Electroreception in early vertebrates: survey, evidence and new information

Electroreception is widespread in living vertebrates, and is often considered a primitive vertebrate character. However, the early evolution of electroreception remains unclear. A variety of structures in early vertebrate fossils have been put forward as potential electroreceptors, but these need to be reassessed in light of the now substantial literature on electroreceptors in living vertebrates. Here we review the evidence for all putative electroreceptors in early vertebrates, and provide new information from CT scans. In the jawless osteostracans, the pore canal system in the dermal skeleton and the lateral and dorsal fields do not resemble electroreceptors in living species. Nevertheless the presence of a recurrent ramus of the anterior lateral line nerve in osteostracans suggests electroreceptors were present, by comparison with lampreys. In placoderms, cutaneous sense organs on arthrodire cheek plates are possible electroreceptors. CT data shows that the orientation of these pits...