Aquilops americanus was the oldest horned dinosaur known to have existed in North America.
This nearly-recognized horned dinosaur was roughly the size of a large modern-day rabbit. They lived in North America around 107 million years ago, during the Early Cretaceous.
Horned dinosaurs migrated to North America from Asia between 113 million and 105 million years before our time. At first, paleontologists only discovered teeth, a tail, and a few bones of these horned dinosaurs, called neoceratopsians. A skull from one of the ancient animals was first discovered in 1997.
Fossils of A. americanus push back the history of horned dinosaurs on the North American continent.
Triceratops, a relative of the newly-named species, lived 40 million years after the smaller horned dinosaur. This is 20 million years before the previously oldest known animal of the type.
Aquilops americanus translates as "American eagle face," a name which refers to their heads, which resemble modern raptors.
Richard Cifelli, curator of vertebrate paleontology at the Sam Noble Oklahoma Museum of Natural History, led the expedition that discovered the new species. He and his team found part of a skull and a lower jaw, which are now housed at the museum where Cifelli is employed.
Bodies of A. americanus weighed about 3.5 pounds, and stretched around two feet in length. Unlike their Triceratops relatives, Aquilops did not possess a bony neck frill or horns.
"Aquilops is the first fossil to show what the earliest horned dinosaurs in North America looked like. Scattered teeth and bones from around the same time showed us that these animals were here, but not much else was known," Andrew Farke, a paleontologist and curator at the Alf Museum, said.
Examination of the newly-discovered fossils revealed A. americanus was more closely related to Asian ancestors of the animals than they were to American species. This discovery is consistent with similar findings from other dinosaur species, lending additional support to the idea of a migration across the Pacific Ocean.
Skull bones in the remains discovered by Cifelli and his team suggest the particular animal being studied was an adolescent, but adults were, likely, not much larger than the specimen found in southern Montana.
Scott Madsen discovered the fossil, consisting of teeth partially encased in rock, during the expedition, funded by National Geographic. At first, the team believed they had found a specimen from Zephyrosaurus. It was not until the teeth were cleared from their matrix that researchers realized they had uncovered a new species.
Discovery of the new species of dinosaur was detailed in the online journal PLOS One.
