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Re: rampant speculation



Justin Tweet wrote-

> I've noticed that in the Morrison, there are small, "medium"
> (dryosaurid-size), and large ornithopods, along with the Wealden.
> However, in the well-sampled North American and Asian faunae of the Late
> Cretaceous, the medium category appears to be mostly gone (except for
> *Thescelosaurus*), and in Asia so is the small category.  I don't know if
> hadrosaurids would have pressured out medium-sized herbivores; in the
> Wealden dryosaurids lived alongside hadrosaur-sized iguanodonts, for
> example.

Nice theory, but perhaps not needed.  There were plenty of Late Cretaceous
hypsilophodonts in North America- Thescelosaurus, Bugenasaura, Parksosaurus,
Orodromeus and lots of undescribed stuff (North Horn, Kaiparowits, Wahweap,
Straight Cliff, etc. Formations).  In addition, Late Cretaceous Asian
ornithopods aren't completely unknown-

undescribed hypsilophodont (Currie and Eberth 1993)
Coniacian-Campanian, Late Cretaceous
Iren Dabasu Formation, China
Material- a few isolted bones
Reference- Currie and Eberth, 1993. Palaeontology, sedimentology and
palaeoecology of the Iren Dabasu Formation (Upper Cretaceous), Inner
Mongolia, People's Republic of China. Cretaceous Research. 14 127-144

undescribed small ornithopod (Russell, Russell and Sweet 1993)
Late Maastrichtian, Late Cretaceous
Pingling Formation, China
Reference- Russell, D.A., D.E. Russell, and A.R. Sweet. 1993. The end of the
dinosaurian era in the Nanxiong Basin. Vertebrata PalAsiatica 31(2):
139-145.

Perhaps their apparent lack is due more to publication bias, as well as
preservational.  After all, we haven't been getting descriptions of new
Protoceratops, Pinacosaurus or hadrosaurid finds in the 90's either.

Mickey Mortimer