What did Megalodon eat? Anything it wanted — including other predators.
A team of Princeton researchers has now discovered clear evidence that Megalodon and some of its ancestors were at the very highest rung of the prehistoric food chain—the highest "trophic level." Indeed, their trophic signature is so high that they must have eaten other predators and predators-of-predators in complicated food web, say the researchers. Harry Maisch of Florida Gulf Coast University, whose hand is holding this Megalodon tooth, gathered many of the samples used in this analysis and is a co-author on the new paper in Science Advances. Credit: Harry Maisch

Mega tooth sharks, the biggest sharks that ever lived, were the highest level predator ever measured.

The megatoothed sharks have large teeth which can be bigger than a human hand. The largest shark that ever lived is in the group.

While sharks of one kind or another have existed since long before the dinosaurs, these megatoothed sharks evolved after the dinosaurs went extinct and ruled the seas until just 3 million years ago.

"We're used to thinking of blue whales, whale sharks, even elephants and diplodocuses as filter feeders, not predators," said Emma Kast, the first author on a new book. Meg went extinct a few million years ago because she was eaten by Megalodon and the other mega tooth sharks.

If Megalodon existed in the ocean, it would change the way humans interact with the marine environment.

Megalodon and some of its ancestors were found to be at the highest level of the prehistoric food chain. They must have eaten other predator and predator-of-predators in the food web.

"Ocean food webs tend to be longer than the grass-deer-wolf food chain of land animals because you start with such small organisms," said Kast, now at the University of Cambridge, who wrote the first iteration of this research as a chapter in her PhD thesis. To reach the trophic levels we're measuring in these megatooth sharks, we don't just need to add one apex predator on top of the marine food chain.

Megalodon is thought to be 50 feet long, while modern great white sharks can top out at fifteen feet.

The sharks' teeth were measured to reach the conclusions about the prehistoric marine food web. Scientists have never before been able to measure the tiny amounts of nitrogen preserved in the teeth of extinct predators, but they know that the more nitrogen-15 an organisms has, the higher it's trophic level.

A graduate student and a co-author on the current paper traced the trophic level of shark teeth from different time periods.

Several lines of evidence show that cannibalism is one of the ways to get an extra trophic level.

There is a nitrogen time machine.

There is no easy way to recreate the food webs of extinct creatures without a time machine.

The knowledge that the nitrogen isotope levels in a creature's cells reveal whether it is at the top, middle or bottom of a food chain has led to the development of other methods.

The research team is looking for organic matter from the distant geologic past.

Plants and other organisms at the bottom of the food web can turn nitrogen into nitrogen in their tissues. Organisms that eat them excrete more nitrogen's lighter isotope, N-14, than its heavier cousin, N-15.

As you climb up the food chain, N-15 builds up compared to N 14.

There hasn't been enough nitrogen left in older animals to measure this approach.

What's the reason? Muscles and skin are not always preserved. Complicating matters is that sharks don't have bones.

The teeth of sharks can be found in the fossil record. The teeth are encased in a rock-hard material that is immune to most decomposingbacteria.

"Teeth are designed to be resistant to the effects of the environment in the mouth, so they can survive and break apart food that is hard to eat," he said. The sharks aren't limited to the 30 or so white teeth that humans have. Every shark has thousands of teeth over the course of its life, because they are constantly growing and losing teeth.

One of the most abundant fossil types are shark teeth. There is a tiny amount of organic matter that was used to build the enamel of the teeth that is trapped within that.

The nitrogen signatures in the teeth of sharks give a way to measure status in the food web, even if the tooth fell from a shark millions of years ago.

The nitrogen component of the largest tooth is very small. With the help of dentist drills and cleaning chemicals, the team has been able to develop more and more refined techniques to extract and measure these nitrogen isotope ratios.

He said that they were like a brewery. Our samples are fed to the growing microbes. We analyze the nitrous oxide they produced.

A custom-built, automated nitrous oxide preparation system is required for the analysis.

A core method to measure trace amounts of nitrogen has been in the works for a long time. They moved on to other types of fossils, like corals and fish ear bones. We are going to apply this to the teeth of mammals and dinosaurs.

There is a deep dive into the literature.

While her friends were making sourdough starters and bingeing netflix, she pored through the ecologic literature to find out how much nitrogen is in the water.

"One of the cool things that Emma did was dig into the literature, all the data that's been published over decades, and relate that to the fossil record," said Michael.

She built a record with more than 20,000 marine mammal individuals and more than 5000 sharks. She wants to go even further. The tool has the ability to decode ancient food webs, but we need samples now. I would love to find a museum that has a collection of different kinds of fossils, from forams near the food web to otoliths, from different kinds of bones. The nitrogen isotope analysis could be used to tell the entire story of an ancient environment.

Their own shark teeth are included in their database. Co-author Kenshu Shimada was connected with aquariums and museums while co-author Martin Becker and co-author Harry Maisch were connected with the sea floor

It's really dangerous and you need to be an expert to get these. If you want to get the best-preserved samples, you need to go down to the bottom of the ocean. Marty and Harry have been collecting teeth for a long time.

He said that it had been a collaborative effort to get the samples. Collaboration with other regional universities is great because the students are great and my colleagues are great to work with.

There is a PhD graduate in the lab.

The work I did for my PhD posed as many questions as it answered, and I was incredibly grateful to have the opportunity to continue working on some of these with a mentor I respect. I'm most excited about the work that's still to be done and the mysteries that haven't been solved.

More information: Emma R. Kast et al, Cenozoic megatooth sharks occupied extremely high trophic positions, Science Advances (2022). DOI: 10.1126/sciadv.abl6529 Journal information: Science Advances