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Re: Ichthyosaur breathing



David Peters (davidrpeters@earthlink.net) wrote:

<...especially since ichthyosaurs did reduce their limbs and increase their
vertebral count early in their history.>

  Cowen notes, without much substantiation, the reason a single lung in a snake
reduces the problem of activity relative to breathing. Incidentally, the title
and premise should be about TETRAPOD breathing, since vertebrates include fish
as well, which lack lungs and thus don't "breathe." Indeed, faster water flow
over the gill rakers will increase oxygen intake which fuels oxygen
consumption, so it's cyclical, but I am not sure the relative detoxification of
oxygen from the blood occurs fast enough to prevent hyperoxygenation, so even
fast fish need to slow down. Cites? No, not yet.

  Ichthyosaurs of the parvipelvian variety have long flippers and a highly
arched dorsal vertebral column with minimalization of vertebral articulations
due to shortening of the centra. Motani has discussed this change in
ichthyosaur evolution from the "eel-like" ichthyopterygian *Utatsusaurus* and
"basal" ichthyosaur *Cymbospondylus* to the more tail-powered *Grippia*,
shastasaurs and mixosaurs, and then the more "dolphin-like" *Temnodontosaurus*
and ophthalmosaurs/stenopterygids. Tail-powered locomotion with relative
decrease in dorsal lateral undulation removes Carrier's constraint, as Cowen
calls it, and removes the need for "porpoising" as an alternative to
sub-surface swimming at high speeds. While it's possible the more
"dolphin-like" ichthyosaurs like *Temnodontosaurus* could have porpoised, I do
not think there is any way such a behavior could be determined in the fossil
record.

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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