for National Geographic Magazine
The tiny, prehistoric seashells swirl, spiral, and twist. Some curl like soft-serve ice cream, others sport crowns of fragile, hollow spines. They evoke tropical reefs, but geologist David Rohr found them 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.
(See more photos and a map of where fossils have been found.)
Fossil Mosaic
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 Alaska's 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.
Rohr, chair of Earth and physical sciences at Sul Ross State University, in Alpine, Texas, believes 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, he 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 says.
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