Re: beak evolutioin in tetrapods

["Patrick Norton" <ptnorton@email.msn.com>]

Darren Naish wrote:

<tetrapod beaks only occur in taxa that exhibit a caruncle (egg tooth) when
hatching. Apparently, the caruncle is an amniote synapomorphy that has been
lost in therian mammals and squamates and it's suggested that beaks evolve
via modification of this structure>

OK. So if a caruncle is an amniote synapomorphy and is truly related to the
potential for beaks, does that mean that the otherwise confusing list of
possible occurrences of beaks in the Dinosauria and other reptiles may be
something other than convergence? Beaks (horny, keratinous, rhamphothecal or
otherwise) are claimed for taxa scattered across the spectrum of the
Dinosauria and throughout the Mesozoic.  As far as I've been able to
determine, they supposedly occur among the Saurisuchians, from the late
Triassic prosauropod clade Melanosauridae) to some of the derived late
Cretaceous Theropoda (the Ornithomimidae and Avialae) and are also claimed
for a wide range of Ornithiscian dinosaurs including the  Marginocephalia
and Ornithopoda. This suggests to me some potential for beaks among at least
the basal archosaurs, if not earlier.

Help me please before I have to tell my parrot he's been right all along!

PTNorton@msn.com
www.geocities.com/capecanaveral/galaxy/1962/