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Tooth - Tyrannosaurus rex

Calcanay

Species: Tyrannosaurus rex

Age: Cretaceous (Maastrichtian), c. 66 million years ago

Location: Hell Creek Formation, Montana, United States

 

Quite small tooth fragment of a juvenile specimen (classically referred to Nanotyrannus, now no longer recognized as a valid genus), but serrations are preserved. Identifiable down to the genus and species level since Hell Creek did not have any tyrannosaurids other than Tyrannosaurus rex.


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Praefectus

Posted

Only some paleontologists regard Nanotyrannus as invalid. I would refer to this tooth as tyrannosaurid indet. 

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Calcanay

Posted

49 minutes ago, Praefectus said:

Only some paleontologists regard Nanotyrannus as invalid. I would refer to this tooth as tyrannosaurid indet. 

From my understanding the Tyrannosaurus vs. Nanotyrannus debate is overblown online, with a majority of paleontologists regarding the Nanotyrannus specimens as juvenile Tyrannosaurus rex. From what I've been told, it has had little support for some time and Carr's 2020 paper put the final nail in the coffin. I don't think Nanotyrannus makes sense from a logical standpoint either - supporters of Nanotyrannus concede that all specimens are juveniles and combined with the otherwise clear lack of juvenile Tyrannosaurus specimens, with the Nanotyrannus ones fitting in perfectly in the expected ontogeny, it makes sense that they are one and the same.

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Praefectus

Posted

Differences in braincase morphology, metacarpal morphology, limb proportion, and tooth count, as well as level of closure of vertebral sutures are used to differentiate Nanotyrannus from Tyrannosaurus. 


Nanotyrannus is in a precarious situation as, until recently, many of the important specimens have remained unstudied in private hands. It is unfortunate that Carr 2020 elected to not include privately owned specimens in its sample size. 


Curiously, have you read this topic by @Troodon? It does a good job of covering the issue. 

 

 

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Calcanay

Posted

24 minutes ago, Praefectus said:

Differences in braincase morphology, metacarpal morphology, limb proportion, and tooth count, as well as level of closure of vertebral sutures are used to differentiate Nanotyrannus from Tyrannosaurus. 


Nanotyrannus is in a precarious situation as, until recently, many of the important specimens have remained unstudied in private hands. It is unfortunate that Carr 2020 elected to not include privately owned specimens in its sample size. 


Curiously, have you read this topic by @Troodon? It does a good job of covering the issue. 

 

 

I had not read Troodon's topic since I'm new to the forum but I think that it, beyond arguing the validity of Nanotyrannus, makes an important point in regards to why scientifically important fossil specimens should not be in private hands (the Montana dueling dinosaurs should definitely be studied); perhaps if the private specimens that display these differentiating features were available for paleontologists to study, the academic understanding of the issue would be different.

 

I'm not a paleontologist myself so I can't comment much on whether these features are enough to differentiate the two (but tooth count and limb proportions particularly don't seem like things that have to stay the same throughout ontogeny). I know that Carr specifically has stated that the differing braincase is not a valid argument as the exterior skull bones on the specimen in question were crushed and damaged, something that would have affected the morphology of the skull internally as well (link, he says this in the comments - this post also points out the problems that Nanotyrannus, as defined in its original description, lacks defining features that separate it from Tyrannosaurus). I respect Troodon's opinion on the issue and the work put in, and I am not knowledgeable enough to debunk anything said in the topic, but (and meaning no disrespect to anyone) I am more inclined to trust Carr's paper (Carr being a Tyrannosaur expert with more than 20 years of experience studying them) than a post consisting mostly of images, many of private specimens that scientists have been unable to study (meaning no academic look at how distinguishing and correctly interpreted the features are). Current academia seems mostly in support of Nanotyrannus being invalid and I'll label the fossils I have based on that consensus; if it shifts in the future I'll shift too. Right now I believe the possibility of Nanotyrannus being considered valid creates more problems than it solves.

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dinosaur man

Posted

Hi may I bud into this conversation?  First off we have Nanotyrannus adults, those other reasons may not be the best but what about fused skull bones which are seen in Bloody Marry, a trait only know in adult animals.  And I wouldn’t fully trust Carr he is extremely biased in that he will not study privately owned specimens which could be of big help.  Also he’s not open to new ideas, I’ve talked to him multiple times during my research on Daspletosaurus and he full out blocked me for asking questions and challenging his theories.  By the way welcome to the forum.  :D

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Calcanay

Posted

3 hours ago, dinosaur man said:

Hi may I bud into this conversation?  First off we have Nanotyrannus adults, those other reasons may not be the best but what about fused skull bones which are seen in Bloody Marry, a trait only know in adult animals.  And I wouldn’t fully trust Carr he is extremely biased in that he will not study privately owned specimens which could be of big help.  Also he’s not open to new ideas, I’ve talked to him multiple times during my research on Daspletosaurus and he full out blocked me for asking questions and challenging his theories.  By the way welcome to the forum.  :D

Thank you for the welcome, I'm happy to be here :) On Bloody Mary; to my understanding it hasn't yet been studied by paleontologists academically due to having been in private hands? If that's the case I don't think a final conclusive assessment can be made in regards to how important the fused skull bones are in terms of differentiating taxa. I can't speak on Carr's character or whether he is rude, but I don't think he can fairly be characterized as extremely biased for not including private specimens in his study; they are not generally included in paleontological studies since specimens talked of in academia should be accessible at museums and whatnot so that they can be studied again in the future. Not including them is the standard as far as I know.

 

I don't think Bloody Mary represents Nanotyrannus - as I mentioned previously, the features that were used to describe and define Nanotyrannus in 1988 do not appear to hold up as features that can actually distinguish it from Tyrannosaurus. In a scientific sense that makes it an invalid taxon. Could Bloody Mary represent a smaller type of tyrannosaur distinct from Tyrannosaurus? Possibly, but it would probably not be under the name Nanotyrannus (since entirely new distinguishing characteristics would need to be established) and we can't know for sure until the specimen is examined by scientists.

 

I also think paleoecology has to be considered. Taking the well-understood Hell Creek as an example, latest Maastrichtian North America was not very diverse in terms of large dinosaurs. Whereas it is not uncommon for earlier formations to preserve several species of ceratopsid or hadrosaur, Hell Creek only preserves a single hadrosaur (Edmontosaurus) and three ceratopsids (Triceratops horridusT. prorsus and Torosaurus - not all of which coexisted at the same time). There is no reason to expect carnivores to be uncharacteristically diverse if herbivores are uncharacteristically low in diversity. The niche Nanotyrannus would have occupied would also already have been filled by Dakotaraptor and young Tyrannosaurus

 

Again, my lack of support of Nanotyrannus is not intended as some disrespect or attack on forum members, but I don't think I am labelling this fossil wrongly for following what is currently in the paleontological literature.

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