The fossil of a tropical Asian freshwater turtle, found in the Canadian Arctic. The turtle has been named auroral. The discovery, detailed today in the journal Geology, suggests animals migrated from Asia to North America not around Alaska, as once thought, but directly across a freshwater sea floating atop the warm, salty Arctic Ocean. It also provides additional evidence that a rapid influx of carbon dioxide some 90 million years ago was the likely cause of a super-greenhouse effect that created extraordinary heat in the polar region.

The discovery of the Asian freshwater tropical turtle fossil in the Canadian Arctic raised the question of how exactly it wound up there. After all, a saltwater ocean separates Asia from North America. The scientists who made the discovery said the fossil dates to about 90 million years ago, a time when massive volcanic eruptions appear to have triggered a bout of super greenhouse warming.

The rapid warming, the scientists suspect, allowed meltwater to pour off the continents into the Arctic Ocean. Because fresh water is less dense than salt water, it may have rested on top of the marine water, creating a freshwater pathway for the turtle’s migration.

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