The dinosaurs of the Early Jurassic Hanson Formation of the Central Transantarctic Mountains: Phylogenetic review and synthesis.

SMITH, N.D.; MAKOVICKY, P.J.; POL, D.; HAMMER, W.R.; CURRIE, P.J.

UNITED STATES GEOLOGICAL SURVEY OPEN FILE REPORT

United States Geological Survey & The National Academies

Año: 2007 vol. 2007 p. 1 - 5

0196-1497

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.