ceratopsids

Ceratopsids are a family of herbivorous, beaked dinosaurs within the larger ceratopsian group. They lived during the Late Cretaceous period, roughly from 100 to 66 million years ago, with fossils concentrated in western North America and, in earlier lineages, in Asia. The family is divided into two major subfamilies, Centrosaurinae and Chasmosaurinae, and includes a range of genera from small to very large species.

Typical ceratopsids walked on all fours, though individuals could rear for feeding. They possessed a rostral beak and cheek teeth arranged in dental batteries for processing tough vegetation. A distinctive skull feature is a bony frill at the back of the head, often elaborately ornamented with horns and spikes. Most ceratopsids had a pair of facial horns above the eyes and a nasal horn in many species; the size and shape of horns and frills varied between lineages and over time. The horns and frills are believed to have been used for display to attract mates or deter rivals, and perhaps for defense against predators.

Classification and paleobiology: Ceratopsidae is divided into two main subfamilies, Centrosaurinae and Chasmosaurinae. Centrosaurines usually have robust skulls with shorter, more elaborate frill ornamentation and prominent facial horns; chasmosaurines tend to feature longer brow horns and larger frills. Notable genera include Centrosaurus, Styracosaurus, Pachyrhinosaurus, Triceratops, Chasmosaurus, and Torosaurus. They occupied diverse plant-rich habitats in the Late Cretaceous and ranged across North America and Asia. Fossil finds in bonebeds indicate possible herding behavior in some species. Their ecology overlapped with apex predators such as tyrannosaurids, which likely constrained behavior and distribution.