The fossil of a dog-sized, horned dinosaur that roamed eastern North America up to 100 million years ago, is evidence of an east-west divide in the evolution of dinosaurs on the continent, a scientist studying the fossil has said.
During the Late Cretaceous period, 66 to 100 million years ago, the North American continent was divided by a shallow sea into two landmasses - Laramidia in the west, and the "lost continent" of Appalachia in the east.
Dinosaurs living in Laramidia were similar to those found in Asia.
But few fossils from Appalachia have been discovered because the areas dense vegetation has made it difficult to discover and excavate them.
Dr Nick Longrich, from the Milner Centre for Evolution at the University of Bath, studied a fragment of jaw bone from a rare eastern fossil.
Although he was unable to identify the exact species accurately, he saw it had a strange twist to the jaw, causing the teeth to curve downward and outwards in a beak shape.
The jaw was also more slender than that of Ceratopsia found in western North America, suggesting the dinosaurs had different diets and evolved along distinct evolutionary paths.
Ceratopsia is a group of plant-eating horned dinosaurs that lived in the Cretaceous period.
The fossil Dr Longrich studied comes from a smaller cousin of the better known Triceratops, the leptoceratopsids, which is about the size of a large dog.
The fossil is kept in the Peabody Museum at Yale University in the US.