Thursday, October 30, 2025

(News) Nanotyrannus specimen "Bloody Mary" was an adult, and Nanotyrannus was related to Dryptosaurus (Zanno and Napoli, 2025)!

Nanotyrannus pack attacking a juvenile Tyrannosaurus by Anthony Hutchings (2025) from Egan (2025):
It's over! Nanotyrannus is a valid species, and is a basal tyrannosauroid! Zanno and Napoli (2025) have uploaded a paper, albeit it's an "unedited version" of the paper that is still being edited. The paper is also behind a paywall (boo!), but the abstract is available on Nature. The "Bloody Mary" specimen of Nanotyrannus, cataloged as NCSM 40000, was "near somatically mature" in terms of age. It also shares characteristics to the holotype of Nanotyrannus lancensis, CMNH 7541, cementing it in the taxon. However, the two scholars throw a curve-ball in their abstract: there are TWO Nanotyrannus species: N. lancensis and N. lethaeus. We officially have two genera of tyrannosaurs coexisting at the end of the Cretaceous in North America (Abstract):
My boy "Luke" sent me a picture of the phylogenetic charts that have been posted on Twitter-X:

My friend on Discord downloaded the paper. Here's the full chart (Figure 6 [p. 38]): 
Description (pp. 18-19):
Aside from Moros flip-flopping between Eutyrannosauria (top) and Pantyrannosauria (bottom), you can see Nanotyrannus and Dryptosaurus being put in the eutyrannosaurian clade. This confirms the results of Longrich and Saitta (2024) and Paul (2025b). Interestingly, the Zanno and Napoli placed Dryptosaurus and Appalachiosaurus in the new Nanotyrannidae clade, named after Nanotyrannus. Since Dryptosaurus was named before Nanotyrannus, I would've gone with Dryptosauridae. Also, I still think calling the taxa Nanotyrannus/Dryptosaurus lancensis and Nanotyrannus/Dryptosaurus lethaeus are still valid taxonomic names. However, I don't care! I'm still elated by the news! More phylogenetic charts are listed in the Extended Data section. As for Moros being a sister taxon to Nanotyrannus in one phylogenetic chart but not in the second one, Zanno and Napoli said that Moros being the sister taxon occurred in the "MP implied weights." This does not occur in the "MP equal weights or BI," so the authors "do not recommend taxonomic action in response," (Phylogenetic Position of Nanotyrannus, para. 2). 

Phylogenetic charts 2 (Zanno and Napoli, 2025, Extended Data Figure 9 [p. 47]):
Description (p. 32):
Phylogenetic charts 3 (Zanno and Napoli, 2025, Extended Data Figure 10 [p. 48]):
Description (p. 32):
I want to make a quick note about "Stygiovenator." Paul (2025b) put NCSM 40000 in "Stygiovenator," but now this specimen is in Nanotyrannus lancensis (Zanno and Napoli, 2025, Discussion: A Skeletally Mature Nanotyrannus, para. 1 [p. 6]; Figures 1 and 2 [pp. 17, and 33-34]). BMRP 2002.4.1 ("Jane") is in N. lethaeus (Discussion: A Skeletally Mature Nanotyrannus, para. 1 [p. 6]; Figure 1 [pp. 17 and 33]). Interestingly, BMRP 2006.4.4 ("Petey") is called Nanotyrannus sp. (Discussion: A Skeletally Mature Nanotyrannus, para. 1 [p. 6]). I'm putting "Stygiovenator" as a synonym of Nanotyrannus lancensis. Also contrary to Paul (2025b), the specimen KUVP 156375 doesn't belong in Tyrannosaurus. Zanno and Napoli (2025) placed it in Nanotyrannus lancensis (Phylogenetic Position of 
Nanotyrannus, para. 1; Figure 6). I don't blame Paul for that. KUVP was considered to be a juvenile Tyrannosaurus some time ago in an abstract from the Society of Vertebrate Paleontology (SVP).

As for its age, Zanno and Napoli stated that NCSM "had begun" an "incipient EFS (external fundamental system) development along the majority of the circumferential section, but had not yet fully ceased skeletal growth at the time of death," (A Skeletally Mature Nanotyrannus, para. 2). The authors stated that "N. lancensis reached skeletal maturity at ~700 kg." N. lethaeus would've reached 1,264 kg at maturity (para. 4). The EFS markers can be seen in Figure 3.

NCSM 40000 with two EFS (External Fundamental Systems) in its femur and tibia (Figure 3 [p. 35]):
Description (p. 18):
I found a picture showing the arm of NCSM 40000 compared to Tyrannosaurus' (Egan, 2025):
I think the Tyrannosaurus arm belongs to either the specimens MOR 980, or FMNH PR 2081. This is Figure 5 in the paper (p. 37):
Description (p. 18):
The Tyrannosaurus forelimb belongs to FMNH PR 2081.

Zanno and Napoli also reiterated what I said about the eutyrannosaurs migrating from Appalachia to Laurasia, and that the two continents were connected in the Late Cretaceous (Implications of Nanotyrannus Validity, para. 4; Figure 6). The specimen BMRP 2002.4.1 ("Jane") is the holotype of Nanotyrannus lethaeus, and that species was larger than N. lancensis (Systematic Paleontology [p. 6]; Figure 1). N. lancensis also existed before N. lethaeus (Figure 1): 
Description (p. 17):
it is also important to note what Zanno and Napoli didn't agree with. One of the biggest objections that I received was the caudal count for Nanotyrannus. I originally postulated that the total caudal count was 25. I got this number from Cope (1869), who said that Dryptosaurus' total caudal count was about 25 (p. 102). I even used pictures of NCSM 40000 to try and get an accurate caudal count, and it still came to about 25. I now know that the count of 25 was based on an incomplete caudal series for the Dryptosaurus holotype. Zanno and Napoli (2025) said that that caudal count for NCSM was 35. I was wrong. My apologies. However, the two scholars stated that this caudal count is still less than Tarbosaurus' (41) and Tyrannosaurus' (40-45). The shorter caudal count is still an autapomorphy for Nanotyrannus 
(Nanotyrannus Traits are Not Ontogenetic, para. 3). The caudal count can be seen in Figure 2:
Description (pp. 17-18):
Second, from what I can tell, Zanno and Napoli said that their "MP typology" didn't agree with lumping Dryptosaurus into Nanotyrannus. Alternatively, they stated that Dryptosaurus and Appalachiosaurus were "the earliest diverging nanotyrannids," (Implications of Nanotyrannus Validity, para. 4). They also stated 
that Dryptosaurus and Appalachiosaurus were nanotyrannids in the Phylogenetic Position of Nanotyrannus section (para. 2). You can see this in Figure 6. Nanotyrannus is called an eutyrannosaurian in the Systematic Paleontology section (pp. 3-6). All-in-all, Nanotyrannus was an eutyrannosaurian alongside Dryptosaurus and Appalachiosaurus. It also had a shorter caudal count compared to the tyrannosaurini taxa Tyrannosaurus and Tarbosaurus. 

I have been through a lot since I posted my own abstract back in 2022. Now, we have undeniable proof that Nanotyrannus was a distinct taxon and was related to Dryptosaurus. We have two adult specimens now (CMNH 7541 and NCSM 40000). Longrich and Saitta (2024), and Paul (2025b), were correct in stating that Nanotyrannus was an eutyrannosaurian alongside Dryptosaurus and Appalachiosaurus.

I have to personally thank my friend "Luke" from Instagram. For years now, he gave support to my hypothesis on Nanotyrannus. He has proven to be a good friend. I did feel like giving up, especially after what happened in 2023, but he helped to keep me motivated. Now, the fruits of that labor have paid off positively. I'm forever indebted to you, my friend. 

Despite our different opinions, I want to give a shoutout to some people: Sebastian Dalman for all the help, advice, and motivation; to Dr. David Martill for the motivation; to Dr. Holly Woodward, Christopher Brochu, Professor Thomas Holtz, and Joshua Smith for answering my questions; to Dr. Philip Currie for having an open mind; and finally, to Dr. Robert Bakker and Peter Larson for their consistent support of the validity of Nanotyrannus. 

Links:

Zanno and Napoli (2025) (Abstract):
https://www.nature.com/articles/s41586-025-09801-6

Egan (2025):
https://phys.org/news/2025-10-nanotyrannus-dueling-dinosaurs-fossil-rewrites.html

Longrich and Saitta (2024):

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

Paul (2025b):

https://mapress.com/mz/article/view/mesozoic.2.2.1

Cope (1869) (P. 102):

https://www.biodiversitylibrary.org/page/39852079#page/108/mode/1up


Update (11/18/25):
My friend "Luke" notified me that Dr. Andrea Cau posted a positive post, or tweet, on 11/3/25 about my 2022 abstract online. He mentioned that my hypothesis for "synonymy" between Dryptosaurus and Nanotyrannus "would require a detailed analysis," but he did seem to support part of my hypothesis because it "could reconciliate the fossil record since it does not need a long ghost lineage for Nanotyrannus." He also gives mathematical data showing the similarities in the arm proportions for Dryptosaurus, and Nanotyrannus:

He wrote a blog post concerning the matter as well. He did his own phylogenetic test for Nanotyrannus, modifying the one from Zanno and Napoli (2025). The results of Cau's chart positioned the Nanotyrannus specimens as a sister taxon to Dryptosaurus aquilunguis (Cau, 11/3/25, para. 1-4). Here is his phylogenetic chart test:
As if that wasn't interesting enough, Cau mentioned my 2022 abstract. He stated that the idea of possible synonymy at the genus level, but not at the species level, "is intriguing, but requires a more detailed comparison than the one present in the abstract," (para. 5):
He noted that the arms of the two taxa "share a very peculiar combination of forelimb proportions." If investigated further, this could potentially "be evidence of a Late Cretaceous clade distinct from Tyrannosauridae." Cau finishes his post by lending his support on the Appalachia immigrant hypothesis, mentioned by me and Zanno and Napoli (2025), which would help to solve the "ghost lineage" problem for Nanotyrannus.

Well, this is a positive surprise! Thank you, Dr. Cau. I want to say that I have updated my opinion since I first wrote my abstract in 2022. I do not lump Nanotyrannus into the species Dryptosaurus aquilunguis anymore. Today, I go with Nanotyrannus/Dryptosaurus lancensis. As for N. lethaeus, I go with Nanotyrannus/Dryptosaurus lethaeus. However, I am still perfectly fine if these two taxa are just sister taxa within Eutyrannosauria. If you want to read my original abstract, along with my 2023 updated version, the links to them are below.

Links:
Cau (11/3/25):
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