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Re: Theropods with avian characters



>I am trying to make up a short list of theropods which have been described
>as either having characters in common with avians and not shared by common
>or garden theropods, or having characters intermediate between 'non-avian'
>theropods and avians (such as the quadrate articulation in _Troodon_)
>
>I have _Troodon_, _Avimimis_ and _Saurornithoides_. Any others?

[Actually, you're average sparrow is a "garden theropod", but I'll let that
pass...]

Basically, go back to Gauthier 1986 (and more recent updates by myself, by
Sereno et al., and by Clark et al.) for cladograms of theropods including
birds.  They will list the taxa and synapomorphies of closer and closer
ingroups to Aves.  In general, the most bird-like theropods are, by
defintion, the Maniraptora (=birds and all theropods closer to birds than to
ornithomimids).  By my most recent (yet-to-be published) analyses, these
include Alvarezsaurus, Dromaeosauridae, and maybe Oviraptorosauria and
Therizinosauroidea.  The Arctometatarsalia and Ornitholestes are other,
"birdy" theropods.  Further out are basal coelurosaurs, allosauroids, and so
on.

In general, we in the theropod systematics world are catching up to the
synapsid systemacists.  The latter do not see a sudden break of
"totally nonmammalian characters" to "totally mammalian characters", but
instead acquisition of features step-by-step that in the modern world are
uniquely mammalian.  Similarly, we now recognize among the theropods the
step-by-step acquisition of avian characters over tens of millions of years,
rather than a sudden "nonbirdy"/"birdy" transition.

In fact (as someone recently pointed out on the net), if Deinonychus,
Troodon, Ornithomimus, Tyrannosaurus, Allosaurus, or any other batch of
tetanurine theropods had survived to the present, zoologists would probably
have long recognized these as avian relations, and the visceral resistance
of many people to the theropod nature of birds would probably be far less.

But, to answer your question as you intended it, the Troodontidae (including
both Troodon and Saurornithoides), the Dromaeosauridae, Avimimus,
Oviraptorosauria, and all the advanced coelurosaurs are very bird-like.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084