with about twice their length. This makes it one of the larger species of troodontids in the ecosystem of the Yixian Formation, the formation where it was found. In the original description some distinguishing traits or autapomorphies were established. The front edge of the antorbital fenestra, the large skull opening in front of the eye socket, is straight and vertically oriented. The frontal bone shows a vertical ridge touching the lacrimal bone. The surangular in the lower jaw has a T-shaped cross-section. The shinbone has a vertical ridge on the upper outer side, the crista cnemialis, touching a lower vertical ridge, the crista fibularis. There is a number of other notable traits. The upper branch of the praemaxilla excludes the maxilla from the nostril. The premaxillary teeth lack denticles; those on the maxillary teeth are small. The maxillary tooth row is positioned at some distance from the jaw rim. A fenestra promaxillaris is present. The branch of the jugal towards the postorbital is long, slender and inclined to the rear. The foramen magnum is much larger than the occipital condyle. The braincase lacks a recessus suboticus and a crista otosphenoidalis. The rear of the pterygoid has a secondary, rod-like, process. The front dentary teeth are closely packed. The rear of the surangular is extraordinarily deep. Five sacrals are present, those of the middle being clearly larger. The ilium is relatively small. The ischium is bird-like: small with a low obturator process and processes on the upper and lower rear edge. The shinbone is wide at the top and has a roughly rectangular lower joint surface. The fourth metatarsal is not strongly developed but the second metatarsal is small. The third metatarsal is pinched at the top but still visible at the upper front of the metatarsus, conforming to the subarctometatarsal condition. Phylogeny In 2002 Sinovenator was placed in the Troodontidae. Sinovenator is a basal or "primitive" troodontid, and shares features with the most basal dromaeosaurids and Avialae. It thus was one of the first fossil specimens conclusively demonstrating the close relation of these three groups in the overarching Paraves. A typical basal trait is the orientation of the pubic bone to the rear, similar to the situation in the Dromaeosauridae and basal birds. This proves that the orientation to the front with later troodontids, is a reversal and not a trait directly inherited from older theropods that also possess a