Re: four chambered croc hearts

[Jeff Poling <jpoling@dinosauria.com>]

At 01:45 PM 6/20/97 -0500, Mickey P. Rowe wrote:
>While the "fully erect" bit is almost certainly correct and the "wholly
>terrestrial" is probably correct, what fossil evidence is there that
>protosuchians and other early crocs had a four-chambered heart?

   Deduction rather than actual fossil record.  Extant crocs have a
physically four chambered heart that is functionally three chambered.
Crocs' closest living relatives, birds, have four chambered hearts.  It is
possible that the physically four/functionally three chambered heart is the
archosaurian condition, but given the erect limbs of early crocs hinting at
an active, terrestrial existence this suggests a need for a four chambered
heart.  Further, one would think pterosaurs would have needed a four
chambered heart for an active flying lifestyle.  Counting the croc heart as
four chambered, if the four chambered heart was not an archosaurian trait
then it evolved independently three times among archosaurs.  Parsimony
dictates that we pick the simpler explanation, that the four chambered heart
was inherited by the three groups from their common archosaur ancestor.
This would mean that early crocs had a four chambered heart.

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