On Tue, 30 Dec 1997 14:21:24 -0800, Cliff Lundberg wrote:
>Stephen Jones wrote:
>SJ>While I provisionally accept some form of common ancestry between
>>major groups like reptiles and birds, I would not be surprised if it
>>does not support a Neo-Darwinian "blind watchmaker" pattern. My
>>expectation is that the gulfs between major groups will turn out to
>>be consistently further back in time than first thought (and
>>hence deeper and wider) and will be better explained by a
>>Pre-Darwinian "archetypal" (or structuralist) model:
CL>At some point, Neo-Darwinians will have to get tired of seeing
>their proposed branching points continually pushed further back
>in time. Their striving to find ancestors among known species
>shows their own microevolution from simplistic 'chain-of-being'
>evolutionary theory.
Agreed. Eldredge candidly admits that the fossil record actually
shows "truly instantaneous, overnight evolutionary leaps", but the
the Neo- Darwinist can always maintain his gradualism by claiming
that the gap occurs when the evolution did.
"The convenient thing about gaps in the record is that we need not
invoke truly instantaneous, overnight evolutionary leaps to explain
the transitions we seem to see in our fossils. With perhaps as much
as a million years missing, and certainly for such modest change as
the column counts in these trilobite eyes, we can easily maintain
that evolution is, after all, a gradual, intergradational affair.
We might regret not being able to "see" that transition-the gap in
preservation unfortunately seeming to occur when the evolution did."
(Eldredge N., "Time Frames", 1985, p72)
CL>But as to the warm-bloodedness of dinosaurs, could they be
>anything else? Could creatures of that volume bring themselves
>up to working temperature with an hour of sunning?
That has been the orthodox theory. Dinosaurs, like all reptiles are
thought to be cold-blooded, ie. poikilothermic:
"homoiothermic animal, or warm-blooded animal, any bird or mammal
characterized by the ability to maintain a relatively constant
internal temperature (about 37 degrees C [99 degrees F] for mammals,
about 40 degrees C [104 degrees F] for birds), regardless of the
environmental temperature. The ability to maintain an internal
temperature distinguishes these animals from poikilothermic, or
cold- blooded, animals, which usually have about the same
temperature as their environment." ("Encyclopaedia Britannica",
15th edition, 1984, Benton, Chicago, v:106)
However, that does not mean they were actually cold-blooded. Their
blood was warm, although not as warm as warm-blooded animals like
mammals. They, like other reptiles, are called "cold-blooded" in
the sense that they could not fully regulate their own temperature
but needed to be warmed by the environment.
"For a long time zoologists supposed that reptiles had no control at
all over the body temperature, and that it helplessly rose and fell
with that of the surroundings. Reptiles were, and until lately have
been, spoken of as "cold-blooded" animals. Now, primarily because
of some shrewd researches of R. B. Cowles and Charles Bogert,
carried out during the 1940'S, this idea has had to be abandoned.
Reptiles are not at the mercy of the temperature of the milieu. If
they were, they would achieve little, even by reptilian standards.
Actually they can maintain a fair control over their blood
temperature, and they do this not by controlling gain or loss of
metabolic heat, but by moving around, by alternately seeking and
avoiding sunlight or warm ground. They practise what is called
behavioural temperature control, and some species, at least,
maintain their preferred temperature at a remarkably steady level.
Not much is known about temperatures in non-basking reptiles, such
as those nocturnal or forest species that would seem shut off from
any heat sources except the air or water around them. But the
studies of Cowles and Bogert have provided the groundwork for a
greatly broadened concept of the habitat of the terrestrial
reptile." (Carr A., "The Reptiles", 1964, p85)
Happy new year.
Steve
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