[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Rahonavis....Both!

> >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).
> Well, yeah, but...I`ve been hearing lately (sorry no specific refs) that
> Dromaeosaurs seem in many ways MORE advanced that Archeopteryx, and for that
> matter,...so is Rahonavis.

This is where using terms like "advanced" can get you into trouble.
Dromaeosaurids are "advanced" in that they have new features not found in
the ancestral eumaniraptor. If, by "advanced", you mean, "sharing more
recent ancestry with modern birds", and are suggesting this tree:

   +--advanced birds

Then I'd like to hear what evidence backs this up.

> So, it dosen`t seem to fit in as a decent intermediate either.
No, but it's preobably a relatively unmodified (at least, the parts we
have of it are relatively unmodified -- who knows, it might have had a
freaky-bizarre head!) descendant of an intermediate between basal
eumaniraptors and basal avians.

> More likely further advanced because it actually had
> more time to evolve into the Cretaceous, and give rise to Dromaeosaurs.

I fail to see how _Rahonavis_ could have given rise to dromaeosaurids when

A) It shares no synapomorphies with them that are not basic eumaniraptoran

B) It's from the very end of the Cretaceous, and dromaeosaurids are known
from the Early Cretaceous (and possibly the Jurassic).

--T. Mike Keesey                                    <tkeese1@gl.umbc.edu>
WORLDS                                  <http://www.gl.umbc.edu/~tkeese1>
THE DINOSAURICON                               <http://dinosaur.umbc.edu>