Re: Birds and archosaurs

[Stan Friesen <swf@ElSegundoCA.NCR.COM>]

>From: CORWIN3210@aol.com
 > An intern of mine is working on a report for her vertebrate morphology class
 > about the origins of the avians. She has come across a number of strange
 > theories which I have not heard of. One, is advanced by a paper by Martin
 > (and others) in the early 80's stating that the crocodilians gave rise to the
 > birds. Does anyone out there know the background of this "theory"?

Well, when I talked to D. Martin last, around 1979, he stated one
of the reasons for his theory was that the inner ear structure of
birds is more easily derived from the crocodilian than the dinosaurian
inner ear.  In fact he claimed that the dinosaurian inner ear was
too specialized to have given rise to the avian inner ear.

Based on his appearences recently on PBS specials, he still holds
this theory.

Also, Dr. Chatterjee, the discoverer of Protoavis, supports this
theory, and he claims that Protoavis is "proof" that it is correct.

Havinf read. Dr. Chatterjee's paper, I can say that advanced
crocodilians and avians have certain convergent similarities,
but most of these are also seen in advanced theropod dinosaurs
(the "maniraptoran" group), so they really do not help determine
the phylogeny.  Now, if Protoavis *is* a bird (yeah, right),
then it is far too early to have evolved from the advanced
theropods, and so must derive from the crocodilians.

 > Also, there was some work published early this year which suggested that Late
 > Cretaceous birds show growh rings within their bones and may have been
 > ectothermic, or at least not totally endothermic. Does anyone know what
 > became of this idea?

No, but it is not ntirely surprising, the boundary between the
two is not as sharp as most people believe.  Bats (and maybe
some monotremes) are not entirely endothermic.  In bats the
body temperature drops radically during hibernation.  Personally,
if bats did not have mammalian style deterministic growth, I
suspect they would show growth rings.  (I would even suggest that
juvenile bats might show growth rings - it needs to be checked).

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.