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Re: Fixing dinosaurian carnivour question



On Thu, 27 May 1999, John M. Dollan wrote:

> And this is a reflection of my own thoughts, amateur though they be, but I
> prefer to think of birds, though being descended from dinosaurs, as a
> completely different form, much like mammals, though descended from
> reptiles, are a different form.  I know that things are not so clear cut
> in the real world, of course, but that's where I stand, for now.....

Ah, but mammals are not descended from reptiles. Reptilia is cladistically
defined as the most recent common ancestor of chelonians (turtles),
lepidosaurs (tuataras, lizards, snakes), and crocodylians, plus all of
its descendants. By most phylogenies, mammals (and all other synapsids)
fall outside. Birds (and other dinosaurs) fall within.

I have heard of some phylogenies under which Mammalia would fall inside
this group, but if that were the case I think (I hope) Amniota would have
precedence as the name for this clade, and Reptilia would be abandoned.

However, there are some good derived characters to unite chelonians,
lepidosaurs, crocodylians, and avians to the exclusion of mammals,
including scaly, non-glandular skin and a higher number of types of color
receptors in the eyes. The creatures once referred to as "mammal-like
reptiles" ("proto-mammals" would now be a better term) most likely lacked
these characteristics.

--T. Mike Keesey                                    <tkeese1@gl.umbc.edu>
WORLDS                                  <http://www.gl.umbc.edu/~tkeese1>