The largest sharks ever to have roamed the oceans parked their young in shallow, warm-water nurseries where food was abundant and predators scarce until they could assume their title as kings and queens of the sea.
However, as sea levels declined in a cooling world, the brutal mega-predator, Otodus megalodon, might have found fewer safe-haven coastal zones where its young could safely reach adulthood, researchers reported yesterday in the Royal Society journal Biology Letters.
Indeed, the reliance of megalodons on nurseries might have contributed to the end of their 20-million-year reign, the research said.
Otodus megalodon — sometimes classified as a Carcharocles megalodon — took 25 years to become an adult — “an extremely delayed sexual maturity,” the authors said in the research paper.
Once it was fully grown, the shark could reach up to 18m, three times the size of the largest great white shark, made famous by the 1975 hit movie Jaws.
As an apex predator, and up until its extinction about 3 million years ago, the adult megalodon had no rivals among other ocean hunters, and feasted on smaller sharks and even whales, but its young were vulnerable to attacks by other predators, often other razor-toothed sharks.
Nurseries on shallow continental shelves with extensive smaller fish for food and few competing predators gave them the ideal space to reach their awesome size.
“Our results reveal, for the first time, that nursery areas were commonly used by the O. megalodon over large temporal and spatial scales,” the authors said.
The research team discovered a nursery zone off the eastern coast of Spain in Tarragona Province after visiting a museum and observing a collection of megalodon teeth.
“Many of them were quite small for such a large animal,” authors Carlos Martinez-Perez and Humberto Ferron from the University of Bristol said.
Judging by the size of the teeth, they surmised the area had once been home to young megalodons.
The Spanish nursery could be described as “a perfect place to grow,” the authors said.
They said that it would have been a “shallow bay area of warm waters, connected to the sea and with extensive coral reefs and plenty of invertebrates, fish species, marine mammals and other sharks and rays.”
The researchers analyzed eight other sets of shark teeth that had previously been gathered, spread across Chile, Panama, Peru and the US. They came to the conclusion that four of them — two in the US and two in Panama — had belonged to younger sharks.
As a result, the authors said that these four areas where the teeth were found might also have been nurseries.
“The remaining four formations ... demonstrate size-class structures typical of populations dominated by adults, suggesting these regions might correspond to feeding or mating areas,” the study said.
Sharks continuously shed their teeth throughout their lifetime, and nurseries are zones with a high abundance of sharks.
“As a consequence, huge numbers of teeth can be shed, increasing the chances of subsequent fossil discoveries,” the authors said.
Megalodons enjoyed the warm and temperate waters of the Miocene period which extended from about 5 million to 23 million years ago, but the cooler Pliocene period suited them far less.
As their prey adapted and headed toward colder waters, the megalodons stayed where the oceans remained warm. The remaining food was also favored by great white sharks, increasing competition with the smaller, but more agile, predator.
The vast reduction of shallow water nurseries due to sea-level losses — caused by a cooler climate — might also have contributed to the megalodons’ eventual extinction.
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