Einiosaurusprocurvicornis

Overview: Einiosaurus, discovered in the Two-Medicine Formation of Montana in the latter part of the 20th Century, was one of many ceratopsids that inhabited western North America during the Campanian stage of the Late Cretaceous. It is known for its unique nose horn, which curves strongly forward and downward, a feature which probably evolved more for display than for defense. It is very well represented for a dinosaur, being known from at least 15 individuals of varying ontogenetic stages.

Discovery: The two bonebeds that would yield Einiosaurus were discovered by paleontologist Jack Horner in 1985. The localities were on the Blackfeet Indian Reservation in northern Montana, USA in rocks of the Late Cretaceous (Campanian Aged) Two-Medicine Formation. The sites were excavated from 1985 to 1989, and in 1994, Scott Sampson named Einiosaurus procurvicornis. Einiosaurus means “bison lizard”, from the Blackfeet word for bison, “eini”, and Greek “sauros” meaning “lizard”. The name honors the Blackfeet tribe and reflects Sampson’s view that ceratopsids were "the buffalo of the Cretaceous". The specific name procurvicornis is Latin meaning “bent forwards horn”, in reference to the animal’s unique nose horn.

Evolution: Einiosaurus was a ceratopsid, a clade of rhinoceros-like herbivorous dinosaurs with parrot-like beaks, horns, and neck frills. Specifically, Einiosaurus was a centrosaurine, centrosaurines having (generally) smaller frills and longer nose horns than chasmosaurines. Within Centrosaurinae, Einiosaurus was more closely related (and may have been ancestral) to Achelousaurus and Pachyrhinosaurus, than to Centrosaurus and Styracosaurus.

Description: Einiosaurus was a medium sized ceratopsid, 4.5 metres (15 ft) long, and about 1.3 tonnes (1.43 tons) in weight, falling at the lower end of the weight range for modern rhinoceroses. Like other ceratopsids, it was quadrupedal, built rather like a rhinoceros, and had a parrot-like beak. Einiosaurus’s most distinctive features were horn and frill. It had a large thick, strongly curved nasal horn, which curved forward and downward (unique among ceratopsids). It also had a pair of small brow horns or bosses (boney lumps) over its eyes, and spike-shaped cheekbones. Its frill had a pair of prominent spikes jutting out of the top. Like most other ceratopsids, the frill also had two holes in it, which most likely would have been covered in skin, perhaps forming a colorful banner for display.

Behavior and Ecology: Einiosaurus lived in the Two-Medicine Formation of what is now Montana about 74.5 to 74 million years ago. It is thought to have inhabited an inland habitat, rather than a coastal one, and it shared its habitat with a variety of other dinosaurs including other ceratopsids as well as duckbilled hadrosaurs. The horns and frills of Einiosaurus were probably used more for display than for defense. Its parrot-like beak and complex dental batteries equipped it to eat tough vegetation. Due to its low posture and inability to stand on its hind legs, Einiosaurus would have been limited to feeding just a few feet above the ground. Like modern wildebeest and bison (for which Einiosaurus was named), Einiosaurus is thought to have formed into large herds, which may have served as a form of protection from carnivores, namely the tyrannosaurid Daspletosaurus which was the apex predator of the region, and which may have been specially adapted for hunting ceratopsians.

Extinction and Legacy: Einiosaurus seems to have gone extinct around 74 million years ago, about the same time that most other centosaurine ceratopsids seem to go extinct, with the exception of Pachyrhinosaurus which appeared 73.5 million years ago, immediately after the disappearance of the other centrosaurines. Why most centrosaurines went extinct at that time is unknown, but it may have been due to competition from other herbivores or possibly fluctuations in sea level and the coastline of the Western Interior Seaway which occurred around that time. Alternatively, Einiosaurus may not have truly gone extinct but rather may have evolved into Achelousaurus, which then may have evolved into Pachyrhinosaurus. If this is the case, then while Einiosaurus itself went extinct about 74 million years ago, its direct lineage would have survived until at least 69 million years ago, and possibly until the end of the Age of Dinosaurs. Today Einiosaurus can be found at the Museum of the Rockies in Bozeman, Montana, USA, where the holotype resides, and replicas can be seen at other museums, including the Los Angeles Natural History Museum in Los Angeles, California, USA, and the Natural History Museum of Utah in Salt Lake City, Utah, USA. Einiosaurus appeared in the 2003 Discovery Channel documentary Dinosaur Planet, fittingly hosted by Dr. Scott Sampson, the paleontologist who named Einiosaurus.