Some 19m years ago the world’s sharks almost disappeared

SHARKS MAY not be the best-loved creatures on Earth, but they are an important part of marine ecology and many of the larger species are in . That threat, though, may be nothing compared with what happened 19m years ago, during the Miocene epoch—for then, it seems, the whole group came perilously close to extinction.The fossil record is a patchy reflection of the past, and rocks from the deep ocean, in particular, only rarely end up on dry land, and thus accessible to the palaeontologist’s hammer. Recent decades have, however, seen a number of drilling expeditions which have collected samples from the ooze that accumulates on the ocean floor. And a few years ago Elizabeth Sibert, a palaeoecologist now at Yale University, came up with a clever way to use these to gain information about life in the seas of the past. This was to look at microscopic, mineral-rich objects shed by sharks (mainly bits of protective skin-covering, known as denticles, pictured) and bony fish (mainly teeth). Counting and classifying these so-called ichthyoliths gives a sense of both the abundance and the diversity of the animals in question.