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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