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You Can't Nitpick a Carnosaur
Appologies to David and Ken, whose statements I cut out. I
thought it might be easier to state mine this way. Please note I
have taken them in account.
First off, Ken is right, historically Carnosauria is such a
wastebasket that, until 1994, it should have been removed from
the taxonomy of dinosaurian usage. Since v.Huene, 1903-4, this
term has included pretty much one diagnostic feature (large
size) and accessory features found to be size related, including
robusticity of the limbs and vertebrae. Holtz, 1994, sat down
and pared the parts of "Carnosauria" apart, removed taxa more
primitive (*Megalosaurus,* *Torvosaurus*) or closer to birds
(tyrannosaurus [the big step], spinosaurs, therizinosauroids
[including segnosaurids], and *Dryptosaurus*) .. all of the
latter set of which are coelurosaurs. Before then, the biggest
coelurosaur known was *Gallimimus,* and even *Deinocheirus,*
thanks in part to Barsbold, 1983, was considered a carnosaur
until its affinities with ornithomimosaurs were recognized. This
left Allosauridae. Holtz realized that on a node-stem set-up,
some taxa came out closer to allosaurids than to birds, or
megalosaurs, or whatnot other things: *Monolophosaurus,*
*Cryolophosaurus,* etc., that were not essentially allosaurids,
and that these could in essense define the parameters of
Carnosauria, so that it was still, in fact, a useful taxon.
Allosauroidea was set up as the strict group that was defined as
the most recent common ancestor of *Sinraptor* and *Allosaurus*
(Sereno et al., 1996), and post-dates Holtz' definition of the
Carnosauria, so they are neither the same taxon by content or
definition. Similarly, he also set up some definitive diagnostic
features of the Carnosauria, and Sereno et al. did similarly for
the Allosauroidea. There is no such thing as an "Allosauria" and
probably should never be.
While the genus *Megalosaurus* remains a wastebasket until
some of these species are described, and a strict analysis of
the *M. bucklandii* and *Poekilopleuran* material can assess
their synonymy, *Megalosaurus* can be inferred to include only
the valid species *M. bucklandii* which can be separated from
most other taxa, including *Torvosaurus* (Britt, 1993), and has
less avian characteristics than that taxon, in agreement with
Holtz (1995, 1996), so that it is probably more basal than
Avetheropoda (Carnosauria + Coelurosauria) while torvosaurs
group with coelurosaurian spinosaurs (Spinosauroidea, replacing
the first name Torvosauroidea) (Sereno et al., 1994, 1996, 1998;
Sereno, 1999, 2000). Some species of *Megalosaurus* are
receiving a lot of attention, so stay tuned to the lit in the
next few years, as this genus is probably going to get a lot
My point: Carnosauria as a historic taxon has been replaced,
as is often preferred by a name, by a definition that gives it a
strict meaning anchored on *Allosaurus*: as a consequence, it is
a very robust and repeatedly tested taxon that now includes
several small to large forms, with an evolutionary history
spanning the Early Jurassic to the early Late Cretaceous. Size
is no longer a factor in phylogeny....
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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