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Re: sauropods: homotherm,heterotherm or gigantotherm?



The foramen ovale is not equivalent to the foramen of
Panizza. The foramen of Panizza is located OUTSIDE of
the actual heart. It occurs between the two aortae.
The foramen ovale in humans, occurs INSIDE the heart,
between the two atria.

Oops, true.

As for the Bennet-Stamper et al article, all I really
gathered from it was this basic argument:

.) Early crocodylomorphs were more active than extant
crocodylomorphs

.) Activity requires endothermy.

.) Therefore early crocodylomorphs were likely to be
endothermic.

As the second assumption has never been experimentally
born out (with plenty extant examples to the
contrary), I don't really buy it.

_Sustained high_ activity does seem to require endothermy, but just how much running the spheno- and protosuchians did may be everyone's guess...


There is also the argument that at least alligators have greatly increased rates of molecular evolution. Those are, however, way above those of mammals and birds as well.

Plus I felt they just glossed over the heart
morphology of pythons and varanids in an attempt to
explain why crocodylians have 4 chambered hearts (both
varanid & python hearts [possibly more species as
well] are functionally 4-chambered, and capable of
pressure separations equivalent to those seen in
mammals & birds).

How does that work?

Yes, but that's not gigantothermy. Those tunas (not
all) and sharks do have increased metabolic rates.

No they don't.

Really?

They use the same counter-current heat
exchange system that _D.coriacea_ uses.

That's clear -- e. g. white sharks only keep their inner muscles at constant high temperatures, while the outer layer is only warmed up for attacks.


Besides that, there is at least one study out there
(that isn't Paladino et al's infamous one), which
shows that the metabolism of _D.coriacea_ does
increase when in colder waters.

Oho.