RE: Raptors Are Not Dinosaurs? Oh, My!

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Mike Taylor
>
> My question: is there _any_ stage in the theropod tree where there
> could possibly be a break from "true" theropods to non-dinosaur
> "theropods" derived from non-dinosaurian birds (which in turn would be
> derived from basal archosaurs).  That is, in the fossil record that
> runs (roughly) _Eoraptor_ -> _Coelophysis_ -> _Megalosaurus_ ->
> Carnosauria -> Tyrannosauria -> "Enigmosaurs" -> Dromaeosauridae ->
> Aves, is there any suspiciously wide morphological gulf between known
> fossil forms where Feduccia's proposed leap from dinosaur to
> non-dinosaurian secondarily flightless bird could take place?

No, there is no such morphological break.  In fact, the biggest jump in the
theropod record is between potential basal theropods (_Eoraptor_,
Herrerasauridae) and "eutheropods" (coelophysoids plus Neotheropoda): Sereno
(1999) demonstrated this graphically. This is why I am ever so pleased that
the "BANDits" now include dromaeosaurids as birds: they set themselves up
for a cascade of inclusion (so, if dromaeosaurids are birds, why not
oviraptorosaurs? or ornithomimosaurs? or tyrannosaurs? or compsognathids? or
carnosaurs? or spinosauroids? or ceratosaurs? or coelophysoids? or
_Eoraptor_? or sauropodomorphs? or herrerasaurids? or ornithischians? or...)

> And if there is such a gap, what kind of fossil animal should we now
> be predicting is due to turn up and fill it? :-)

See above.  Incidentally, at SVP there will be a poster that pins down the
phylogenetic position of at least some of the BANDits' favored bird ancestor
models.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796