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Re: Dino heart--Williston's prediction comes true!



At 07:09 AM 5/1/00 -0400, Larry Febo wrote:
(snip)

>However, this does not settle the issue of the ancestral archosaurian
>condition.  The earliest classical archosaurs, the so-called
>"proterosuchians", may also have been aquatic predators, in which case the
>switch-hitting heart may have evolved then. The fully four-chambered heart
>of birds (and presumably dinosaurs) would then have evolved from the
>crocodilian style heart when their ancestors abandoned aquatic hunting.
>

And I thought that the modern crocs ancestors were all terrestrial, "high
walkers", which would lead me to believe that (if anything), the gap between
the crocs ventricles and it`s cold-bloodedness were a secondary development
from a primary four chambered condition. Forgot where I read that (about the
terrestrial nature of early croc ancestors), ...someone please tell me if
I`m wrong here.

I don't have the latest cladograms, but the issue is complex.

"Proterosuchians" - the basal archosaurians - have been interpreted as semi-aquatic, and as terrestrial. Many of the earliest crocodilians per se are the fully terrestrial protosuchians (note the difference in spelling). In some cladograms, at least, the protosuchians form a clade that is the sister group to "modern" crocdilians. This leaves the state in the actual crocodilian ancestor uncertain, in my opinion. Were the protosuchians a terrestrial sideline, or a persistent branch of the basal crocodilian group?

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May the peace of God be with you.         sarima@ix.netcom.com