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3-Foot “Shrimp” Discovered—Dominated Prehistoric Seas

Anomalocaridids (model pictured) grew a third longer and survived 30 million years longer than thought. Image courtesy Esben Horn

“It would have made enough scampi to feed an army for a month.”

Christine Dell’Amore

National Geographic News

Published May 27, 2011

Fossils of a meter-long (3.3-foot) prehistoric ocean predator have been found in southeastern Morocco.

The specimens include the largest yet of its kind and suggests the spiny, somewhat shrimplike beasts dominated pre-dinosaur seas for millions of years longer than thought.

Early offshoots of an evolutionary line that led to modern crustaceans, the so-called anomalocaridids looked sort of like modern cuttlefish. But the fossil creatures had spiny limbs sprouting from their heads and circular, plated mouths, which opened and closed like the diaphragm of a camera.

Previous anomalocaridid fossils had shown the animals grew to perhaps 2 feet (0.6 meter) long, which already would have made them the largest animals of the Cambrian period (542 to 501 million years ago)—an evolutionarily explosive time, when invertebrate life evolved into many new varieties, such as sea lilies and worms.

(See “Earliest Animals Were Sea Sponges, Fossils Hint.”)

But at a foot longer than previous specimens, the largest of the new anomalocaridids suggests the segmented animals grew to bigger sizes than scientists had imagined.

“It would have made enough scampi to feed an army for a month—it was giant, and no doubt very tasty,” quipped study co-author Derek Briggs, director of the Yale Peabody Museum of Natural History.

(Watch a video of Briggs describing the anomalocaridids’ odd body.)

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