A Small Derived Theropod from Öösh, Early Cretaceous, Baykhangor Mongolia

ALAN H. TURNER, SUNNY H. HWANG, MARK A. NORELL
2007 American Museum Novitates  
A new theropod dinosaur, Shanag ashile, from the Early Cretaceous Ö ö sh deposits of Mongolia is described here. The new specimen (IGM 100/1119) comprises a well-preserved right maxilla, dentary, and partial splenial. This specimen exhibits a number of derived theropod features, including a triangular anteriorly tapering maxilla, a large antorbital fossa, and maxillary participation in the caudally elongate external nares. These features resemble the Early Cretaceous dromaeosaurids
more » ... aurids Sinornithosaurus millenii and Microraptor zhaoianus, as well as the basal avialan Archaeopteryx lithographica. A comprehensive phylogenetic analysis including 58 theropod taxa unambiguously depicts the new Ö ö sh theropod as a member of Dromaeosauridae. Relative to other dromaeosaurids, Shanag ashile is autapomorphic in its lack of a promaxillary fenestra and in the presence of interalveolar pneumatic cavities. The discovery of IGM 100/1119 expands our knowledge of Early Cretaceous dromaeosaurids and the faunal similarity between the Ö ö sh and the Jehol biotas. more rare than the plentiful fossils of Psittacosaurus mongoliensis and sauropods at the locality (Osborn, 1923 (Osborn, , 1924b . In some places, however, isolated theropod material of a range of sizes is encountered frequentlyespecially unguals, phalanges, and teeth. The deposits at Ö ö sh are considered to be Early Cretaceous (Berriasian-Barremian). This is roughly coeval with beds forming the
doi:10.1206/0003-0082(2007)3557[1:asdtfs]2.0.co;2 fatcat:rev6uph3engmfjf5ivlclw4gwy