Triceratops

Triceratops is the largest, last, and most-collected ceratopsian. Its defining features are the long postorbital brow horns (up to 1 m), a shorter nasal horn, and a solid (non-fenestrated) parietal-squamosal frill. That solid frill is what separates it from many of its centrosaurine and chasmosaurine relatives, whose frills had large windows. The skull alone could exceed 2.5 m, which puts it among the largest skulls of any land animal that has ever lived.

The body was massive and quadrupedal, with a barrel chest, short tail, and graviportal limbs. Skin impressions show large polygonal scales of varying size. Some workers (Bell et al. 2014) have argued for sparse bristle-like structures based on Psittacosaurus-like preserved integument in basal ceratopsians, but no direct Triceratops evidence confirms this.

Two species are universally accepted: T. horridus (older, typical of the lower Hell Creek) and T. prorsus (younger, typical of the upper Hell Creek). Scannella et al. (2014) found strong evidence that the first evolved anagenetically into the second through the Maastrichtian. A third species, T. utahensis, is sometimes recognised.

Triceratops was the dominant herbivore of the latest Cretaceous Laramidian ecosystem. It coexisted with Tyrannosaurus rex, Edmontosaurus, Ankylosaurus, Pachycephalosaurus, and Thescelosaurus. Tooth-marked Triceratops bones, including a famous healed bite wound on a squamosal, confirm direct interaction with T. rex. Tooth wear suggests bulk feeding on fibrous low vegetation: palms, cycads, ferns.

The horns and frill probably did more than one job. Healed puncture and scraping wounds on adult skulls point to intraspecific combat, with animals locking horns in rutting-style fights like modern ungulates. Species recognition based on frill morphology also has good support. Thermoregulation through the frill is an older idea and less well supported. Herd behaviour is debated. Triceratops mass bonebeds are rarer than they are for centrosaurines, and many workers think the animal lived solitarily or in smaller groups.

• Big John — largest known Triceratops, ~8 m skull length 2.62 m, sold at auction 2021, now in Glasgow.
• Lane (HRS08-1, Triceratops horridus) — Houston Museum of Natural Science; preserves skin impressions.
• YPM 1820 (Marsh's original holotype) — Yale Peabody Museum.
• Kelsey — well-preserved Hell Creek specimen, Black Hills Institute.

Triceratops vs Torosaurus: Scannella & Horner (2010) proposed that Torosaurus is a fully mature Triceratops, which would sink the older genus. Longrich & Field (2012) and most workers since rejected the synonymy on the basis of morphological gaps that the ontogenetic series doesn't bridge. Anagenesis vs species pluralism: T. horridus → T. prorsus is a popular textbook example of anagenesis, though the boundary is somewhat fuzzy. Combat vs display vs species recognition: all three are in play; the relative weight is the live argument.

The Triceratops vs T. rex matchup is the most-depicted dinosaur scene in popular culture, going back to Charles Knight's 1901 painting and forward through Jurassic Park. Triceratops is the state dinosaur of South Dakota and Wyoming.

• ceratopsia
• styracosaurus
• centrosaurus
• pachyrhinosaurus
• protoceratops
• tyrannosaurus-rex

• Dodson, P. (1996). The Horned Dinosaurs. Princeton University Press.
• 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.
• Scannella, J. B., et al. (2014). Evolutionary trends in Triceratops from the Hell Creek Formation. PNAS, 111, 10245–10250.
• Farke, A. A., et al. (2009). Evidence of combat in Triceratops. PLOS ONE, 4, e4252.