Re: Tyrannosaur Evolution

[Tim Williams <twilliams_alpha@hotmail.com>]

Jaime Headden wrote:

> There have been notes and records of material attributed to *Nodosaurus* 
> from Alabama and New Jersey, and form what is apparently a "refugial" 
> condition in the east comparable to the older Cretaceous fauna in the west. 
> This includes nodosaurs, "primitive" hadrosaurs, etc., also not forgetting 
> *Lophorrhothon,* the *Hadrosaurus* synonym(?) *Ornithotarsus,*

Overall, I agree with you: East Coast dinosaurs do appear to be more 
generalized than their western kin.  However, _Lophorhothon_ is a rather 
contentious taxon.  The material comes from a small individual, and the 
pyramid-like crest is weakly developed.  But _Lophorhothon_ is based on 
juvenile hadrosaur material, and may even be a young _Prosaurolophus_.  
Thus, any report that _Lophorhothon_ is small-bodied or "primitive" 
hadrosaur must take into account the immature nature of the type material.

The rest of the hadrosaur material from the East Coast is rather fragmentary 
and/or lacks good skull material (such as the _Hadrosaurus foulkii_ 
holotype).  This makes an assessment of the phylogenetic position of these 
hadrosaur specimens very difficult.  Some researchers even consider 
_Hadrosaurus_ to be a nomen dubium.

> The East had
> huge Campanian hadrosaurs in any case, like Hypsibema crassicauda.

I haven't seen any length estimates for _Hypsibema_, but it is nonetheless 
huge.  For a long time, _Hypsibema_ was even thought to be a sauropod.


Tim