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Re: Variation in Caudipteryx



Daniel Bensen (dbensen@bowdoin.edu) wrote:

<There are now several good skeletal reconstructions of Caudipteryx
floating around out there, and they seem to fall into two camps.  One (HP
Jaime Headden's original skeletal reconstruction) depicts an animal with a
rounded skull that abruptly tapers to a short snout.  The others depict a
more generally triangular skull, where the cranium bulge is less
pronounced, and tapers smoothly into a long snout.>

  Since my reconstructions have been queried, I would like to clarify my
reasons for separating the skulls. It has a lost to do with general
relations of bones and a little gross morphology, but the lower jaws
differ more between the type and paratype skulls and those described in
2001 by Zhou et al. The reason the snout is slender in the restored
paratype skull I have drawn is largely superficial in making
slender-snouted predators sensu Greg Paul, with some idea that the nasals
had a slight curve in them to permit this. Greg Paul's restoration of the
skeleton of *Caudipteryx* appears in his edition of the _Scientific
American Book of Dinosaurs_ (I don't have it on me, so I can't get the
page number) and includes a shallow snouted animal based on the original
two specimens, previous to the discovery of *C. dongi* (headless). This
skull is shallow snouted, not so much as mine, and is essentially what I
agree as being more likely to be true. He, however, restores the palate in
a distended fashion based on (re: _Dinosaurs of the Air_) a reconstruction
by Nick Longrich, and I so far have seen no evidence of this;
*Incisivosaurus* has similar palatal bones where those of *Caudipteryx*
can be reasonably identifies, and that taxon does not have a distended
palate, though in the latter it may still be possible [just not likely, in
my opinion]. The new skulls, especially BMP 0001 (referred to *C. zoui*),
are much more robust in appearance and have a massive premaxilla with
smaller teeth, and a larger maxilla, resulting in a deeper, longer snout.
I am faithful to the skull in attempting to reproduce this in my
"portrait", and the skull should be available very soon on my own website.
I will also explain my reasons for species separation and conflation in
more detail there, re:

<However, Jaime Headden's comment in his Dinosauricon implies there are at
least two varieties of Caudipteryx skull shape. I smell something like the
Oviraptor/Citipati/Rinchenia mess going on, and I'd like some
clarification.>

  Mickey notes many individual variations and preservation regimes among
the skulls, which is expected and occurs among *Allosaurus* as well. And
this is one species complex, no skull is like any other that I have so far
seen, including shapes of premaxillae, dentaries, maxillae and the rostral
lobe of the maxilla, lachrymal horns and the lachrymal/maxillary
suprantorbital bar, the postorbital, variation in jugal expression on the
antorbital fossa, and braincase pneumatization, which seem to have been
ignored in favor of generalizations that don't exist. One is likely to see
the same variation in *Coelophysis* in relative bone size and shape among
same-age individuals, or among genders, or among age-classes, as one sees
in various centrosaurines like *Pachyrhinosaurus*, *Einiosaurus*, a new
Oldman Formation centrosaurine with only knobby ornamentation (SVP '99),
and *Centrosaurus*. We have plenty of skulls of *Iguanodon
bernissartensis* from which to test this, as well as work Galton has done
and is doing on *Plateosaurus*. Gracile vs. robust morphs are also a
problem and have plagued systematics for centuries, and only recently (on
a systematic slide-rule, a few decades ago) have taxa been shown to
possibly include two different, possibly sexual morphs, especially among
coelophysids. How one can use robusticity or shape indicators to define a
species anymore is beyond me, without any real proof of taxonomic
information in this.

  Gripe over.

  *Caudipteryx* just appears to represent some possible dimorphism, as in
birds, and *C. dongi* could be real. The jaws vary more so than the rest
of the skull, and the rostral snout bones vary almost as much. As for
doming of the skull, no frontals available in side view means it's largely
a matter of taste how far one domes the skull.

  Cheers,

=====
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.

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