Sharks 19 million years ago
Washington, Jun 5 (Plenglish) Shark populations became extinct 19 million years ago without the occurrence of any climate event or changes in the ecosystem, a study published in Science magazine revealed.
A team of scientists from Yale University, in the United States, headed by Elizabeth Sibert, postdoctoral associate at the Department of Earth and Planetary Sciences of that educational center, confirmed the finding after studying the teeth of microfossil fish and scales of sharks in sediments in the deep sea. Sibert, who is also a member of the Institute for Biospheric Studies from that university, said that by generating a record of 85 million years of abundance of those marine species, it discovered a sudden drop of more than 70 percent in the number of shark specimens.
The higher number of deaths occurred in the open sea compared with coastal waters, a figure that is twice the level of extinction recorded in the Cretaceous-Paleogene period 66 millions ago, which wiped out three-fourths of plant and animal species on Earth, she noted. Future research will allow confirming whether the deaths of sharks caused remaining populations to change their habitat and why they did not recover after that event 19 million years ago, the publication commented.
Today, Shark populations in the high seas have fallen by 71% since 1970, researchers have found. The main cause is overfishing, which has put three-quarters of these species at risk of extinction. Humans have hunted sharks for centuries for their meat and fins. A related group of fish, the rays, are caught for their gills, which are used in traditional Chinese medicine. Studies have identified severe regional declines of specific species, such as the loss of scalloped hammerhead sharks in the northwest Atlantic Ocean, but no one had compiled trends in all oceans.