In a 1981 magazine essay, the evolutionary biologist Stephen Jay Gould let readers in one of his field's counter-intuitive truths. Aquatic animals, including lungfish and coelacanths, are more closely related to tetrapods ' four-limbed vertebrates ' than to salmon, sticklebacks and many other things people call 'fish' ' or, as Gould quipped, 'there is surely no such thing as a fish'. Sharks could be in a similar situation. A genomic study of dozens of shark species and their close relatives suggests that the ocean's top predators might also not be a natural biological group, contrary to what studies using more-limited genetic data have suggested. The analysis, posted last month to the bioRxiv preprint server, finds that, when researchers look at some 'ultra-conserved' parts of the genome, a peculiar family of sharks called Hexanchiformes might be part of an evolutionary lineage that is distinct from the group that includes all other sharks, as well as skates and rays1. The results,...
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