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Re: Endothermic Crocs in Nature



OK, I have some questions.

First, how do we know that crocodiles didn't have hearts intermediate
between other reptiles and dinosaurs because they evolved from an ancestor
who was basal to dinosaurs, and are more closely related to dinosaurs than
to other reptiles?

Second, how in the world is it that we have mitochondrial DNA from Jurassic
crocodiles, and we can't seem to manage any sort of DNA from Cretaceous eggs
and innards of tyrannosaurus legs but may be able to isolate some highly
corrupted proteins if we're lucky?

Well, I see someone else states flatly that there is no mitochondrial DNA
from Jurassic crocodiles - alright, it's going to take me awhile to get to
UT and get my paws on Nature, even online - how do they say it is that they
have mitochondrial DNA from Jurassic crocodiles?


Yours,
Dora Smith
Austin, Texas
villandra@austin.rr.com
----- Original Message -----
From: <MariusRomanus@aol.com>
To: <dinosaur@usc.edu>
Sent: Thursday, April 14, 2005 11:08 PM
Subject: Endothermic Crocs in Nature


> Has anyone else seen the article in 14 April's Nature (pgs 833-34)
entitled
> "Warm-hearted Crocs"? I haven't seen it mentioned.
>
> It's a report on an article written by Seymour et. al. and published in
> "Physiological and Biochemical Zoology", the conclusion of which states
that
> crocodilians may have had active, endothermic ancestors. Taking what one
can from
> the summary, the article seems to have a nice explanation for the mosaic
> characteristic of croc hearts; 4 chambered but with a shunting system
(though unlike
> that found in other reptiles). The gist is that crocodilian ancestors,
like
> the terrestrial nasties in the Triassic (eg. "Terrestrisuchus" and the
bipedal
> "Saltoposuchus"), were endothermic and as such evolved a four chambered
heart
> for pressure separation (lung and systemic). This has since re-evolved a
> shunting system that we see in modern aquatic crocs. It's stated that the
> terrestrial crocs of the Triassic are thought to have had an active
lifestyle and show
> indications of having a diaphragmaticus to inflate the lungs, which would
have
> allowed for higher rates of ventilation than contemporary crocs require.
It
> was only in the Jurassic that we begin to see larger, fully aquatic crocs,
which
> in turn are presumed to have adopted the same sit-and-wait strategy
employed
> by modern crocs. Since the rate of heat loss is greater in water than in
air,
> and since larger animals have higher metabolic rates, there would have
been
> selective pressure against endothermy during the return to the water.
> Furthermore, animals employing lengthy dive times characteristic of ambush
predators
> would have gained great benefits from having a shunting system capable of
> isolating the lungs, or increasing their relative prufusion. The article
also goes on
> to say that mitochondrial DNA from Jurassic crocs shows a high rate of
> evolution.... roughly equivalent to that seen in the mitochondrial DNA in
modern
> endotherms. All of this points to ancestral crocs with elevated metabolic
rates
> above that possessed by crocs today.
>
> There is also a short discussion dealing with the question of the lack of
> respiratory turbinates in modern crocs, and their apparent lack in
ancestral
> forms. The article states that the absence of turbinates could mean that
it is
> possible that the four chambered heart is a characteristic of an active
> lifestyle, rather than of endothermy perse.... (I have issues with that,
but why waste
> the time when one can simply read past DML discussions pertaining to
> turbinates.)
>
> The article concludes with stating how evidence from birds and crocs,
which
> bracket dinosaurs, is very useful. If ancestral crocs had high resting
> metabolic rates, and birds (in a nut shell) have high resting metabolic
rates, then
> there is a clear implication that dinosaurs did as well.
>
> As a side bar...... I'd like to know some opinions on chapter 28 of the
new
> "Dinosauria"... "Physiology of Nonavian Dinosaurs" by Chinsamy and
Hillenius,
> where they conclude "active, dynamic, but ectothermic dinosaurs".  Of
course, I
> could just read Padian and Horner's article in the following chapter, but
I'd
> like to hear some opinions from the peanut gallery if anyone would like to
> offer some.
>
> Kris
> http://hometown.aol.com/saurierlagen/Paleo-Photography.html