Giant sea creature hints at early arthropod evolution

Newly discovered fossils of a giant, extinct sea creature show it had modified legs, gills on its back, and a filter system for feeding - providing key evidence about the early evolution of arthropods. The new animal, named Aegirocassis benmoulae in honor of its discoverer, Mohamed Ben Moula, attained a size of at least seven feet, ranking it among the biggest arthropods that ever lived. It was found in southeastern Morocco and dates back some 480 million years. " Aegirocassis is a truly remarkable looking creature," said Yale University paleontologist Derek Briggs, co-author of a paper describing the animal. "We were excited to discover that it shows features that have not been observed in older Cambrian anomalocaridids - not one but two sets of swimming flaps along the trunk, representing a stage in the evolution of the two-branched limb, characteristic of modern arthropods such as shrimps." Briggs is the G. Evelyn Hutchinson Professor of Geology and Geophysics at Yale and curator of invertebrate paleontology at the Yale Peabody Museum of Natural History. First author Peter Van Roy, an associate research scientist at Yale, led the research; Allison Daley of the University of Oxford is co-author. Since their first appearance in the fossil record 530 million years ago, arthropods have been the most species-rich and morphologically diverse animal group on Earth.