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Re: Phorusrhacids and dinos



At 01:02 AM 10/29/98 -0500, Chris Srnka wrote:
>I'm horribly out of touch with the current understanding of the
>relationship of theropods to the great flightless predatory birds of the
>Tertiary. At what point do we begin to see beaks replace the toothy jaws
>of most of the theropods? Oviraptorinae? Ornithomimidae? Both of those
>groups are usually considered nonpredaceous, right? So when do we see
>true raptorial beaks make an appearance?

Yikes!  Looks like we have a misunderstanding of the evolutionary process
here...

Okay, birds are a monophyletic group (that is, they had a single origin)
within Theropoda.  This origin happened at least by the Late Jurassic, and
possibly even much earlier.  At the time of the split of birds from all
other lines of theropods, they still had a fairly good compliment of teeth:
see _Archaeopteryx_, enantiornithines, _Ichthyornis_, _Hesperornis_, etc.
_Confuciusornis_ had a toothless beak, but this seems to have evolved
independantly of the condition in modern birds, because most birds more
closely related to modern birds than to _C._ are toothy.

Phorusrhachids, falconiforms, and other modern birds with hooked beaks
evolved so WITHIN the clade Neornithes (the clade of modern birds), and in
fact within the group Neognathae (the "modern jawed" modern birds).  I don't
know if any true raptorial beaks within neognaths are known prior to the
Cenozoic.

The condition of the jaws in oviraptorosaurs and ornithomimids evolved
independantly of the toothlessness condition in birds, or for that matter of
each other (the oldest known ornithomimosaurs are toothy).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661