Fossils Challenge Theory of Rapid Animal Evolution in Cambrian

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Earlier Emergence

The fossils indicate that a crustacean was already evolved in the early Cambrian. The scientists said this suggests that the necessary steps in the evolutionary tree of arthropods that led to the design of crustaceans must have begun in the late Precambrian.

Scientists are now scouring other deposits like the Shropshire limestone for fossils of other multi-celled animals, as additional evidence to support the idea that a long evolutionary fuse preceded the Cambrian explosion.

Regardless of how long the evolutionary fuse to the Cambrian explosion may have been, the Cambrian is marked by the sudden appearance of animals of increased size and with shells.

"It is still clear that something very important happened at the Cambrian, and the choice is between the appearance of animals themselves or changes in pre-existing animals that forced the explosion," said Fortey. "It's asking a lot of evolution to manage all the business together at once, as some have claimed."

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