During the Late Cretaceous period, North America was divided by a body of water known as the Western Interior Seaway. This shallow sea, which spanned from the Arctic Ocean to the Gulf of Mexico, split the continent in two—the west known as Laramidia and the east known as Appalachia.

While fossils found where Laramidia once resided show similarities to those found Asia, the former Appalachia has proven difficult to excavate due to heavy vegetation. However, a jaw bone fragment from a small relative of Triceratops gave researcher Nicholas R. Longrich, of the Univ. of Bath, a unique window into Ceratopsia evolution.

“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,” Longrich said.

The research was published in Cretaceous Research.  

Ceratopsians were herbivores notable for their beaks and horns. Scientists believe they traveled in herds. According to Univ. of California Museum of Paleontology, bone beds containing bones from hundreds of individuals have been found in the western U.S.

Longrich’s studied specimen is known as leptoceratopsids, which was roughly the size of a large dog. The jaw bone fragment is housed at the Peabody Museum at Yale Univ. According to the Univ. of Bath, leptoceratopsids sported a more slender jaw with a twist, “causing the teeth to curve downward and outwards in a beak shape.”

“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,” said Longrich.

Since many land masses—including Europe, Africa and South America, among others—were isolated by water, Longrich said there are many more unique dinosaur species to discover.