The surprising find of a freshwater, tropical turtle fossil in Arctic Canada suggests that the first turtles to migrate from Asia to North America may have taken the most direct route, swimming and island hopping straight through the Arctic Ocean. This was possible, researchers say, because the Arctic was warmer and ice-free 90 million years ago, when carbon dioxide levels were extraordinarily high. “The fossil record is giving us more and more information about how ancient animals responded to a warming world,” [says] geophysicist John Tarduno…. “They moved toward the poles” [Wired News].
The freshwater turtle was able to survive in the ocean, Tarduno says, because of a floating freshwater highway that led from Russia to Canada. Numerous rivers from the adjacent continents would have poured fresh water into the ancient Arctic sea…. Fresh water, which is lighter than marine water, may have rested on top of the salty ocean water allowing animals such as the turtle to migrate with relative ease [Telegraph].
The fossil was found on an island within the Arctic Circle called Axel Heiberg, which is covered with lava flows. Says Tarduno: “We found this turtle right on top of the last flood basalts – a large stretch of lava from a series of giant volcanic eruptions. That leads us to believe that the warming may have been caused by volcanoes pumping tremendous amounts of carbon dioxide into the Earth’s atmosphere. There is evidence that this volcanic activity happened all around the planet – not just the Arctic” [Telegraph].
Today, those volcanoes form the peaks of the Alpha Ridge, an underwater Arctic mountain chain connecting the northern coasts of Russia, the United States in Alaska and Canada [National Post]. But researchers believe that the tops of many volcanoes poked above the ocean’s surface 90 million years ago, allowing the turtles to island-hop from one peak to the next.
The fossil found on Axel Heiberg turned out to be a new species that researchers named Aurorachelys, which will be described in the February issue of Geology; it belongs to a family of extinct Asian turtles with very round shells.
Image: University of Rochester/John Tarduno