Scientists know that at one point or another, North America was split down the middle. Not by politics or religion, but by a winding body of water known as the Western Interior Seaway that connected the Gulf of Mexico to the Arctic Ocean and divided the continent into east and west. But when exactly the land on either side connected hasn't been exactly clear. Paleontologists have stumbled upon a very helpful clue in the form of a tooth from a triceratops-like dinosaur, which sheds new light on the movements of these horned beasts and adds new detail to this story of how two became one.

Hundreds of miles wide and thousands of miles long, the Western Interior Seaway is thought to have separated North America during much of the Late Cretaceous Period, from roughly 100 million to 66 million years ago. Therefore, the animals that evolved on the each side after its formation stayed there. Large herds of dinosaurs wandered the western shoreline, leaving a bounty of tracks to create what paleontologists today call the Dinosaur Freeway.

Among the creatures stuck on the western side of the seaway were the horned dinosaurs, known formally as the ceratopsids. Or so we thought. A single dinosaur tooth discovered on the eastern side by George Phillips, a paleontology curator at the Mississippi Department of Wildlife, Fisheries, and Parks' Museum of Natural Science, suggests otherwise.

"The shape of this tooth, with its distinctive split root, is absolutely unique among dinosaurs," said Andrew Farke, a paleontologist at the Raymond M. Alf Museum of Paleontology at The Webb Schools in Claremont. "We only have the one fossil, but it's more than enough to show that an animal very similar to Triceratops – perhaps even Triceratops itself – made it into eastern North America."

The researchers say the tooth is between 68 and 66 million years old, indicating that the two halves of the continent became connected before the major global extinction event 66 million years ago. It was discovered in a creek formation in northern Mississippi, which was underwater at the time although fairly close to land. This leads the scientists to speculate that it likely came from a horned dinosaur living along the coastline before the animal washed out to sea.

The research is published in the journal PeerJ.

Source: PeerJ (PDF)

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