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Important new papers on basal theropods and ornithischians



Greetings,

Some very significant analyses of basal theropods and basal ornithischians
have just come out.

Smith, N. D., P. J. Makovicky, D. Pol, W. R. Hammer, and P. J. Currie
(2007), The dinosaurs of the Early Jurassic Hanson Formation of theCentral
Transantarctic Mountains: Phylogenetic review and synthesis, in
Antarctica: A Keystone in a Changing World??Online Proceedings of the 10th
ISAES, edited by A. K. Cooper and C. R. Raymond et al., USGS Open-File
Report 2007-1047, Short Research Paper 003, 5 p.;
doi:10.3133/of2007-1047.srp003.

http://pubs.usgs.gov/of/2007/1047/srp/srp003/of2007-1047srp003.pdf

Abstract The Hanson Formation of the Central Transantarctic Mountains has
yielded a diverse Early Jurassic terrestrial fauna, which includes the
nearly complete theropod dinosaur, Cryolophosaurus ellioti, and a
fragmentary basal sauropodomorph dinosaur. The Hanson Formation dinosaurs
are important for understanding early dinosaur evolution because: 1) they
preserve a mosaic of morphological traits that render them useful for
interpreting poorly known parts of the dinosaur evolutionary tree; 2) they
are from the Early Jurassic, a critical period in early dinosaur evolution
about which knowledge is scant; and 3) they are the only known Early
Jurassic dinosaurs from Antarctica, making them particularly valuable for
understanding patterns of biotic interchange during this time. Recent
research suggests that Cryolophosaurus belongs to a geographically
widespread clade of mid-sized, Early Jurassic theropods with cranial
crests that includes Dilophosaurus wetherilli, ?Dilophosaurus? sinensis,
and Dracovenator, and renders Coelophysoidea sensu lato non-monophyletic.
The Antarctic sauropodomorph represents a distinct taxon that is a member
of a similarly diverse massospondylid clade. This taxon shares a number of
features with more derived sauropodomorphs, and provides additional
evidence for the paraphyly of Prosauropoda. The phylogenetic relationships
of the Antarctic dinosaurs are also consistent with a pattern of worldwide
faunal homogeneity between Early Jurassic continental biotas. Furthermore,
these analyses support a ?ladder-like? arrangement for basal theropod and
basal sauropodomorph phylogeny, suggesting that these groups passed
through ?coelophysoid? and ?prosauropod? stages of morphological
organization early in their respective evolutionary histories.

The theropod portion of this brief report is coming VERY soon to a major
journal, so I'll talk more about it later. Smith et al. do not name the
clade, but Madsen & Welles' Dilophosauridae would seem to be the most
reasonable version.

The other major paper is:

Butler, R.J., P. Upchurch & D.B. Norman. 2007. The phylogeny of
ornithsichian dinosaurs. Journal of Systematic Palaeontology.  early
online edition.

SYNOPSIS Ornithischia is a familiar and diverse clade of dinosaurs whose
global phylogeny has
remained largely unaltered since early cladistic analyses in the mid
1980s. Current understanding of ornithischian evolution is hampered by a
paucity of explicitly numerical phylogenetic analyses that consider the
entire clade. As a result, it is difficult to assess the robustness of
current phylogenetic hypotheses for Ornithischia and the effect that the
addition of new taxa or characters is likely to have on the overall
topology of the clade.

The new phylogenetic analysis presented here incorporates a range of new
basal taxa and characters in an attempt to rigorously test global
ornithischian phylogeny. Parsimony analysis is carried out with 46 taxa
and 221 characters. Although the strict component consensus tree shows
poor resolution in a number of areas, application of reduced consensus
methods provides a well-resolved picture of ornithischian
interrelationships. Surprisingly, Heterodontosauridae is placed as the
most basal group of all well-known ornithischians, phylogenetically
distant from a stem-defined Ornithopoda, creating a topology that is more
congruent with the known ornithischian stratigraphical record. There is no
evidence for a monophyletic ?Fabrosauridae?, and Lesothosaurus (the
best-known ?fabrosaur?) occupies an unusual position as the most basal
member of Thyreophora. Other relationships within Thyreophora remain
largely stable. The primitive thyreophoran Scelidosaurus is the sister
taxon of Eurypoda (stegosaurs and ankylosaurs), rather than a basal
ankylosaur as implied by some previous studies.

The taxonomic content of Ornithopoda differs significantly from previous
analyses and basal
relationships within the clade are weakly supported, requiring further
investigation. ?Hypsilophodontidae? is paraphyletic, with some taxa
(Agilisaurus, Hexinlusaurus, Othnielia) placed outside of Ornithopoda as
non-cerapodans. Ceratopsia and Pachycephalosauria are monophyletic and are
united as Marginocephalia; however, the stability of these clades is
reduced by a number of poorly preserved basal taxa.

This analysis reaffirms much of the currently accepted ornithischian
topology. Nevertheless, instability in the position and content of several
clades (notably Heterodontosauridae and Ornithopoda) indicates that
considerable future work on ornithischian phylogeny is required and causes
problems for several current phylogenetic definitions.

Butler has made the paper (and the Nexus file!) available online. The
paper is at:
http://www.richardjbutlerphd.com/PDF%5Cphylogeny.pdf

And congrats to Nate, Richard, and their colleagues.

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, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Fax: 301-405-0796

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