Scientists have discovered the largest mass extinction since the dinosaurs.
About 19 million years ago, a mysterious event nearly drove the world’s entire shark population to extinction , according to a new study published in the journal Science. Approximately 90% of sharks disappeared from the oceans in less than 100,000 years , something that significantly affected the ancient marine environment, and why the oceans went from being full of sharks to never recovering from this extinction event.
It’s amazing because sharks have survived the Great Dying, the mass extinction event of 200 million years ago, and even the asteroid that wiped out most of the dinosaurs roughly 66 million years ago.
“Sharks have been around for 400 million years; they have withstood many mass extinctions, some of which wiped out almost all life. However, during the early Miocene epoch, something happened that almost wiped this group off the face of this Earth “, explains Elizabeth Sibert, from the Institute of Biospheric Studies at Yale University and co-author of the work.
An extinction event larger than the Cretaceous
Sharks are known to have lived longer than any species , but the new study reveals that this event killed one in ten sharks, nearly eliminating them from ocean bodies, a fact that puzzles scientists. The extinction event that occurred during the early Miocene period had to be colossal to nearly exterminate 90% of sharks overnight. Scientists still have no idea what exactly happened, but they are sure it was two or three times more catastrophic than the asteroid that killed the dinosaurs and the sharks never recovered.
According to the experts, it is a fairly clear assumption to say that there were many more species of sharks in the oceans, so there was more ecological diversity.
The ocean floor is the key to answering the mysterious disappearance of ancient sharks
Scientists came to this conclusion after analyzing a group of ichthyolites, microscopic fossils of shark scales (called denticles) and fish teeth buried in sediments deep on the ocean floor that have accumulated over millions of years, allowing one species time travel: every X centimeters deepening towards the nucleus, it is X years in evolutionary history. Ichthyoliths, although found in most sediments, are rarely studied in depth because they are small and relatively rare compared to other microfossils.
When they compared the proportion of ancient shark denticles in samples from the Pacific Ocean with other fish teeth buried up to 5,700 meters deep in the seafloor , they noticed a clear change in ocean life about 19 million years ago. Before this time, sediment samples contained a large number of denticles and teeth; after this date, only a third of the samples contained some shark denticles. This unexpected drop in shark abundance is twice as large as what was found for the Cretaceous-Paleogene extinction event, which saw the disappearance of three-quarters of all plant and animal life approximately 66 million years ago.
In sediment samples deposited after the extinction event, the researchers found no new types of shark denticles, suggesting that very few shark species have emerged since then.
What would cause such devastation? What is clear is that this extinction that decimated the number of sharks in the deep sea, paved the way for other predators, such as certain types of whales, to dominate the open ocean.
Referencia: An early Miocene extinction in pelagic sharks Elizabeth C. Sibert Leah D. Rubin Science 04 Jun 2021: Vol. 372, Issue 6546, pp. 1105-1107 DOI: 10.1126/science.aaz3549
