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Re: Air sacs in extant non-avian reptiles?



At 04:39 PM 31/07/00 -0500, chris brochu wrote:
Mammals are not, and are thus not reptiles.  In
this scheme, the amniotic egg arose only once, but the ancestral amniote
was not a reptile, because "reptile" is no longer a wastebasket for
non-mammalian non-avian amniotes.

Furthermore, even if you ignore cladistics entirely it doesn't make a whole lot of sense to define any taxon heavily represented in the fossil record by a character that rarely fossilizes. As far as I am aware we do not know (and please correct me if I am wrong!) at what point the amniotic egg appeared, and there is no way to tell from a fossil whether it had hatched from one or not. I gather we do have evidence that at least some labyrinthodonts had gilled aquatic larval stages, suggesting that they at least probably did not lay amniotic eggs, but what about (say) Seymouriamorphs? Surely, if nothing else, taxa should be defined in such a way that decent skeletal remains are assignable (or not) with some degree of certainty to the taxon. Amniotic eggs don't qualify.



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