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From: owner-dinosaur@usc.edu
[mailto:owner-dinosaur@usc.edu]On Behalf Of philidor11
> Figure 4 on
the following page shows that ichthyostega apparently had 7 digits, 3 small and
close together, 4 larger behind:
> Can someone tell me, or point the
direction to find out, whether 7 digits is a widespread condition, and whether
this has
> significance for the separate 5th digit
which in one group is a thumb?
> Thanks.
Other primitive stegocephalians had many digits: Acanthostega had eight fingers, Tulerpeton had six
fingers. No post-Devonian stegocephalian (i.e., tetrapods and their
closest allies) had more than five digits per chiridium (hand or foot), except
in pathological conditions. See the related pages for the various
Devonian critters linked on:
As
for Ichthyostega: it is a foot, not a hand, so the "clumping" of
digits is in the region of the big toe, not the thumb (and there actually are
probably four digits there: the small medialmost one is somewhat obscured
underneath the next one in). The precise homologies of the individual
digits is problematic at present, but is of interest to developmental
biologists.
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
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