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



The crocs bounced around between purely terrestrial and wholly marine 
forms, with everything in between, until at least the mid-Miocene.  There 
is nothing I'm aware of that makes the croc flexible 4-chambered design any 
worse for any particular environment.  Its simply a better design than the 
bird or mammal heart for all environments.  The problem (according to some 
medical types I've pestered) is that the design involves a couple of more 
valves and shunts.  Thus, there are simply that many more moving parts to 
go wrong.  If one really doesn't *have* to spend a lot of time sitting 
around under water and have other adaptations for the occasional cold 
spell, one can dispense with the sun roof and automatic transmission. So 
birds and mammals didn't get a better heart, they just traded adaptability 
for simplicity and reliability.

If anyone's interested, the Benton & Clark (1998) cladogram (still the best 
IMHO), and links to the Clark (1994) cladogram and Mike Keesey's cladogram 
may all be found at:
http://home.houston.rr.com/vnotes/notes/Crocodyliformes.html
I don't put too much faith in the current crop of croc cladograms for 
reasons I discuss on that page.  However, I understand that there's a new 
and much improved one which will eventually be published.

  --Toby White

Vertebrate Notes at
http://home.houston.rr.com/vnotes/index.html
and http://www.dinodata.net



-----Original Message-----
From:   T. Mike Keesey [SMTP:tmk@dinosauricon.com]
Sent:   Monday, May 01, 2000 8:05 PM
To:     Stanley Friesen
Cc:     -Dinosaur Mailing List-
Subject:        Re: Dino heart--Williston's prediction comes true!

On Mon, 1 May 2000, Stanley Friesen wrote:

> 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?

I have a cladogram at this URL:
<http://dinosauricon.com/taxa/archosauromorpha.html>

I think it is reasonably up to date, but, if it isn't, someone let me
know!

In this cladogram, there is no "Protosuchia", so I assume it's
paraphyletic. (Proterosuchidae, however, is a clade at the base of
Archosauriformes.) Outgroups to Crocodylomorpha (=={_Sphenosuchus_ +
_Crocodylus_}) are Poposauridae, then Postosuchidae (and
_Gracilisuchus_?), then Rauisuchidae.

-- T. Michael Keesey .................................. 
<tmk@dinosauricon.com>
   My Worlds (including The Dinosauricon) ... 
<http://dinosauricon.com/keesey>
   AOL Instant Messenger ........................................ <Ric 
Blayze>