[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: maxillary fenestration & WHAT are "segnosaurs"?



Ken Kinman (kinman@hotmail.com) wrote:

<In fact, it brings up the question once again of whether
segnosaurs are coelurosaurs AT ALL, or even if we can
confidently place them among tetanurans.>

  My lord, do we have to go through this AGAIN? This whole
concept of segnosaurs being doubtful theropods are coelurosaurs
is bad enough, but to be brought up again and again and again it
is sincerely aggravating.... But anyway, once more unto the
breach...

<I don't know whether the new "Nothronychus" will have any
bearing on this problem (I surely hope so), but I am once again
troubled by the status of the "therizinosaurians" (a possibly
paraphyletic or even polyphyletic group) and whether or not some
of them (segnosaurs, i.e. therizinosaurines, in particular)
should be excluded from "coelurosaurians" or even "tetanurans".>

  Yuk. Why, because *Erlikosaurus* (to say nothing of the other
taxa which lack maxillae to compare to and thus should not be
included in the removal concept here) lacks a maxillary
fenestra? You say nothing about this concerning *Chirostenotes*
which, under the name *Caenagnathus*, was once a bird....

  Perle, Norell & Makovicky, 1994, describe the skull of
*Erlicosaurus [sic] andrewsi*, and quite comfortably place the
taxon withing coelurosaurs. The basicranium is entirely fused
and pneumatic, as is the quadrate; the forament magnum has a
greater area than the occipital condyle, and the endocranial
cavity is itself arched in the region of the cerebrum,
suggesting expansion of the frontal lobes; the arrangement of
the cranial nerves is largely congruous with oviraptorids, and
what can be seen in the skull of the specimen that Sues uses to
synonymize *Caenagnathus* and *Chirostenotes* (incorporating the
same topic maxilla) shows that there is an identical arrangement
of fossae and pneumatic recesses as in troodontids,
dromaeosaurids, oviraptorids, and caenagnathids, as in
therizinosaurids (well, one specific therizinosaurid); features
of the palate also indicate several features, including a
pneumatic ectopterygoid and palatine, seen in tetanurans and
coelurosaurs, and the arrangement of the palate is seen in
oviraptorids for the most part (ectopterygoid triradiate, as in
birds, lacking the lateral "jugal" process which is often a hook
in most theropods, producing an extensive subtemporal fenestra
for the mandibular adductor musculature); the anterior ramus of
postorbital is turned dorsally, which is a maniraptoran feature;
and the anterior ramus lacks a prominent rostral emargination on
the orbital rim, looking as it the bone simply "goes" up.

  Apomorphic to most theropods is the elongate vomer, but this
is ridiculous and seen in light of the theropodan features of
the skull, it is seen as an ambiguous autapomorphy of
*Erlikosaurus* until further upper cranial material is known.
And the same can be seen as true for the remainder of the
features. They outwiegh any possible significance the lack or
prescence a maxillary fenestra might have on the relationships
of *Erlikosaurus*, and this is even discounting the postcranial
features the unite *Erlikosaurus*, *Therizinosaurus*,
*Segnosaurus* (all definable on humeral, scapular, manal, or
forearm material that overlap), along with *Beipiaosaurus* and
*Alxasaurus*, more basal forms that get more and more similar to
oviraptorosaurs and dromaeosaurids as we go back in time.
*Beipiaosaurus* is a classic maniraptoran, as one can read from
my post to Marjanovic way back when.

  Hindlimb material in *Erlikosaurus* is identical to
*Segnosaurus*, *Beipiaosaurus*, and *Alxasaurus* in the degree
to which segnosaurs as a whole are concerned, as well as a hind
limb Perle refers to *Therizinosaurus,* pelvic material unites
*Segnosaurus*, *Enigmosaurus*, *Beipiaosaurus*, and
*Alxasaurus*, etc. I could go on, and on....

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail
http://personal.mail.yahoo.com/