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Andrew McDonald response re: European iguanodonts



Below is Andrew McDonald's response to Greg Paul's posting concerning
Dollodon. McDonald (not a DML subscriber) asked me to post this.

Please note that I am agnostic on this issue, and an interested in seeing
how this plays out. I think the most significant point here is that Greg
Paul certainly got the field pointed in the correct direction in
dismantling (dis-Mantell-ing, if you will...) the lumptastic genus
"Iguanodon".

-----------

Reply:

My thanks to Greg Paul for his interest in my paper; I do disagree with
the points
he raises, as I explain below. The final version of my paper is not yet on
Cretaceous Research's website, but when it does appear, I hope all of you
will
consider my arguments.

- First, stratigraphy. As Greg points out, there is uncertainty regarding the
precise age of the Bernissart Quarry; Schnyder et al. (2009) narrow it to
the upper
Barremian-lowermost Aptian. Greg uses the imprecision to argue for the
distinction
of Dollodon; however, the imprecision of the age of the Bernissart Quarry
means that
temporal disparity should not be used to distinguish Dollodon and
Mantellisaurus.
The possibilities that Mantellisaurus and Dollodon are the same age and
that they
are of different ages must be considered equally likely given the current
evidence.
Greg cites the Dinosaur Park and Hell Creek formations as instances of rapid
evolution and species turnover in dinosaurs; however, the difference is
that, while
the ages and stratigraphic ranges of dinosaur taxa in those units are
either well
constrained or becoming well constrained, the age of the Bernissart
Quarry, as Greg
himself acknowledges, is not as well constrained.

- Second, morphology. Even if Mantellisaurus and Dollodon are of different
ages,
there is no morphological basis for separating the two taxa, as I
thoroughly explain
in my paper. Despite Greg's contentions, skull reconstructions and skeletals,
however useful they might be for visualizing an animal, should not constitute
diagnostic features. Diagnoses should rest upon well substantiated discrete
characters or thoroughly tested (to rule out ontogenetic and individual
variation)
proportional differences, and Dollodon has neither of these in its favor.
Tooth
count and snout proportions change with ontogeny. Simply because
Mantellisaurus is
reconstructed in a bipedal pose and Dollodon in a quadrupedal pose does
not mean
that they are different taxa or that those poses reflect the habitual
poses of those
animals. What biometric evidence is there that Mantellisaurus was "so
strongly
bipedal" and that Dollodon was "so strongly quadrupedal"? What constitutes
a "strong
biped" versus a "strong quadruped"? Reconstructions are subjective. In his
2008
paper, Greg presents a new skull reconstruction of Dakotadon, which
differs from
those of Weishampel and Bjork (1989) and Brill and Carpenter (2006). If the
diagnosis of Dakotadon rested solely upon whichever skull reconstruction is
considered more likely at a given time, its diagnosis might change with
each new
reconstruction.

- Third, caveats of my study. As Greg points out and as I acknowledge in
my paper,
some of the fossils (postcranium of the holotype of Mantellisaurus, skull
of the
holotype of Dollodon) of these animals are not easily accessible. My study
is not
perfect, but neither is Greg's, and despite those difficulties there is
sufficient
reason to be very skeptical of the distinctiveness of Dollodon.

To summarize, I am not inherently averse to the idea of more than two taxa
(Mantellisaurus atherfieldensis and Iguanodon bernissartensis) of
large-bodied basal
iguanodont in the Barremian-lower Aptian of Europe. My new study simply
indicates
that IRSNB 1551 should not be used to argue for the presence of additional
taxa, and
that, in my view, the current evidence indicates only two taxa. Iguanodont
taxonomy
should certainly not become Greg Paul on one side, me and David Norman on
the other.
I fully support Greg's naming of Dakotadon and as Greg indicates, we agree
that
Iguanodon seelyi is not the same as Dollodon. David Norman and I do not
agree on
every detail. We are all working towards the same goal, a stable revised
taxonomy of
basal iguanodonts, but our interpretations of some fossils differ.

Again, my thanks to Greg for his interest in my work, to Tom Holtz for
forwarding my
email to the DML, and to you for reading.
Best regards,
Andrew McDonald

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA