Re: Mesozoic-ware

[ornstn@inforamp.net (Ronald Orenstein)]

>
>   I'm still in the process of switching from Linneanism to cladistics.  As
>I recally, amniotes are characterized by an egg with a fluid filled
>(amniotic) sack.  Would this not, then, include amphibians?  I am assuming
>that the choice of "amniota" in cladistics has a similar connotation, even
>though it's based on descent rather than physical characteristics.
>

No, because a true amniotic egg, with (more or less) waterproof shell, is
unknown in living amphibia.  Of course, who knows what fossil amphibians
had?  This is one of the problems with using characters like this one (which
is why mammals are defined by the jaw articulation, not by the presence of
fur or mammary glands or other things whose presence normally cannot be
determined in fossils.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
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