paper suggests Tyrannosaurus to be split into 3 species

[DD1991]

12 hours ago, Troodon said:

More reactions from notable paleontologists Dr Andrea Cau

from his blog Theropoda

 

"In yesterday's post , I anticipated the article by Paul et al. (2022), but I hadn't been able to read it yet.  In that post, I pointed out that a critical evaluation of the hypothesis that North American Tyrannosaurus were distinguishable into 3 species ( T. rex , T. imperator , T. regina ) was only up to North American tyrannosaurid experts, since I believed that the hypothesis of Paul et al. (2022) was based on a detailed comparison of numerous skeletal elements distributed throughout the various Tyrannosaurus specimens , and therefore required a weighted critique based on detailed anatomical evidence.  I was wrong. I had overestimated the scientific depth of that article. Sorry to be direct, but after reading the article, I must conclude that the hypothesis proposed by Paul et al. (2022) is very weak indeed and immediately rejected, even without being a Tyrannosaurus expert .  The hypothesis of Paul et al. (2022), in fact, is based only on two alleged anatomical elements:  - the strength of the bones of the limbs, which the authors believe demonstrates the existence of two morphotypes ("puny" and "robust") in the sample they analyzed (about thirty specimens);  - the number of incisiviform rostral teeth in the dental (two or one) in the sample analyzed by them.  In practice, the authors believe that the three species are definable by these combinations of the two characters:

T. imperator : robust shape with two incisive teeth.

T. rex : strong shape with an incisive tooth.

T. regina : gracile shape (and with an incisive tooth).

Furthermore, the authors argue that the three species are stratigraphically segregated along the terminal part of the North American Maastrichtian, with  T. imperator older and the other two contemporary and more recent. Unfortunately, the stratigraphy of the majority of Tyrannosaurus specimens is not so accurate as to allow for such a segregation for the alleged species.

A similar tripartite division of the specimens on the basis of only 2 characters (one of which, moreover, an alleged morphometric dimorphism in the strength of the bones) is unsustainable. It is not realistic to separate three species on the basis of these two anatomical elements alone. In the first place, because with that sample of only about thirty specimens there is no clear differentiation between "frail" and "robust". I have plotted the measurements reported by the authors, but I cannot identify a clear distinction between those two morphologies, and this, in the first place, because the statistical sample is too small to be able to rigorously separate any morphotypes.

Furthermore, separating dinosaur species on the basis of the shape of the first two teeth of the dental is a very weak criterion, since dinosaurs have a great variability in adult teeth (also linked to the fact that during life they reciprocated their teeth in alternating waves) , far greater than that observed in mammals. Therefore, distinguishing two or more dinosaur species only on the basis of the shape of the first two teeth of the dental, and without being able to consider other elements of the morphology, is unsustainable.

In summary, T. imperator and T. regina are just two junior synonyms of T. rex ."

I should emphasize that Paul et al. refer LACM 23845 (holotype of 'Dinotyrannus megagracilis') to T. regina (for which they designate USNM 555000 as the holotype), but the epithet  megagracilis has priority over regina, and the authors also leave out LACM 28471 (holotype of 'Stygivenator molnari') in their analysis of T. rex specimens. While there's no denying that the Nanotyrannus lancensis holotype is a juvenile Tyrannosaurus, Witmer and Ridgely (2010) note a number of features in CMNH 7541 that are hard to attribute to ontogeny (e.g. presence of a quadratojugal foramen), and an undescribed T. rex specimen (KUVP 156375) found in Montana (Burnham et al. 2018) has the same maxillary count as adult T. rex (12 maxillary teeth), unlike the count of 15-16 maxillary teeth in the Nanotyrannus holotype and “Jane”, despite being a juvenile, supporting Thomas Carr's argument that there was a decrease in the number of maxillary teeth as T. rex individuals matured. Carr et al. (2017) note that the pneumatic foramen on the quadratojugal that was once used to distinguish Nanotyrannus from T. rex is also present in Daspletosaurus horneri and the indeterminate specimen CMN 57080, so the description of "Jane" and KUVP 156375 should settle the matter whether Witmer and Ridgely (2010) are correct that a number of features in CMNH 7541 and "Jane" are hard to attribute to ontogeny.  

 

Burnham, Atkins-Weltman, and Jevnikar, 2018. A new juvenile Tyrannosaurus rex from the Hell Creek Formation of eastern Montana provides insights into cranial and dental ontogeny. SVP 78th annual meeting, Albuquerque, New Mexico, p. 99. http://vertpaleo.org/Annual-Meeting/Annual-Meeting-Home/SVP-2018-program-book-V4-FINAL-with-covers-9-24-18.aspx

 

Carr, Thomas D.; Varricchio, David J.; Sedlmayr, Jayc C.; Roberts, Eric M.; Moore, Jason R. (2017). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports 7: 44942. doi:10.1038/srep44942.

 

Witmer, L.M, and Ridgely, R.C., 2010.: The Cleveland tyrannosaur skull (Nanotyrannus or Tyrannosaurus): new findings based on CT scanning, with special reference to the braincase. Kirtlandia 57: 61-81. DOI: http://doi.org/10.5281/zenodo.3898946

 

 

[Troodon]

Smithsonian Mag :  March 3 article

Why a New T. Rex Study Is Riling Up the Paleontology World

 

https://www.smithsonianmag.com/smart-news/scientists-propose-that-the-t-rex-was-actually-three-different-species-180979663/

[Troodon]

Would you like to hear from one of the Author's and find out why they published this paper and the thinking behind it.  Dr. Parsons one of the authors makes a very entertaining case and it's well worth the time to hear what he has to say.   The video will NOT put you to sleep and is informative, not an old school presentation

 

 

 

Now on the other side there is Tom Carr who went on Wisconsin Public radio and provided his views against the hypothesis of three species. 

 

https://www.wpr.org/node/1927081

[jpc]

He makes a good argument for having more than one species of Genus X living together, but just because it can happen, doesn't mean it did for Tyrannosaurus.  Mammal paleontologists have found that mammal species last about 2 million years.  I don't know if dino paleos have done anything along these lines, but his argument that the tyrannosaurs of the late Cretaceous lasted 1.5 million years so there should be some speciation falls flat n its face, in my book.   

 

I personally agree with Carr on this one.  

[Troodon]

I think it will raise awareness with future discoveries to see if there are differences.  He does state in the video that this hypothesis needs to be tested and its too early in the process to validate the existence of these species. 

[doushantuo]

https://pterosaurheresies.wordpress.com/2022/03/03/tyrannosaurus-more-than-one-species/

[doushantuo]

some of you may like(slightly less tha 6 MB):

 

Bouabdellah, Florian, Lessner, Emily, and Benoit, Julien. 2022. The rostral neurovascular system of Tyrannosaurus rex.
Palaeontologia Electronica, 25(1):a3. https://doi.org/10.26879/1178
palaeo-electronica.org/content/2022/3518-t-rex-trigeminal-canals

1178.pdf

Edited March 19, 2022 by doushantuo

[doushantuo]

Some of you may like(about 27 MB):

Unearthing the background of Naturalis Tyrannosaurus rex: taphonomy, stratigraphy and paleoenvironment

Master''s thesis,free University ,amsterdam/2016

1822151903_Kaskes(2014).pdf

 

keywords: Flag Butte lectostratotype,granulometry,magnetostratigraphy,chemostratigraphy,cyclostratigraphy,taphonomy,sedimentology,Milankovitch forcing

edit: this comes with a very high recommendation by me

edit two: the document doesn't allow copying,so:

figures 4.1 to 4.5 are priceless,but i realize that's personal opinion

edit three: those who know me best will vouchsafe this: this recommendation is solely based on the manuscript's inherent quality,the nationnality of the

author plays NO ROLE whatsoever

 

 

 

Edited March 19, 2022 by doushantuo

[Troodon]

Tom Carr et al. response to this paper.  Very predictable and a scolding ( #5 below)

 

https://link.springer.com/article/10.1007/s11692-022-09573-1

 

Paper  concludes:

  1. Paul et al. (2022) have not provided sufficient evidence to support the hypothesis that T. rex can be split into three taxa. 

 

2. There is no current evidence to suggest that more than one tyrannosaurid was present in Laramidia during the last ~ 1 million years of the Cretaceous. The short time duration of herbivorous dinosaurs (~ 300 ka; Mallon et al., 2012) is not seen in tyrannosaurids of other units, which are invariant (aside from ontogeny) for up to 1.7 Myr (Currie, 2005; Mallon et al., 2012). Therefore, it is not unreasonable to expect T. rex to be invariant for ~ 1 Myr. 

 

3. New sympatric taxa must be diagnosed by unique and exclusive morphological characteristics appropriate to the specimens in hand.

 

  4. A robust and high-resolution geochronologic and stratigraphic framework is required for a hypothesis of speciation for short time spans such as that represented by the Hell Creek Formation and lateral equivalents. 

 

5. Scientists need to do their due diligence and vet the collections where specimens are stored; specimen availability (i.e., curation in a recognized institution) is essential for reproducibility and continued testing of taxonomic hypotheses

[Troodon]

Article: AMNH

https://www.amnh.org/explore/news-blogs/research-posts/t-rex-one-species

[Troodon]

Another article

https://www.newscientist.com/article/2330552-controversial-idea-that-t-rex-was-three-species-comes-under-fire/