Nanotyrannus a Distinct Species of Tyrannosauroid

[TyBoy]

Just saw this on a Facebook a preprint just released from a very prestigious dinosaur paleontologist Nicholas Longrich.  

 

From the abstract

"Here, we review multiple lines of evidence and show that the totality of evidence strongly supports recognition of Nanotyrannus as a distinct species."

 

 "placement  of Nanotyrannus outside  of Tyrannosauridae as a non-tyrannosaurid member of Tyrannosauroidea."

 

 

https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs

[TyBoy]

What will Carr say

Jane and the Dueling on this list

 

 

[Tidgy's Dad]

Interesting.

I look forward to reading this and what other dinosaur palaeontologists have to say.

[Randyw]

I knew it! I knew it! Take that naysayers! My faith has been rewarded!  

Seriously though I can't wait to get home so I can actually read it. My eyes just aren't good enough to read it on my phone. But I did make out 77 morphological differences!

Now let the debate begin! And please keep it civil!

[jpc]

Carr and Zanno... what will they say?

 

 

[Kikokuryu]

What I'm surprised is Alioraminae (although, isn't it Alioramini ?) falling outside of Tyrannosauridae. Or is it the inclusion of Nanotyrannus that's causing the alioramines to fall outside of true tyrannosaurids which would otherwise be found as true tyrannosaurids. I'm not super well versed in how these phylogenetic analysis are done.

 

Edit: I guess that makes sense since if Nanotyrannus does actually fall outside of Tyrannosauridae, and alioramines are more basal than it, by default, they also get kicked out of Tyrannosauridae.

Edited October 24, 2023 by Kikokuryu

[Mochaccino]

Oh wow, some work that supports Nano as distinct from T. rex. And even more surprising that Nano may not be a Tyrannosaurid at all!

Edited October 24, 2023 by Mochaccino

[piranha]

26 minutes ago, Mochaccino said:

Oh wow, finally some peer-reviewed work that supports Nano as distinct from T. rex. And even more surprising that Nano may not be a Tyrannosaurid at all!

 

PaleorXiv is only a paleo portal....not a peer reviewed journal.

 

[Mochaccino]

51 minutes ago, piranha said:

 

PaleorXiv is only a paleo portal....not a peer reviewed journal.

 

Oh. For preprints, like biorxiv. My bad

[NickG]

11 hours ago, TyBoy said:

Just saw this on a Facebook a preprint just released from a very prestigious dinosaur paleontologist Nicholas Longrich.  

 

From the abstract

"Here, we review multiple lines of evidence and show that the totality of evidence strongly supports recognition of Nanotyrannus as a distinct species."

 

 "placement  of Nanotyrannus outside  of Tyrannosauridae as a non-tyrannosaurid member of Tyrannosauroidea."

 

 

https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs

This is only a preprint. It has not been peer reviewed. While I am fully in support of preprints in the publishing ecosystem, it is important to understand their place is for gathering feedback prior to submitting for publication. 
 

The very basal position near alioramines isn’t surprising given how immature taxa tend to drift more stemward in phylogenetic analyses. Also, the analysis is very small compared to other analyses which have not supported a distinct species for Nanotyrannus.

Edited October 25, 2023 by Nick G.
Corrected a typo

[Randyw]

I finally got a chance to read this through and I must say that it’s a very compelling argument. And it draws on a huge lot of previously published papers (even carr’s) to support it.

disclaimer: I am a nano supporter and nano material is still on my bucket list LOL!

[BirdsAreDinosaurs]

Personally, it does not really matter to me if Nanotyrannus is real or not, but as a biologist and dinosaur enthusiast I do find the discussion quite fascinating.

 

The preprint raises some interesting points, but I do not think that the authors convincingly show that Nanotyrannus is a distinct taxon. I am no paleontologist, so take it with a grain of salt, but here are my thoughts on the six lines of evidence in the preprint.

 

1. Patterns of diversity in Tyrannosauridae: the authors show that the coexistence of two species of tyrannosaur was quite common. But this does not mean that this necessarily was always the case, so this is far from conclusive evidence.

 

2. Morphological differences between Nanotyrannus and T. rex. The authors list 77 morphological differences and mention that there are no known intermediate morphologies when you look at only those 77 characteristics (which they also test using a clustering analysis of 12 specimens). In my opinion, this is nothing new: we all knew Nanotyrannus specimens look quite different from adult T. rex specimens. The fact that no intermediates are known can be explained by a fast metamorphosis, as suggested by Carr.

 

I think it is worthwhile to mention that Carr’s 2020 analysis included 44 specimens and looked at 1850 morphological characters. Using this much bigger sample, Carr did not find that the supposed Nanotyrannus specimens clustered separately from the T. rex ones.

 

3. Ontogenetic patterns seen in other tyrannosaurs. Based on other tyrannosaurs, Nanotyrannus does not resemble what they would expect a young T. rex to look like. But T. rex is its very own and distinct species, so I do not think this is a very strong argument.

 

4. Adult specimens referable to Nanotyrannus. The authors claim that some Nanotyrannus specimens were relatively slow growing, which would be consistent with a decelerating growth in the final years of life (as seen in T. rex). But growth rates in theropods fluctuate through life, depending on environmental factors (e.g. the availability of food). In addition, others have concluded that Nanotyrannus specimens were in fact not mature. The authors also mention themselves that additional evidence suggest that these Nanotyrannus specimens were not mature at all (none of these Nanotyrannus specimens has an external fundamental system, something that some adult T. rex specimens do have).

 

5. Juvenile tyrannosaurs showing diagnostic features of T. Rex The authors discuss that a 800 mm long skull shows clear T. rex features and that this skull must represent a juvenile T. rex. But this skull is larger than all of the skulls of the supposed Nanotyrannus specimens. Despite this, the authors claim that the skull is only slightly larger than the largest Nanotyrannus skulls and that is not what would be expected.

 

I would say that this is exactly what you would expect in case of a fast metamorphosis. Also, Carr shows that size and age do not necessarily have a 1:1 relationship in T. rex.

 

6. Phylogenetic analysis The authors claim that Nanotyrannus is not a tyrannosaurid based on phylogenetic analysis but is a more basal tyrannosauroid instead. But assuming all Nanotyrannus specimens are juvenile, it does not really make sense to compare them to adult specimens of other species. Also, apparently this phylogenetic analysis is based on a small and outdated dataset, but I cannot judge that myself at the moment.

 

All in all, I am not convinced and I actually think all of the evidence presented matches quite nicely with Carr's hypothesis that T. rex had a very fast metamorphosis around age 14.

 

Also, it kind of bugs me that the authors take it as evidence favoring the existence Nanotyrannus that no intermediate specimens are ever found, while they downplay the fact that no real T. rex juveniles the size of smaller Nanotyrannus or undisputed Nanotyrannus adults have ever shown up. In case of a fast metamorphosis, I would say the chance of finding an intermediate is much smaller than finding a specimen of the other two.

 

Just my two cents

 

[-Andy-]

It's a good paper. I hope it gets peer-reviewed soon

[Jaybot]

Everyone here has watched the Dino hunters tv show, right?  Great watch, would recommend.  The guy that is finding these Nanos is in the show.

[Joseph Fossil]

On 10/24/2023 at 10:06 AM, TyBoy said:

Just saw this on a Facebook a preprint just released from a very prestigious dinosaur paleontologist Nicholas Longrich.  

 

From the abstract

"Here, we review multiple lines of evidence and show that the totality of evidence strongly supports recognition of Nanotyrannus as a distinct species."

 

 "placement  of Nanotyrannus outside  of Tyrannosauridae as a non-tyrannosaurid member of Tyrannosauroidea."

 

 

https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs

 

@TyBoy Thanks for letting me know about this paper bro! I'll admit I've always been a tad bit conflicted about Nanotyrannus as both sides of the debate have brought up pretty good arguments (I've though always thought the best argument put forward by the "Nanotyrannus is a valid taxon side" is the brain case analysis and how different the shape of the brain is to Tyrannosaurus rex's brain). But this paper seems pretty legitimate and I definitely hope it gets peer reviewed soon.

[Joseph Fossil]

On 10/24/2023 at 10:06 AM, TyBoy said:

Just saw this on a Facebook a preprint just released from a very prestigious dinosaur paleontologist Nicholas Longrich.  

 

From the abstract

"Here, we review multiple lines of evidence and show that the totality of evidence strongly supports recognition of Nanotyrannus as a distinct species."

 

 "placement  of Nanotyrannus outside  of Tyrannosauridae as a non-tyrannosaurid member of Tyrannosauroidea."

 

 

https://osf.io/preprints/paleorxiv/nc6tk/?fbclid=IwAR3_YkPSpKBQXk5Aiff0sJRKsl59dIqqO5DXveSjV-tx24Vs6ZLuRZdcaHs

 

@TyBoy This is also not the only impressive paper (or at least paper abstract) about Tyrannosaurs that has come out this week that sure to have a massive impact on the study of these theropod dinosaurs.

 

A GIANT TYRANNOSAUR FROM THE CAMPANIAN-MAASTRICHTIAN OF SOUTHERN NORTH AMERICA AND THE ORIGINS OF TYRANNOSAURUS (Page 135 or 136 of the SVP document)

Dalman et al. 2023 (abstract)

https://vertpaleo.org/wp-content/uploads/2023/10/2023_SVP_Program-Final-10032023.pdf

 

 

Here's also a Paper describing the Tyrannosaur fossil specimens described in the paper abstract:

 

Tyrannosaurus rex from the McRae Formation (Lancian, Upper Cretaceous), Elephant Butte reservoir, Sierra County, New Mexico

Gillette et al. 1986

https://nmgs.nmt.edu/publications/guidebooks/downloads/37/37_p0235_p0238.pdf 

 

 

 

This is a short abstract, but what it strongly indicates is that the previous hypothesis about a unique Giant Tyrannosaur from Southern Laramidia's Ojo Alamo Formation, McRae Formation, and Hall Lake Formation existing around 73-70 Million Years ago (also of which was given a variety of names over the years: Alamotyrannus brinkmani, Tyrannosaurus brinkmani, and Tyrannosaurus mcraensis) is correct. It's definitely worth a read and I'm pretty excited for when that peer reviewed paper is published.

[Joseph Fossil]

@TyBoy There's also a paper abstract in the Society for Vertebrate Paleontology link about Javelina Formation Tyrannosaurs you might like as well!!!

 

T.L. Adams, R.S. Tykoski, S.K. Drumheller, H. N. Woodward  TYRANNOSAURID HINDLIMB FROM THE JAVELINA FORMATION (LATE CRETACEOUS, MAASTRICHTIAN) OF BIG BEND NATIONAL PARK, TEXAS 

(It's on page 68 or 69 of the link)

https://vertpaleo.org/wp-content/uploads/2023/10/2023_SVP_Program-Final-10032023.pdf

 

[BirdsAreDinosaurs]

I cannot judge how reliable this analysis is, but someone apparently remade the neighbor-joining tree that was performed in the preprint-study, but this time using the complete data set from Carr (2020).  Seems like when you include those specimens and additional characteristics, there are plenty of intermediates between the adult Tyannosaur and the "Nanotyrannus" specimens (just like Carr himself concluded using his own analysis).

 

Here is the link: https://www.facebook.com/TheropodaBlog/posts/pfbid0T4pY6YM4r9Vz5bH1d19Pm4aWtwhmGQ79WyA6vzSTSn4vFztg6ESffQP87T8jmGsyl

 

Regardless of these results, it really makes you wonder why the authors of the preprint only include a limited number of specimens and a selected group of characteristics to perfrom such an analysis, while there is much more data available...

Edited October 31, 2023 by BirdsAreDinosaurs
typo

[Ptychodus04]

All this discussion about Tyrannosaurs when everyone knows Avialae is the best dinosaur clade. 

[jpc]

52 minutes ago, Ptychodus04 said:

All this discussion about Tyrannosaurs when everyone knows Avialae is the best dinosaur clade. 

As a lifelong birdwatcher, I agree.