Megatooth sharks, a group that includes the biggest sharks that ever lived, were apex predators at the highest level ever measured, even eating other predators, a new study has suggested.
This group of sharks, which includes the 15m long Megalodon – the largest shark that ever lived – evolved after dinosaurs went extinct and ruled the seas until just three million years ago, say scientists, including those from Princeton University in the US.
The new study, published on Wednesday in the journal Science Advances, found that megalodon and some of its ancestors were at the very highest rung of the prehistoric food chain – what scientists call the highest “trophic level.”
“Megalodon and the other megatooth sharks were genuinely enormous carnivores that ate other predators, and Meg went extinct only a few million years ago,” study first author Emma Kast said in a statement.
“If Megalodon existed in the modern ocean, it would thoroughly change humans’ interaction with the marine environment,” Danny Sigman, another co-author of the study, added.
Scientists used a new technique to measure forms of the element nitrogen in the sharks’ fossil teeth.
The more nitrogen-15 an organism has, the higher its trophic level, researchers say, adding that until now, the tiny amounts of nitrogen preserved in the enamel layer of these extinct predators’ teeth have not been measured.
Analysing a series of shark teeth from different time periods, scientists could trace their trophic level and compare it to their size.
The nitrogen isotope levels in a creature’s cells, researchers say, reveal whether it is at the top, middle or bottom of a food chain.
Scientists also assessed existing literature, published over decades, to look for the nitrogen isotope measurements of other marine animals that lived across different time periods.
They built up a record with over 20,000 marine mammal individuals and more than 5,000 sharks using which they decoded ancient food webs.
Based on the new study, scientists say megatooth sharks were likely globally distributed, contributing to the ancient ocean food chains of their times which may have been a few steps longer than any modern-day food chain.
Researchers suspect the very high trophic level of these megatooth sharks may have contributed to them evolving toward gigantism, growing up to 15m in length.
They say the methods used in the study could be developed further to build a tool that can decode ancient food webs.
“I’d love to find a museum or other archive with a snapshot of an ecosystem – a collection of different kinds of fossils from one time and place, from forams near the very base of the food web, to otoliths – inner ear bones – from different kinds of fish, to teeth from marine mammals, plus shark teeth,” Dr Kast said.
“We could do the same nitrogen isotope analysis and put together the whole story of an ancient ecosystem,” she added.
