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Re: DEFENDING MODERN BIOLOGY



>     Thecodontia was virtually universally recognized until strict cladists
>came along.  A list of authorities would be very long, but let's start with
>Romer, 1966 (and Carroll, 1988, if I recall correctly).

>      Thecodontia is a paraphyletic group, not a polyphyletic "trash-can".

    Carroll (1988) says the following things about "Thecodontia" and its
members:  "the interelationships within the assemblage are subject to
continuing debate...pseudosuchians are a heterogeneous group...a variety of
poorly known forms may connect these families..."  The reason "Thecodontia"
was universally recognized before the cladists came along was that the
realtionships between basal archosaurs was so confused and controversial
that it was more convenient to lump them as a big group.  Thecodontia may be
paraphyletic in stead of polyphyletic, but it is still a trash can.
     Personally, I tend to agree that taxonomy shoud include paraphyletic
groups, BUT only if they are useful and make a meaningful distinction
between groups with a distinctly different suite of features or habitats or
whatever.  This certainly does not describe "Thecodontia".  What do
aetosaurs, rauisuchians, phytosaurs, ornithosuchians, erythrosuchians,
proterosuchians, proterochampsids, and Euparkeria all have in common with
each other that unifies them and makes them significantly different from
both crocodilians and dinosaurs?  They are mostly quadrupedal, armoured
carnvores, but then so are crocs, and aetosaurs are herbivores and some
poposaur-rauisuchians were bipeds like dinosaurs.  Did all 'thecodonts"
share a particular habitat or lifestyle that strongly distinguished them
from crocodilians and dinosaurs?  Not likely.  Thecodonts went extinct by
the end of the Triassic but crocodilians and dinosaurs survived?  Sort of
true, but not all dinosaurs and crocodylomorphs suvived either, and why that
is exactly isn't entirely clear.  "Thecodontia" isn't just paraphyletic, it
is impractical.

LN Jeff
************************
Jeff Martz
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