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Re: Tyrannosaurid Growth Spurts

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.


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