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Re: Carboniferous Endothermy



In a message dated 98-07-08 07:18:58 EDT, LarryF wrote:

<< What I was proposing was that perhaps an early synapsid type, with
development of endothermy already underway, might have become arboreal, and,
being of small size, would have needed the endothermic condition as well as an
insulative covering (fuzzy scales) to survive a colder micro-enviorn in the
treetops. As to why there exist diapsids today that are not endotherms
(ie.squamosa),  I can only figure them to be secondarily ectothermic. I see
evidence for this in the partial separation of the ventricle. Why any
separation at all in a cold blooded type unless the remnants  of a once four
chambered heart? I think that early diapsid development took place in the
trees, where they were isolated from competing synapsids, and where they
eventually developed into birds, (with dino descendants along the way). >>

I can say that indeed the diapsids evolved into tree and water -dwelling
animals to escape competition from the Permian's ubiquitous and unquestionably
ruling synapsids (some of the best examples of these diapsids being
Coelurosauravus, Heleosaurus, and Hovasaurus) and to avoid competition in the
small stocky insectivore/herbivore niche dominated by parareptiles, but there
is absolutely no evidence of any form of arboreality in any synapsid prior to
mammals and furthermore synapsid phylogeny strongly contradicts any form of
arboreal ancestry at any point (perhaps there were some specialized offshoots
of the  eupelycosaur line that were arboreal, but this is unlikely and if such
animals did exist they have not been found). Your argument is also
contradictory. You say that the endothermic arboreal diapsids (note that there
are many ectothermic modern arboreal squamates that have a far more advanced
osteology than the arboreal diapsids of the Permian) had secondarily
ectothermic ground-based descendants in the form of modern reptiles and also
gave rise to birds, and first became arboreal and endothermic to escape
synapsid competition but you also say that the endothermy first evolved in
arboreal synapsids. This destroys your entire concept of one-time endothermy
and the concept of diapsid evolution in the trees separate from synapsids on
the ground. I can see the possible reconciliation of this based on your view
that diapsids are derived from a synapsid condition, but as I have said before
diapsids are DEEPLY nested within the Sauropsida and the synapsids are an
entirely different group of animals. There is no way for the diapsids to be
synapsid descendants based on everything that is known about the groups. As
for the modern ectotherms being secondarily ectothermic, there is the
possibility of this in crocodilians given the light, running build of the
protocrocs, but the ancestors of lizards (and thus their descendants the
snakes) and tutataras looked exactly like, had skeletons exactly like (more or
less) lizards and tuataras, and thus there is a very good chance they lived
exactly like their modern counterparts, ectothermically of course. 

And Tom Hopp wrote:
<<Who said anything about endothermy?>>

Larry did, responding to your post, which I responded to.

<<I just said, "Fuzzy Devonian
salamanders."  What's so crazy about that?>>

Nothing, given comparison with such things as say, the Lake Titicaca frog, but
as  for these Devonian "salamanders"'s (you should have gone with
Carboniferous for this debate, since all Devonian eotetrapods are basically
fish with legs, and the fossilized skin of these is distinctly fish-scaled. Of
course, If you want to say that Eusthenopteron, Elpistostege and the
coelacanth are furry, go ahead.) fur being the ancestral follicle that was
retained in mammals and birds, I would have to say there is much craziness
inherent. 

<<P.S. A couple of smooth skinned fossils don't prove much, it seems to me.  I
stand by my notion of follicles arising only once.>>

Not a couple, absolutely ALL the preserved skin from when vertebrates came on
land to the mid-Triassic (and there are more of these than you might think) is
either scaly or lissamphibian-style. And ALL synapsid skin impressions are
lissamphibian-style soft skin, suggesting strongly that this is the dermal
covering from which hair evolved, given the extraordinarily complete sequence
of synapsid fossils leading up to mammals. With hair evolving probably among
the more advanced theriodont therapsids, there becomes a 120 million year gap
between your fuzzy salamanders and hair, a gap filled with scaly, smooth-
skinned, or scuted animals of every color, race, and creed, but with no
follicles similar to or ancestral to those found in modern mammals and birds.

I would advise both Mr. Hopp and Mr. F to drop this debate as it is almost
entirely an untenable position, and I hate to sound like I'm ranting.

Sincerely,
Christian Kammerer