New Thecodontosaurus paper available free online

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

Adam Yate's new paper on _Thecodontosaurus_ is available online at:
http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1051894528&REQSESS=208
36&117000REQEVENT=&REQINT1=149544&REQAUTH=0

It is the very first paper in the very first issue of the new Journal of
Systematic Palaeontology.

Yates, A.M. 2003. A new species of the primitive dinosaur _Thecodontosaurus_
(Saurischia: Sauropodomorpha) and its implications for the systematics of
early dinosaurs.  JSP 1: 1-42.

Summary:
The Pant-y-ffynnon specimens of _Thecodontosaurus_, previously described in
brief by Kermack, is now fully described and identified as a new species:
_Thecodontosaurus caducus_ (trivial nomen means "the fallen", as this
specimen was recovered from a fissure fill deposit).  The reconstructed
skull is the winner of the "_Eoraptor_-Look-Alike Contest": average these
two critters out, and you probably have a good working model for the
ancestral saurischian.  It is distinguished from _T. antiquus_ by the lack
of several derived features in that form and by the autapomorphy of
pleurocoel-like pits on the neurocentral sutures of cervicals 6-8.  (One
might wonder, however, if these might not be manifestations of a shared
primitive air sac system...).

The reconstruction Yates provides suggests that the often-copied Kermack
reconstruction has the arms too short, the head too small compared to the
ilium, and the hindlimbs too long in relation to the torso.  Yates considers
_Theco._ only a facultative biped.

His phylogenetic analysis (21 ingroup taxa, 3 outgroups, 164 characters) is
the largest such study of basal sauropodomorphs to date.  The main
conclusions:
        *"Prosauropoda" is hopelessly paraphyletic with the respect to 
Sauropoda.
        *_Saturnalia_ is the basalmost sauropodomorph, _Thecodontosaurus_ next 
up,
and (other than _Thecodontosaurus_) the only clade supported in the
traditional prosauropods was Massospondylidae (not so called, but a clade of
_Masso._, _Yunnanosaurus_, and _Lufengosaurus_); otherwise, prosauropods
represent a series of outgroups to Sauropoda.
        *Herrersauridae lies outside a clade of neotheropods and 
sauropodomorphs;
_Eoraptor_ is not included in this study.

Yates goes on to look at previous studies of prosauropod relationships.
Benton et al.'s 2000 study of _Thecodontosaurus_ found a weakly supported
Prosauropoda, but recoding one dental character in the matrix to accurately
reflect the condition in basal sauropods results in a collapse of
prosauropod monophyly.

Sereno's 1999 analysis is examined in depth.  Yates points out that no
really primitive "prosauropods" nor really basal sauropods were included as
OTUs in that study, and he finds flaw with the polarity of some of the
characters in that study.

Cool stuff.  Looking forward to _Zalmoxes_ next issue!

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796