Science

Mysterious extinction event wiped out 70 percent of Earth's sharks

Mysterious extinction event wi...
Researchers used fossilized denticles (teeth and scales) to discover a previously unknown die-off of sharks 19 million years ago
Researchers used fossilized denticles (teeth and scales) to discover a previously unknown die-off of sharks 19 million years ago
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Researchers used fossilized denticles (teeth and scales) to discover a previously unknown die-off of sharks 19 million years ago
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Researchers used fossilized denticles (teeth and scales) to discover a previously unknown die-off of sharks 19 million years ago

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

2 comments
2 comments
Nelson Hyde Chick
By the time humanity has swelled by billions more there will be little life in our oceans. Go anthropocene. Humanity is a cancer on this planet.
Worzel
This planet orbits the sun, and the sun, and its solar system orbits the centre of the galaxy, independently from the rotation of the galaxy. The solar system follows a sinusoidal path through the plane of the galaxy. The length of this 'wave' is around sixty million years. So, the solar system passes through the plane, roughly every 30 million years.
When the solar system passes through the plane of the galaxy, the Earth suffers a minor extinction event, due to the attenuation of solar radiation by interstellar dust. Approximately every 150 million years, it passes through one of the arms of the galaxy, and experiences an Ice Age* and a major extinction event. Presently, the planet has been in an ice age, for some 30-40 million years, with at least the same to go before it exits, back to 'normal'.
*(Not to be confused with a Glacial Period, caused by the Milankovitch cycle.)
Therefore, palaeontologists need to take this into consideration when puzzling over their finds.