Prehistoric fossils provide clues to Alaska's Eurasian roots

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Washington, Nov 19 : Prehistoric fossils of snails found in gray Alaskan limestone are adding to the evidence about the Alaska-Eurasia connection.

According to a report in National Geographic News, geologist David Rohr found the tiny, prehistoric seashells lodged in gray Alaskan limestone.

These 18 Paleozoic-era snails, half of them new to science, did live on reefs some 420 million years ago, when jawless fishes spread throughout the seas and the ancestors of spiders and centipedes began creeping about on land.

Many of the snails resemble no other fossils from North America's landmass. Instead, they're linked to creatures whose fossils have been discovered as far away as Eastern Europe and Russia's Ural Mountains.

These new finds are adding to a growing body of evidence about Alaska's diverse and far-flung geological roots.

Modern Alaska is a geological puzzle, a mosaic of fragments from other parts of the world. Geologists suspect the state contains only a small triangle of original North America, located along its east-central boundary with Canada.

Fossils suggest that the rest of Alaska was formed from a patchwork of small land chunks, known as terranes, that collected against North America like flotsam during the Mesozoic and early Cenozoic eras, between 251 million and 60 million years ago.

Paleontologists began noting weirdly similar fossils in Alaska and Eurasia as far back as 1907, and they've been working ever since to trace their links and decipher their origins.

According to Rohr, the spreading prehistoric seafloor carried his snails' limestone grave to the southeast panhandle of Alaska on a 100,000-square-kilometer chunk of land called the Alexander terrane.

With support from the National Geographic Society's Committee for Research and Exploration, Rohr and his colleague Robert Blodgett have found striking similarities between the Alaskan fossil shells and shells from Europe and Russia that date back to the same time, the Paleozoic era's Silurian period, between 417 million and 443 million years ago.

"We were impressed because some of these fossils seemed to match species in Europe," Rohr said.

One of the fossils, a smooth, loosely spiraled shell, exactly matches specimens of Beraunia bohemica collected in the Czech Republic; and a tightly swirled cone matches Medfracaulus turriformis shells found in the eastern Urals.

Neither had been found before in North America.

These snails lived in a warm, shallow sea near Siberia during a period when coral reefs first formed.

Rohr speculates that they didn't move around much, but when necessary, could propel themselves along the seafloor or reef surfaces by lifting their shells with their muscular foot and then falling forward.

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