Ah, Gregory S. Paul. Possibly the most famous paleo-artist to ever live. His 1988 book
Predatory Dinosaurs of the World was the inspiration for Michael Crichton to write
Jurassic Park (1990). Yet, he is known as being a notorious lumper, and is mocked ceaselessly for it. However, when someone is right you have to admit that they are. He recently had a paper published detailing the validity of the tyrannosauroids in the late Maastrichtian of North America. He concluded that there are three
Tyrannosaurus species in the late Maastrichtian (
T. rex, T. imperator, and
T. regalis from Paul et al., 2022), and that
Nanotyrannus is a valid taxon and an eutyrannosaurian.
This is a long paper (59 pages), so I'm just going to focus on the
Nanotyrannus information. If I missed something, I'll add it to the post later on. It should be noted that Paul (2025) is the published version of Paul (2022) (preprint). Both versions are linked below. I will also link "
Stygiovenator" into
Nanotyrannus for now until I believe that it is a separate taxon. I'm down for having multiple tyrannosauroids in the late Maastrichtian of North America, but I want to be careful.
Nanotyrannus (and "
Stygiovenator") skulls (Paul, 2025, p. 119 Figure 10):
The first skull is the holotype CMNH 7541 (adult), the second is "Jane" (subadult), and the third is "Bloody Mary" (age uncertain). I also noticed that Paul called them "nontyrannosaurid tyrannosaur(o)id skulls."
First, Paul (2025) said that
Nanotyrannus (and "
Stygiovenator") was an eutyrannosaurian and not a tyrannosaurid (p. 94 Figure 1; p. 117; p. 118 Figure 9; pp. 120, 126, and 128-129). I wrote my abstract for
Academia saying the same thing towards the end of 2024, so it's good to see someone else say that as well. Second, Paul stated that
Dryptosaurus shares “a close relationship to the long armed TT-zone baso-eutyrannosaurians,” (p. 120). He mentioned that Nanotyrannus (and "
Stygiovenator") had
“dryptosaur style” arms. This has been “widely discussed online” as well (p. 128). I don't want to toot my own horn, but I wonder if that was a reference to me, my friend "Luke," and others who've made that connection between Nanotyrannus and Dryptosaurus? Anyways, Paul continues to state that Nanotyrannus (and "
Stygiovenator") and
Dryptosaurus could potentially form a clade, but the fragmentary nature of the
Dryptosaurus specimens should be put into perspective before making a clear decision on this (p. 128). Despite that, I think that
Nanotyrannus and
Dryptosaurus do form a clade.
The best part about this is that Paul stated that some of the Nanotyrannus (and "
Stygiovenator") specimens could potentially be
Dryptosaurus aquilunguis, or be a species of
Dryptosaurus (p. 128). I stated this in my abstract back in 2022! I recommend
Nanotyrannus/
Dryptosaurus lancensis myself nowadays, and I stated this in my 2024 abstract calling
Nanotyrannus an eutyrannosaurian. Paul cited Griffin et al., (2024), which stated that the
Nanotyrannus holotype CMNH 7541 was a fully-grown adult (p. 124). Finally, Paul said that the two landmasses that made up North America during the Cretaceous (Laramidia and Appallachia) reconnected during the Maastrichtian. This would've allowed the eutyrannosaurs of Appalachia to interact with the tyrannosaurids of Laramidia (p. 127). I stated this in my 2022 abstract as well.
Paul acknowledging the online discourse surrounding the hands of
Nanotyrannus (and "
Stygiovenator") and
Dryptosaurus (p. 128):
Nanotyrannus (and "
Stygiovenator") and
Dryptosaurus could form a clade, and some
Nanotyrannus (and "
Stygiovenator") specimens could potentially belong to
Dryptosaurus (p. 128):
Third, Paul stated that the arms of the
Nanotyrannus (and "
Stygiovenator") specimens exclude them from being lumped into
Tyrannosaurus. Actual juvenile, and adult,
Tyrannosaurus specimens possess arm and manus bones that are shorter than the arm bones of
Nanotyrannus (and "
Stygiovenator"). Paul said that this physical trait links
Nanotyrannus (and "
Stygiovenator") to the eutyrannosaurian clade, which originated and immigrated from the East (Appalachia). Therefore,
Tyrannosaurus' arms didn't shrink during ontogeny. This is also the case in the growth series of
Tarbosaurus/Tyrannosaurus bataar and
Gorgosaurus, which means that the more derived tyrannosaurids didn't have their arms shrink during ontogeny (pp. 118-120; p. 118 Figure 9; p. 121 Figure 11). The humerus in
Nanotyrannus (and "
Stygiovenator") is short, but the lower arm and manus are long (p. 120). This is also characteristic in the arm of
Dryptosaurus aquilunguis (Brusatte et al., 2011, pp. 1, 5, and 46-47). Paul concludes that the arms of young
Tyrannosaurus specimens were smaller than the adults' (p. 126).
Arms of
Tyrannosaurus and
Nanotyrannus (and "
Stygiovenator") (p. 118 Figure 9):
The adult
Tyrannosaurus specimens MOR 980 and FMNH PR 2081 ("Sue") have longer hands, and humeri, than the younger specimen UCRC PV-1. Meanwhile, the two hands of
Nanotyrannus (and "
Stygiovenator") on the right are longer than all three
Tyrannosaurus specimens on the left and middle.
Fourth, Paul used the young
Tyrannosaurus specimen BHI 6439 in his paper (p. 96; p. 116 Figure 8; p. 117, 120-121, and 126). It's been a long time since anybody even referenced the specimen, but Paul actually used it in his paper! Not only that, he used "Baby Bob" (pp. 96, 121, and 126)! I know that's gonna be a huge criticism, but I admire Paul's guts to use those specimens. He even criticized the exclusion of such specimens on p. 128. I understand the points-of-views for both sides of the argument regarding this specimens, but both BHI 6439 and "Baby Bob" are in reputable institutions (
Field Museum of Natural History in Chicago for BHI and
University of Kansas/KU in Kansas for "Baby Bob") and have been used in previous peer-reviewed publications before. Therefore, I believe that they should be used more often. Paul uses BHII 6439 and "Baby Bob" to demonstrate that the tooth counts, and tooth morphologies, of
Tyrannosaurus do not change over time. They're consistent throughout the animal's lifetime (pp. 125-126). I also mentioned this on the blog before, so this is also pleasing to see stated again. Then again, Napoli (2024) (preprint) also disputed the tooth-loss theory as well. In summation,
Tyrannosaurus didn't lose teeth or change tooth morphology, nor did its hands shrink as it grew older. Its ontogenetic growth was similar to that of
Tarbosaurus', and other tyrannosaurids.
I do have one complaint, aside from "
Stygiovenator,"
T. regina, and
T. imperator possibly being valid. Paul lists KUI 56375 as being a juvenile
T. rex (p. 116 Figure 8; p. 117). However, I remember this specimen being changed to being listed as
Nanotyrannus. The maxilla of this specimen matches the morphology of
Nanotyrannus as well, so I'll place it in
Nanotyrannus for now.
Young
T. rex specimens BHI 6439 (B) and "Baby Bob" (D) dentaries (p. 116 Figure 8B and D):
The maxilla of KUI 56375 is C. Notice how the maxilla is identical to the other
Nanotyrannus (and "
Stygiovenator") maxillae in E-I.
In conclusion, this is the second paper (after Longrich and Saitta, 2024) to state that
Nanotyrannus is an eutyrannosaurian, alongside
Dryptosaurus aquilunguis. Heck, Paul (2025) even said that some specimens of
Nanotyrannus (and "
Stygiovenator") could potentially
be Dryptosaurus! All of this information, along with Griffin et al., (2024) and Napoli (2024) (preprint), demonstrates that
Nanotyrannus/Dryptosaurus lancensis is a distinct taxon from
Tyrannosaurus. Also, this means that the ontogeny of
Tyrannosaurus wasn't as extreme as previously believed. The animal had a normal tyrannosaurid ontogenetic growth curve.
Links:
Paul (2025):
https://mapress.com/mz/article/view/mesozoic.2.2.1
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
My post on Griffin et al., (2024) (Abstract):
https://psdinosaurs.blogspot.com/2024/10/news-nanotyrannusdryptosaurus-lancensis.html
Napoli (2024) (Preprint):
https://www.biorxiv.org/content/10.1101/2024.10.25.620216v1My 2022 abstract:
https://psdinosaurs.blogspot.com/2023/02/nanotyrannus-is-dryptosaurus-abstract_10.html
My 2024 abstract:
https://psdinosaurs.blogspot.com/2024/12/nanotyrannus-as-eutyrannosaurian.html
Extra:10/3/25:
I was notified by my friend "Luke" that a recent paper was mentioned in the YouTuber Ben G. Thomas video that said that the
Tyrannosaurus specimen "Sue" has a tooth socket in its maxilla that was closed. This shows that
Tyrannosaurus lost teeth as it matured. Paul (2025) mentions this paper in his Supplementary Materials (
Nanotyrannus not a juvenile). This paper is Voris et al., (2025). Paul said that "This is contradicted by the multiple lines of evidence against significant tooth reduction in reptile ontogeny, tyrannosaurids included, cited in the main text that are not addressed by Voris et al., (2025)." Voris et al. also stated that
Nanotyrannus' characteristics are juvenile ones. This was also mentioned by Ben G. Thomas. Paul said that the
Nanotyrannus specimens were not juveniles, which makes that statement false (
Nanotyrannus not a juvenile). Also, CMNH 7541 has an EFS in its hyoid (Griffin et al., 2024), so we have an adult specimen for
Nanotyrannus. Napoli (2024) (preprint) also stated that
Nanotyrannus,
Tyrannosaurus, and crocodilians, didn't lose teeth as those two taxa matured. I agree with Paul that Voris et al., (2025) are incorrect in saying that
Nanotyrannus' characteristics were due to the specimens being juveniles. I tried to access Voris et al., (2025), but it's blocked behind a paywall.
Paul's comments on Voris et al., (2025) (Supplementary Materials,
Nanotyrannus not a juvenile):
Links:
Ben G. Thomas' Video (
YouTube):
https://youtu.be/v1gKWxoSjHI?si=pIXwZlpCiDkjeTtl
Voris et al., (2025) (Preview only):
https://www.researchgate.net/publication/392596951_A_new_Mongolian_tyrannosauroid_and_the_evolution_of_Eutyrannosauria
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