Protoceratopsidae is a family of small to medium-sized ceratopsian dinosaurs, part of the broader horned-dinosaur lineage, known from the Late Cretaceous of Asia, roughly 100 to 71 million years ago. Unlike their larger relatives such as Triceratops, protoceratopsids lacked prominent facial horns, though they had a well-developed bony frill extending from the back of the skull and a strong, hooked beak adapted for cropping tough vegetation. Most species were quadrupedal, ranged from about 1 to 2.5 meters in length, and are thought to have lived in groups based on the number of specimens found together at single sites.
The type genus Protoceratops, from Mongolia and northern China, is exceptionally well represented in the fossil record, including a famous specimen locked in combat with a Velociraptor at the moment both animals died, preserved together at Ukhaa Tolgod. Numerous Protoceratops skeletons spanning a range of ages have also made the genus a key reference point for studying dinosaur growth, with younger individuals showing a proportionally smaller frill that enlarged substantially with maturity. Related genus Leptoceratops extended the family's range into North America, indicating protoceratopsids or their close relatives crossed between continents before the group's Late Cretaceous decline.