Bizarre shrimp-like monsters that were the world's largest predators for millions of years grew even larger and survived much longer than thought, scientists find.

The creatures, known as anomalocaridids, were giant predators (ranging from 2 to possibly 6 feet in length) with soft-jointed bodies and toothy maws with spiny limbs in front to snag worms and other prey. [Image of the ancient sea monster]

"They were really at the top of the food chain," said researcher Peter Van Roy, a paleobiologist at Ghent University in Belgium, and formerly at Yale. "The uncontested top predators of their time."

Past research showed they dominated the seas during the early and middle Cambrian period 542 million to 501 million years ago, a span of time known for the "Cambrian Explosion" that saw the appearance of all the major animal groups and the establishment of complex ecosystems....