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Is Nanotyrannus A Separate Species Or Is It A Juvenile T Rex?


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Is Nanotyrannus proven to be a separate species than T Rex or is it really just a jeuvenile Rex? Some people believe that it's a separate species. Others believe the latter. I don't know which one is correct. Let me know your thoughts!

"Or speak to the earth, and let it teach you" Job 12:8

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I'm firmly in the camp that they are two separate and distinct species. I actually spent some time examining a 99% complete Nanotyrannus skeleton and came away with even more conviction that it is different than T rex.

There are still those naysayers out there but the evidence continues to mount. I think the most convincing argument for Nanotyrannus is that CT scans of the braincases of known skulls are very different than T Rex. This characteristic would not change with age. There are also a number of skeletal differences and two of the most convincing are the Arms and Jaws. The arms of a Nanotyrannus are longer with more robust bones than Sue one of the largest T Rex found. Which says they had more functional arms than Rex at half the size. The maxillary tooth count is very different 15-16 for Nano versus 11-12 for Rex. The attempt to resolve the tooth count through ontogentic change is weak but exits. I have examples, in my collection, of infant to juvenile Rex teeth that are more robust than Nano teeth of similar age. There are also a number of other skeletal differences in the skull. A good book that makes the case for Nanotyrannus is Tyrannosaurid Paleobiology published by Indiana Press. I also talked to the leading theropod paleontologist in the world and Phil Currie, David Evans and Robert Bakker all support Nanotyrannus.

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I'm firmly in the camp that they are two separate and distinct species. I actually spent some time examining a 99% complete Nanotyrannus skeleton and came away with even more conviction that it is different than T rex.

There are still those naysayers out there but the evidence continues to mount. I think the most convincing argument for Nanotyrannus is that CT scans of the braincases of known skulls are very different than T Rex. This characteristic would not change with age. There are also a number of skeletal differences and two of the most convincing are the Arms and Jaws. The arms of a Nanotyrannus are longer with more robust bones than Sue one of the largest T Rex found. Which says they had more functional arms than Rex at half the size. The maxillary tooth count is very different 15-16 for Nano versus 11-12 for Rex. The attempt to resolve the tooth count through ontogentic change is weak but exits. I have examples, in my collection, of infant to juvenile Rex teeth that are more robust than Nano teeth of similar age. There are also a number of other skeletal differences in the skull. A good book that makes the case for Nanotyrannus is Tyrannosaurid Paleobiology published by Indiana Press. I also talked to the leading theropod paleontologist in the world and Phil Currie, David Evans and Robert Bakker all support Nanotyrannus.

Okay cool, thanks for clearing that up for me. I didn't know much about the subject. You know a lot about these things!

"Or speak to the earth, and let it teach you" Job 12:8

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Many distinguished theropod experts still disagree. This paper highlights the evidence against "Nanotyrannus"

 

 

Carr, T.D. (1999)

Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria).

Journal of vertebrate Paleontology, 19(3):497-520

 

 

If anyone wants to read this excellent paper, please send a PM with email address and I'll be happy to send it.

 

 

 

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Yes there are still distinguished theropod experts that disagree and may never agree on this matter. What we have today that did not exist when Carr wrote his paper in 1999 and the discussion in 2011 are two skeletons one 99% complete and several skulls that have changed our understanding of this dinosaur.

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Here is a portion of a Stephen L. Brusatte book review of an earlier book from Peter Larson: “Tyrannosaurus rex, the Tyrant King”

 

"As a tyrannosaur systematist, I was particularly annoyed that the book completely lacks cladistic studies or robust quantitative analyses of any kind. Furthermore, it is clear from the tone of many chapters that several authors are staunch believers in the validity of Nanotyrannus, the so-called pygmy tyrannosaur that has been thoroughly discredited as a juvenile Tyrannosaurus based on careful consideration of ontogeny and variation (Carr, 1999; Carr and Williamson, 2004). Nowhere in the book do authors provide a firm rationale for re-erecting Nanotyrannus as a valid taxon, despite the fact that the onus is them to argue against the thoughtful arguments of Thomas Carr and colleagues. The one specific feature that is constantly stated as a ‘key’ character separating Tyrannosaurus and Nanotyrannus is tooth count, specifically that the latter animal has more teeth than adult Tyrannosaurus. However, Carr and colleagues have interpreted this difference as ontogenetic variation: teeth are lost during growth. In his chapter on variation, Larson asserts that no extant animal loses teeth throughout ontogeny, but provides no citations to back this strong claim. Not only that, but Carr (1999:table 2) actually provided concrete evidence that Albertosaurus, a close relative of Tyrannosaurus, loses teeth throughout ontogeny. These data are rarely cited by proponents of Nanotyrannus, which befuddles me."
 
 
Since this discussion has been brought up again, does anyone have access to this recent book review by Thomas Carr? I'm curious to know how he responds to Larson's latest claims in the chapter from the book "Tyrannosaurid Paleobiology", entitled "The case for Nanotyrannus"
 
Review by: Thomas D. Carr (2014)
Tyrannosaurid Paleobiology by J. Michael Parrish, Ralph E. Molnar, Philip J. Currie, Eva B. Koppelhus
The Quarterly Review of Biology, 89(2):165-166
 
 

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Yes there are still distinguished theropod experts that disagree and may never agree on this matter. What we have today that did not exist when Carr wrote his paper in 1999 and the discussion in 2011 are two skeletons one 99% complete and several skulls that have changed our understanding of this dinosaur.

I would refer you to Stephen L. Brusatte's book review posted above. That was published in 2010 in the Journal of Vertebrate Paleontology 30(1):304-305

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Here's what Wikipedia has to say about the debate-

"The primary differences that some scientists have used to distinguish Nanotyrannus lancensis from Tyrannosaurus rex primarily concern the number of teeth. Nanotyrannus had more teeth in its upper and lower jaws than an adult Tyrannosaurus. N. lancensis had 14-15 teeth in each side of the upper jaw (maxilla) and 16 teeth in each side of the lower jaw (dentary). T. rex, on the other hand, had 11-12 tooth positions in the upper jaw and 11-14 in the lower. The exact implications of this difference in tooth count has been controversial. In his 1999 study of tyrannosaurid growth patterns, Carr showed that, in Gorgosaurus libratus, the number of teeth decreased as the animal grew, and he used this data to support the hypothesis that N. lancensis is simply a juvenile T. rex. The team of scientists who studied growth in the related Tarbosaurus bataar found little to no decrease in tooth count as that species grew, even though they had juvenile specimens much younger than the Nanotyrannus specimens. These researchers also noted, however, that in both Tyrannosaurus and Gorgosaurus, there were significant differences in tooth count between individuals of the same age group, and that tooth count may vary on an individual basis not related to growth.[4] A juvenile Tarbosaurus skull discovered in 2006 exhibits the same tooth count as do adult Tarbosaurus skulls, supporting the retention of Nanotyrannus as a distinct genus. Larson has also contended that, along with skull features, Nanontyrannus can also be distinguished from Tyrannosaurus by proportionally larger hands with phalanges on the third metacarpal and in the furcula morphology."

I personally think they are different animals, there seems to be too many differences to explain away with ontogeny.

-Lyall

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Since this discussion has been brought up again, does anyone have access to this recent book review by Thomas Carr? I'm curious to know how he responds to Larson's latest claims in the chapter from the book "Tyrannosaurid Paleobiology", entitled "The case for Nanotyrannus"
Review by: Thomas D. Carr (2014)
Tyrannosaurid Paleobiology by J. Michael Parrish, Ralph E. Molnar, Philip J. Currie, Eva B. Koppelhus
The Quarterly Review of Biology, 89(2):165-166

Relevant quotes from Dr. Thomas Carr's 2014 review of "Tyrannosaurid Paleobiology":

"This volume is a mixed bag that could have been trimmed to five articles."

"Several articles could have been excluded. Larson defends the problematic taxon Nanotyrannus lancensis, an effort plagued by informality, verificationist tone, osteological misapprehensions (e.g., misidentification of the subnarial foramen), and limited assessment of variation."

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Oh yes, let's cite Wikipedia - what a precedent.

The Nanotyrannus proponents never fail to omit the fact that 1) the only "Nanotyrannus" specimen ever sampled histologically is a young juvenile (Jane) - hence why Nanotyrannus is considered by most specialists in tyrannosaurid taxonomy as a juvenile T. rex, and 2) most of the differences in skull shape are caused by allometric growth, including the loss of tooth positions - an intermediate size specimen, "B rex" (MOR 1128, I think) has an intermediate number of tooth positions.

Maintaining Nanotyrannus as a separate taxon is only possible if you ignore a wealth of histologic evidence and widespread patterns of ontogenetic change already well established for dinosaurs and even tetrapods in general.

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IMHO we dont even need to talk anatomy or biology at all to have a clear answer. Surely 1000s of specimens of Trex and Nanno teeth each have been found over time. If we were to suppose that the 2 are distinct, then there becomes no remotely reasonable explanation as to why no juvenile Trex teeth have been found. Its a statistical near-impossibility. Mother nature and father time have given us a broad sample and the math is clear. Any counter-arguments to the effect of "we dont know the Trex juveniles habitat or behavior, maybe they lived somewhere else" miss the point. Statistical determinations are at the core of paleontology, even if sometimes we may not realize it.

---Wie Wasser schleift den Stein, wir steigen und fallen---

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Honestly non-remanie, I've found this to be one of the simplest, most common sense approaches - except (as above) most supporters always fall back to "ooh but look, they're so different looking" and even when presented with evidence for ontogenetic transition, they repeat "ooh but look, they're so different looking". Regardless, I find the lack of juvenile T. rex finds hilariously convenient and suspicious.

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Oh yes, let's cite Wikipedia - what a precedent.

Some of us are just trying to learn with what is available to us...a lot of good research is locked away or costs money to read. In a professional setting, your snarkasm is well suited.

Anyhow, sorry to detour a fascinating and very informative conversation. :)

"I am glad I shall never be young without wild country to be young in. Of what avail are forty freedoms without a blank spot on the map?"  ~Aldo Leopold (1887-1948) 

 

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I have mixed feelings on the subject. I have prepared and mounted examples of both dinosaurs. What I took away from my own experience is that they are definitely related. There are some remarkable similarities. There are also some differences in the two as well. These differences can be explained away as simply the differences in development that come with age. Can tooth shape be explained away bast on this theory? It has been proven in other species. T-Rex also has fewer teeth than our little buddy Nano. Less space in the mouth for larger more robust teeth? I don't know. Skull shape is very similar, although Nano is much more gracile. This could be accounted for due to age and maturity. Due to the lack of juvenile skeletons of Rex that are conclusive it may not soon be settled.

I guess this is similar to the debate over Triceratops and Torosaurus.

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IMHO we dont even need to talk anatomy or biology at all to have a clear answer. Surely 1000s of specimens of Trex and Nanno teethw each have been found over time. If we were to suppose that the 2 are distinct, then there becomes no remotely reasonable explanation as to why no juvenile Trex teeth have been found. Its a statistical near-impossibility. Mother nature and father time have given us a broad sample and the math is clear.

For those that are interested in seeing smaller T-rex teeth here are a couple: First is a baby T-rex rooted tooth that has been ID by Robert Bakker and Pete Larsen at (1 1/8"). Second from a slightly older animal at 2". I have more of these without roots and all sizes up to adults. These teeth are fat with pronounced serrations. My collection also includes juvenile Nanotyrannus teeth at are clearly different than Rex.

There is hope for Nano believers, trust me :-)

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For those that are interested in seeing smaller T-rex teeth here are a couple: First is a baby T-rex rooted tooth that has been ID by Robert Bakker and Pete Larsen at (1 1/8"). Second from a slightly older animal at 2". I have more of these without roots and all sizes up to adults. These teeth are fat with pronounced serrations. My collection also includes juvenile Nanotyrannus teeth at are clearly different than Rex.

There is hope for Nano believers, trust me :-)

attachicon.gifRex 24AJ.jpg

attachicon.gifTrex F1a.jpg

Great Pictures. Thanks for sharing those with us.

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Let me continue to add to the discussion. Here is a statement from a paper which summarized a CT scan done on the tyrannosaurus skull brain case at the Cleveland museum.

"Although the possibility cannot be ruled out, it seems hard to believe that the animal pertaining to CMNH 7541 would have ontogenetically transformed all of these attributes (both primitive and derived) and grown up to be a typical member of Tyrannosaurus rex".

This is not a hypothetical, theoretical discussion it's dealing with fact. They did add that additional study was needed to firm up if this is a new taxon.

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Let me continue to add to the discussion. Here is a statement from a paper which summarized a CT scan done on the tyrannosaurus skull brain case at the Cleveland museum.

"Although the possibility cannot be ruled out, it seems hard to believe that the animal pertaining to CMNH 7541 would have ontogenetically transformed all of these attributes (both primitive and derived) and grown up to be a typical member of Tyrannosaurus rex".

This is not a hypothetical, theoretical discussion it's dealing with fact. They did add that additional study was needed to firm up if this is a new taxon.

Not coincidentally, the Cleveland skull shares 48 important features with a juvenile stage Albertosaurus libratus.
Thomas Carr has addressed this topic in great detail at his 2013 internet blog: Nanotyrannus Isn’t Real, Really.

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There should be similarities they are both tyrannosaurids, however don't see any mention about the braincases or that Nano's arms are bigger and stouter than Sue's.

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For those that are interested in seeing smaller T-rex teeth here are a couple: First is a baby T-rex rooted tooth that has been ID by Robert Bakker and Pete Larsen at (1 1/8"). Second from a slightly older animal at 2". I have more of these without roots and all sizes up to adults. These teeth are fat with pronounced serrations. My collection also includes juvenile Nanotyrannus teeth at are clearly different than Rex.

There is hope for Nano believers, trust me :-)

attachicon.gifRex 24AJ.jpg

attachicon.gifTrex F1a.jpg

A few questions....in the first tooth, is the tip worn, rounded or broken? and may we see some juvenile Nanotyrannus teeth, please?

"I am glad I shall never be young without wild country to be young in. Of what avail are forty freedoms without a blank spot on the map?"  ~Aldo Leopold (1887-1948) 

 

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Slight wear on the very top of the baby Rex tooth see attachment.

Don't have images at the ready on the Nano teeth but will get some.

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On 7/13/2015 at 3:45 PM, Troodon said:

There should be similarities they are both tyrannosaurids...

 

 

The skull comparison isn't based on both being tyrannosaurids, it's based on the comparison of 48 shared juvenile features.

 

Here is Thomas Carr's summary: LINK

 

1) The Cleveland skull is of a juvenile tyrannosaurid.
2) The diagnosis of Nanotyrannus lancensis fails under scrutiny: the characters reflect the specimen’s relative maturity, damage to the skull, and characters shared with other tyrannosaurids. Consequently, N. lancensis is an invalid taxon; it entirely lacks defining features.
3) The Cleveland skull shares many specializations that are seen nowhere else except in adult T. rex, the species with which it happens to be sympatric.
4) Therefore, the Cleveland skull is a juvenile T. rex.
5) Ergo, the ‘dueling tyrannosaurid’ cannot belong to a taxon that does not exist.
 
 
 

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A few questions....in the first tooth, is the tip worn, rounded or broken? and may we see some juvenile Nanotyrannus teeth, please?

The first image are three juvie Nano teeth, crown 3/8" to 1/2"

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Thought I would add a couple of Juvie Rex teeth. I'll let you decide which ones they are

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The Nano teeth are compressed finer serrations. This appears to be typical from juvie to adult teeth. The Maxilla is an example of an adult.

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"The first image are three juvie Nano teeth, crown 3/8" to 1/2"

I'll note that the only specimen conforming to the "Nanotyrannus" morph for which the ontogenetic status is known is a juvenile (Jane - Burpee Museum), and by extension all "Nanotyrannus" specimens are juveniles.

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