RE: Bakker's Brontosaurus and Late Cretaceous populations

[Tim Williams <twilliams_alpha@hotmail.com>]

Denver Fowler wrote:

> I don't really agree with the oversplitting of alot of the North American 
> taxa (especially ornithischians); it gives a very false idea of dinosaurian 
> diversity. For example, it is extremely difficult (if not impossible) to 
> tell one lambeosaurine from another postcranially, even size- wise there 
> isn't huge variation, yet the likes of Lambeosaurus, Corythosaurus, 
> Parasaurolophus etc are afforded enus-level distinction. Substitute any of 
> the ornithischian subfamilies and the result is similar.
> Contrast this with my old buddy Iguanodon, which shows as much variation 
> between the contemporaneous I.bernissartensis and I.atherfieldensis as is 
> seen between the Hadrosaurinae and Lambeosaurinae

Like a lot of things, 'lumping' and 'splitting' are often in the eye of the 
beholder.  Nevertheless there are obvious examples of oversplitting.  In 
recent years there has been a tendency to consolidate.  The Morrison 
sauropods are a good example: _Cathetosaurus_, _Ultrasaurus_, _Supersaurus_, 
_Seismosaurus_ and maybe _Dystylosaurus_ have either already sunk or are 
about to be sunk into long-established genera.  Against the flow, heroic 
efforts have been made to reinstate _Brontosaurus_; and I don't know what to 
make of _Eobrontosaurus_.  _Coelophysis_/_Syntarsus_ and 
_Ornithomimus_/_Dromiceiomius_ are other examples.  On the ornithischian 
side, a case could be made to unite the 
_Lambeosaurus_-_Corythosaurus_-_Hypacrosaurus_ complex into a single genus, 
but I don't see this happening.

At the other end of the spectrum, there are genera that look rather 'lumpy', 
and perhaps (in some cases, definitely) deserve to split up into more than 
one genus: _Plateosaurus_, _Alamosaurus_, _Iguanodon_, _Probactrosaurus_, 
_Psittacosaurus_, _Euoplocephalus_, &c.  This has already happened with 
_Chilantaisaurus_, _Dilophosaurus_ and _Titanosaurus_.  The process of 
breaking up European _Plateosaurus_ has already begun: one study spun off 
_Gresslyosaurus_ as a valid genus, another resurrected _Efraasia_, another 
erected _Ruehleia_, and more may be on the way.  (The process is not 
entirely one-way: _Sellosaurus_ was sunk into _Plateosaurus_, although as a 
separate species from the type.)  Work is being done to break up others 
among the aforementioned 'lumpy' genera, and some new names have already 
been coined - but these have yet to be published.

Cheers

Tim