[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Kiwi Wings (was RE: Moasaurus)

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Stephen
> "Thomas R. Holtz, Jr." wrote:
> > Actually, in kiwis the finger (with ulna) develops on only the

Typo on my part: read "(with ungual)"

> If these distinct forms were found in mesozoic theropod skeletons, would
> they typically be treated as distinct taxa, and if so, might they be
> considered different species, or even different genera?

It the limb alone were found, they would almost certainly be called
different genera.  However, given that the rest of the animals are the same,
I suspect that it depends on the current conventions (and ultimately the
taxonomist at hand, so to speak).  For example, in the early 20th Century
people were naming new species and new genera on the slightest variation;
during other waves people tend to lump.  For example, there are two morphs
of large double crested Kayenta theropods.  Some regard these as two species
_Dilophosaurus wetherilli_ and the self-published name "Dilophosaurus
breedorum", or even two genera (stated in the text of Welles 1984, although
the second taxon is never named); on the other hand, many workers (Gauthier,
Rowe, etc.) regard these as two (?sexual) morphs of the same species.

> > By comparison with more completely digited birds (and with
> tetrapod hands in
> > general), the first form is producing a morphological
> metacarpal II with its
> > digit, and then a digitless mc III; the other form is producing a
> > morphological mc I with its digit, and then a digitless mc II.
> Does this have any implications for the BAND argument that birds' three
> toes are different from dinosaurs' three toes?

It does indeed; and is part of the argument of Wagner & Gauthier (1999.
Proceedings of the National Academy of Science 96: 5111-5116).  It was from
a Gauthier talk that I first learned about this.

> still trying to work out the implications of the (small) size of the
> human genome in terms of phenetic evolution of other species - like
> dinosaurs.

Not too hard, although the media (and, it seems, the gene jockies) are
trying to make it seem  stranger than it is.  (Of course, to the media and
perhaps to the gene jockies, it violates their sense of the old Scala Natura
that humans aren't more "special" than they thought: then again, the
geneticists should have kept in mind that there are plenty of taxa (onions,
for example) with much longer DNA strands (if not genomes per se) than

Okay, too many parentheses!

As to the implications: remember that humans (and other vertebrates) have
four main embryonic tissue types: endoderm, ectoderm, mesoderm (the first
two shared with all animals, the latter with other triboblastic metazoans),
and neural crest (strictly verts).  Because of this, you can potentially
have a great variety of potential interactions even with the same number of
genetic commands than in taxa with fewer numbers of embryonic tissue types.
Additionally, there are some genes that affect multiple traits.  The weird
and wonderful world of genetics.

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