Scientists have discovered a hitherto unknown mass extinction event that decimated the global shark population some 19 million years ago. It is currently a mystery as to what happened to the shark population, but the study authors say the event saw sharks almost entirely disappear from the open ocean in its wake.

Sharks and their ancestor species have been swimming Earth’s oceans for the past 450 million years. They are an extraordinarily resilient form of life that has endured numerous extinction events, and are now among the apex predators in Earth’s modern oceanic world.

Now, the results of a recently published study have revealed a new chapter in the history of these ancient predators, during which time their population was devastated on a global scale. The discovery was made by researchers from Yale University and the College of the Atlantic in Bar Harbor, Maine, who were compiling an 85-million-year fossil record of shark abundance in order to gain a greater understanding of how their population varied over vast swathes of time.

The record showed a 40-million-year period of relative stability, during which the ratio of shark to fish parts in the fossil record hovered at 1 to 5. However, around 19 million years ago this ratio was observed to dramatically shift to one shark fossil in 100. This finding points to a period of sudden, widespread change in the ancient open ocean ecosystem.

According to the authors of the study, the mystery event led to the extinction of roughly 70 percent of all sharks – roughly twice the levels experienced by sharks in the wake of the Chicxulub asteroid strike some 66 million years ago, which led to the decline of the dinosaurs. Furthermore, the death rate for sharks that dwelled in the open ocean was significantly higher when compared to populations that lived in coastal regions.

The cause of the extinction currently remains a mystery. It occurred in what is believed to have been a relatively stable time in our planet’s history, when Earth’s ecosystems were undergoing relatively little transformation, and no calamities such as asteroid strikes were recorded to have taken place.

“The current state of declining shark populations is certainly cause for concern and this paper helps put these declines in the context of shark populations through the last 40 million years,” explained study co-author Leah Rubin, who at the time of conducting the research was a student at the College of the Atlantic. “This context is a vital first step in understanding what repercussions may follow dramatic declines in these top marine predators in modern times.”

The paper has been published in the journal Science.

Source: Yale University

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