Description and Classification

Aquilops was a relatively small dinosaur, especially when compared to its later, giant relatives like Triceratops and Styracosaurus. Paleontologists estimate that Aquilops was about the size of a large raven or a small cat, measuring approximately 60 centimeters (2 feet) in length and weighing around 1.5 kilograms (3.3 pounds). Despite its small stature, it shared key features with other horned dinosaurs.

Aquilops belongs to the group Neoceratopsia, which is a major clade of herbivorous dinosaurs characterized by their beaks and, in many later forms, horns and frills. It is considered one of the earliest and most primitive neoceratopsians found in North America. Its discovery has helped scientists understand how these dinosaurs, many of which originated in Asia, spread to other parts of the world. Its classification places it as a basal (early-diverging) member within this group, closely related to similar early forms from Asia, like Liaoceratops.

Distinguishing Features

Aquilops possessed several unique anatomical traits that help paleontologists distinguish it from other dinosaurs, particularly other early ceratopsians:

• A prominently hooked rostral bone. This bone formed the tip of its upper beak and was sharply curved downwards, giving it the “eagle-like” appearance for which it was named.
• A small, distinct bump or boss on its snout, located in front of its eyes. This was not a true horn but might have been used for display to other Aquilops or for species recognition.
• An elongated, unusually shaped depression (known as an antorbital fossa) in the skull bone situated in front of the eye socket.
• Like other ceratopsians, it possessed a toothless beak for cropping vegetation, with batteries of teeth further back in the jaws for processing food.

Paleoenvironment and Diet

The fossil of Aquilops was found in the Cloverly Formation of Montana. During the Early Cretaceous, this region was a diverse landscape. The environment likely consisted of floodplains with rivers and streams, interspersed with open woodlands and fern-rich prairies. The climate would have been seasonal, experiencing both wet and dry periods.

As a neoceratopsian, Aquilops was a herbivore. Its sharp beak was well-suited for snipping off tough plant material, such as ferns, cycads, and possibly early flowering plants. The teeth located further back in its jaws would have then been used to shred this vegetation before swallowing. Aquilops shared its habitat with a variety of other dinosaurs. These included large predatory theropods like Acrocanthosaurus, the feathered dromaeosaurid Deinonychus (which could have posed a threat to a small dinosaur like Aquilops), and large ornithopods such as Tenontosaurus.

Significance and Ongoing Research

The discovery of Aquilops is highly significant because it represents the oldest definitive neoceratopsian dinosaur known from North America. This finding suggests that horned dinosaurs arrived on the continent earlier than previously thought, likely migrating from Asia across a land bridge. Its anatomy provides crucial evidence supporting theories about the dispersal patterns and evolutionary origins of North American ceratopsians.

Ongoing research focuses on further analyzing the single known skull to better understand its exact placement within the ceratopsian family tree. Comparisons with other early ceratopsians from Asia and North America help paleontologists piece together the evolutionary steps that led to the larger, more elaborate horned dinosaurs of the Late Cretaceous. Future discoveries of more complete Aquilops fossils, or similar early North American forms, would provide even more data to clarify the early history and diversification of this important dinosaur group on the continent, and its relationship to Asian relatives like Archaeoceratops.