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

Re: Allosaur cladogram (erratum)

I had written:

  "Garrido and Coria" ... in reference to work on *Giganotosaurus*'
braincase. The actual citation is Coria and Currie, 2003 (JVP 22(4):
802-811 [published 1/14/2003]). Similarly, the study did not indicate the
condition in *Allosaurus*, and the condition of the braincase in
*Acrocanthosaurus* is shown to be unique to itself (OMNH 10146, type)
given the nearly flat parietal table and sharp angle between the
parietofrontal plane and the nuchal/basituberal plane, whereas in other
carnosaurs it is either 90 degrees or higher. This may be the result of
deformation of the relatively isolated braincase, partial taphonomic
distortion, but is not guaranteed. The angle in *Allosaurus*, using
Madsen, 1976, is close to the condition seen in *Sinraptor*, with greater
pneumatization and robust basitubera, as in *Acrocanthosaurus*, and
without the massively spherical form of the occipital condyle as in
*Giganotosaurus* or *Carcharodontosaurus*. As in *Allosaurus*,
*Sinraptor*, and *Yangchuanosaurus*, the condyle is not as spherical but
more lenticular (kidney-bean- or lens-shaped). It appears to be generally
plesiomorphous without the Gigi+Carch features, but that has been the
conclusion of most of the analyses to include both taxa. Unlike
*Allosaurus* and *Sinraptor*/*Yangchuanosaurus*, the postorbital bears a
supraorbital ossification or elaboration that contacts the lachrymal and
bridges the dorsal gap above the orbit; this is nearly the condition in
sinraptorids, but is absent in *Allosaurus*, as well as other basal
tetanurans; unlike *Carcharodontosaurus*, the nasal is smooth with
laterally prominent paired ridges, as in *Allosaurus* and sinraptorids.
*Acrocanthosaurus* lacks the parietal lateral expansions of the nuchal
region that overhang the supratemporal fossae as in *Giganotosaurus* and
to a limited degree in *Carcharodontosaurus*.

  *Acrocanthosaurus* appearsd to bear a great deal of general
plesiomorphies in relation to other allosauroids which it shares with
sinraptorids, and may therefore represent a stem taxon of the basic
*Allosaurus*+*Carcharodontosaurus* clade.

  One consistent measure in all allosaur/carnosaur trees is that
*Giganotosaurus* and *Carcharodontosaurus* are sister taxa, except for the
original analyses that selected abelisaurid-like features. These are known
in renowned allosauroids sensu Sereno et Holtz, and can be dismissed
generally as convergent plesiomorphies of allosauroids. *Fukuiraptor* has
some qualities of the anatomy that leads one to suspect it is also a basal
allosauroid, but appears basal to the
sinraptorid/carcharodontosaurid/allosaurid arrangement. *Saurophaganax*,
as per Chure, is a large allosaurid possibly the sister taxon to
*Allosaurus* itself, based on shear similarity in the postcrania. other
allosauroids are speculative, refer to a megalosaur or spinosauroid
morphology, are more basal, or are basal coelurosaurs. Holtz finds both a
basal coelurosaur in *Gasosaurus* (more recent) and as a basal carnosaur
(less recent, re 2000), so this is less than universal, and *Gasosaurus*
lacks a skull and caudal vertebrae to which one can really identify
typical allosauroid characters. It may also be a basal tetanuran, a
neotetanuran of "spinosauroid" grade perhaps. It will be interesting to
plug it into Allain & Chure's analyses, once they are elucidative in the
postcranial work.

  Anyways, this is my errata ... a full-scale analysis is, of course, way
beyond my means at this point and what I've seen so far just gives me an
insight into the lack of resolution of non-coelurosaurian tetanurans. In
other words, ditto to Holtz.

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)

Do you Yahoo!?
SBC Yahoo! DSL - Now only $29.95 per month!