A basal troodontid from the Early Cretaceous of China

Abstract

Troodontid dinosaurs form one of the most avian-like dinosaur groups. Their phylogenetic position is hotly debated, and they have been allied with almost all principal coelurosaurian lineages. Here we report a basal troodontid dinosaur, Sinovenator changii gen. et sp. nov., from the lower Yixian Formation of China. This taxon has several features that are not found in more derived troodontids, but that occur in dromaeosaurids and avialans. The discovery of Sinovenator and the examination of character distributions along the maniraptoran lineage indicate that principal structural modifications toward avians were acquired in the early stages of maniraptoran evolution.

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

“…In comparison with other maniraptoriformes, the maxillary fenestra is small and located more caudally. 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).…”

A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America

“…Phalanx II-1, the proximal phalanx, is long and slender, as in basal deinonychosaurs (20)(21)(22)(23)(24)39) (Fig. 2C).…”

“…As in many other paravians (20,23,24,30,(33)(34)(35)37), the pubic shaft projects posteroventrally. The proximal end of the pubis has a distinct scar on its anterior surface, in the same position as the large tubercle found in Velociraptor (33).…”

“…Unlike the situation in Velociraptor, in which the ilia diverge posteriorly and the dorsal margin is laterally everted (30,33,34), the posterior alae of the ilia would have been approximately parallel, and the postacetabular blade projects vertically. As in basal paravians (23,(35)(36)(37), the posterior wing of the ilium is tapered and curved ventrally in lateral view. Along the dorsal edge of the posterior ala, there is a distinct tubercle, a common maniraptoran feature (36).…”

“…That dinosaurs might have left the small-carnivore niche vacant in North America is still more perplexing when one considers that many small carnivorous dinosaurs are known from Europe, Asia, and Gondwana (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). This raises the question of whether small-bodied, endothermic carnivores were truly rare in these assemblages, or whether our picture of these ecosystems is incomplete.…”