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Re: Megalosaurids




"T. Michael Keesey" wrote:
 
> Thanks for the PDW summary! I just wanted to clarify one point.

> --- Sean Carroll <sean@kua.net> wrote:
> > He first set up the 'Intertheropoda', a group intermediate between the
> > Ceratosauria and the 'Avetheropoda' (roughly equivalent to the
> > Tetanurae).

> _Avetheropoda_ is not equivalent to _Tetanurae_; it is equivalent to
> _Neotetanurae_. _Tetanurae_ is a broader stem-based clade descending from the
> first ancestor of modern birds which was not also an ancestor of
> _Ceratosaurus_; it includes _Megalosaurus_, _Spinosauridae_, etc. while
> _Avetheropoda/Neotetanurae_ does not. Holtz 1994 used Paul's _Avetheropoda_ 
> for
> Clade(_Allosaurus_ + modern birds). In his phylogeny it had the same content 
> as
> Paul's taxon, but a different internal topology. Sereno et al. 1994 (which I
> believe was just barely published earlier) used _Neotetanurae_ for the exact
> same clade. Which term you use depends on whether you want to follow seniority
> of nomination or of phylogenetic definition.

Ah, thanks for pointing that out. The reason I conflated Avetheropoda
with the Tetanurae is because in Paul's own footnote in PDW, he mentions
that he was trying to figure out a term for 'advanced theropods of this
general mold', and he says that he decided to come up with his own name,
Avetheropoda, because Gauthier had named Tetanurae and Bakker had named
Dinoaves, and it wasn't clear which had priority. Either Paul was simply
mistaken as to the exact definition of Tetanurae, or the definition has
evolved since 1988, or Paul simply did not care since he was not writing
a cladogram, but merely creating grade-based general Linnaean categories
for the major groups of theropods. Perhaps he simply figured it was good
enough to point out, 'There is one group that is very birdlike, and
includes everything from _Compsognathus longipes_ on up to the
Neornithes, and another group that's more primitive, from
_Procompsognathus triassicus_ through the ceratosaurids, and then the
rest of these guys sort of in between.' Perhaps he simply didn't care
whether the 'intertheropods' were grouped with the 'avetheropods' or
'neotetanurines' in something called the Tetanurae, or with the
ceratosaurs in his own Paleotheropoda, since he wasn't trying to make
the groups monophyletic anyway, just to provide a general impression of
progression from basal to intermediate to derived theropods.

Also, in 1988 most of the popular dinosaur books were still using the
old 'Coelurosaurs are the little ones, Carnosaurs are the big ones, and
sometimes the Deinonychosaurs/Ornithomimosaurs/Oviraptorosaurs are
placed in their own mid-size group' system. (Even as late as 1990, such
a comprehensive source as the _Dinosaur Data Book_ from David
Lambert/The Diagram Group didn't mention any other way of classifying
theropods besides the coelurosaur/carnosaur dichotomy, though they did
reprint Paul Sereno's then-new cladogram of the Ornithischia as an
alternative to the old 'six suborders' system. I'm not sure why they did
this for the ornithischians but not the theropods, sauropodomorphs, or
herrerasaurs.) So I think he can be forgiven for not going to great
lengths to keep 'Neotetanurae' separate from 'Tetanurae', since the most
important thing in his mind at the time seems to have been (at least,
this is my impression) to show a popular audience that the old
size-based system is completely obsolete and now there is a new view
that shows a gradual evolution from _Procompsognathus_ up to birds with
a lot of side branches.

-- 
--Sean
http://www.livejournal.com/users/spclsd223/