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Segnosauria vs. Therizinosauria
In response to the sustained thread this has spawned,
and added to the even longer and more numerous ones in
the past focused on the relationship and definition of
the groups involved, I hereby reply:
[a sentence that could have been avoided entirely
just by writing my message :)]
Segnosauria is a historic taxon including
*Segnosaurus* and *Erlikosaurus* and the unnamed taxon
(at the time) *Enigmosaurus* (Perle and Barsbold,
1981). Therizinosauria, while implied, doesn't stand
up to the criteria of formal taxon until it's actually
used. This has only been done colloquially, and as
such, doesn't validate a consideration by both ICZN or
PT standards, if I've read my material right (but I do
not have the 1966 or 1999 ICZN, so... and nor have I
read all the de Quieroz and Gauthier stuff).
Russell's read of "therizinosaurs" from the
_Encyclopedia of Dinosaurs_ probably stems from
Russell and Dong, 1993, and by implication is probably
his colloquial use of Therizinosauroidea, a grouping,
as detailed by Tom Holtz, was made in Barsbold and
Maryanska, 1990, in _The Dinosauria_, so is likely to
imply that group and assemblage, plus *Alxasaurus*, so
"therizinosaurs" is Alxa + all other "therizinosaurs"
like Segno, Therizino, and Erliko.
Segnosauria still stands as the most valid and
oldest grouping of taxa including a higher relative
rank (pardon the term) than Segnosauridae, or by
inclusion, Therizinosauridae. However, a formal
taxonomical, anatomical, or historical study has yet
to be performed on the taxa involved, and even
*Enigmosaurus* involves material not pictured,
including some vertebrae and ribs, and was never
pictured or well illustrated, so definite works needs
to be done on the taxa involved. Thus far, only
*Erlikosaurus* and the refered PIN arm and claws have
been properly or even close to being fully described,
and as such are the dependant specimens for
comparison. I used *Erlikosaurus* and will continue to
use it as the anchor, at least informally, until a
proper description of the type and two refered
specimens of *Segnosaurus* are properly described, and
the type of *Therizinosaurus* is shifted to more
diagnostic material, like one of the PIN specimens.
Thus, Segnosauria is a vague clade since by original
inclusion it contains _three_ taxa that would
correspond to Segnosauridae Perle, 1980.
Dong's Segnosaurischia is a junior synonym of
Segnosauria, by priority; and because a segnosaur
taxon (*Beipiaosaurus*) falls outside
Therizinosauroidea, and it most certainly clades there
(Xu et al. 1999), Segnosauria can be used to reflect
this clade, and another appropriate stem can be used
once a definite matrix or consensus turns up the more
likely position of segnosaurs compared to ornithomimes
or ovis (I don't accept Sereno, 1999, not by very
much, though the likelyhood of mononykes being related
to ornithomimes is high, in my opinion).
This is Report no. 2 of the 4/6/00 expedition of the
Jaime A. Headden writing spree, who is probably
spending too much time sitting up, thinking, reading
ecology and speciation papers by Vermeij and others,
and writing about theropods because he wishes he had
more papers and knowledge of ornithischians and
sauropods, so duly appologizes to Buchholz, Bonnan,
Wedel, Brochu, the venerable ZenLizard,
Thescelosaurus, and will devote more time to
theropods. I shall also stop worshipping Currie and
bow to Ahlberg and Cundall, whose non archosaur work
is so vast, and incredible, and....
Jaime "James" A. Headden
"Come the path that leads us to our fortune."
Qilong---is temporarily out of service.
Check back soon.
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