Abstract
Therizinosauria are an unusual group of theropod dinosaurs, found mostly in the Cretaceous deposits in Mongolia, China and western USA. The basal forms of this group are represented by incomplete or disarticulated material. Here, we report a nearly complete, articulated skeleton of a new basal therizinosaur from the Early Cretaceous Yixian Formation of Jianchang County, western part of Liaoning Province, which sheds light on our understanding of anatomy of basal therizinosaurs. This new dinosaur shows some typical therizinosaur features, such as neural spines of the anterior caudal vertebrae that possess anterior and posterior alae, a rectangular buttress on the ventrolateral side of the proximal end of metacarpal I, and appressed metatarsal shafts. Our phylogenetic analysis suggests that it is a basal therizinosaur (sister taxon to Therizinosauroidea) because it bears many basal therizinosaur characters in the dentition, pelvis and hind limbs. The new therizinosaur described here has unique tooth and jaw characters such as the offsetting of the tooth row by a shelf and dentary teeth with labially concave and lingually convex dentary teeth, similar to ornithopods and ceratopsians.
Highlights
Therizinosauria are an unusual group of theropod dinosaurs, found mostly in the Cretaceous deposits in Mongolia, China, and western USA
Jianchangosaurus yixianensis is recovered from the same formation as the most basal known therizinosauroid, Beipiaosaurus inexpectus, but differs from it in some characters
Jianchangosaurus yixianensis differs from Beipiaosaurus inexpectus in the following four features
Summary
Therizinosauria are an unusual group of theropod dinosaurs, found mostly in the Cretaceous deposits in Mongolia, China, and western USA. Three taxa have been reported from the Early Cretaceous in China; Beipiaosaurus inexpectus from the Yixian Formation (Barremian), Alxasaurus elesitaiensis from the Bayin-Gobi Formation (Aptian-Albian), and Suzhousaurus megatherioides from Xinminpu Group (Albian) [3,4,5]. Despite the richness of vertebrate fossils from the Yixian Formation, this taxon is represented by only two skeletons (IVPP 11559 and STM31-1) [3,6,7] and is the only basal therizinosaur (non-therizinosaurid therizinosaur) known from the formation. The emended diagnosis by Zanno [2] is based on postcranial features (manual phalanx I-I, ischium, femur, pygostyle, and metacarpal I) because the skull preservation of IVPP 11559 is poor and the skull of STM31-1 is not described yet
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