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Re: more therizinosauroid talk



In a message dated 95-08-30 23:26:17 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
writes:

> This
>is also how you recognize the theropodan nature of Therizinosauroidea (NOT
>Segnosauria, as agreed by Perle Altangerel, conamer of "Segnosauria"!!).

Segnosauria is the name I use for the phytodinosaurian suborder, the
historically first name to be used above the family level for this group. It
may contain as many as three families: Alxasauridae, Segnosauridae, and
Therizinosauridae. If you synonymize the latter two, then you must use
Therizinosauridae in favor of Segnosauridae. If you group them together
(excluding Alxasauridae) as distinct families within a superfamily, the name
of the superfamily must be Therizinosauroidea. That's where that name comes
from. The Code does not govern names above the family level, so I am free to
employ Segnosauria at the subordinal level and am not compelled to invent
something like Therizinosauria.

Almost all the supposed theropodan characters of Segnosauria reside in the
single skull of _Erlikosaurus_ as recently described by Clark et al.
Unfortunately for skulls, they are very evolutionarily labile, and reversals
and convergences run rampant in cranial anatomy throughout Vertebrata.
(Consider the classic case of the marsupial thylacine and the placental
wolf.) Cranial characters for cladistics should be chosen with great care and
due consideration of the difficulties involved in their analysis--something I
haven't really seen happen in dinosaurology. When postcranial anatomy screams
"derived prosauropod" but cranial anatomy whispers "well, maybe theropod," I
opt for the postcranial.

G.O.