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Dinosaur Genera List corrections #55



Yes, the June 20 issue of _Nature_ carries the description of a new dinosaur,
_Siamotyrannus isanensis_ Buffetaut, Suteethorn & Tong, 1996.

This is supposedly a small tyrannosaurian of some kind from the Early
Cretaceous of Thailand. The full reference is:

Buffetaut, E., Suteethorn, V. & Tong H., 1996. "The earliest known
tyrannosaur from the Lower Cretaceous of Thailand," _Nature 381_: 689-691.

I haven't seen the actual reference yet; this is off _Nature_'s Web site at

http://www.nature.com

Tracy Ford sent independent material on this creature from a Compuserve press
release. Here are the relevant sections:

A story on the UPI newswire today "officially" reported the discovery of 
a new theropod dinosaur from Thailand.

The new theropod comes from Early Cretaceous strata approximately 120 
million years old.  The material recovered includes a pelvis and a number 
of back and tail vertebrae.  More material may be forthcoming, but 
removing the bones from the rock has proven extremely difficult, as the 
sandstone matrix in which they were found is extremely hard.

The discoverers have named the new theropod _Siamotyrannus isanensis_: 
"Siamese tyrant from Isan".  The name honors the area where it was found, 
the Isan region of Thailand, once called Siam, and also indicates its 
taxonomic placement as the oldest and most primitive tyrannosaurid ever 
found, an early ancestor of such later beasts as _Tarbosaurus_ and 
_Tyrannosaurus rex_.  Based on the recovered material, _Siamotyrannus_ 
was a middling-large theropod: 6.5 meters long, about half the size of an 
adult _T. rex_.  It was identified as a tyrannosaurid based on some 
distinctive features of the pelvis and vertebrae.

However, there seems to be some dispute over whether the identification 
of the new animal as a tyrannosaur is valid.  The article I have fogs the 
issue badly here, by using the genus name _Tyrannosaurus_ where it seems 
the family Tyrannosauridae is meant.  However, the article says that 
theropod expert Paul Sereno doesn't think it's a tyrannosaur because the 
known material doesn't show all the right features for a tyrannosaur.  
Mark Norell of the AMNH agrees, and also says that the discoverers should 
not have named the animal yet.  While he says it's an important find (as 
is anything from the Early Cretaceous), he believes the material is not 
complete enough for a full, formal description.

Thomas Holtz, vertebrate paleontologist for U. Maryland, both agrees and 
disagrees with Sereno.  Holtz's doctorate was on tyrannosaur origins.  He 
sees the new animal as being _similar to_ tyrannosaurs, close enough that 
it could represent a tyrannosaur ancestor.  The discoverers, led by Eric 
Buffetaut of the Centre National de la Recherche Scientifique in Paris, 
are defending their find as the oldest and most primitive known 
tyrannosaurid, ancestral to all the later ones.

So--add the following to the genera list:

Siamotyrannus Buffetaut, Suteethorn & Tong, 1996

and the count increments to 792.