The “eagle-faced American,” Aquilops americanus, was a raven-sized horned dinosaur with spiky cheeks and a funky little bump on its beak. And the paleontologists who examined its fossilized skull fragments are calling it “a really cute little dinosaur.” At 106 million years old, the pint-sized Aquilops is also the oldest horned dinosaur described in North America—beating the previous record by nearly 20 million years. The findings were published in PLOS ONE this week.
Over a decade ago, paleontologists working in the Cloverly Formation of Carbon County, Montana, unearthed the partial skull, lower jaw, and teeth of a small horned dinosaur. Previous work has shown that horned dinosaurs (or neoceratopsians) originated and diversified in the Early Cretaceous, but findings from that time period in the North American fossil record were limited to isolated teeth and bits of the post-cranial skeleton. Beloved triceratops showed up much later.
Now, based on several features—including a hook on its beak-like structure (or rostral bone) and a long, pointed cavity over its cheek—the skull belongs to a previously unknown species, according to Andrew Farke from the Raymond M. Alf Museum of Paleontology and colleagues.
The genus name is derived from the Latin aquila, meaning “eagle,” and the Greek ops, which means “face.” These refer to the hooked beak on its skull. “No idea what it was for (fighting? digging? something else?),” Farke writes in a PLOS blog, “but it sure was cool.” The species name means “American” in Latin, to reflect its status as the earliest, unequivocal neoceratopsian in North America.
The small skull is only about 84 millimeters long. And Aquilops was probably no longer than 0.6 meters and weighed about 1.6 kilograms—“about as much as a large bunny rabbit,” Farke tells National Geographic. The skull size, development of the teeth, and fusion of the bones suggest that the animal was young but definitely not a baby. It was likely a teenager. Using what's known about skeletons of close relatives, the team was able to reconstruct the rest of the dinosaur. The body plan of early horned dinosaurs was fairly conservative, according to Farke: large head, long hindlimbs, shorter forelimbs, mostly bipedal, long tail.
Surprisingly, Aquilops isn’t that closely related to later horned dinos from North America. Rather, it’s more closely related to dinosaurs who lived in Asia at around the same time—which supports the idea of an intercontinental migratory event between 113 million and 105 million years ago in the late Early Cretaceous. "Aquilops lived nearly 20 million years before the next oldest horned dinosaur named from North America," Farke says in a news release. "Even so, we were surprised that it was more closely related to Asian animals than those from North America."