Protoceratops

Protoceratops (; ) is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 75 to 71 million years ago. The genus Protoceratops includes two species: P. andrewsi and the larger P. hellenikorhinus. The former was described in 1923 with fossils from the Mongolian Djadokhta Formation, and the latter in 2001 with fossils from the Chinese Bayan Mandahu Formation. Protoceratops was initially believed to be an ancestor of ankylosaurians and larger ceratopsians, such as Triceratops and relatives, until the discoveries of other protoceratopsids. Populations of P. andrewsi may have evolved into Bagaceratops rozhdestvenskyi through anagenesis.

Protoceratops were small ceratopsians, up to long and around in body mass. While adults were largely quadrupedal, juveniles had the capacity to walk around bipedally if necessary. They were characterized by a proportionally large skull, short and stiff neck, and neck frill. The frill was likely used for display or intraspecific combat, as well as protection of the neck and anchoring of jaw muscles. A horn-like structure was present over the nose, which varied from a single structure in P. andrewsi to a double, paired structure in P. hellenikorhinus. The "horn" and frill were highly variable in shape and size across individuals of the same species, but there is no evidence of sexual dimorphism. They had a prominent parrot-like beak at the tip of the jaws. P. andrewsi had a pair of cylindrical, blunt teeth near the tip of the upper jaw. The forelimbs had five fingers of which only the first three bore wide and flat unguals. The feet were wide and had four toes with flattened, shovel-like unguals, which would have been useful for digging through the sand. The hindlimbs were longer than the forelimbs. The tail was long and had an enigmatic sail-like structure, which may have been used for display, swimming, or metabolic reasons.