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RE: Do we have dromaeosaurid evolution backward?



Tim Williams 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.

Eh, lots of carnivorous taxa have at least one character Zanno and Makovicky 
identify as herbivory-related.
Decurved dentary- Masiakasaurus.
Dentary symphysis U-shaped- abelisaurids, carcharodontosaurids.
Conical anterior teeth- coelophysoids, megalosauroids, compsognathids.
Elongate anterior teeth- Daemonosaurus, Masiakasaurus, Ornitholestes.
Unserrated premaxillary teeth- coelophysids, spinosaurines, juvenile 
tyrannosaurines, most basal coelurosaurs, microraptorians.
Teeth lack recurvature- spinosaurines.
Heterodont dentition- More or less developed in most theropods, but notable in 
e.g. tyrannosaurids.
Pubic shaft anteriorly concave- some tyrannosaurids.
Pubis retroverted- Herrerasaurus, dromaeosaurids.
And that's not even mentioning carnivorous birds.

> 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.

Again, the only coding difference from compsognathids is the decurved (right) 
dentary (since compsognathids are miscoded as lacking conical anterior teeth).  

> > 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.

And many other sauropodomorphs, where Eshanosaurus probably belongs.
Has anyone seriously suggested fruit for Masiakasaurus?  Surely it's too large 
to be an insectivore.  Fish sure, but that's hypercarnivory.

> > 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.

I dunno, my examination of the holotype suggests the anterior teeth have a flat 
lingual side.  But as noted above, this isn't much of an indicator of diet.  
Besides the carnivorous taxa with conical anterior teeth, you also get 
herbivorous taxa with D-shaped teeth like Incisivosaurus (first pair), 
Pelecanimimus and Falcarius.

> > 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_.

The metatarsofemoral ratio is ~57% in Ornitholestes, but Velociraptor's is 42% 
(IGM 100/986).  Eudromaeosaurs' in general are low, which might be another 
ancestral character shared with Ornitholestes (but not basal birds, 
oviraptorosaurs, troodontids, ornithomimosaurs, etc.).

Mickey Mortimer