Re: Bainoceratops & other basal neoceratopsians

["Jaime A. Headden" <qilongia@yahoo.com>]

George Olshevsky (Dinogeorge@aol.com) wrote:

<Someone else said Chaoyangsaurus (it's easy to check spelling if you're
in  doubt; just go to my Dinosaur Genera List and click on C) had a "jugal
thingie," which I believe is better known as a "jugal boss" (and I should
have called it that originally in this thread). As with so many
morphological minifeatures, we have no idea whether this is a true
synapomorphy or some kind of homoplasy; we just plug it into our PAUP
programs and let them chug away.>

  The use of "jugal thingie" is a joke and not intended to be
nomenclature. However, *Chaoyangsaurus* lacks any form of process, knob,
flang, or otherwise and bears reather a broadened, rounded jugal arch.
This expansion of the jugal laterally is rather a second feature in common
among Ceratopsia and is likely a character apart from the actuall "boss"
or "ridge" or "horn" as occurs in other taxa. In *Heterodontosaurus*, as
in *Goyocephale*, *Orodromeus*, and *Zephyrosaurus*, the jugal is not so
laterally expanded, but has a lateral flange that, as Pete Buchholz
described, looks like an altoid stuck on the side, projecting posteriorly
only. In psittacosaurids, the jugal horn is accented by a vertical ridge
and projects ventrally, as it does in *Protoceratops*; in ceratopsids, it
projects caudally. In leptoceratopsids (Makovicky coined the name with an
"s", however one would wish to see otherwise), the jugal is a caudal
flange that lacks a ridge on the dorsal and lateral surface, but this
ridge is also lacking in *Liaoceratops* and thus may be convergent in
psittacosaurids and higher coronosaurians. The lateral jugal is expanded
into a caudal "horn" in both *Bagaceratops* and *Liaoceratops*, ending in
a distinct triangular structure, as in *Archaeoceratops*, whereas in
*Liaoceratops* and *Chaoyangsaurus*, the jugal has a longitudinally
horizontal acme laterally divides the lateral jugal into a dorsolateral
and ventralateral pair of faces. Yet the horn, or any knob, or prominence,
is lacking in *Chaoyangsaurus* as present in any ceratopsian. In
pachycephalosaurs, there are lateral jugal ossifications or nodes, and
these "epijugals" are convergent in ceratopsians as well. Only
*Goyocephale* among known pachycephalosaurs that preserve the bone show
any ridge or process on the lateral jugal that is not a node, and this is
a reduced version of what is seen in *Orodromeus*, *Heterodontosaurus*, or
so forth. Because of this, no jugal feature appears to really link
*Heterodontosaurus* to Marginocephalia. However, Ceratopsia can be (and
has been) diagnosed [in part] by the lateral expansion of the jugal into a
jugal arch; a smaller group, higher than *Chaoyangsaurus* if it is basal
to node based Ceratopsia = {Psittacosauridae + Neoceratopsia} , can be
partly diagnosed by the triangular ventral or dorsal aspect of the jugal.
However, *Chaoyangsaurus* may be a basal psittacosaurid, as suggested by
Zhao et al., 1999, and there are ample reasons to suggest that if this is
so, then psittacosaurids are VERY convergent with Neoceratopsia; these may
be based on plesiomoprhiues retained by *Chaoyangsaurus*, or questionable
given the possibly juvenile nature of the animal (very large orbit, short
facial region even breifer in length to skull length than in any adult
*Psittacosaurus* species, and very distinct, partially open neurocentral
sutures with open scapulocoracoid contact, very few and relativelty large
teeth).

  Hence the reason for not wanting to declare a monophyly or paraphyly
based on a questionable relationship of ill-defined features. The presence
of a lateral jugal ornament or projection hardly defines a clade in
Cerapoda, and nor should it. The multitude preserves more detail, and when
all things general add up to something similar, as Holtz has shown among
Coelurosauria analyses, something is ringing true.

  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.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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