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Re: Rahonavis....Both!

On Wed, 24 Feb 1999, Thomas R. Holtz, Jr. wrote:

> At 08:38 AM 2/24/99 -0500, Larry Febo wrote:

> _Rahonavis_ does NOT have the long bony rods in the tail that dromaeosaurids
> have.  At present, only _Deinonychus_, _Velociraptor_, _Saurornitholestes_,
> and _Utahraptor_ are known to have these among theropods.
> The large sickle claw is certainly dromaeosaurid-like, but as most analyses
> show dromaeosaurids and/or troodontids are bird outgroups, this feature is
> probably basal to the bird-dromaeosaurid (& troodontid) group, and later
> lost in more advanced birds (_Archaeopteryx_ and some other basal birds do
> retain a hyperextensible digit II without keeping the sickle claw).

_Alvarezsaurus_ has a short mtII and divergent second toe (Bonaparte
1991, p. 98), which may be evidence that the alvarezsaurs had
hyperextensible toes/sickle claws in their ancestry, which jibes well with
Dr. Holtz's scenario (incidentally, I agree with Chiappe that the
alvarezsaurs are just outside the (Archie + Neornithes) clade--
_Alvarezsaurus_'s feet and hips are entirely un-ornithomimid-like.)

A "new ornithomimosaur" from the Sao Khua Formation
(?Valangian/Hauterivian of Thailand) also shows a shortened, divergent
mtII (Buffetaut and Suteethorn 1998, p. 207), so the occurrence of
hyperextensible toes *may* go back to the divergence of the
ornithomimosaurs (pining for a foot of _Pelecanimimus_!).  That is,
assuming the animal in question really is an ornithomimosaur.  All that is
illustrated is a metatarsus, which could conceivably come from an
alvarezsaur or a tyrannosaur or troodont relative.

Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447