Re: Broader than Dinosauria

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Kinman (kinman@hotmail.com) wrote:

<However, I do believe that a combination of a few (maybe 3 or 4) of the most 
significant
"synapomorphies" could be combined to make a good case for dinosaur holophyly.  
What I don't like
is a long list which throws the more significant ones in among a bunch of 
questionable ones.>

  But on what basis do you question the significance of certain aopmorphies to 
be synapomorphic of
Dinosauria? And what apomorphies do you consider to be less significant?

<But I rejected the "fully open acetabulum" from my list back in 2000 (and Tom 
Holtz agreed that
it probably developed at least three times among dinosaurs), and to me it is 
still (dare I say
it?) "weak", and it detracts from more "significant" characters. I would like 
to have a highly
significant skull character as well, but "vomeral extension" sounds rather 
nebulous (although if
it could be quantified, perhaps it could be shown to be significant).>

  I think that of what Tom said, it was probable for the open acetabulum 
developing more than
three times, as it was the development of three, two, one, or fifteen times. 
However, parsimony of
the data indicates this is not so. However, the open acetabulum is an 
unquantified character, so
let me narrow the concept for interpretation.

  In *Lagerpeton*, the acetabulum is completely closed.

  In *Marasuchus* and *Lewisuchus* and, I believe, *Psuedolagosuchus*, there is 
a triangular apse
between ischium and pubis, with a level ventral margin of the intra-acetabular 
portion of the
ilium. This is a "partially open acetabulum" as not all elements appear to be 
"regressing" from
the apse.

  In *Pisanosaurus*, *Staurikosaurus*, *Camposaurus*, and *Herrerasaurus*, the 
ischiadic margin of
the apse has regressed somewhat, and the pubic margin nearly complete pulled 
back, while the iliac
margin is ventrally concave, forming a very wide and effective "fully open 
acetabulum". The
femoral head can now fully penetrate and be stradded upon by the supracetabular 
iliac crest
[horizontal].

  In basal ornithischians and all theropods and sauropodomorphs, all margins 
except for a remnant
of the pubic rim are contracted to the pedicles of the pelvic bones and do not 
enclose the
acetabulum.

  In stegosaurs, the ischium has a flange (present in ornithischians to some 
degree or another
rather prevalently) the extends from the medial margin and rises up to form a 
medial
antitrochanter; this is present to the derived degree only in stegosaurs, where 
is progresses the
distance of the former ischiadic extent. However, in the most basal stegosaurs, 
this is reduced
relative to, say, *Stegosaurus* or *Lexovisaurus*: the condition is derived, 
and further derived
in later stegosaurs, and likely represents an apomorphy rather than a reversal 
(function indicates
use as a locomotor process, and while I suppose this could be a reversal, I do 
not consider it
likely).

  In ankylosaurs, as George Olshevsky and Ken Carpenter (not together, the 
latter published to
some degree on this; Tree of Life webpage, anyway, and an abstract) the 
acetabulum iscomprised of
mostly the iliac surface, wheres the pubis has atrophied to the point that it 
has largely become
medially positioned and no longer forms most of the cranial margin of th 
socket, the ilium does.
This is an apomorphy of Ankylosauria, as the condition is unique to _any_ 
terrestrial or aerial
vertebrates. It has been noted in the past, especially by Pete Buchholz, that 
basal ankylosaurs,
including *Mnimi* with a partially open acetabulum and elongated pubis with a 
post pubic shaft,
and by Carpenter online, that *Scelidosaurus* (George adds *Scutellosaurus*) 
are purportedly basal
ankylosaurs ... both have a completely open acetabulum, as in the basal 
ornithischian condition.

  All other ornithischians and theropods have open acetabula. It should be 
noted that if
considering cartilage, the acetabulum in juvenile birds is closed, whereas the 
cartilage is
resorbed in ontogeny. I personally see this in chickens.

<One correction. I did not include Lagerpetonidae, Lagosuchidae, or Plesion 
Pseudolagosuchus in
the Theropoda, but rather as basal clades of Saurischiformes. I think it may be 
George who regards
lagosuchids as early theropods>

  Correction noted. However, I believe Paul (1988) mentioned lagosuchids and so 
forth as basal
dinosaurs exclusively. He called the group Paleodinosauria. I posted on his 
alternative
classification scheme a few months back. It is also unique to place them within 
Saurisachia [or
-formes as you prefer], as this defies their basal and "primitive" or 
plesiomorphic nature, and
the abscence of either saurischian or dinosaurian [read, features in common 
with *Eoraptor*,
*Herrerasaurus*, *Pisanosaurus*, *Lesothosaurus*, *Saturnalia*, etc., being key 
taxa to look at
dinosaurian monophyly].

<(but I will need more convincing if I am to do this in my classification). I 
am open to the idea,
but presently that's as far as it goes (and the same applies to the position of 
Pisanosauridae
among ornithischians).>

  Why do you worry about the ornithischian nature of *Pisanosaurus*?

  To formally present an alternative scheme, one must contradict the standing 
schemata, plus
present reasons _for_ your own. You have yet to do this. In the present scheme, 
it is a matter of
apomorphies, which *Pisanosaurus* does posses with regards to Ornithischia, 
especaly in the form
of the dentary (enlarged and elevated, laterally offset coronoid process).

  But that's mainly my comments on the acetabulum issue, which benefits from 
conversations with
Pete Buchholz, so dude, take a bow.


> ********************************************
> >From: "Jaime A. Headden" <qilongia@yahoo.com>
> >To: dinosaur@usc.edu
> >CC: kinman@hotmail.com
> >Subject: Broader than Dinosauria
> >Date: Fri, 7 Sep 2001 21:16:55 -0700 (PDT)
> >
> >   It is just not a matter of the monophyly of Dinosauria that must be 
> >questioned here, and though
> >I know that Kinman has included them in Theropoda, the synapomorphies for 
> >the more inclusive
> >groups to Dinosauria must also be considered. That is, what puts 
> >*Marasuchus*, *Lagerpeton*,
> >*Pseudolagosuchus*, *Lagosuchus*, and *Lewisuchus* closer to dinosaurs than 
> >to crocodiles. This
> >means the synapomorphies of Dinosauromorpha and Dinosauriformes must also 
> >be considered along with
> >those of Dinosauria.
> >
> >   For one thing, a fully perforate acetabulum is present in all except 
> >*Lagerpeton*, and
> >*Lewisuchus* et al. have the distinct deltopectoral crest, and all have a 
> >tall ascending process
> >of the astagalus, though *Lagerpeton* [odd name, "crawling bunny" :) ] has 
> >a distinct morphology
> >that is perhaps not analogous, though homologous, I would code it absent on 
> >this mark. Other
> >features, including vomeral extension, are unknown. *Lewisuchus* lacks the 
> >apparent postemporal
> >fenestra, and no dinosaur except for maybe the well-nested and therefore 
> >irrelevant theropod
> >*Scipionyx* have a postfrontal bone [see DalSasso and Signore, 1996; 
> >Mortimer, pers. comm., 2001,
> >though I doubt the identification.] All possess a distinct femoral head, 
> >but this _is_ an
> >adaptation to the position of the femur in a subvertical posture, as is the 
> >"twisted" humeral
> >shaft to aligning the distal condyles parallel to the humeral head for most 
> >quadrupedal dinosaurs.
> >I would not use this as an synautapomorphy based on it's functional aspect, 
> >but it _is_ still a
> >feature not prezent in the immediate outgroups to the included paradigm, 
> >and thus such a feature
> >becomes a diagnostic synapomorphy. Note: just because a group may reverse a 
> >character state or
> >present an apomorphy that does not preserve the "original" synapomorphy, 
> >does not mean that the
> >feature is no longer diagnostic for a group. Thus, it is singularly notable 
> >that there is in fact
> >not one apparent synapomorphy present in all Dinosauria exclusive of it's 
> >outgroups, or of
> >Dinosauromorpha, or Dinosauriformes. In this, Tracy is right and 
> >commendably so. It is not
> >relevant for the reasons given above, addressed both to Tracy and to Ken.
> >
> >   Thanks for the air time...
> >
> >
> >=====
> >Jaime A. Headden
> >
> >   Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
> >   Where the Wind Comes Sweeping Down the Pampas!!!!
> >
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=====
Jaime A. Headden

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

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