RE: UNGUALS

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

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Matthew Bonnan
>
> Thanks for clarifying.  Yes, in reptiles generally the most
> distal phalanx
> (for those who don't know, phalanx is the singular of phalanges)
> is a bony
> claw core covered by a living claw.  In other vertebrates like
> mammals, an
> ungual is usually considered to be the most distal phalanx that bears a
> claw, hoof, nail, etc.-- at least, that's my understanding.  I
> guess I was
> just speaking dinosaurese before. =)

Same difference, as they say.  The primitive condition for the distal most
phalanx in an amniote is a relatively simple conical shape, which in life is
surrounded (at least in the distal part) by the living tissue and the horny
claw sheath.

In various derived groups, the shape of that distalmost phalanx (and the
horny sheath around it) can vary greatly: from the hooves of ungulates
(within which there is a lot of toe diversity) and the flat toes of some
ground birds to the highly recurved claws of the manus of many tetanurines
and the talons of raptorial birds to the weird fingers and toes of higher
primates, in which the claw has become a nail restricted to just the upper
surface of the phalanx.

                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