The horned dinosaur (neoceratopsian) dates from the Early Cretaceous period in North America and has been named Aquilops americanus by scientists.
The limited fossil record for neoceratopsian dinosaurs has hampered previous efforts to reconstruct the early evolution of this group in North America. But the skull found in Montana has revealed new insights into this group.
The authors of the study, which is published in journal PLOS ONE, say it represents the first example of early North American neoceratopsian dinosaurs that they can identify to the species level.
The dinosaur, whose name means "American eagle face", is housed at the Sam Noble Oklahoma Museum of Natural History. It is distinguished by several features, including a strongly hooked rostral bone, or beak-like structure, and an elongated and sharply pointed cavity on the cheeks.
The skull is comparatively small, measuring 84 mm (3.3 ins) long, and is the only known specimen of Aquilops americanus. Scientists estimate the dinosaur was about the size of a crow.
They say it shows clear neoceratopsian features and is closely related to similar species in Asia.
"Aquilops lived nearly 20 million years before the next oldest horned dinosaur named from North America," said Andrew Farke, from Raymond M. Alf Museum of Paleontology, who led the study.
"Even so, we were surprised that it was more closely related to Asian animals than those from North America.
By combining the discovery with other neoceratopsian fossil records, researchers believe the ancestors of Aquilops americanus may have originated from Asia, supporting theories of a late Early Cretaceous (~113-105 million years ago) “intercontinental migratory event” between Asia and North America, as well as further migratory events later in the Cretaceous.