Einiosaurus procurvicornis

Einiosaurus procurvicornis was a short-frilled ceratopsid from the upper Two Medicine Formation of Montana. At least fifteen individuals from two bonebeds preserve juveniles, subadults and adults, making it possible to study how its elaborate skull ornament changed during growth. Mature animals developed a long nasal horn that curved strongly forward, rounded masses of bone above the eyes and a pair of long rear frill processes. Younger individuals began with a more upright, backward-curving nasal horn and small pointed brow horns.

Its fossils occur between approximately 75.5 and 74.5 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

A deep beak and dental batteries sliced tough vegetation. The adult nasal horncore was elongated and bent forward, while the brow region carried rounded bosses rather than tall horns. The short parietal frill bore a pair of long, mostly straight P3 processes projecting backward and smaller marginal ornaments. Growth studies show that the frill approached adult size before the face and its ornaments finished changing. A powerful neck, broad trunk and columnar limbs supported the heavy skull and quadrupedal body.

• Long adult nasal horncore curving strongly forward
• Rounded masses of bone above the adult eyes
• Short frill with a pair of elongated rear processes
• Deep beak and stacked dental batteries
• Growth series from juvenile through adult skull ornamentation
• Two monospecific, multi-individual bonebeds

Museum of the Rockies teams led by Jack Horner and Carrie Ancell discovered the Canyon Bonebed and Dino Ridge Quarry in the upper Two Medicine Formation during the 1980s. Scott Sampson formally described Einiosaurus procurvicornis in 1995, selecting the adult skull MOR 456 8-9-6-1 from Canyon Bonebed as the holotype. The name combines eini, a Blackfeet word for bison, with Greek sauros, lizard; procurvicornis refers to the adult's forward-curving nasal horn.

Discovery credit: Carrie Ancell, Jack Horner.

Naming authors: Scott D. Sampson.

The upper Two Medicine Formation records inland river plains east of the growing Rocky Mountains. The climate was strongly seasonal, with periodic droughts, volcanic ash falls and episodes of heavy runoff. Einiosaurus shared the region with hadrosaurs, ankylosaurs, small theropods and larger tyrannosaurids. Both principal bonebeds lie on the Blackfeet Reservation, and DinoTree deliberately uses broad map markers rather than sensitive excavation coordinates.

The presence of many Einiosaurus individuals in two single-species bonebeds is consistent with groups gathering or moving together, but transport and repeated mortality can concentrate remains without preserving normal herd structure. Horns and frill ornaments probably contributed to visual signalling as well as physical interactions. Their dramatic change during growth supports a signalling role, but sex differences and exact behaviours remain unknown.

• At least fifteen individuals document several growth stages.
• Young animals had upright nasal horns that changed into the strongly forward-curving adult form.
• Its name honours the Blackfeet people and compares ceratopsids with bison.
• The frill reached near-adult size before the facial ornamentation finished developing.

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1. 01
   Two new horned dinosaurs from the Upper Cretaceous Two Medicine Formation of Montana; with a phylogenetic analysis of the Centrosaurinae

   Scott D. Sampson · Journal of Vertebrate Paleontology 15(4), 743–760 · 1995

   Open source
2. 02
   Comparative cranial osteology of subadult eucentrosauran ceratopsid dinosaurs from the Two Medicine Formation, Montana, indicates sequence of ornamentation development and complex supraorbital ontogenetic change

   John P. Wilson, John B. Scannella · Acta Palaeontologica Polonica 66(4), 797–814 · 2021

   Open source
3. 03
   Paleontology Department and Dinosaur Research

   Museum of the Rockies

   Open source