An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures

Ornithischia is one of the two major groups of dinosaurs, with heterodontosauridae as one of its major clades. Heterodontosauridae is characterized by small, gracile bodies and a problematic phylogenetic position(1,2). Recent phylogenetic work indicates that it represents the most basal group of all well-known ornithischians(3). Previous heterodontosaurid records are mainly from the Early Jurassic period (205-190 million years ago) of Africa(1,3). Here we report a new heterodontosaurid, Tianyulong confuciusi gen. et sp. nov., from the Early Cretaceous period (144-99 million years ago) of western Liaoning Province, China. Tianyulong extends the geographical distribution of heterodontosaurids to Asia and confirms the clade's previously questionable temporal range extension into the Early Cretaceous period. More surprisingly, Tianyulong bears long, singular and unbranched filamentous integumentary (outer skin) structures. This represents the first confirmed report, to our knowledge, of filamentous integumentary structures in an ornithischian dinosaur.