The chimaeroid fishes enter the fossil record in the Triassic, multiply and diversify to at least 16 genera in the later Mesozoic (Stahl, 1999), and then dwindle during the Cenozoic to only six extant genera (Didier, 1995). Their origin and subsequent evolution have been difficult to trace because, like many other chondrichthyans, their remains consist most often of isolated teeth and fin spines freed and scattered after the cartilaginous skeleton disintegrated. Fossil species are commonly based on dental elements—tooth plates that were not shed like shark teeth but worn at the occlusal surface as they...

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