Sereno's Prosauropoda

[TWILLIAMS@canr1.cag.uconn.edu]

Tom Holtz wrote, quoting from Sereno's paper on Dinosaur Evolution (which I 
just finished browsing):

>Sauropodomorpha
>  Sauropoda *
>  Prosauropoda
>    _Riojasaurus_ *
>    _"Griposaurus" sinensis_ *
>   unnamed
>     _Ammosaurus_ (= _Anchisaurus_) * [note: now there's some news!]
>     Plateosauria
>       Plateosauridae
>         _Lufengosaurus_ *
>         unnamed
>           _Coloradisaurus_ *
>           unnamed
>             _Sellosaurus_ *
>             _Plateosaurus_ *
>       Massospondylidae
>         _Yunnanosaurus_ *
>         _Massospondylus_ *

Putting _Riojasaurus_ at the base of the Prosauropoda is interesting.  This 
is one of the bigger (~10m), bulkier, and (inferring from its skeleton) more 
quadrupedal members of the Prosauropoda.  Galton (1990, in _The Dinosauria_) 
regarded _Riojasaurus_ as a melanorosaurid, and one of the more derived 
prosauropods.  Sereno mentions the proportionately short neck (compared to 
other prosauropods) as one of the characters that puts _Riojasaurus_ at the 
base of the Prosauropoda.

Does this mean the Melanorosauridae could be the basal prosauropod family?  
Sereno regards the Prosauropoda as monophyletic i.e. the sister-group to the 
Sauropoda, and not a paraphyletic series of outgroups.  This could mean that 
the melanorosaurids are closest to the origin of the sauropods after all - 
not as the most "advanced" prosauropod group, but as the most "primitive" 
prosauropod group.


Tim