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In a message dated 3/3/01 1:57:27 PM Eastern Standard Time,
> How could Postosuchus have sprayed mammal like urine, when all living
> archosaurs (and most diapsids) are uricotelic? Also, I have a question that
> think is interesting: If living synapsids (mammals) are not uricotelic but
> evolved from basal ammniotes along with diapsids, why would they have ever
> lost something as advantageous in terms of water retention as uricotelism?
They (we) probably didn't. Living synapsids, the basalmost living amniotes,
are non-uricotelic, and our closest living non-amniote relatives,
lissamphibians, are non-uricotelic as well. Thus, basal amniotes were likely
non-uricotelic, and uricotely probably first evolved in reptiles proper.