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RE: Rahonavis; sickle claws



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> ELurio@aol.com
>
> In a message dated 11/25/01 12:37:42 PM, aspidel@freegates.be writes:
>
> << BTW: how many times did the sickle claws appear in dinosaur evolution?
> Twice (once in maniraptorans, once in ceratosaurs: _Noasaurus_)?
> May we say
> it's convergent evolution? >>
>
> No. This is the proof that maniraptors are in fact flightless birds.
>
Despite Eric's comments: yes, sickle claws evolved more than once in the
history of theropods.  _Noasaurus_ is most definitely not a maniraptoran
(bird or otherwise), and has a sickle claw.

The number of times this featured evolved within Maniraptora is uncertain.
Seriamas have it, and are derived modern birds, so this origin is separate
from any of the Mesozoic origins.  It *might* have appeared only a single
time in Maniraptora: inherited by Troodontidae, Dromaeosauridae, and
_Rahonavis_, and lost in _Archaeopteryx_ (which arguably as a
hyperextensible digit II, but no sign of a true enlarged sickle claw) and in
more derived birds.  Alternatively, it might have evolved multiple times in
this part of the tree (which is notoriously unstable).

Even placing troodontids and dromaeosaurids as birds more derived than
Archie doesn't clarify things, as their precise relationship to each other
AND to _Rahonavis_ AND to later birds would have to be established to
determine the number of origins and losses.

                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