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True Semilunates



Ken Kinman (kinman@hotmail.com) wrote:

  [...]

  A true semilunate is not the full and complete morphology of the fused
distal carpals 1 + 2, it is merely the shape of the carpals themselves.
The condition of fusion, shape and expression of the trochlea, and extent
of the carpals over the first two metacarpals. A seventh feature, the
prescence of a flange on the proximomedial edge of the first metacarpal,
has a similar distribution in theropods as does the fully semilunate
apsect of the coossified distal carpals 1 + 2. I ran the previous matrix
through PAUP (Phylogenetic Analysis Using Parsimony, version 4.0b8a,
Sinauer Assoc.) and arrived at a tree that had only two real beleiveable
consensus in relationship of the distribution. It clear does not allow a
true phylogenetic information to be derived from the carpals alone.

  *Mononykus*, euornithines, *Avimimus*, and *Confuciusornis* form the
core group closest to neornithines (obviously). Distribution between right
and left wrists have not been researched. Outside the above grouping,
*Oviraptor,* *Archaeopteryx,* and *Velociraptor* (not *Deinonychus*,
Mickey ... I chose to use a more distinct wrist in comparison, but it is
true, that velociraptorine has a less avian distal carpal block than does
the Asian taxon, however, coding for Deinonychus places it) group in a
polytomy with the more "avian" group, *Coelurus* lies outside that, and
then all other taxa are in a polytomy. One other association is allowed,
*Allosaurus* + *Acrocanthosaurus*, but this appears in only half of the
trees.

  The addition of several taxa (*Pelecanimimus,* *Ingenia,* *Deinonychus,*
*Alxasaurus,* *Beipiaosaurus,* and *Caudipteryx*) resolves some positions,
and rooting on *Herrerasaurus* produced the following tree:

--+--Herrerasaurus
  `--+--Coelophysis
     |--Ceratosaurus
     |--+--Pelecanimimus
     |  `--Gallimimus
     `--+--Allosaurus
        |--Acrocanthosaurus
        `--+--Caudipteryx
           `--+--Tyrannosaurus
              |--+--Therizinosaurus
              |  |--Beipiaosaurus
              |  `--Alxasaurus
              `--+--Coelurus
                 `--+--+--Ingenia
                    |  |--Oviraptor
                    |  |--Deinonychus
                    |  |--Velociraptor
                    |  `--Archaeopteryx
                    `--+--Avimimus
                       |--Mononykus
                       |--Confuciusornis
                       `--Euornithes

  It is may become clear that the distribution of features do not in any
way resolve relationships among bird-like theropods; *Caudipteryx,* ID'd
as key to avian evolution, is apparently more primitive than even
*Tyrannosaurus.( In some trees, Acro and Allo are sister groups, and in
others, *Tyrannosaurus* is the sister group to Segnosauria, which is
outside Maniraptoriformes. In few trees does *Caudipteryx* group closer to
birds than ornithomimes or tyrannosaurs. This is indicative of the
non-viability of carpal morphology alone to identify avian relationships.

  Secondly, I'd like to ask why Maniraptora is a bad clade to apply "bird"
to if you're so inclined to attach the vernacular to that particular node.
While I note Ken disagrees with the application of the etymology because
birds do not grasp prey with their manus (having been modified from the
original "snatching" manus a few nodes down the road). Evolution happens
and if a taxon developes a snatching manus into a fused flight structure
no longer capable of "snatching", this no more invalidates its ancestry
than whales were to develop from terrestrial ungulates, from animals like
the Carnivora only with hooves.... Evolution happens, it does not suddenly
become inappropriate ... whales don't have hooves, but they are ungulates.

=====
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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