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

Re: crocodylomorphs?/ birds



>From: "Considine, Blaise" <BPC.APA@email.apa.org>
 > 
 > 1) what is a crocodylomorph?

It is a member of a subgroup of the archosaurs that are more
or less closely related to the crocodylians.

Crocodylomorphs include crocodyles, and some Triassic and
Early Jurassic terrestrial forms, such as Hesperosuchus.

 > 2) so the current theories re birds are 1) they and the dromaeosaurs
 > came from the same stock, and branched apart during the early jurassic

Yes, or perhaps branching in the Middle Jurassic.
 >
 >  2) dinosaurs are an offshoot from reptiles to birds

I am not sure what this is intended to mean.
Dinosaurs in the traditional sense are believed to be more
or less intermediate between birds and stem reptiles.

 > 4) are archaeopteryx and protoavis properly considered birds

Yes and no.
Archaeopteryx is held to be a bird by most workers.
Only two or three people believe Protoavis to have been a
bird, and at least one of those is known to be unreliable
on phylogenetic issues from other suggestions he has made.

 >, or are they their own group?

At one level, Archaeopteryx is in its own group - its own
particular subgroup of birds.  But it is still more or less
a bird.  (Actually it is so close to being exactly intermediate
that placement is difficult).

The proper position for Protoavis in undetermined, at least as
far as I know.  I have heard it suggested it is a very early
coelurosaur (modern sense), a crocodylomorph, or a ceratosaur.
I cannot see how to decide which right now, based on Chatterjee's
paper.

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

The peace of God be with you.