Re: Do we have dromaeosaurid evolution backward?

[Tim Williams <tijawi@gmail.com>]

Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> Not to contradict you here ;) , but Zanno and Makovicky actually left 
> Ornitholestes unassigned, as they said its diet was inconclusive.


To me, the fact that _Ornitholestes_ didn't fall in with the
predominantly predatory theropods is itself interesting.


I guess I interpreted Zanno and Makovicky's statement a little
differently: "Intermediate numbers of CHTs in these taxa may indicate
omnivory or dietary specializations not manifest widely in other
coelurosaurians (e.g., insectivory)."  Clearly _Ornitholestes_ could
not be assigned to the same trophic category as compsognathids,
tyrannosaurids and dromaeosaurids.


> The only "herbivorous" characters it is coded as having are-
> 1. Decurved dentary.  Not obviously true in the left mandible, this is also 
> found in Masiakasaurus, Coelurus and many (probably insectiviorous or 
> piscivorous) Mesozoic birds.


Also in _Eshanosaurus_, a likely herbivore.  The diet of
_Masiakasaurus_ has been the subject of much speculation: fruit, fish,
insects?  As for _Coelurus_, the dentary is the only cranial material
known for this genus, and this element is extremely slender and
gracile.


> 2. Ischium longer than 66% pubic length.  This is the basic arrangement for 
> theropods... er... archosaurs... er amniotes.  So this is present in 
> carnosaurs, tyrannosauroids, megalosauroids, ceratosaurs, etc.. Not a 
> herbivory-related character at all.


Yeah, that one's a wash.


> Given the fairly large, recurved teeth and generally 
> carnosaurian-tyrannosauroid nature of the taxon, I would doubt if 
> Ornitholestes had more plants in its diet than modern coyotes and such.


I also thought that the teeth of _Ornitholestes_ were rather conical,
especially the premaxillary teeth.  Am I mistaken here?  This
appraisal of _Ornitholestes_ dentition comes from Paul (1988).  I
disagree with GSP's "neoflightless" hypothesis, but surely I can trust
him when it comes to determining the shape of a theropod's teeth.


> The "rather weak cursorial abilities" are based on a tibia which seemingly 
> doesn't exist.  I'd like to know what happened to whatever bone Osborn 
> identified as a tibia.


Actually, I wasn't thinking of the phantom tibia at all.  The
metatarsus of _Ornitholestes_ is only about half the length of the
femur.  Even compsognathids and archaeopterygids had longer metatarsi
(~ three-quarters the length of the femur).  The mt/femur ratio of
_Ornitholestes_ is about the same as that of the basal therizinosaur
_Falcarius_.





Cheers

Tim




Cheers

Tim