A POSSIBLE EARLY CAMBRIAN CHORDATE

THE first chordate recorded from the Early Cambrian is the cephalochor date Yunnanozoon lividum from the 525 million-year-old Chengjiang faun a. Chordate features of Yunnanozoon are a notochord and an expanded fi lter-feeding pharynx with an endostyle. Segmented musculature and meta meric branchial arches are shared with cephalochordates and craniates. Metameric gonads and an anteriorly extended notochord indicate cephal ochordate affinities. Yunnanozoon expands the range of cephalochordate morphology known from the younger Pikaia gracilens and crown group fo rms 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.