The most famous of the herbivorous, beaked dinosaurs classified as ceratopsians—and better known as horned dinosaurs—was Triceratops. Known for its three horns and the bony frill on the back of its neck, Triceratops lived during the last several million years of the Cretaceous Period, which ended some 65 million years ago, and is the most common dinosaur recovered from the uppermost Cretaceous deposits in western North America. Before the latest discovery, the earliest known horned dinosaur found in North America was Zuniceratops, which lived some 90 million years ago.
Paleontologist Scott Madsen of the Utah Geological Survey uncovered the rock containing the new ceratopsian fossil during a 1997 expedition to Montana funded by the National Geographic Society. Madsen initially thought it was another dinosaur, a Zephyrosaurus, but after he extracted the fossil from the rock he quickly realized it was a ceratopsian. This was a stunning find, as up until that point paleontologists had found only a scattering of teeth, bones and a tail belonging to early horned North American dinosaurs.
According to a report published this week in the journal PLOS ONE, paleontologists have dubbed the new species Aquilops americanus. Though it lacks the prominent horn and bony neck frill of Triceratops, the newly identified dinosaur sports other features unique to horned dinosaurs—most notably, a strongly hooked, toothless beak, called a rostral bone. Most likely used to crop the flowering plants and other vegetation that made up its diet, the beak gives the dinosaur’s skull the appearance of an eagle; the name “Aquilops” means eagle-face in Latin. The skull, which measures 3.3 inches (8.4 centimeters) long, also features a large cavity over the cheek region, as well as cheek spikes that might have been merely ornamental, or might have served as a type of defense mechanism.
To their surprise, the study’s authors found that Aquilops americanus appears much more closely related to Asian ceratopsian species such as Archaeoceratops oshimai and Leptoceratops gracilis than to other previously discovered North American ones. “In most features, it’s virtually identical to them,” lead researcher Andrew Farke of the Raymond M. Alf Museum of Paleontology in Claremont, California, told LiveScience. “And that’s cool because it adds support for this idea that, around 110 million years ago or so, there was a big influx of animals from Asia into North America.” At the time, Asia and North America were further away from each other than they are today, but scientists believe a land bridge might have connected the two continents, enabling the horned dinosaurs to migrate between them.
Using comparisons with similar ceratopsians from Asia, paleontologists estimate that Aquilops was no more than 2 feet (0.6 meters) long and weighed about 3 pounds, 8 ounces (1.6 kilograms), about as much as a cat or a large rabbit. By comparison, Triceratops weighed up to 4,000 times more. Judging from the skull bones, the study’s authors determined this particular dinosaur was an adolescent, but they believe an adult Aquilops wouldn’t have gotten much bigger. According to their analysis, Aquilops probably hid among bushes and other vegetation to escape predators like Deinonychus, a close relative of Velociraptor.
Though paleontologists hope the discovery of the oldest known North American horned dinosaur will help them reconstruct the early evolution of ceratopsians, they don’t expect to find many other fossils to guide them on this path. Scientists have combed over the rock unit where the Aquilops fossil was found, known as the Cloverly Formation. While they have turned up multiple fossils belonging to other dinosaurs, such as Tenontosaurus and Deinonychus, no others belonging to the earliest horned dinosaurs have surfaced, suggesting that—as Farke told National Geographic—Aquilops americanus may have been “a fairly marginal player at the fringes of the ecosystem.”