Two-Faced Fish Clue That Our Ancestors 'Weren't Shark-Like'

An investigation of a 415 million year-old fish skull strongly suggests that the last common ancestor of all jawed vertebrates, including humans, was not very shark-like. It adds further weight to the growing idea that sharks are not 'primitive'.The 415-million-year-old fish Janusiscus provides critical evidence for a well-developed external skeleton (shown in blue) in the shared ancestor of bony fishes and cartilaginous fishes such as sharks. Placoderm image courtesy of K Trinajstic.Credit: Oxford University/K TrinajsticThe fossil skull's external features meant it had always been thought to belong to the bony fishes (osteichthyans), a group which includes familiar fishes such as cod and tuna as well as all land-dwelling creatures with backbones. But when scientists from Oxford University and Imperial College London used X-ray CT scanning to look inside the skull they found the structure surrounding the brain was reminiscent of cartilaginous fishes (chondrichthyans) such as sharks and rays.



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