By Will Dunham
WASHINGTON (Reuters) - It was a dinosaur about the length of a crow and the weight of a bunny. But this modest plant-eater that lived about 108 million years ago in southern Montana foreshadowed the monstrous horned dinosaurs that trod North America millions of years later.
Scientists on Wednesday announced the discovery of the fossil of the oldest known horned dinosaur species from North America, a creature called Aquilops americanus that was a close cousin to similar dinosaurs from Asia.
The horned dinosaur lineage, called ceratopsians, arose in Asia but reached its apex in North America with the likes of Triceratops, a 30-foot-long (nine meters), six-ton beast with lengthy, sharp horns over its eyes, another over its nose and a bony shield above its neck.
Aquilops lived about 40 million years before Triceratops and nearly 20 million years before Zuniceratops, the next oldest ceratopsian identified from North America.
"Aquilops is known from a skull and lower jaws, which allow us to nail down its position in the dinosaur family tree pretty precisely," said paleontologist Andrew Farke of the Raymond M. Alf Museum of Paleontology in Claremont, California, who led the study published in the scientific journal PLOS ONE.
"Most importantly, Aquilops is far more closely related to horned dinosaurs from Asia than it is to horned dinosaurs from North America such as Triceratops. This shows that horned dinosaurs probably migrated into North America from Asia at least two different times, maybe even more," Farke added.
Aquilops is estimated at about 2 feet (60 cm) long and 2.5 pounds (1.1 kg), with a skull 3.3 inches (8.4 cm) long.
Like later horned dinosaurs, it possessed a sharp beak used to snip off the plants it munched. Unlike later ceratopsians, it was probably bipedal and did not have horns on its face. It did have a set of spikes on its cheeks.
"Aquilops is part of a building body of evidence that shows Asian dinosaurs, and early mammals, showing up in North America during the Early Cretaceous Period, between 110 and 105 million years ago," added Farke, who said early members of Tyrannosaurus rex's lineage also had Asian origins.
Horned dinosaurs were remarkably successful in terms of species diversity and abundance, said University of Oklahoma paleontologist Richard Cifelli, another of the researchers.
"By virtue of their slicing-style jaw movement and blade-like tooth series, they appear to have been well adapted to plant eating," Cifelli added.
Aquilops americanus means "Eagle Face from the Americas."
(Reporting by Will Dunham; Editing by Sandra Maler)