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Re: Air sacs in extant non-avian reptiles?
In a message dated 7/31/00 11:02:08 AM, email@example.com writes:
<< The question of whether or not to recognize Aves as a class strikes me,
though, as (a) moot and (b) certainly not to be decided on the basis of
similarity. For example, compare (say) a lungfish and a bluefin tuna - as
different, I would think, as geckos and pigeons (if not more so) and yet
both members of the traditional "class" Osteichthyes.>>
That's because they both lack the singular trait that makes tetropods, toes.
They also have two chambered hearts and gill slits all their lives. The gills
in amphibians, are external and look and work differently than fishes.
<<The point is that in a phylogenetic sense, even if we only consider living
animals, a crocodile is more closely related to a pigeon than to a gecko
-whatever their level of similarity. Therefore if crocodiles are reptiles
along with geckos, birds must be too. >>
But Birds have four chambered hearts and are ectothermic. geckos do not and
are not.Birds are covered with feathers and geckos with scaly skin. Something
clearly happened to birds to stop them from being reptiles, just as the
evolution of toes stopped amphibians from being fish.