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RE: Terrestriality is a bias

From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of Gigi and Ralph

Regarding the physical difficulties of getting dromaeosaurs up a tree, this is less problematical in the recently described smaller forms, such as _Bambiraptor_ and the eagle-sized _Sinornithosaurus_.  Even smaller species may well have existed, and not been preserved, particularly if their habitat was a tropical forest, and immature dromaeosaurs would surely have been "small enough" to have jumped around in the trees if they had wanted to, long arms, retroverted pubes, cat-like claws and all.  And the pivotal theropod ancestor of the birds need not have been a dromaeosaur per se, but rather the most recent common ancestor of both dromaeosaurs and early birds (such as _Archaeopteryx_).

 Well, almost NOBODY claims that dromaeosaurs are the ancestors of birds!

Sister group, yes, but not ancestors.

(I said "almost" because some recent evidence suggests that "Dromaeosauridae" as traditionally defined is paraphyletic with regards to birds, in which case the ancestors of birds (and thus birds themselves) would indeed be dromaeosaurs.  Will have to wait and see on that one!)


-- Ralph W. Miller III      gbabcock@best.com

Question:  Is "dromaeosaur" or "deinonychosaur" the preferred term, or are they not synonymous?  

They are not synonymous.
"Dromaeosaur" (or formally Dromaeosauridae) comprises all descendants of the most recent common ancestor of _Dromaeosaurus_ and _Velociraptor_.
Deinonychosauria comprises _Deinonychus_ and all taxa sharing a more recent common ancestor with it than with modern birds (Neornithes).  (alternatively, we could use Sereno's definition: all descendants of the most recent common ancestor of _Dromaeosaurus_ and _Troodon_).
So, in most analyses "deinonychosaur" would potentially include more critters than "dromaeosaur".

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742      
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843