Dog sized dinosaur discovered in North America, lived during Late Cretaceous period

A dog sized dinosaur fossil that lived during the Late Cretaceous period has been found in eastern North America and identified by Dr. Nick Longrich, from the University of Bath’s Milner Centre for Evolution in England. The extremely rare fossil provides evidence of an east-west divide in North American dinosaur evolution.

The land mass, which is now North America, was split in two continents by a shallow sea during the Late Cretaceous period (66 to 100 million years ago). The shallow sea – the Western Interior Seaway – ran from the Arctic Ocean to the Gulf of Mexico.

The dinosaurs that lived on the western continent – called Laramida – were similar to their cousins that lived in Asia.

Dog sized dinosaurThe dog-sized dinosaur, one of the leptoceratopsids, had a slender, beaked-shaped jaw, suggesting its diet was different from that of its western relatives. (Image: University of Bath)

It has been extremely difficult to find fossilized specimens from the eastern ‘lost continent’ of Appalachia because the area is densely vegetated.

Dr. Longrich studied one of these rare fossils, a jaw fragment kept at Yale University’s Peabody Museum. He said it was a member of the horned dinosaurs – the Ceratopsia.

Dr. Longrich wrote about his findings in the academic journal Cretaceous Research.

Ceratopsia were plant-eating horned dinosaurs

Ceratopsia were plant-eating horned dinosaurs that lived during the Cretaceous period. The fossil Dr. Longrich studied was the smaller cousin of the better known Triceratops – the leptoceratopsids. It was about the size of a German shepherd dog.

The fossil was too incomplete for Dr. Longrich to identify the exact species accurately, but he detected a strange twist to the jaw, causing the teeth to curve outwards and downward in a beak shap.

It had a slender jaw compared to those of Ceratopsia found in western North America. This suggests that these dinosaurs had a different diet compared to their western cousins, and had evolved along a different evolutionary path.

North America in the Late Cretaceous periodNorth America looked quite different during the Late Cretaceous period. The dog sized dinosaur was found in Appalachia.

Dr. Longrich said:

“Just as many animals and plants found in Australia today are quite different to those found in other parts of the world, it seems that animals in the eastern part of North America in the Late Cretaceous period evolved in a completely different way to those found in the western part of what is now North America due to a long period of isolation.”

“This adds to the theory that these two land masses were separated by a stretch of water, stopping animals from moving between them, causing the animals in Appalachia to evolve in a completely different direction, resulting in some pretty weird looking dinosaurs.”

“Studying fossils from this period, when the sea levels were very high and the landmasses across the Earth were very fragmented, is like looking at several independent experiments in dinosaur evolution. At the time, many land masses – eastern North America, Europe, Africa, South America, India, and Australia – were isolated by water.”

“Each one of these island continents would have evolved its own unique dinosaurs – so there are probably many more species out there to find.”

Citation: “A ceratopsian dinosaur from the Late Cretaceous of eastern North America, and implications for dinosaur biogeography,” Nicholas R. Longrich. Cretaceous Research, Volume 57, January 2016, Pages 199–207. DOI: 10.1016/j.cretres.2015.08.004.