Daliansaurus

Daliansaurus (meaning "Dalian reptile") is a genus of small troodontid theropod dinosaur, measuring approximately long, from the Early Cretaceous of China. It contains a single species, D. liaoningensis, named in 2017 by Shen and colleagues from a nearly complete skeleton preserved in three dimensions. Daliansaurus is unusual in possessing an enlarged claw on the fourth digit of the foot, in addition to the "sickle claw" found on the second digit of the feet of most paravians. It also has long metatarsal bones, and apparently possesses bird-like uncinate processes (a first among troodontids). In the Lujiatun Beds of the Yixian Formation, a volcanically-influenced region with a cold climate, Daliansaurus lived alongside its closest relatives - Sinovenator, Sinusonasus, and Mei, with which it forms the group Sinovenatorinae. Daliansaurus is a small, lightly-built, and most likely feathered troodontid measuring approximately in length, similar in size to Sinovenator and Sinusonasus. Typical of mature troodontids, the neural arches are fused to the vertebral centra in the dorsal (trunk) vertebrae of the only known specimen. Overall, Daliansaurus is very similar to Sinovenator, Sinusonasus, and Mei, its closest relatives, but differs from them in subtle ways. The skull of Daliansaurus, which measures long, is proportionally larger than that of Mei. Daliansaurus also has a smaller nostril. The projection of the premaxilla above the nostril is flattened instead of rod-like like in Sinovenator, while another projection below the nostril is straight like Sinusonasus but unlike Sinovenator. There are two openings of the skull in front of the eyes: the teardrop-shaped premaxillary fenestra, and the large, oval antorbital fenestra. Like Mei, Sinovenator, and Sinornithoides but unlike Sinusonasus, the bottom edge of the lower jaw is straight and not convex. There are at least 21 tooth positions in the upper jaw and 24 in the lower; the latter is less than Sinovenator (27) and other troodontids.