Sunday, October 27, 2024

(News) Griffin et al., (2024) said the Nanotyrannus holotype was an adult (EFS found)!

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
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