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Re: Nanningosaurus (was Re: Planet of the New Papers)



On 9/1/07, Michael Mortimer wrote:
> Tim Williams wrote-
>
> >(1) WRT your tree, it shows _Gyposaurus_ and _Aralosaurus_ as consecutive
> >outgroups.  This implies that traditional Hadrosaurinae is paraphyletic.
> >I'm not sure of the current definitions of Hadrosaurinae or Lambeosaurinae,
> >although Sereno's (1998) stem-based definitions use _Saurolophus_ and
> >_Parasaurolophus_ as mutually exclusive specifiers.  (Incidentally,
> >TaxonSearch revises these definitions, with the intention of including the
> >name-giving genera as additional specifiers; but the exact definitions are
> >addled with regard to content.)
> >
> >(2) What happens when _Pararhabdodon_ is included?
>
> As Nick is slow to respond...
>
> I'm not sure about Pararhabdodon, but Aralosaurus was recently reidentified
> as a lambeosaurine (Godefroit et al., 2004), so Nick's tree doesn't imply a
> paraphyletic Hadrosaurinae.
>
> Godefroit, P., Alifanov, V., and Bolotsky, Y. (2004). A re-appraisal of
> Aralosaurus tuberiferus (Dinosauria, Hadrosauridae) from the Late Cretaceous
> of Kazakhstan. Bulletin de l`Institut Royal des Sciences Naturelles de
> Belgique, Sciences de la Terre 74 (Supplement): 139-154.
>
> Mickey Mortimer
>
>
>

Inclusion of Pararhabdodon recovers the following:

50% majority rule of 54 MPTs, 122 steps, CI 0.828, RI 0.874

Same as the previous topology with Pararhabdodon in a polytomy with
Amurosaurus and the clade in which "corythosaurinids", and
"parasaurolophinids" are closer to each other than either of the other
two taxa.

Pararhabdodon is:
- Closer to Gryposaurus and other hadrosaurids on the basis of having
eight sacral vertebrae present (69.1) and a deltopectoral crest that
extends to at least the midshaft or longer (76.1).
- Closer to Nanningosaurus and other lambeosaurines on the basis of
mediolaterally flared distal humeral condyles (78.1) and a pendent
ischial foot (89.1).
- Closer to other lambeosaurines than Jaxartosaurus on the basis of
humerus deltopectoral crest angular and enlarged (77.1).

Oddly, enough, Evans and Reisz scored all of these as unknown in
Amurosaurus, when a complete humerus is in fact known for at least
that taxon (Godefroit et al., 2004). I'm not sure what criteria are
supposed to define mediolateral flaring of the distal humeral
condyles, however, Mo et al. regarded those of Nanningosaurus as
having the condition, while from their figures, they don't seem any
more expanded than say those of "corythosaurinids" which were scored
by Evans and Reisz as not being expanded (which from what figures I've
been able to see, I'd agree). Very odd, isn't it? Clearly a conflict
of definition exists between these authors. But the condyles of
Pararhabdodon are certainly more expanded than those in Amurosaurus,
Nanningosaurus, or Probactrosaurus (oddly, enough Bactrosaurus seems
to have very expanded condyles- refer to Godefroit et al., 1998), but
not as expanded as those in say, Parasaurolophus. Scoring
Pararhabdodon and Nanningosaurus as "0" does not change their
position. It'd be interesting to see if further re-examination of the
character states assigned to Amurosaurus conflicted with the
redescription by Godefroit et al.

For those who were interested, constraining Pararhabdodon outside of
the Hadrosauridae only requires two more steps (122) from the
unconstrained tree (124).

Nick Gardner