Researchers report in the June 4 issue of Science that fossils recovered from Pacific Ocean strata suggest a previously unknown and severe shark extinction event in which predator numbers collapsed by up to 90%. And experts have no idea what triggered the die-off.
“It’s a tremendous mystery,” says Yale University paleobiologist and oceanographer Elizabeth Sibert. “Sharks have been on the planet for 400 million years. They’ve gone to the underworld and back. Despite this, the incident wiped away [up to] 90% of them.”
According to ScienceNews Magazine Sharks lost 30 to 40% of their population in the aftermath of the asteroid catastrophe that wiped out all nonbird dinosaurs 66 million years ago (SN: 8/2/18). However, sharks had approximately 45 million years of tranquil ocean supremacy after that, cruising through major climate disturbances such as the Paleocene-Eocene Thermal Maximum — a 56 million-year-old occurrence marked by a dramatic increase in global carbon dioxide and soaring temperatures.
Now, indications discovered in the thin red clay layers underneath two enormous parts of the Pacific add a fresh, surprise chapter to the narrative of sharks.
The scientists weren’t hoping to see anything especially surprising. From 66 million years prior to around 19 million years prior, the proportion of fish teeth to shark scales in the silt held consistent at around 5 to 1. Yet, suddenly — the group gauges inside 100,000 years, and conceivably considerably quicker — that proportion drastically changed, to 100 fish teeth for each 1 shark scale.
The unexpected vanishing of shark scales corresponded with an adjustment of the plenitudes of shark scale shapes, which give a few hints to changes in biodiversity. Most present-day sharks have direct striations on their scales, which may offer some lift to their swimming proficiency. In any case, a few sharks come up short on these striations; all things being equal, the scales arrive in an assortment of mathematical shapes. By investigating the adjustment of the various shapes’ plenitudes when 19 million years prior, the specialists assessed a deficiency of shark biodiversity of somewhere in the range of 70 and 90 percent. The elimination occasion was “specific,” says Rubin, presently a sea life researcher at the State University of New York College of Environmental Science and Forestry in Syracuse. After the occasion, the mathematical scales “were practically gone, and never truly appeared again in the variety that they [previously] did.”
There’s no undeniable environmental occasion that may clarify a particularly huge shark populace shift, Sibert says. “Nineteen million years prior isn’t known as a developmental time in Earth’s set of experiences.” Solving the secret of the cease to exist is at the highest point of a not insignificant rundown of inquiries she desires to reply. Different inquiries incorporate better arrangement how the various denticles may identify with shark genealogies, and what sway the unexpected loss of such countless huge hunters may have had on other sea tenants.