One of America's favorite varieties of seafood is shrimp. Did you know that they fossilize as well? Rodney Feldmann, professor emeritus of geology, and Carrie Schweitzer, associate professor of geology, report on the oldest fossil shrimp known to date in the world. The creature in stone is as much as 360 million years old and was found in Oklahoma. Even the muscles of the fossil are preserved.

Their study will be published in Journal of Crustacean Biology.

"The oldest known shrimp prior to this discovery came from Madagascar," Feldmann says. "This one is way younger, having an age of 'only' 245 million years, making the shrimp from Oklahoma 125 million years older."

The three-inch-long fossil shrimp was discovered by fellow paleontologist Royal Mapes of Ohio University and his students. Feldmann and Schweitzer named the fossil after Mapes: Aciculopoda mapesi.

The discovery is also one of the two oldest creatures in the decapod, or 10-footed, classification to which shrimp, crabs and lobsters belong. The other decapod, Palaeopalaemon newberryi, is of similar age and was found in both Ohio and Iowa. "The shrimp from Oklahoma might, thus, be the oldest decapod on earth," Feldmann explains.

The fossil is a very important step in unraveling the evolution of decapods. However, more finds are necessary. "The common ancestor of the two species can probably be found in rocks that once formed the old continent Laurentia," Schweitzer says. "Nowadays, these rocks can be found primarily in North America and Greenland. Who's going to find it? Possibly one of the numerous amateur collectors, who often graciously donate specimens to science."

The description of the fossil is remarkable not only because of its age, but also due to its remarkable preservation. In this case, the muscles that once made up the tail part of the shrimp were preserved. This is extremely rare in fossils. Feldmann knows why the muscles are still visible. "When the animal died, it came to rest on the seafloor," he says. "The muscles then were preserved by a combination of acidic waters and a low oxygen content as the animal was buried rapidly."

The shrimp lived in deeper waters of the ocean where currents were too weak to destroy the shrimp. Other animals that were found in the same rock include the extinct ammonites, nautiloids, brachiopods and sponges.

For more information about Kent State's Department of Geology, visit www.kent.edu/geology.

Accompanying Pictures:
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The fossil shrimp from Oklahoma and a recent shrimp. Credit: Rodney Feldmann/NOAA

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The fossilized muscles (left) were compared with muscles of a recent shrimp (right). Credit: Rodney Feldmann