Deep sea fish such as the black swallower, with an extendable stomach that enables it to eat fish larger than itself, and manefishes, some sporting spiky fins like a Mohican haircut, are close cousins to mackerels and tuna despite having completely different body shapes and lifestyles.

‘Discovering that such radically different fish species are related is a bit like finding that a seal is more closely related to a cat than it is to a walrus!’ said Dr Matt Friedman of Oxford University’s Department of Earth Sciences, a co-author of the PLOS ONE paper. ‘By comparing genetic data with fossil evidence we were able to show that the origins of all these disparate groups lie in a period of rapid evolution that occurred around 65 million years ago. This is significant because this is when the Cretaceous extinction event that wiped out the dinosaurs also killed off many groups of large fishes inhabiting the open ocean.