[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Chromogisaurus novasi, new guaibasaurid (basal sauropodomorph)


Ezcurra, M. D. 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from
the Late Triassic of Argentina: a reassessment of dinosaur origin and
phylogeny. Journal of Systematic Palaeontology 8: 371-425.

Discussed at:


It was traditionally thought that the oldest known dinosaur assemblages were
not diverse, and that their early diversification and numerical dominance
over other tetrapods occurred during the latest Triassic. However, new
evidence gathered from the lower levels of the Ischigualasto Fm. of
Argentina challenges this view. New dinosaur remains are described from this
stratigraphical unit, including the new species Chromogisaurus novasi. This
taxon is distinguished from other basal dinosauriforms by the presence of
proximal caudals without median notch separating the postzygapophyses,
femoral lateral surface with deep and large fossa immediately below the
trochanteric shelf, and metatarsal II with strongly dorsoventrally
asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to
lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early
branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys,
Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first
time suggested for Guaibasaurus, whereas Panphagia is not recovered as the
most basal sauropodomorph. Furthermore, Chromogisaurus is consistently
located as more closely related to Saturnalia than to any other dinosaur.
Thus, the Saturnalia + Chromogisaurus clade is named here as the new
subfamily Saturnaliinae. In addition, Eoraptor is found to be the
sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian
saurischians. The new evidence presented here demonstrates that dinosaurs
first appeared in the fossil record as a diverse group, although they were a
numerically minor component of faunas in which they occur. Accordingly, the
early increase of dinosaur diversity and their numerical dominance over
other terrestrial tetrapods were diachronous processes, with the latter
preceded by a period of low abundance but high diversity.

No, I do not yet have a pdf, but am working on it.

Congrats to Martin Ezcurra on the paper, and to Fernando Novas (as I am
assuming he is the honoree of the trivial name).

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
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
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