[N] 2006 New Ceratosaurs from the Jurassic Shishugou Formation of Western China
Xu, X. & Clark, J, (2006) New Ceratosaurs from the Jurassic Shishugou Formation of Western China. JVP 26(3) Abstracts pp. 142
From 2001 through 2005, our excavations in the Middle-Upper Jurassic Shishugou Formation in the Junggar Basin, Xinjiang Uighur Autonomous Region, western China have yielded numerous vertebrate specimens covering several major vertebrate groups. Four specimens in this collection are here identified as two new species of ceratosaurian theropod (=neoceratosaurian theropod), which represent the earliest known species of the group. Ceratosaurians represent a large radiation of theropod dinosaurs mainly in the Cretaceous of the southern hemisphere. Although current phylogenetic hypotheses predict their presence deep in the Jurassic, there are only two unquestionable Jurassic ceratosaurians, which hinders our understanding of their origin and early evolution. Recent phylogenetic analyses posit ceratosaurs either as the sister group to coelophysoids or to tetanurans, hypotheses that have profound effects on the timing and pattern of the basal splitting of theropod dinosaurs.
The two new ceratosaurians from the Late Jurassic part of the Shishugou Formation display an unusual combination of character states. While similar to other ceratosaurs in many derived character states, they share a number of derived cranial and limb characters with tetanurans and also a few salient cranial and pelvic features with coelophysoids, which shortens the morphological gaps between the three major theropod groups. Our phylogenetic analyses support a monophyletic Cetatosauria-Tetanura clade and character distributions on the recovered tree indicate that some tetanuran, coelophysoid, and ceratosaurin diagnostic features now have broader distributions and characterize much more inclusive clades.
These new ceratosaurians also represent the first record of the group in Asia and have implications on the paleobiogeographical reconstructions of Middle-Late Jurassic time period. Our analysis suggests that Asia remained connected to other major landmasses at least until the Late Jurassic and more intense prospecting in outcrops of this time period promises to provide further support for a close-relationship of Asian dinosaur faunas and those of other continents.