Re: Tyrannosaurid Growth Spurts

[Tim Williams <twilliams_alpha@hotmail.com>]

John Hunt wrote:

> BTW, has Gorgosaurus been re-instated, I thought it was a synonym for 
> Albertosaurus.

Based on two recent studies, yes, _Gorgosaurus libratus_ and _Albertosaurus 
sarcophagus_ appear to represent distinct genera:

Currie, P.J., Hurum, J.H., and Sabath, K. (2003). Skull structure and 
evolution in tyrannosaurid dinosaurs. Acta Palaeontologica Polonica 48 (2): 
227-234.

Hurum, P.J. and Sabath, K. (2003). Giant theropod dinosaurs from Asia and 
North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared. 
Acta Palaeontologica Polonica 48 (2): 161-190.

Overall, the Tyrannosauridae have undergone a taxonomic implosion in recent 
years.  The current consensus is that _Tyrannosaurus_, _Tarbosaurus_, 
_Daspletosaurus_, _Albertosaurus_,
_Gorgosaurus_, and _Alectrosaurus_ are valid genera.  (This may change once 
the type material for _Alectrosaurus_ is re-studied.)  _Shanshanosaurus_, 
_Maleevosaurus_ and _Jenghizkhan_ are likely junior synonyms of 
_Tarbosaurus_, with the first two representing early ontogenetic stages of 
_Tarbosaurus_.  Likewise, _Aublysodon_, _Stygivenator_ and_Dinotyrannus_ are 
considered junior synonyms of _Tyrannosaurus_, with these genera 
representing early ontogenetic stages of _Tyrannosaurus_.

The jury is still out on the validity of _Nanotyrannus_ and _Alioramus_.  
_Nanotyrannus_ is undoubtedly based on a young tyrannosaur specimen (not an 
adult specimen of a "dwarf" tyrannosaur taxon); but this specimen may not be 
referrable to _Tyrannosaurus_.  _Alioramus_ is also probably based on a 
juvenile specimen, and is provisionally regarded as distinct from 
_Tarbosaurus_.

There are also some more basal tyrannosaur genera (_Eotyrannus_, 
_Stokesosaurus_, _Aviatyrannus_, possibly _Iliosuchus_), as well as 
_Itemirus_, which shows both dromaeosaur and tyrannosaur-like features.  
_Dryptosaurus_ and perhaps even _Bagaraatan_ may also belong somewhere  in 
the tyrannosaur clade.  As for_Siamotyrannus_, recent phylogenies have 
pushed this taxon further down the Theropoda tree, closer to (or among) the 
carnosaurs.



Tim

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