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Re: [Re: Reptilia]

Archosaur J wrote:

<The only problem I have with the cladistic definition is that it does
not tell one what the diagnostic features are. All it says is the most
recent common ancestor.>

  Precisely. The diagnosis is mutable, the definition is not. Research
and/or further discoveries could make any feature undiagnostic of that
group, and so they are not placed together.

<So what constitutes being the common ancestor?>

  Something similar to the most primitive living reptilians (turtles)
and the most derived (crocs or snakes, take your pick); it would be
four-legged, most likely, with scales or stud-like dermal ossicles,
and even an open infratemporal fenestra; it would not give live birth
(certainly descendants managed this), and the egg includes a soft,
non-avian--like, calcium shell. Among some more features, I'm sure.

  Look at the skulls of a *Mosasaurus* and an *Ophiophagus*, and tell
me the many features they possess that crocodiles do not, that turtles
do not; then you would have some good concrete basis to establish a
"Lepidosauria". And it has been done. Compare the two, and you can get
a pretty good idea of what the common ansector _might_ look like.

  Anyway, that's enough of my gibberish.

Jaime A. Headden

Qilong, the website, at:
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