Fossil finds

摘要

Palaeontologists have been trying to resolve early events in vertebrate evolution by attemptingto illuminate the journey from a jawless to a jawed existence. A pressing challenge has been to make sense of the masses of extinct jawed fish that seem to shoal around this evolutionary transition and place the acquisition of anatomical features onto a timeline. And some fossil finds raise questions about the validity of groups such as the heavily armoured placoderms and the spiny-shark-like acanthodians.