An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia

Abstract

Troodontidae is a clade of small-bodied theropod dinosaurs. A new troodontid, Gobivenator mongoliensis gen. et sp. nov., is described based on the most complete skeleton of a Late Cretaceous member of this clade presently known, from the Campanian Djadokhta Formation in the central Gobi Desert. G. mongoliensis is different from other troodontids in possessing a pointed anterior end of the fused parietal and a fossa on the surangular in front of the posterior surangular foramen. The skull was superbly preserved in the specimen and provides detailed information of the entire configuration of the palate in Troodontidae. Overall morphology of the palate in Gobivenator resembles those of dromaeosaurids and Archaeopteryx, showing an apparent trend of elongation of the pterygoid process of the palatine and reduction of the pterygopalatine suture toward the basal Avialae. The palatal configuration suggests that the skull of Gobivenator would have been akinetic but had already acquired prerequisites for later evolution of cranial kinesis in birds, such as the loss of the epipterygoid and reduction in contact areas among bones.

New Specimens ofAnchiornis huxleyi(Theropoda: Paraves) from the Late Jurassic of Northeastern China

“…similar to the condition in basal troodontids and basal dromaeosaurids, such as Sinovenator and Microraptor, as well as Archaeopteryx Mayr et al, 2005Mayr et al, , 2007Pei et al, 2014). In derived troodontids and dromaeosaurids, the lateral lamina of the ascending process is broad (Osborn et al, 1924;Norell et al, 2006;Xu et al, 2010;Tsuihiji et al, 2014).…”

“…Laterally, the nasal sutures with the maxilla along a straight line, as observed in BMNHC PH804, but does not contribute to the dorsal margin of the antorbital fossa ( fig. 6), as it does in Archaeopteryx, dromaeosaurids, and troodontids (e.g., Burnham et al, 2000;Makovicky et al, 2003;Rauhut, 2014;Pei et al, 2014;Tsuihiji et al, 2014). The nasals are well exposed in dorsal view in BMNHC PH822 ( fig.…”

“…Anteriorly, the nasal processes of the premaxillae insert between the nasals, as in other paravians. Posteriorly, the nasals suture the frontal with a W-shaped suture typical of paravians, but unlike the condition in Zanabazar and Gobivenator, where the nasals wedge between the frontals Tsuihiji et al, 2014). The nasals extend posterior to the anterior margin of the orbit, a basal paravian condition also observed in Jinfengopteryx and Archaeopteryx (Mayr et al, 2005;Ji and Ji, 2007).…”

“…The anterior and posterior processes are broken away from the ventral process and attached to the displaced frontal. The remaining parts of the anterior and posterior processes are subequal in length, a primitive condition of paravians, but in contrast to the longer anterior process of derived troodontids (Makovicky et al, 2003;Norell et al, 2009;Tsuihiji et al, 2014). Unlike troodontids and dromaeosaurids, the lacrimal of PKUP V1068 lacks a recess ventral to the anterior process (e.g., Burnham et al, 2000;Makovicky et al, 2003;Xu et al, 2010;Tsuihiji et al, 2014).…”

“…The remaining parts of the anterior and posterior processes are subequal in length, a primitive condition of paravians, but in contrast to the longer anterior process of derived troodontids (Makovicky et al, 2003;Norell et al, 2009;Tsuihiji et al, 2014). Unlike troodontids and dromaeosaurids, the lacrimal of PKUP V1068 lacks a recess ventral to the anterior process (e.g., Burnham et al, 2000;Makovicky et al, 2003;Xu et al, 2010;Tsuihiji et al, 2014). The lacrimal does not bear an expanded supraorbital ridge anterodorsal to the orbit, which is different than in most troodontids (Makovicky et al, 2003;Xu and Norell, 2004;Norell et al, 2009;Tsuihiji et al, 2014).…”