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

Re: A critique of Lu et al.'s (2002) Oviraptorosaurs compared to birds

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:

<The only real difference here is oviraptorids being inside Aves. The
Oviraptoridae + Metornithes node is supported by premaxillary teeth
absent, prominent anterior dorsal hypapophyses and ischiopubic ratio >.66.
Adding more basal birds with premaxillary teeth (eg. Omnivoropteryx,
Protopteryx, Longipteryx, Jibeinia, yanornithids) would destroy the first

  You would need to perform the matrix with them to make this assumption
anything more than conjecture. Its an hypothesis, really. Test it.

<The third would be compromised by including Chirostenotes and Nomingia,
with short ischia.>

  Well, see there's the problem. How does one rate the ischiadic length?
The ishium of *Khaan* is relatively stright, but that in *Chirostenotes*
for instance has a distinct inflection caudally, producing both a
shallow-C in the former, and a distinct-L in the latter. The problem is,
cut the latter ischium in half and "straighten" it, and you get the same
condition, and relative shape is approximated. This implies the
oviraptorid ischium was transformed only really in "straightening" it out,
and some basal oviraptorids have a more curvy ischium to attest to this.
Means we need another meter when ischium length is estimated from a curved
element. Measuring along the posterior curve might work, but who would
try? :)


  Just to comment on the rest of the post: Bravo, but the point of this
matrix was that you never saw the actual file perform, you do not know if
"Velociraptorinae" was arbitrarily made the "outgroup" as one can do with
an explicit command in PAUP*, just that is was assigned this status,
probably after the analysis was performed. Which was, granted, done to
test only one thing and therefore didn't need a huge elaborate mechanism
and taxa: just a few birds, including many basal ones, exclude the
hodgepodge of basal "enants", add what are considered the outgroup to
birds (dromies), and add in taxa that are considerably more avian in other
respects. Hell, the avian condition of the skull is hard to get around,
I'm sure, and there are some really sweet features in oviraptorid anatomy
that only a few people know about, but lots do see the progressively more
avian-ness of many of it:

  Oviraptorids have nearly every cervical, dorsal, sacral, and proximal
half of the tail pneumatic with a large foramen. Oviraptorosaurs in
general have huge "whopping" cervicodorsal hypapophyses, but these are
linked to certain air sacs and muscles in birds, and the correlation has
been lost recently in the mess to scramble to matricizing them.
Caenagnathoids (oviraptorids and caenagnathids) have a palatal system
whereby it is depressed below the cheek and visible in lateral view; in
*Incisivosaurus*, only the pterygoid/palatine are exposed ventrally, as in
many other theropods, but further forward than others as well, and in
*Caudipteryx* the complex is crushed and open to some interpretation. The
jaw and quadrate in oviraptorids is very avian in nature, but only
excluding basal oviraptorosaurs and postulated oviraptorosaurs does this
condition correlate evolutionarily with birds; otherwise, its convergent,
and the main argument working against the paper above is the absence of
basal taxa and doing what Maryanska, Osmólska, and Wolsan did earlier this
year, and present a "genera"-level matrix with specimens and sources
listed. I'm sure the whole thing is in Lü's (don't forget the umlaut)
thesis, and I would talk to him about this in detail. The main problem is
that _Oviraptoridae_ is very avian, and adding in basal forms makes the
trajectory travel away from birds and closer to dromies and segnosaurs in
such a way that the results are simply not important, though the
hypothesis is still sound on its face. This won't die, and one requires
that some postulated basal oviraptorosaurians are not so, one reason I
think that Lü excluded *Caudipteryx* (Maryanska et al. did not, and got
similar results with a unique matrix and much, much more accurate codings
-- even though the support is low and also based on some convergence and
features not known in basal forms, or known in pliable outgroups).

  I get the odd feeling that you are disagreeing more with the hypothesis
than the data in it.


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

Do you Yahoo!?
HotJobs - Search new jobs daily now