithsonian Institution Archives, African American Groundbreakers at the Smithsonian: Challenges and Achievements, Louis R. Purnell: The Education of Louis R. Purnell, para. 1). After serving as a pilot, and lieutenant in the Tuskegee Airmen, in World War 2 (Into the Air), Purnell got a BS in Psychology at Lincoln University (Into the Air, para. 1; An Insatiable Curiosity, para. 2). In order to make some money for his family, he worked at the Post Office. Looking for some excitement though, he went through a number of different jobs until he landed at the Smithsonian Museum of Natural History in 1961. He became a "museum specialist in the Division of Invertebrate Paleontology and Paleobotany," (An Insatiable Curiosity, para. 1-2). He went on several expeditions to collect specimens, and studied the nautiloid collection in the Smithsonian (An Insatiable Curiosity, para. 5-6). This is where Purnell gets into trouble. He noticed that some specimens were missing, and eventually found them. He was going to "write a new catalog based on his research." However, his colleagues said that he was crazy because he didn't have an education in Geology. Purnell took some "classes at George Washington University to learn how to identify the nautiloids and cephalopods that were in the Smithsonian's collections." He published his catalogue in 1968, and the Smithsonian Institution Archives said that it's "still in use today," (para. 6). It's also stated that Purnell "taught himself Geology and paleontology," (Louis R. Purnell, para. 1). The journey to finishing his catalogue was a rough one, due to "the collections manager" trying to stop him. This was due to, once again, Purnell not having a degree in Geology. Even when his catalogue was finished, most of the credit went to his supervisors in the Forward section of the work. These supervisors were the same people who tried to thwart him from publishing his catalogue! Purnell was also promised that he would get a promotion after he published his catalogue. Unfortunately, this didn't happen. Luckily, Purnell never let this experience subdue his "intellectual ambition" (An Insatiable Curiosity, para. 7). 

Purnell had success at the National Air and Space Museum (The National Air and Space Museum), but I wanted to focus on Purnell's experience at the Natural History Museum. I've had a similar experience to Purnell back in 2022-2023. Purnell had a strong will to never give up. He said that "he learned to 'roll with the punches' and 'overlook - not forgive, but overlook - [the] prejudice' he faced," (The National Air and Space Museum, para. 8). You have to get around any barrier (para. 9). Racial barriers were very large during Purnell's time with the Smithsonian (The National Air and Space Museum, para. 1, and 8-9). Nowadays, it's gender and political barriers in the sciences in general. Paleontology has been hit by this as well, and I went through it firsthand. I don't know about racial prejudice in paleontology, but I doubt that it doesn't exist presently in the science. Racism, in general, never goes away. However, no matter who you are, you have to keep going if you want to succeed. That's something that I had to remind myself of.

I hope that Purnell's story inspires you, like it did for me. I'll also leave the link to Purnell's catalogue for you to read if you're interested.

Links: 
Smithsonian Institution Archives. African American Groundbreakers at the Smithsonian: Challenges and Achievements. Louis R. Purnell: 
https://siarchives.si.edu/history/featured-topics/African-Americans/louis-purnell
-Purnell's Nautiloid catalgoue:
https://repository.si.edu/bitstream/handle/10088/10174/USNMB_2621968_unit.pdf?sequence=1&isAllowed=y

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Monday, December 30, 2024

Nanotyrannus as an Eutyrannosaurian (Abstract).

Link:
https://www.academia.edu/126691661/Nanotyrannus_as_an_Eutyrannosaurian_Abstract_

                                                                        Abstract

Throughout 2024, several publications have shed new light on the highly-debated tyrannosauroid taxon Nanotyrannus lancensis, or as this author calls it, Nanotyrannus/Dryptosaurus lancensis. Nanotyrannus has been placed outside of tyrannosauridae, and into the basal tyrannosauroidea clade. Even more surprising, the holotype of Nanotyrannus, CMNH 7541, had an external fundamental system (EFS) located within its hyoid. This indicates that the specimen was an adult. Although we now have a mature specimen for the species, this author raises a question: where does Nanotyrannus lie within tyrannosauroidea? There are two groups within the basal tyrannosauroidea clade: pantyrannosauria and eutyrannosauria. Based on the skeletal characteristics Nanotyrannus shares with Raptorex, Dryptosaurus, and Appalachiosaurus, and since the latter two taxa are within eutyrannosauria, this author hypothesizes that Nanotyrannus can be placed within eutyrannosauria. This author also believes that Raptorex, another debated tyrannosaur, could fit within eutyrannosauria as well. Another potential member is the Bissekty tyrannosauroid. A possible hypothetical growth series for Nanotyrannus could be the following: BMRP 2002.4.1 (“Jane”), BMRP 2006.4.4 (“Petey”), and CMNH 7541. 
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Sunday, December 22, 2024

(News) Hello Allosaurus anax, and Goodbye "Saurophaganax" (Danison et al., 2024b)!

"Saurophaganax" skeleton (Sam Noble Museum/Oklahoma Museum of Natural History Facebook Reel):
It's okay, "Saurophaganax." You can rest now (paraphrased from Avengers Endgame, 2019).

I knew some Allosaurus bones got mixed in with the "Saurophaganax" material! I've been saying this for years. Now, a new paper written by Danison et al. states exactly what I've been saying! 

Note: Download the paper. Some things in the abstract are different from what's stated in the paper.

"Saurophaganax" is officially a nomen dubium, and a chimera (pp. 81, 106, and 108). The atlas and dorsal vertebrae, and chevrons, are neosauropoda (like Camarasaurus), a diplodocid, or nomen dubium (pp. 81, 89-90, 93-95, and 108-109). Amazingly, the authors recognized that carcharodontosaurids had similar morphologies in their dorsal vertebrae compared to "Saurophaganax's" (the "Saurophaganax" holotype OMNH 1123), in particular Tyrannotitan/Giganotosaurus chubutensis and Lusovenator! I said that! However, the authors disagreed that OMNH 1123 could be definitively referred to a theropod. They didn't even know if it could accurately be assigned to a sauropod, but they decided that it probably was a sauropod that resembled Apatosaurus sp. (pp. 93 and 95). Either way, they put OMNH 1123 as a nomen dubium (pp. 95 and 108). I was right about "Saurophaganax" being a chimera! I'm also surprised that the authors also noticed a possible carcharodontosaurid connection to "Saurophaganax!" 

Atlas vertebrae of Allosaurus jimmadseni (A), "Saurophaganax" (B), and Camarasaurus sp. (C) (p. 89 Figure 4):
"Saurophaganax" holotype OMNH 1123 (A) compared to Apatosaurus sp. OMNH 1366 (B). The sprl in Apatosaurus sp. seem to match the al in "Saurophaganax" (p. 94 Figure 8):
See p. 93 for the comparison between the laminae of the two bones. I wonder... Are the laminae in OMNH 1123 so wide because the specimen was a hatchling, or juvenile? If the animal grew, would the laminae become elongated like Apatosaurus' are? That's just a guess though.

The Allosaurus material was either named Allosaurus anax, or Allosaurus sp. (pp. 82-83, 106-109). The giant humerus, OMNH 1935, which I thought had to be Allosaurus, was "indistinguishable from that of Allosaurus fragilis and Allosaurus jimmadseni." The authors said it was an allosaurid, despite it's great size (pp. 100-101, and 106), but for some reason they didn't put it as Allosaurus anax or Allosaurus sp. Since the authors agreed with me that OMNH 1935 was basically Allosaurus, I'll place the giant humerus under Allosaurus sp. myself. 

Originally, I put the femora in Allosaurus but switched to putting it in "Saurophaganax." I also put the tibiae in "Saurophaganax." It turns out that the femora were Allosaurus after all, but not A. fragilis or A. jimmadseni. The authors called it Allosaurus sp. (pp. 102 and 109). The tibiae were also assigned to Allosaurus sp. (pp. 104 and 109). The postorbital, a cervical vertebra, two dorsal centrum, and fibulae, were assigned to Allosaurus anax and not "Saurophaganax" (pp. 82-83, and 108-109). The metatarsals, which I thought were either Allosaurus or a carcharodontosaurid, were put under Allosaurus sp. (pp. 106 and 109). I was VERY conservative in estimating how much of the "Saurophaganax" material belonged to Allosaurus! That is shocking!

Speaking of Allosaurus maximus, it's a synonym of "Saurophaganax maximus" because it used the specimen OMNH 1123 as the holotype. That's probably the reason why Allosaurus anax was erected as the new genus name, along with the fact that the authors see the Allosaurus material as distinct from A. fragilis and A. jimmadseni (p. 107).

"Saurophaganax" was a chimera (like I've stated before), and a nomen dubium. "Saurophaganax" wasn't even a carcharodontosaurid, like I originally hypothesized. It probably didn't even exist! However, I'm just glad that I was right about the Allosaurus bones being lumped into the "Saurophaganax" material. Heck, almost all of the bones were Allosaurus sp. or Allosaurus anax! I wasn't going far enough! However, it's good to double-check and be cautious at times. 

Vindication, once again! I was made fun of, and criticized, for my abstract that I wrote on Saurophaganax. I said that it was a chimera that contained carcharodontosaurid and Allosaurus bones. Now, this paper comes out and confirmed 2/3 of what I proposed. I've said this before, and I'll say it again: don't give up!

Hello Allosaurus anax, and goodbye "Saurophaganax maximus." 

Link:
Danison et al., (2024b):
https://journals.library.ualberta.ca/vamp/index.php/VAMP/article/view/29404
"Saurophaganax" skeleton (Sam Noble Museum/Oklahoma Museum of Natural History Facebook Reel):
https://www.facebook.com/reel/1063663955214929
-Pic:
https://images.app.goo.gl/QoSobE8zMQ7QGo3g7
-Sam Noble Museum’s Facebook Page:
https://www.facebook.com/SamNobleMuseum/reels/
My previous post on "Saurophaganax" being a carcharodontosaurid:
https://psdinosaurs.blogspot.com/2019/12/is-saurophaganax-carcharodontosaurid_21.html
My abstract:
https://www.academia.edu/101770036/Saurophaganax_is_a_Carcharodontosaurid_An_Abstract

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Saturday, November 2, 2024

(News) Is Saurophaganax a chimera (Danison et al., 2024a)!?

Saurophaganax in Planet Dinosaur (2011):

I already talked about one abstract from SVP (2024), but there's another one that I need to discuss regarding another theropod I've talked about before.

We finally got some more research on the enigmatic theropod, Saurophaganax, brought to us by Danison et al., (2024). However, the authors of this abstract have made some pretty surprising claims that could change our view on the theropod completely... For example, the scientists claim that Saurophaganax wasn't even a theropod!

Danison et al., (2024) examined the Saurophaganax material. They started off with a fourth metatarsal, which showed signs of fast growth and what appears to be an External fundamental System (EFS). This doesn't seem to match the growth trajectory of Allosaurus, thus the authors separate Saurophaganax from Allosaurus. That is, if "the appositional rate of the metatarsal is representative of the whole animal." However, it's the last conclusion that floored me. The authors stated that the Saurophaganax vertebral elements (atlas and dorsal vertebrae, and the caudal chevrons) belonged to sauropods and not theropods! In fact, they might belong to an already established sauropod taxon. The holotype of Saurophaganax is the mid-dorsal neural arch (dorsal vertebra) (Chure, 1995, pp. 104 and 106). Based on Danison et al., (2024), this would make Saurophaganax a sauropod or a synonym of another sauropod! The name "Saurophaganax" might not even exist anymore... The skull and limb/long bone elements, said to have belonged to Saurophaganax, do resemble theropoda though. In particular, they are "largely consistent with Allosaurus." (SVP, 2024, pp. 164-165).

Danison et al., (2024 [SVP, 2024]):
P. 164:

P. 165:
Honestly, I don't know what to think. I was certain that the Saurophaganax material belonged to a  carcharodontosaurid. However, some of the bones did resemble Allosaurus, like the giant humerus OMNH 01935. Chure (1995) said that the bone was "robust," yet "closely resembles that of Allosaurus," (p. 103). Smith (1998) said that the humerus matched the Allosaurus growth chart and "non-size-related variation," despite being large (pp. 131, 134, 138-139). In fact, Smith said that the Saurophaganax material "lies on the same growth trajectory for Allosaurus in almost every case," (p. 140). I've also noted before that OMNH 01935 is morphologically indistinct from other humeri of Allosaurus. Saurophaganax was more of a chimera than people thought. Heck, I originally asserted that Saurophaganax was a chimera (half carcharodontosaurid and half Allosaurus) until I discovered that other carcharodontosaurid taxa had similar bones to it, excluding OMNH 01935. The giant humerus still confused me, but I still thought that it belonged to Allosaurus. I still think that. In fact, aside from (possibly) the fourth metatarsal and the vertebrae, other postcrania bones resemble Allosaurus', according to Danison et al., (2024). 

I decided to see if it was possible for the "Saurophaganax" atlas to resemble a sauropod's atlas, or not. I saw Apatosaurus louisae's atlas, and... Yeah, they look really similar:

Apatosaurus louisae's atlas and axis ("at" is atlas) (Gilmore, 1936, p. 192):
"Saurophaganax's" atlas (OMNH 01135) (Chure, 1995, p. 104):
"Saurophaganax" was a chimera after all... I truly believe that some Allosaurus bones got jumbled up in the skeletal material. Now, it seems that some Allosaurus AND probably some sauropod bones got mixed in there as well. I wonder if there's any actual "Saurophaganax" material left to keep the taxonomic name alive?

I'm not going to make any final conclusions until the authors finish their paper. I want to give them a chance, and go about this with an open mind. If this is the end of "Saurophaganax,' then so be it. It was a lot of fun to research the animal. 

Links:
Danison et al., (2024) (SVP, 2024, pp. 164-165):
https://vertpaleo.org/wp-content/uploads/2024/10/2024_SVP_Program_Final3.pdf
Gilmore (1936) (P. 192):
https://www.biodiversitylibrary.org/page/53145444#page/254/mode/1up
Chure (1995):
https://www.researchgate.net/publication/230892243_A_reassessment_of_the_gigantic_theropod_Saurophagus_maximus_from_the_Morrison_Formation_Upper_Jurassic_of_Oklahoma_USA
Smith (1998):
https://www.researchgate.net/publication/272151969_A_morphometric_analysis_of_Allosaurus

Update (6/20/26):
I knew some Allosaurus bones got mixed in with the "Saurophaganax" material! I've been saying this for years. Now, a new paper written by Danison et al. states exactly what I've been saying! 

Note: Download the paper. Some things in the abstract are different from what's stated in the paper.

"Saurophaganax" is officially a nomen dubium, and a chimera (pp. 81, 106, and 108). The atlas and dorsal vertebrae, and chevrons, are neosauropoda (like Camarasaurus), a diplodocid, or nomen dubium (pp. 81, 89-90, 93-95, and 108-109). Amazingly, the authors recognized that carcharodontosaurids had similar morphologies in their dorsal vertebrae compared to "Saurophaganax's" (the "Saurophaganax" holotype OMNH 1123), in particular Tyrannotitan/Giganotosaurus chubutensis and Lusovenator! I said that! However, the authors disagreed that OMNH 1123 could be definitively referred to a theropod. They didn't even know if it could accurately be assigned to a sauropod, but they decided that it probably was a sauropod that resembled Apatosaurus sp. (pp. 93 and 95). Either way, they put OMNH 1123 as a nomen dubium (pp. 95 and 108). I was right about "Saurophaganax" being a chimera! I'm also surprised that the authors also noticed a possible carcharodontosaurid connection to "Saurophaganax!" 

Atlas vertebrae of Allosaurus jimmadseni (A), "Saurophaganax" (B), and Camarasaurus sp. (C) (p. 89 Figure 4):
"Saurophaganax" holotype OMNH 1123 (A) compared to Apatosaurus sp. OMNH 1366 (B). The sprl in Apatosaurus sp. seem to match the al in "Saurophaganax" (p. 94 Figure 8):
See p. 93 for the comparison between the laminae of the two bones. I wonder... Are the laminae in OMNH 1123 so wide because the specimen was a hatchling, or juvenile? If the animal grew, would the laminae become elongated like Apatosaurus' are? That's just a guess though.

The Allosaurus material was either named Allosaurus anax, or Allosaurus sp. (pp. 82-83, 106-109). The giant humerus, OMNH 1935, which I thought had to be Allosaurus, was "indistinguishable from that of Allosaurus fragilis and Allosaurus jimmadseni." The authors said it was an allosaurid, despite it's great size (pp. 100-101, and 106), but for some reason they didn't put it as Allosaurus anax or Allosaurus sp. Since the authors agreed with me that OMNH 1935 was basically Allosaurus, I'll place the giant humerus under Allosaurus sp. myself. 

Originally, I put the femora in Allosaurus but switched to putting it in "Saurophaganax." I also put the tibiae in "Saurophaganax." It turns out that the femora were Allosaurus after all, but not A. fragilis or A. jimmadseni. The authors called it Allosaurus sp. (pp. 102 and 109). The tibiae were also assigned to Allosaurus sp. (pp. 104 and 109). The postorbital, a cervical vertebra, two dorsal centrum, and fibulae, were assigned to Allosaurus anax and not "Saurophaganax" (pp. 82-83, and 108-109). The metatarsals, which I thought were either Allosaurus or a carcharodontosaurid, were put under Allosaurus sp. (pp. 106 and 109). I was VERY conservative in estimating how much of the "Saurophaganax" material belonged to Allosaurus! That is shocking!

Speaking of Allosaurus maximus, it's a synonym of "Saurophaganax maximus" because it used the specimen OMNH 1123 as the holotype. That's probably the reason why Allosaurus anax was erected as the new genus name, along with the fact that the authors see the Allosaurus material as distinct from A. fragilis and A. jimmadseni (p. 107).

"Saurophaganax" was a chimera (like I've stated before), and a nomen dubium. "Saurophaganax" wasn't even a carcharodontosaurid, like I originally hypothesized. It probably didn't even exist! However, I'm just glad that I was right about the Allosaurus bones being lumped into the "Saurophaganax" material. Heck, almost all of the bones were Allosaurus sp. or Allosaurus anax! I wasn't going far enough! However, it's good to double-check and be cautious at times. 

Vindication, once again! I was made fun of, and criticized, for my abstract that I wrote on Saurophaganax. I said that it was a chimera that contained carcharodontosaurid and Allosaurus bones. Now, this paper comes out and confirmed 2/3 of what I proposed. I've said this before, and I'll say it again: don't give up!

Hello Allosaurus anax, and goodbye "Saurophaganax maximus." 

Link:
Danison et al., (2024b):
https://journals.library.ualberta.ca/vamp/index.php/VAMP/article/view/29404
"Saurophaganax" skeleton (Sam Noble Museum/Oklahoma Museum of Natural History Facebook Reel):
https://www.facebook.com/reel/1063663955214929
-Pic:
https://images.app.goo.gl/QoSobE8zMQ7QGo3g7
-Sam Noble Museum’s Facebook Page:
https://www.facebook.com/SamNobleMuseum/reels/
My previous post on "Saurophaganax" being a carcharodontosaurid:
https://psdinosaurs.blogspot.com/2019/12/is-saurophaganax-carcharodontosaurid_21.html
My abstract:
https://www.academia.edu/101770036/Saurophaganax_is_a_Carcharodontosaurid_An_Abstract

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Sunday, October 27, 2024

(News) Nanotyrannus holotype was an adult (Griffin et al., 2024)!

Update (12/5/25):
Full paper has been released:

Griffin et al., (2025):
https://www.science.org/doi/10.1126/science.adx8706?fbclid=PAVERFWAOgC4FleHRuA2FlbQIxMABzcnRjBmFwcF9pZA8xMjQwMjQ1NzQyODc0MTQAAaeDc5JF0qycTqEA749YCOkRehMLbusYoDsHTA2XL-zYcYq3ANzssLHjTatoNg_aem_bnEV9_2W5YRextcMPVcdTA
My blogpost on the paper:
https://psdinosaurs.blogspot.com/2025/12/news-nanotyrannus-holotype-cmnh-7541.html

Nanotyrannus/Dryptosaurus lancensis holotype CMNH 7541 (Dalman et al., 2018, p. 135 Figure 15):

One of the biggest critiques against Nanotyrannus/Dryptosaurus lancensis being a valid taxon was that all the specimens were apparently juveniles. As a result, they must've been juvenile Tyrannosaurus rex specimens because no juvenile T. rex specimens have been discovered. However, it has been stated numerous times now that most of the N./D. lancensis specimens were actually slow-growing individuals that were close to maturity, and not fast-growing juvenile T. rex specimens. Now, we have an actual adult N./D. lancensis specimen and it was hiding in plain sight the entire time: CMNH 7541!

CMNH 7541 is the holotype specimen of N./D. lancensis. For the longest time, people thought that it was a hatchling at 8 years of age (Erickson et al., 2006, Supplementary Materials, p. 13) (Carr, 2020, Figures 2 and 12). Some people even labelled the specimen as a nomen dubium (Paul, 2022, p. 67 [Preprint]). Now, it turns out that the real age of the specimen was almost double of that! Griffin et al., (2024), an abstract from SVP 2024, studied the hyoid of CMNH 7541, along with other extinct and extant animals. The hyoid of CMNH 7541 revealed that the specimen was about 14 years old (14 LAGs "at minimum" were present in the hyoid), along with extensive (Haversian) remodeling and secondary osteons within the bone itself. The best part was that an EFS marker was found within the "outermost cortex" of the hyoid. The authors concluded that, although they're not throwing out the possibility that CMNH 7541 couldn't have been a T. rex, the best conclusion based on the evidence is that CMNH 7541 was a distinct taxon of "tyrannosaurid" that was "fully grown," (Abstract [SVP, 2024, pp. 232-233]).

Griffin et al., (2024) (SVP, 2024):
P. 232:
P. 233:
The EFS, or External Fundamental System, indicates that an individual was mature at the time of death. Neither the 13-year old N./D. lancensis specimens BMRP 2002.4.1 ("Jane"), or the 15-year old BMRP 2006.4.4 ("Petey"), had the EFS in their limb bones (Woodward et al., 2020, p. 4). Neither does "Zuri," but "Zuri's" growth was slowing down and wasn't a juvenile despite being "at minimum 12-13 years old when it died." "Zuri" also had extensive Haversian remodeling in its bones as well (Griffin, 2014, Abstract). Both "Jane" and "Petey" were also slowing down in their growth, and they didn't fit in the Tyrannosaurus growth trajectory pattern (Jevnikar and Zanno, 2021, Abstract [SVP, 2021, p. 151]) (Longrich and Saitta, 2024, pp. 38-39). Longrich and Saitta (2024) also said that "Zuri" "was apparently near full size when it died," (p. 39). CMNH 7541, although being 14 at least, has the EFS present in its hyoid (Griffin et al., 2024, Abstract [SVP, 2024, pp. 232-233]). It seems that N./D. lancensis aged extremely quickly, and died young. Other basal tyrannosauroids that did something similar were the basal pantyrannosaurian Dilong (Xu et al., 2004, p. 680), and the eutyrannosaurian Raptorex (Sereno et al., 2009, p. 419; Supplementary Materials, p. 2). This is interesting, since I believe that Nanotyrannus/Dryptosaurus lancensis was also a basal eutyrannosaurian. Dryptosaurus aquilunguis, and Appalachiosaurus/Dryptosaurus montgomerensis, were also eutyrannosaurians (see Delcourt and Grillo, 2018).

This is amazing! I contacted Mr. Griffin back in 2021 regarding "Zuri." He was leaning towards N./D. lancensis being a juvenile T. rex at that time. I was doing so as well, even though I had my doubts. Now, his work is helping to demonstrate that the opposite is true. He actually helped to find an adult N./D. lancensis! Congratulations to him, and his team!

We finally have an adult Nanotyrannus/Dryptosaurus lancensis!

Links:
Griffin et al., (2024) (SVP, 2024, pp. 232-233):

https://vertpaleo.org/wp-content/uploads/2024/10/2024_SVP_Program_Final3.pdf

Woodward et al., (2020):

https://www.researchgate.net/publication/338331660_Growing_up_Tyrannosaurus_rex_Osteohistology_refutes_the_pygmy_Nanotyrannus_and_supports_ontogenetic_niche_partitioning_in_juvenile_Tyrannosaurus

Jevnikar and Zanno (2021) (SVP, 2021, p. 151):

https://vertpaleo.org/wp-content/uploads/2021/10/SVP_2021_VirtualBook_final.pdf

Paul (2022) (Preprint):

https://www.biorxiv.org/content/10.1101/2022.08.02.502517v1.full

-V2 (PDF):

https://www.biorxiv.org/content/10.1101/2022.08.02.502517v1.full.pdf

Longrich and Saitta (2024):
https://www.mdpi.com/2813-6284/2/1/1
Griffin (2014):
-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
Xu et al., (2004):

https://www.researchgate.net/publication/8246151_Basal_tyrannosauroids_from_China_and_evidence_for_protofeathers_in_tyrannosauroids
Sereno et al., (2009):

https://www.researchgate.net/publication/26820186_Tyrannosaurid_Skeletal_Design_First_Evolved_at_Small_Body_Size

-Supplementary Materials:

https://www.science.org/doi/10.1126/science.1177428

V2:

https://d3qi0qp55mx5f5.cloudfront.net/paulsereno/i/docs/09-SCI-Raptorex-SOM.pdf?mtime=1591813921

Delcourt and Grillo (2018):

https://www.sciencedirect.com/science/article/abs/pii/S0031018218302566

-Phylogenetic chart:

https://images.app.goo.gl/wFSumFkc5vq7WGi28


Update (2/13/26): Nanotyrannus (black) and Tyrannosaurus rex (red) by Andrey Atuchin (2025). Retrieved from Shelton (2025):

Nanotyrannus fans are eating good this year! My friend "Luke" notified me that Dr. Christopher Griffin's paper describing the Nanotyrannus holotype's age has officially been published. I contacted Griffin earlier this year, and he said that the paper was submitted for peer-review. Now, it's out! We officially have two specimens of Nanotyrannus that are adults!

In their 2024 abstract, Griffin et al. said that the Nanotyrannus lancensis holotype, CMNH 7541, had an EFS (External Fundamental System) in its hyoid bone. This determined that the individual was mature when it died, and not a juvenile. Now, Griffin et al., (2025) provides us a figure showing the EFS in the hyoid (Figure 3):

Description:
The EFS is shown in the middle (B), and posterior/caudal (C), portions of the ceratobranchial/hyoid bone. It's possible that the EFS is located at the anterior/cranial area of the bone (A), but it's not entirely certain. The bone is damaged at the front. However, the EFS is present throughout the rest of the hyoid (pp. 2-3, Results: The ontogenetic status of Nanotyrannus lancensis type specimen). Other reptiles, but extant and extinct, contained EFS in their ceratobranchial bones as well. This includes a mature specimen of Coelophysis that has an EFS in its ceratobranchial, and femur. This indicates that the hyoid can be used to determine maturity (pp. 1-2, Results: Ceratobranchial histology in extant reptiles; Ceratobranchial histology in extinct dinosaurs; Figures 1-2).

Extant archosaurs with EFS in their ceratobranchial/hyoid bones (Figure 1):
Description:
Extinct archosaurs/dinosaurs (Figure 2):
Description:
Aside from the maturity of the specimen, the scholars hypothesize that CMNH might be different from BMRP 2002.4.1 ("Jane"), and a SWAU specimen. Heck, it might be another eutyrannosaur taxon. Speaking of, the scholars concluded that Nanotyrannus was an eutyrannosaurian. They laid out two hypotheses: that CMNH could've been a dwarf specimen of Tyrannosaurus, possibly a male; or, the specimen was an eutyrannosaurian. The scholars went with the latter hypothesis (p. 3, Results: The ontogenetic status of Nanotyrannus lancensis type specimen):
The SWAU specimen is the Nanotyrannus specimen SWAU HRS 08438 ("Zuri"). This specimen is immature (Supplementary Materials, p. 19 Figure S9). Another figure showing the EFS in CMNH 7541 can also be seen in the Supplementary Materials (p. 13 Figure S4B):
We now have two specimens of Nanotyrannus that were skeletally mature, or were borderline mature. The first is CMNH 7541 (Griffin et al., 2025), and the second is NCSM 40000 ("Bloody Mary") (Zanno and Napoli, 2025). Nanotyrannus has officially struck back, and it won twice. This makes me wonder if Stygimoloch, and Dracorex, were separate taxa from Pachycephalosaurus? I'm definitely not lumping Torosaurus into Triceratops until further evidence forces me to do so. Other dinosaur taxa previously studied more-than-likely suffered the same fate, so they should probably be re-examined too. Either way, lumping a taxon into a previously established one just because it's not fully grown may not always be the best method. I'm guilty of this myself, which is why I thought Nanotyrannus could've been Dryptosaurus aquilunguis back in 2022. Nowadays, I use the generic names Nanotyrannus or 
Dryptosaurus interchangeably, but I stick to the species names lancensis or lethaeus, for the animal.
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