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Re: dinosaur synapomorphies?



Ken Kinman (kinman@hotmail.com) wrote:

<It amazes me that so many people now take the holophyly of Dinosauria for 
granted.>

  I amazes me that the assumption is that it should be challenged. No one 
assumes its true... just
that there is no pertinent contradictiung hypothesis that can muster greater 
evidence in favor of
it and to refute the monophyletic Dinosauria hypothesis. Until then, 
challengers have a great deal
to fight against.

<Many of the purported synapomorphies are very weak, and many remind me of the 
"kitchen list" of
synapomorphies that was proposed for Ornithodira (sensu stricto).>

  Heh, well, a synapomorphy is a synapomorphy... there's no such thing as a 
"what I feel is right"
synapomorphy or a "I don't like that one, it's not a" synapomorphy...

<Sereno himself points out that some of these synapomorphies are not present in 
Sauropods or other
groups of dinosaurs. And many of these synapomorphies involved the pelvis and 
hind legs, and being
interconnected changes in the evolution of an "abductor-based balancing 
system", they could have
happened more than once (just like the development of the perforate 
acetabulum).>

  Right. Pick a taxon that might refute the hip synapomorphies of Dinosauria, 
then we'll talk. So
far, not even pterosaurs possess the same synapomoprhies, as they 1) lack an 
upright femur; 2)
they bear derived phalanges on pedal digit 5; 3) the first toe is weight 
bearing; 4) the
acetabular is closed 5) the hip configuration is basal to the Archosauria or 
Archosauriform
paradigma, especially that of crocs and dinosaurs (they bear a dead-on 
resemblance to
prolacertiform pelves in shape and arrangement); 5) the femoral head is 
[sub]spherical; 6) there
is no flange-like anterior trochanter; 7) the acetabulum faces laterally or 
mostly dorsally. The
hip arrangement is not similar. One sees the hips of crocs and rauisuchians 
(basal crocodyliforms)
as more similar on the basis of the restriction of the participation of the 
pubis in the
acetabular rim, the closed off acetabulum, the [sub]spherical femoral head and 
strongly elevated
and constricted femoral neck, the shallow and marginal expression of the 
trochanters, including
lacking a flange-like anterior trochanter ... these features indicate that the 
femoral and pelvic
synapomorphies of *Marasuchus*, *Lewisuchus*, *Pseudolagosuchus*, *Eoraptor*, 
*Herrerasaurus*,
*Guaibasaurus*, *Saturnalia*, *Procompsognathus*, *Thecodontosaurus*, 
*Pisanosaurus*, and
*Lesothosaurus* etc... all form a unity exclusive of crocs & allies, and 
pterosaurs & allies,
*Euparkeria*, *Archosarus*, proterosuchians, and so forth. Thus, they are 1) 
archosauriforms,
which pterosaurs are not apparently, 2) they are archosaurs, which *Euparkeria* 
is not, 3) they
are ornithosuchians, which crocs are not, 4) "Ornithodira" is synonymous with 
Archosauromorpha, as
is "Ornithotarsi", but I think the name should be defined to form an exclusive 
clade of
pterosaurs, dinosaurs, but not crocs, prolacertiforms, etc., so the name can be 
considered viable
in any case (but still dead).

  On elast thing, the absence of three characters in Sauropoda is a very good 
thign as that taxon
is diagnosed by an additional 3 synapomorphies (reversals), whereas there are 
about 8-12
"prosauropods" arrayed before the plateosaur--sauropod split. My personal 
observation suggests to
me that the only monophyletic groups in "Prosauropoda" are a Melanorosauridae 
(incl.
*Blikanasaurus*), and a Plateosauridae (*Plateosaurus*, *Lufengosaurus*, 
*Ruehleia*, etc.), and
that one of these groups may be the sister group to Sauropoda, but also perhaps 
a monophyletic
Yunnanosauridae including *Massospondylus*. All other taxa appear to be arrayed 
more basal to
Sauropoda. The cases made by Galton and Crompton on the matter of 
Melanorosaurids being "too
derived" to be sauropod ancestors is irrelevant, and until Britton's analysis 
is published, it is
untested in a data matrix or anything as rigorous as.

  So unless you can find support to suggest that all 17 of those synapomorphies 
Sereno has are
"weak" beyond a general feeling, this would be a good dead horse to leave alone 
... at least for
now. My opinion anyway...


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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