Ceratopsia

Ceratopsia, whose name means "horned face," is a well-documented dinosaur clade thanks to an extensive Late Cretaceous fossil record. These dinosaurs originated in the Late Jurassic of Asia as small bipedal animals like Yinlong. During the Cretaceous, the group diversified into larger, more ornamented lineages, including Psittacosaurus, Protoceratops, the leptoceratopsids, and the North American Ceratopsidae, which includes both Centrosaurinae and Chasmosaurinae.

The defining characteristic of Ceratopsia is the rostral bone, a unique unpaired bone at the tip of the upper jaw. Along with the predentary bone found in all ornithischians, this provided ceratopsians with a powerful beak for cropping vegetation. Behind this beak, complex batteries of teeth shredded fibrous plants, while fleshy cheeks kept food within the mouth. Horns appeared in various locations depending on the lineage: chasmosaurines like Triceratops typically had long brow horns, while centrosaurines like Centrosaurus and Styracosaurus often featured prominent nasal horns. Additional ornamentation frequently grew along the edges of their frills.

The parietal-squamosal frill is the most varied feature within the clade. It could be solid, flat, domed, or perforated with large openings. Researchers believe these structures primarily served for display, species recognition, or thermoregulation. Combat was likely a secondary use in most species.

Fossil bonebeds provide strong evidence for social behaviour in ceratopsians. Large-scale sites in the Dinosaur Park Formation, for example, contain thousands of Centrosaurus individuals, suggesting they lived in massive herds. Because frill shapes are so specific to each species, they likely played a critical role in identification within a group. Sexual selection remains the primary theory for the diversity of frill ornaments. Studies of tooth wear and preserved gut contents indicate these dinosaurs were low-to-mid-level browsers that ate fibrous plants, including palms and cycads.

• Hell Creek Triceratops series (multiple) — including FMNH P 12003 and the Black Hills Institute specimens.
• Protoceratops andrewsi "Fighting Dinosaurs" specimen (MPC-D 100/25) — preserved locked in combat with Velociraptor; Mongolian Academy of Sciences.
• Big John (largest known Triceratops) — sold at auction 2021, now on display in Glasgow.
• Pachyrhinosaurus Pipestone Creek bonebed — Pipestone Creek Dinosaur Initiative, Alberta.

Triceratops vs Torosaurus: Scannella & Horner (2010) controversially proposed that Torosaurus is a fully mature Triceratops, requiring sinking the genus. Most workers (Longrich & Field 2012; others) reject the synonymy. Frill function: species-recognition has gained ground over thermoregulation and combat as the dominant explanation. Whether ceratopsians had quill-like integument similar to Psittacosaurus across the clade is unresolved.

Triceratops is the second most famous dinosaur after T. rex; the Triceratops–T. rex matchup is the iconic dinosaur scene. Protoceratops anchors the Mongolian "Fighting Dinosaurs" tableau, one of the most famous fossils ever found.

• triceratops
• protoceratops
• styracosaurus
• centrosaurus
• pachyrhinosaurus
• ornithischia

• Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press.
• Sampson, S. D., et al. (2009). New horned dinosaurs from Utah provide evidence for intracontinental dinosaur endemism. PLOS ONE, 5, e12292.
• Scannella, J. B., & Horner, J. R. (2010). Torosaurus Marsh, 1891, is Triceratops Marsh, 1889. Journal of Vertebrate Paleontology, 30, 1157–1168.
• Longrich, N. R., & Field, D. J. (2012). Torosaurus is not Triceratops. PLOS ONE, 7, e32623.