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Re: SVP Preview



Nick Longrich (longrich@alumni.princeton.edu) writes:

<Yangchuanosaurs apparently had a fully enclosed pubic obturator fenestra,
a fourth metacarpal, a low, massive astragalar ascending process which is
more reminiscent of _Torvosaurus_ than _Allosaurus_, and caudal
hyposphene-hypantra articulations.>

  Most of these can be considered symplesiomoprhic of avetheropods, as
they are present in some coelurosaurs. Their loss in Allosauridae (Allo
and Acro) is unique, with some questionable referrences. The leading
expert on Allosaurus, Dan Chure, has helped described with Octavio Mateus
a skeleton of Allosaurus from Portugal with an enclose obturator fenestra.
A fourth metacarpal is present in *Coelurus* (referred); short astragalar
processes yes, but coupled with deep fossae, pneumatic foramina, deep
grooves, that are synapomoprhic of allosaurs. I think that how easy it is
to confuse symnplesiomorphies with non-autapomorphic support has led to
several similar considerations in relationships as in "prosauropod,"
megalosaur, and maniraptoran phylogeny, as well as ceratopsians, and
perhaps the biggest kicker, ornithopods. I mean, one of them,
*Heterodontosaurus*, has been linked to ornithopods but a very distinct
feature, premaxilla contacts lachrymal above maxilla.

  Incidentally, Allain proposed *metriacanthosaurus* may be a megalosaur,
which would sort of contradict relation to sinraptorids. I do not think
there is anything to "magic characters" which supercede any others if
present, like tarsal-mtI contact, mt V phalanges, which actually vary in
the taxa that are somehow supported by them and in outgroups (for example,
some "prosauropods" have em, some don't, but *Herrerasaurus* also has
them, suggesting they are symplesiomorphic to dinosaurs).

  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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