Description and Classification

Sierraceratops was a four-legged plant-eating dinosaur, estimated to be about 4.5 meters (15 feet) long. Like other ceratopsid dinosaurs, it had a large head with a prominent frill at the back of its skull, horns over its eyes, and a horn on its nose. The frill of Sierraceratops was relatively long and somewhat rectangular, with two large openings in the bone called parietal fenestrae. These openings helped to make the large frill lighter.

Sierraceratops belongs to the family Ceratopsidae, a group of horned dinosaurs that includes famous members like Triceratops and Styracosaurus. Within this family, it is classified as a chasmosaurine. Chasmosaurines are known for typically having longer frills and more prominent brow horns compared to their relatives, the centrosaurines. The discovery of Sierraceratops has helped scientists better understand the diversity and evolution of chasmosaurine dinosaurs in southwestern North America, providing a link between older and younger species found in the region.

Distinguishing Features

Sierraceratops had several unique features that help scientists tell it apart from other horned dinosaurs:

• A long, somewhat rectangular frill with a straight back edge.
• Two large, forward-curving horns above its eyes.
• A relatively small horn on its nose.
• Distinctive bony knobs, called episquamosals, along the side edges of its frill (squamosal bones). It had fewer, but larger, bony knobs (epiparietals) along the back edge of its frill compared to some other chasmosaurines.
• A unique, D-shaped bump on the underside of the squamosal bone (the bone forming the side of the frill).

Paleoenvironment and Diet

Sierraceratops lived about 72 million years ago in what is now New Mexico. During that time, this area was part of a coastal plain near the Western Interior Seaway, a large inland sea that split North America in two. The environment was likely warm and wet, with rivers, swamps, and forests. This habitat, preserved in the rocks of the Hall Lake Formation, supported a variety of plant life.

As a herbivore, Sierraceratops would have eaten these plants. It used its strong beak to snip off tough vegetation like ferns, cycads, and possibly early types of flowering plants. Inside its mouth, it had rows of teeth that worked like scissors to slice and grind the plant material. Sierraceratops shared its world with other dinosaurs, such as duck-billed hadrosaurs, armored ankylosaurs, and large predatory tyrannosaurids like Bistahieversor. Other animals like crocodiles, turtles, and small mammals also lived in this ancient ecosystem.

Significance and Ongoing Research

The discovery of Sierraceratops is important because it adds another unique species to the growing family tree of horned dinosaurs. It shows that there was more diversity among chasmosaurine ceratopsids in southwestern North America than previously known, especially during the Late Campanian to Early Maastrichtian stages of the Late Cretaceous.

Sierraceratops helps paleontologists understand how these dinosaurs evolved and spread across the continent. Its particular mix of features contributes to ongoing discussions about the relationships between different chasmosaurine species, such as its connection to other southern North American forms like Coahuilaceratops and Bravoceratops. Further study of its bones may reveal more details about its growth, behavior, and its exact place within the ceratopsid family. The fossils from New Mexico continue to provide valuable clues about life during the age of dinosaurs.