An Unusual Basal Therizinosaur Dinosaur with an Ornithischian Dental Arrangement from Northeastern China

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.

Cranial anatomy ofErlikosaurus andrewsi(Dinosauria, Therizinosauria): new insights based on digital reconstruction

“…Three smaller, ancillary foramina are positioned dorsal to the main ones. The number and position of the individual foramina is similar to the condition found in a therizinosauroid embryo (Kundrat et al, 2008) and Jianchangosaurus (Pu et al, 2013). Three large foramina are present on the dorsomedial surface of the main portion of the premaxilla (Fig.…”

“…A promaxillary fenestra, as found in troodontids (Xu et al, 2002b), dromaeosaurids (Norell et al, 2006), and other theropods (Witmer, 1997), is absent in E. andrewsi. A small promaxillary fenestra has been described for a therizinosauroid embryo (Kundrat et al, 2008), but is absent in the basal therizinosaurian Jianchangosaurus (Pu et al, 2013). In contrast to E. andrewsi, the latter taxon was reconstructed with a large maxillary fenestra, approximately half the size of the antorbital fenestra.…”

“…The CT scans do not show clear evidence for the presence or absence of such a foramen, but the superimposition of the left and right premaxillae produces a solid surface. Subnarial foramina have not been described or illustrated in other therizinosaurians (Kundrat et al, 2008;Pu et al, 2013), although a small recess in the caudal margin of the disarticulated premaxilla in Jianchangosaurus (Pu et al, 2013) might indicate such a foramen. Abbreviations: a.n, nasal articulation; a.pmx, premaxilla articulation; af, ancillary foramina; f 1-18 , neurovascular foramina; fi, incisive foramen; ml, medial lamina; mp, maxillary process; nc, narial chamber; np, narial process.…”

“…The floor of the narial chamber is deeply excavated and forms a prominent fossa, which is clearly separated from the incisive foramen. The presence of similarly developed fossae in a therizinosauroid embryo referred to Neimongosaurus or Erliansaurus (Kundrat et al, 2008), and the basal taxon Jianchangosaurus yixianensis (Pu et al, 2013) suggests an ontogenetically early development and more widespread distribution of this feature amongst Therizinosauria.…”

“…Most taxa are represented by single, often fragmentary, specimens. With few exceptions, cranial remains are especially rare and descriptions are restricted to a handful of taxa or consist of isolated fragments (Zanno, 2010a;Pu et al, 2013). Although other, partially articulated cranial remains have been discovered, these have not been thoroughly described (Xu et al, 2009a; see also Zanno, 2010b).…”