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

Re: dinosaur anatomy



> From: JSeward123 <JSeward123@aol.com>
>  I especially liked Ruben's recent article in Science vol. 278 p. 1267.
There
> it was stated directly that early birds and Archaeopteryx > were
ectothermic.

Presumably any birds prior to 70 million years ago, in accordance with 
the team's respiratory turbinate research (as reported in _Discover_
magazine, December 1996).

>I
> found this very surprising. To me it only seems logical that a beast with
some
> form of insulation would be naturally endothermic. Could it be that
feathers
> had the primary use of flight and the secondary use of insulation for
those
> birds?

See Gregory S. Paul's message from October 23, 1996, entitled "Subject: A
TICKLISH SCIENCE LESSON (long)," which argues for a causal link between
insulating fibers and endothermy.  See also _Science_ magazine , volume
274, November 15, 1996 (the report on a hypothesis proposing an early
adaptive radiation of birds), which describes and pictures
_Confuciusornis_, a primitive bird known from dozens of specimens dating
from approximately 121 to 142 million years ago, and which is preserved
with a downy coat of feathers.  If downy insulation is a disadvantage to an
"ectothermic bird," then why are these birds covered in down?  Why are
hollow fibers found all over _Sinosauropteryx_?

> If so, that seems to indicate something about the environment of that
> time. The Jurassic environment was hot and tropical, right? So maybe
> endothermic metabolisms were not needed for those birds (and dinosaurs by
> extension).

Or perhaps early birds and dinosaurs did not require the refinement of
respiratory turbinates in order to succeed as endotherms on some level in
the Mesozoic.  It is also likely that dinosaur metabolism varied quite a
bit, depending on species, size, age, locale and lifestyle.  But if you can
accept the Ruben model of early flying birds, covered with feathers, being
ectothermic (a pill I find very hard to swallow), then you might have to
concede that the line between endothermy and ectothermy is practically
meaningless.  Yet, this is not the opinion expressed by John Ruben, Andrew
Leitch, Nicholas Geist, and Terry Jones in Chapter 35 of _The Complete
Dinosaur_: _New Insights Into the Metabolic Physiology of Dinosaurs_.  They
begin the chapter by stating that: "Endothermy, or <warm-bloodedness,> is
one of the major evolutionary developments of vertebrates, and among the
most significant features that distinguish existing birds and mammals from
reptiles, amphibians, and fishes."  The paragraph goes on to credit most of
the success of birds and mammals to endothermy.

In _The Complete Dinosaur_, the article also states: "Consequently, the
confirmed absence of respiratory turbinates, or similar structures, is
likely to be strongly indicative of ectothermic, or near-ectothermic, rates
of lung ventilation and metabolism, in any taxa, living or extinct."  This
quote does imply <some> room for interpreting the meaning of absence of
RT's.  Unfortunately, the term "near-ectothemic" is not defined.

I do value much (but not all) of the research presented by Ruben et al in
helping us to understand certain details of dinosaur anatomy, but I am
hard-pressed to agree with their conclusions in this case, which paint with
too broad a brush, in my opinion.

Ralph Miller III <gbabcock@best.com>