Chasmosaurinae

Chasmosaurinae is a subfamily within the Ceratopsidae, the group of horned, beaked herbivorous dinosaurs known from the Late Cretaceous. Members of this subfamily inhabited North America and are known from roughly 76 to 66 million years ago, during the Campanian to Maastrichtian stages, though exact ranges vary by taxon.

A defining feature of chasmosaurines is an elongated frill at the back of the skull, often with pronounced posterior processes or spikes, and large brow horns above each eye. The frill and horn arrangements are highly diverse and are interpreted as adaptations for display, species recognition, and possibly defense. In general, chasmosaurines tend to have longer frills and more prominent brow horns than many centrosaurines, though the two subfamilies are distinguished by a combination of skull ornamentation and skeletal features used in taxonomic diagnoses.

As a group, chasmosaurines include several well-known genera and species, among them Triceratops and Chasmosaurus, which have become emblematic of Late Cretaceous ceratopsids. The subfamily also contains other taxa described from a variety of North American formations, contributing to differences in frill geometry and horn morphology observed across the lineage. Ongoing research continues to refine the relationships within Chasmosaurinae and its position relative to Centrosaurinae within Ceratopsidae.

Prior to the Cretaceous–Paleogene extinction event, chasmosaurines were among the most conspicuous ceratopsids in their ecosystems, likely engaging in social and display behaviors that are inferred from their ornate skull adornments. Their fossil record helps illuminate patterns of ceratopsid evolution and biogeography in North America during the final chapters of the dinosaurs.