Rare Dinosaur Fossil Highlights How Isolated Species Evolve Differently

A rare fossil sighting provides valuable evidence supporting an east-west divide in North American dinosaur evolution, according to researchers from the University of Bath.

During the Late Cretaceous period between 66 and 100 million years ago, Earth's major landmasses were oriented a bit differently than they are today. In fact, what is now North America was actually divided by a shallow body of water known as the Western Interior Seaway. Therefore, differing prehistoric species could be found on either side of the divide.

In a recent study, Dr. Nick Longrich from the University of Bath's Department of Biology and Biochemistry analyzed a specimen composed of jaw fragments from the Peabody Museum at Yale University. In doing so, he discovered the fossils that were originally unearthed in eastern North America represent a rare dog-sized, horned dinosaur belonging to a herbivorous group known as Ceratopsia, according to a news release. 

While dinosaurs living on the continent of Laramidia, which was west of the Western Interior Seaway, are similar to those found in Asia, locating and identifying fossils from the eastern continent of Appalachia is more difficult because dense-growing vegetation tends to keep vital paleontological evidence hidden. However, the recent discovery represents the first fossil evidence of a ceratopsian dinosaur identified from this period in eastern North America. 

"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 explained in the university's release. "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."

When analyzing the jaw fragments, Longrich found a strange twist that caused the teeth to curve downward and outwards in a beak shape. Additionally, the specimen's jaw was more slender than that of Ceratopsia found in western North America, suggesting these dinosaurs had a different diet than their western relatives. Ultimately, this finding proves the two separated populations evolved along distinctly different evolutionary paths. 

"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," Longrich added. "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."

His findings were recently published in the journal Cretaceous Research.

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