Comments on: The Origin of a Little Tyrant

By: Tomozaurus

Tomozaurus — Thu, 10 Nov 2011 07:31:36 +0000

Am I the only one more interested in if the ceratopsian in said specimen is a juvenile “Torosaurus” or perhaps new species?

By: Thomas R. Holtz, Jr.

Thomas R. Holtz, Jr. — Wed, 09 Nov 2011 14:49:22 +0000

In response to Horner: while I am generally sympathetic to the taxonomic reduction process, and am (provisionally) accepting the Nano as juvenile Tyrannosaurus model, there is nothing peculiar about having multiple tyrannosaurids in the same environment. Gorgosaurus and Daspletosaurus co-occur in the Campanian, and these definitely overlap in size. And in non-tyrant dominated communities, there are often multiple giant-sized co-occurring theropods (e.g., in the Morrison Allosaurus, Torvosaurus, and Ceratosaurus; in the Bahariya Spinosaurus, Carcharodontosaurus, Rugops, Deltadromeus; etc.).

By: JBJaval

JBJaval — Wed, 09 Nov 2011 14:06:08 +0000

Recently, Dr. Horner showed in a public talk that there’s a complete series of Tyrannosaurus mandibles that fill in size and number of teeth the differences between “Nanotyrannus” and adult T.rex: so, we can follow the bizarre idea that there were several tyrannosaurid species in the Hell Creek, differing in size and number of teeth (with each species having more teeth than those species larger than it) or simply a single species that reduced teeth number during ontogeny. Teeth number reduction is linked to tooth size enlargement.

By: Thomas R. Holtz, Jr.

Thomas R. Holtz, Jr. — Wed, 09 Nov 2011 14:00:42 +0000

Timothy: in contrast with having "read the literature", the most vocal advocate for the ""Nanotyrannus" as juvenile T. rex" hypothesis has clocked more hours pouring over tyrannosaurid skull material than any human who has ever lived (and as someone who has spent his fare share of time doing the same, my hat is off to him!) Thom Carr's analyses do recognize that there are differences, but they are not insurmountable. For example, maxillary and dentary tooth counts do vary in T. rex: big adult specimens are indeed typically 11-12 teeth per maxilla, but there are smaller specimens with 13 or 14. Additionally, this tooth replacement model would resorb the old tooth sockets, thus removing the old traces. (That said, there may indeed be traces of old ones in some subadults: more on this to come.) All that said, the "dueling dinos" specimen is intriguing. It is NOT the slam-dunk that its proponents claim, but it is very significant. The critical analyses about this specimen are all in the future, so no human knows what they will find: to pretend otherwise is mere speculation. It could indeed reveal that Nanotyrannus is distinct; or it may not. We do not yet know its ontogenetic status, for instance, or have a good grasp of the variability of the various proportions that some have proposed as demonstrating its distinctiveness from Tyrannosaurus. All scientific scenarios are subject to further revision. That said, it is sometimes possible to select a "best" option until new data comes to overturn it. As I've said for over a decade, the "Nano as juvenile" hypothesis remains the simplest solution until such time as: a) the discovery of an adult Nanotyrannus that is clearly not Tyrannosaurus rex, or the discovery of a juvenile Tyrannosaurus rex of the same ontogenetic stage as the Nano fossils which are demonstrably not Nano. Beckmann: the premaxillary (front) tooth count is identical in all tyrannosaurids except for pathological individuals: indeed, the vast majority of theropods have only 4 teeth per premaxilla. I suspect Larson actually referred to the lateral teeth (maxillary and dentary), which are indeed more numerous in Jane and the Cleveland skull than in fully adult T. rex.

By: 'Dr'. S Beckmann, BS

'Dr'. S Beckmann, BS — Tue, 08 Nov 2011 22:12:29 +0000

Ahhh, the suburbs of Chicago are a fine place to inhabit. I have girls on two sides: ‘Jane’ to the west and ‘Sue’ to the east!
I remember showing the ‘Jane’ pamphlet/brochure from Burpee Museum to Peter Larson when I met him at the Waugh Dig in ’07. He mentioned something about the number of front teeth in ‘Jane’ not matching up with number of front teeth in any known adults.

By: Timothy Larson

Timothy Larson — Tue, 08 Nov 2011 21:52:39 +0000

For as many features Nanotyrannus bears that are similar to T. rex there are features that differ. I think it is a very difficult thing to say that Nanotyrannus being a juvenile T. rex is the “best-supported” hypothesis. One who would say that has not read all the material which stirs this debate. There is one feature in particular that tells me Nanotyrannus was a different species: tooth placement. Nanotyrannus had more teeth than T. rex, and no T. rex skull shows evidence of what would have once been tooth sockets, there is no evidence in the bone of T. rex to support the idea of loss of tooth placement. There is one specimen (duelingdinos.com) that will answer these questions for a certainty and close the book on this decades old argument. I, for one, am excited to see the outcome.