Re: Thoughts on endothermy

["Larry Febo" <larryf@capital.net>]

{ hello, I`m back in these brackets again! Larry.}.      Dr Holtz: (no
brackets).

>{ ( I still don`t think diapsids could have developed warm
>from a cold-blooded condition, if the synapsids already had it, and
>dominated the landscape).}

Again, why not? Do you consider the possibility that endotherms might not
dominate in all climate conditions,


{Maybe I`m not getting all of what you`re implying here, but it dosen`t seem
to be a good argument against a one time only development of endothermy. For
example,  In the late Pennsylvanian Synapsids did exist, and , by my theory,
were to a good degree on the warm blooded side already, enough to allow them
to "out-class" cold-blooded competitors in many environs,... except perhaps
steamy hot jungle ones. OK, So the (assumed by you) cold-blooded diapsids
would dominate these select "jungle" niches. They would, in effect be
separated. The diapsids could go on to evolve, but what incentive would they
have to evolve their warm-bloodedness? I`m assuming it evolved mainly to
protect and insure the development of the young in a colder environment. If
the diapsids were stuck in the jungle, how could they venture out into a
world filled with synapsids, and from the early stage of cold-bloodedness,
evolve into warm bloods at all, let alone to a greater degree than the
synapsids.
     What I think happened is that they started, more or less on equal
ground metabolically, diapsids at first being smaller, developed an arboreal
nich (or perhaps their anapsid type precursors were already up in the
trees), this to escape from the larger synapsid predators. Their development
into gliding, and flying forms enhanced their metabolic state even  further,
to the degree that the could have sent
descendants back down to the ground, not only to compete with the synapsids,
but to outclass them in their own environment.}

 or the possibility that a
mass extinction of therapsids might have "opened up" the "endothermic niche"
for diapsids;]

{Yes, some extinction of larger ground predators would be necessary for
these arboreal species to send descendants to the ground, which would then
develop into larger cursorial forms. A meteor strike would be a reasonable
cause for periodic extinction of larger land forms.}

or that some other physiological difference between therapsids
and archosaurian diapsids may have been favored? There are many
possibilities here.

{I don`t see which other  physiological or morphological would be more
important or necessary for the above scenario to unfold. I would "speculate"
though, that after the KT extinction, these arboreal diapsids (by now were
talking birds) had much ossified carpal structure, and could no longer
develop descendants with very effective claws. They also might not have had
the strong toothed stock to enhance their descendants with a "cutting edge".
In other words, no more theropod dinosaurs that were "red of  tooth and
claw", only large flightless birds from then on.  This lack of  armorment
might have given the synapsids back their edge.} {I know, speculation,
speculation, speculation. Where is the fossil proof? Unfortunately, due to
the lack of preservation of these small hollow-boned skeletons, probably at
the bottom of some as yet undiscovered inland lake bed, and then , extremely
few and far between}