Hongshanosaurus (hawng-SHAN-o-SAWR-us; "Red Hill lizard") is a genus of psittacosaurid ceratopsian dinosaur from the Early Cretaceous Period of eastern Asia. Although two skulls are the only fossil material known, comparisons with close relatives suggest it was a small, bipedal herbivore with a bony beak on the end of both upper and lower jaws. This is one of the many exceptionally well-preserved fossils to be recovered from the Yixian Formation of Liaoning, China.
The generic name Hongshanosaurus is derived from the Mandarin Chinese words 紅 (hóng: "red") and 山 (shān: "hill"), as well as the Greek word sauros ("lizard") . This name refers to the ancient Hongshan culture of northeastern China, who lived in the same general area in which the fossil skull of Hongshanosaurus was found.
The one named species (H. houi) honors Hou Lianhai, a professor at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing, who curated the specimen. Genus and species were both named by Chinese paleontologists You Hailu, Xu Xing, and Wang Xiaolin in 2003.
The holotype specimen of Hongshanosaurus is a juvenile skull, completely preserved except for part of the right side and the tip of the upper jaw. This skull is slightly less than 5 centimeters (2 in.) long (You et al. 2003). A much larger adult skull was later described, which is almost 20 centimeters (8 in.) long. It is very similar to skulls of the closely related Psittacosaurus, although several differences exist which serve to differentiate the two genera. Hongshanosaurus has a lower skull than any species of Psittacosaurus and the orbit (eye socket) is elliptical instead of round (You & Xu 2005). These skull were recovered from the Yixian Formation of Liaoning China, which is famous for the exceptional preservation of its fossils, including most of the known feathered dinosaurs. The age of this formation has been disputed, but recently radiometric dating has confirmed an Early Cretaceous age, probably in the Barremian stage (130 to 125 million years ago). Several specimens of Psittacosaurus have also been recovered from the Yixian, including one with a row of long bristles on the tail which may have had a display function in life. As Hongshanosaurus is known only from skull material, it is unknown whether it also had these bristles.