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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.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com