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Re: Unidirectional gator breathing in Science



I was thinking this would mean one argument less against the linkage
of at least some features of avian-style breathing and endothermy, if
the croc has it, as for the four-chambered heart. However, it suggests
that at least the first archosaur was an ectothermic critter with some
improvements which helped it getting more oxygen (as does the more
divided heart).
This may have permitted more activity, or in the case of submerged
taxa, to get more oxygen with the last inhalation before submerging
(accepting the lung has not to be inflated for the animal to sunk, and
not knowing if the oxygen concentration in the blood was able to
increase to marine mammal-like levels).
That the croc is a reversal from a more active ancient archosauriform
state appears likely as Erythrosuchus possesses pneumatic features in
its postcranium, as do some crurotarsans, which indicate a more
bird-like respiratory system, which the croc and other semiaquatic
archosaurs (and some basal archosauriforms) reverted..

Regarding the amphibious lifestyle hypothesis for sauropods: how many
profound, wide rivers or lakes would be needed in a given area to
support viable population numbers of different sauropod species? Not
saying it could be not, an perhaps this can help explaining the low
sauropod diversity of Cretaceous small continental masses.