A new species of dromaeosaurids from the Yixian Formation of western Liaoning

Abstract

A nearly complete specimen of dromaeosaurid has been recently collected from the Yixian Formation near Toutai in Yixian County,western Liaoning.It shows many features of Sinornithosaurus,e.g.the presence of ornament-like pits on the anterolateral surface of the antorbital fossa,unserrated premaxillary teeth,dentary bifurcated posteriorly,manual phalanx II-I-1slightly more than twice the length of phalanx III-2,and partially arctometatarsalian metatarsal III.But this new specimen differs from S.millenii in some bones.So a new species,S.haoiana sp.nov.,is erected based on this specimen.It can be distin guished from S.millenii in that:(1)the main body of the premaxilla is higher,its length being slightly longer than its height ;(2)the anterior margin of the premaxilla is vertical;(3)the maxillary process of the premaxilla is very long;(4)the maxilla is separated from external naris;(5)maxillary fenestra is circular and relatively small;(6)the ascending process of quadratojugal is remarkably longer than the jugal process;(7)the ratio of the dentary length/height is distinctly small;and(8)the pubic peduncle of ilium is longitudinally narrower than acetabulum and so on.There differences indicate that the specimen from Toutai should be a new species of Sinornithosaurus and so is named S.haoiana sp.nov.