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Re: [dinosaur] Ornithoscelida sister clade: Sauropodomorpha or Pachypodosauria, not Saurischia



Indeed, I prefer the "Sauropodomorpha + Ornithoscelida" option.

I sent around a graphic with alternative dinosaurian nomenclatures shortly after the original paper came out:
https://twitter.com/TomHoltzPaleo/status/846428150183739395 

A paper detailing these and addressing other issues is in early stages of preparation...

On Thu, May 4, 2017 at 9:45 PM, Tim Williams <tijawi@gmail.com> wrote:
This just out (well done Tom!)...

Holtz, T.R. Nomenclature: Share names for dinosaur divisions. Nature
545: 30  doi:10.1038/545030d

First paragraph: "Matthew Baron and colleagues propose a radical
revision of dinosaur relationships (Nature 543, 501-506; 2017). I
suggest that borrowing from the field's rich history could help to
prevent unnecessary confusion."

Holtz argues that Saurischia should be abandoned if it doesn't include
Theropoda - I completely agree.  He further suggests that the name
Sauropodomorpha, or alternatively Pachypodosauria, should be used for
the remaining 'saurischians' (= traditional sauropodomorphs + more
basal taxa, like herrerasaurids).  I like the rationale for reviving
Huene's Pachypodosauria ("Initially used to unite larger theropods
with the sauropodomorphs, the term could now be applied to a clade of
dinosaurs that have four or more weight-bearing toes, as distinct from
their lighter-footed ornithoscelidan sister taxon with three
weight-bearing toes.").  But I think the preferred option is to use
Sauropodomorpha for this clade, rather than Pachypodosauria.
Sauropodomorpha would simply be expanded to include herrerasaurids (or
whichever taxa are recovered as closer to sauropods than to theropods
or ornithischians).

IIRC, Pachypodosauria originally included teratosaurids, many of which
were based on the erroneous combination of predatory teeth (including
from rauisuchians) and associated basal sauropodomorph ('prosauropod')
bones.  Hence these teratosaurids were regarded by Huene as primitive
carnivores that provided a link between large theropods (Huene's
'carnosaurs') and sauropods.  I don't think this historical 'baggage'
interferes with resurrecting Pachypodosauria as a new dinosaurian
clade.  However, given that inclusion of herrerasaurids in the
Sauropodomorpha has precedent, I think Sauropodomorpha is the best way
to go for the name of the sister taxon to Baron et al.'s
Ornithoscelida.



--

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu         Phone: 301-405-4084
Principal Lecturer, Vertebrate Paleontology

Office: Geology 4106, 8000 Regents Dr., College Park MD 20742

Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/

Phone: 301-405-6965
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Faculty Director, Science & Global Change Program, College Park Scholars

Office: Centreville 1216, 4243 Valley Dr., College Park MD 20742
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