Mysterious mass extinction
The term “shark” inspires predictable images of stealthy and streamlined marine predators that are key components of modern ecosystems. Studying shark teeth buried in deep sea sediment, Sibert and Rubin reveal that current shark diversity is a small remnant of a much larger array of forms that were decimated by a previously unidentified major ocean extinction event (see the Perspective by Pimiento and Pyenson). The extinction led to a reduction in shark diversity by more than 70% and an almost complete loss in total abundance. There is no known climatic and/or environmental driver of this extinction, and its cause remains a mystery. Modern shark forms began to diversify within 2 to 5 million years after the extinction, but they represent only a minor sliver of what sharks once were.
Science, aaz3549, this issue p. 1105; see also abj2088, p. 1036
Shark populations have been decimated in recent decades because of overfishing and other anthropogenic stressors; however, the long-term impacts of such changes in marine predator abundance and diversity are poorly constrained. We present evidence for a previously unknown major extinction event in sharks that occurred in the early Miocene, ~19 million years ago. During this interval, sharks virtually disappeared from open-ocean sediments, declining in abundance by>90% and morphological diversity by>70%, an event from which they never recovered. This abrupt extinction occurred independently from any known global climate event and ~2 million to 5 million years before diversifications in the highly migratory, large-bodied predators that dominate pelagic ecosystems today, indicating that the early Miocene was a period of rapid, transformative change for open-ocean ecosystems.