Dog-Sized Dinosaur Fossil Reveals US Was Split

Scientists have uncovered the fossil of a dog-sized dinosaur - which they say shows prehistoric North America was split in half.

Jaw fragments from the creature which roamed eastern North America up to 100 million years ago were found on the eastern side of the continent.

Experts say it is so different to those found on the western side that a shallow sea probably once divided the two continents.

The shallow sea, the Western Interior Seaway, ran from the Gulf of Mexico to the Arctic Ocean.

Dinosaurs living in the western continent, called Laramidia, were similar to those found in Asia.

However, few fossils from the eastern "lost continent" of Appalachia have been discovered as the areas are densely vegetated, making it difficult to discover and excavate fossils.

Dr Nick Longrich, from the Milner Centre for Evolution based at the University's of Bath's Department of Biology and Biochemistry, studied the specimen.

He 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."

Dr Longrich's study is published in the journal Cretaceous Research.