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follow-up on follow-up on sauropods
As I said, birds and mammals are more limited in their ability to adjust
their growth to food intake than ectotherms. This does not mean that there
is no such thing as a badly stunted endotherm. Norway rats, for example,
may adjust their growth as much as 80% according to food intake. But this
may be contrasted with reptiles, which can adjust as much as 95%(!). A
five-year-old western diamondback rattlesnake, for example, can be as
little as 200 g or as much as 4 kg (although this degree of variation is
not seen in wild populations). It is amazingly difficult to starve a
reptile, an astonishingly small rate of intake will sustain them.
Dwarfism also occurs in the African elephant, by the way, some populations
have much smaller elephants than others. Extirpated populations on
Mediterranean islands were smaller still.
My conclusions that Brachiosaurus brancai could neither sit down nor lay
down are based on my observations of its skeletal structure. Unlike some
others, this particular sauropod is poorly designed even for raising up on
its hind feet (contrary to Jurassic Park depictions), much less assuming a
sitting posture. Laying down is quite out of the question in my view. But
the fact is, very large mammalian herbivores do not generally make a habit
of laying down in nature. It is not very wise when there are critters
around wanting to eat you, and unthinkable for a sauropod to put itself
into such a vulnerable position. Sauropods may well have had stay
mechanisms and other adaptations to reduce the energy requirements of
staying erect. But I can envision no adaptations that would obviate the
need for an endothermic metabolism.
Thanks for all your responses. You folks are terrific as usual.