Image: Courtesy of SCIENCE

Digging in the Lower Cambrian limestone deposits in Shropshire, England, scientists have unearthed some of the oldest examples ever found of crustaceansa class of animals that includes lobsters, shrimp and crabs. Making the discovery all the more valuable, the two 511-million-year-old fossils are exquisitely preserved. Even the animals' soft tissues, cast in calcium phosphate, are clearly defined.

David J. Siveter of the University of Leicesterworking with Mark Williams of the British Geological Survey and Dieter Waloszek of the University of Ulmwas able to identify and analyze sections of exoskeleton, sternum, antenna and jaw, among other body parts (see image). The researchers describe the find in detail today in Science.

The anatomy of these crustaceans appears rather advanced, the scientists say, which suggests that the group as a whole likely originated during the Pre-Cambrian, a period of time that stretches from the earth's birth to 540 million years ago. Many scientists believe that the diversity of animals living on earth did not expand dramatically until later Cambrian times. But these fossils help build a case that animals were steadily diverging, evolutionarily speaking, well before the so-called Cambrian explosion. The scientists now hope that the Shropshire deposits will yield additional early fossils as stunningly well-preserved as this set.