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Re: dinosaur/pterosaur competition



--- StephanPickering@cs.com wrote:
 
> (I have seen no evidence that ornithischians possessed feathers, and believe
> it improbable; it has, yet, to be demonstrated with extant fossils, how 
> ornithischians and saurischians derived from the same common ancestor: 
> perhaps, it was ancestors in different clades)

No evidence required - it's mandated by the definitions.

_Ornithischia_ has been defined as the first ancestor of _Triceratops_ which is
not also an ancestor of modern birds, plus all of its descendants. _Saurischia_
has been defined as the first ancestor of modern birds which is not also an
ancestor of _Triceratops_, plus all of its descendants.

When PhyloCode is implemented, it may be desirable to emend these to something
like:
_Ornithischia_ = Clade(_Iguanodon bernissartensis_ <- _Megalosaurus
bucklandii_)
_Saurischia_ = Clade(_Megalosaurus bucklandii_ <- _Iguanodon bernissartensis_)

In either case, the two clades cannot fail to descend directly from a single
common ancestor.

What definitions are you using for these clades?

(Agree about feathers in ornithischians being highly unlikely, but feather
homologues less so.)

=====
=====> T. Michael Keesey <keesey@bigfoot.com>
=====> The Dinosauricon <http://dinosauricon.com>
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