Paleontologists have discovered a rich array of exceptionally preserved fossils of marine animals that lived between 480 million and 472 million years ago, during the early part of a period known as the Ordovician. The specimens are the oldest yet discovered soft-bodied fossils from the Ordovician, a period marked by intense biodiversification.

The findings, which appear in the May 13 issue of the journal Nature, greatly expand our understanding of the sea creatures and ecosystems that existed at a crucial point in evolutionary history, when most of the animal life on the planet was found in the oceans.

The team -- led by Peter Van Roy, a Yale postdoctoral associate, and Derek Briggs, the Frederick William Beinecke Professor of Geology & Geophysics and director of the Yale Peabody Museum of Natural History -- uncovered more than 1,500 fossils of soft-bodied marine animals in newly discovered sites in southeastern Morocco during a field expedition last year. Many are complete fossils, and include sponges, annelid worms, mollusks and horseshoe crabs -- in particular, a species similar to today's horseshoe crab, which appeared some 30 million years earlier than previously known.