The mystery of the ‘mass shark death’: Sharks nearly disappeared from Earth’s oceans 19 million years ago when numbers fell by more than 90 percent — but scientists have no idea what caused it
- Researchers led by Yale University studied tiny fossil shark teeth and scales
- They recorded the abundance and diversity of sharks over the past 40 million years
- Sharks never really recovered from the newly discovered die-off, the team said
- The reason for the die-off is unclear – there were no known upheavals at the time
Sharks nearly disappeared from the world’s oceans about 19 million years ago, with populations declining by more than 90 percent, a study found.
Researchers led by Yale University constructed a record of shark diversity and abundance over the past 40 million years based on fossil teeth and scales.
The episode came, the team explained, at a time when shark numbers were about ten times what they are today, and they never really recovered.
This fundamental shift in the ecological makeup of pelagic predators paved the way for the large, migratory shark lines that now dominate our oceans.
However, the cause of this mysterious “mass shark die-off” and its broader implications are unknown to scientists, at least for now.
Sharks nearly disappeared from the world’s oceans nearly 19 million years ago — with populations declining by more than 70 percent — a study finds. Pictured: A negative image of a shark made up of ‘teeth’, the teeth on sharks’ teeth
“We came across this extinction almost by accident,” said author and paleobiologist Elizabeth Sibert of Yale University in New Haven, Connecticut, who studies microfossil fish teeth and shark scales in deep-sea sediments.
“We decided to generate an 85-million-year-old record of fish and shark abundance just to get a sense of what the normal long-term variability of that population looked like,” she added.
“What we found, however, was this sudden decline in shark abundance about 19 million years ago, and we knew we needed to investigate further.”
While much of what is known about ancient marine species is derived from fossils preserved in shallow water deposits, Dr. Sibert and colleagues found tiny teeth and scales that found deep-sea sediment cores collected around the world.
The researchers found that more than 70 percent of the world’s shark species died, with a higher death toll among those living in the open ocean compared to those swimming in coastal waters.
In fact, the team said sharks suffered twice as many losses in this episode than they did during the Cretaceous-Paleogene mass extinction 66 million years ago, which wiped out three-quarters of all living species (including the dinosaurs).
One mystery lies in the fact that no climate catastrophe or other ecosystem disruption was known at the time shark populations plummeted.
Researchers led by Yale University constructed a record of shark diversity and abundance over the past 40 million years based on fossil teeth and scales. Pictured: Megalodon, an extinct shark species that lived about 23-3.6 million years ago
“This interval is not known for major changes in Earth’s history,” said Dr. Sibert.
But, she added, “it has completely changed the nature of what it means to be a predator living in the open ocean.”
“The current state of declining shark populations is certainly cause for concern,” added the paper’s author Leah Rubin of the State University of New York.
The study, she said, “helps put this decline in the context of shark populations over the past 40 million years.”
“This context is an essential first step in understanding the implications of the dramatic decline of these apex predators in modern times.”
Yale paleontologist Pincelli Hull – who was not involved in the study – said future work should look at “to understand this period and its implications not only for the emergence of modern ecosystems, but also for the causes of major collapses in the shark diversity’.
“It represents a major shift in ocean ecosystems at a time previously considered unremarkable.”
Further research may be able to confirm whether the extinction event caused the remaining sharks to avoid the open ocean — and perhaps explain why their populations failed to bounce back in the wake of the die-off.
The study’s full findings were published in the journal Science.
HOW SHARKS EARN THEIR MIND REPUTATION?
Sharks are the most efficient predators on Earth and have long terrified humans.
Their basic design has never really changed over 200 million years and they are considered complex and intelligent.
Their teeth are fear factor number one, with the great white’s teeth growing up to two and a half inches long.
Their prey is impaled on the pointed teeth of the lower jaw where they saw away parts of the flesh. The serrated edges of the teeth aid in this process.
Their teeth are brittle and constantly break down, but also grow back continuously and on average there are 15 rows of teeth in the mouth at a time.
Sharks are the most efficient predators on Earth. Their basic design has never really changed over 200 million years
Their speed is fear factor number two.
They are very fast in the water compared to humans with the shortfin mako shark being able to reach an incredible 60 mph in bursts.
The great white can reach speeds of 25 mph.
In comparison, 5 mph is the fastest a human can reach.
The strength and size of a shark also scares us.
The great white shark can grow up to 6 meters in height and while it has no particular taste for humans, even an exploratory bite is enough to cut a man in half.
Most sharks release a human after its first bite, but sometimes that’s all it takes to kill a person.
However, sharks have much more reason to be afraid of humans. We kill up to a million a year, often cutting off their fins just to make soup and throwing the rest of the shark back into the water, where it starves or drowns.