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Re: mammalian reptiles
Chris Nedin's post is much appreciated; it's nice to see how many
"fact police" there are in this group. I just wanted to make a quick
comment about one thing before I collapse from exhaustion (not the
fault of the post!). The "euryapsid" group is no longer recognized as
a "natural" (monophyletic) group by anyone who studies fossil
vertebrates (apparently the following paper argues otherwise: Mazin,
J.-M. 1982. Affinites et phylogenie des Ichthyopterygia. Geobios,
Memoire Speciale 6:85-98). All of the critters in that group are
derived from WITHIN the diapsids - most of the reptiles one can think
of are diapsids, except the turtles (god's gift to the planet Earth,
as far as I'm concerned) and the "mammal-like reptiles," which are a
paraphyletic stem-group for mammals, of course. The traditional
"euryapsids" include two major groups: the ichthyosaurs and the
sauropterygians. According to Rieppel (1994: J Vert Paleo 14:9-23)
the sauropterygia includes plesiosaurs, the nothosaurs, the
placodonts, and another primitive group called the pachypleurosaurs.
I'm not familiar with the pachypleurosaurs; everyone has seen
paintings and pictures of plesiosaurs and nothosaurs; and the
placodonts are really bizarre and deserve being looked up if you can
find an illustration. Everyone seems to agree that nothosaurs are
closely related to plesiosaurs, and perhaps a paraphyletic stem-group
leading up to them, although Rieppel argues that the nothosaurs are
monophyletic. Apparently there is no strong evidence linking the
sauropterygians and ichthyosaurs, and hence, "Eurapsida" isn't really
a useful term. Night all...