A POSSIBLE EARLY CAMBRIAN CHORDATE

THE first chordate recorded from the Early Cambrian is the cephalochordate Yunnanozoon lividum from the 525 million-year-old Chengjiang fauna. Chordate features of Yunnanozoon are a notochord and an expanded filter-feeding pharynx with an endostyle. Segmented musculature and metameric branchial arches are shared with cephalochordates and craniates. Metameric gonads and an anteriorly extended notochord indicate cephalochordate affinities. Yunnanozoon expands the range of cephalochordate morphology known from the younger Pikaia gracilens and crown group forms such as amphioxus. Our identification predicts that other chordate clades (tunicates and craniates) had evolved by the tate Atdabanian, in the main burst of the Cambrian Explosion.