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No modern sea predator can compare to the megalodon. As adults, these ancient sharks were larger than the length of a city bus. Last year, an analysis revealed that megalodons preyed on the brain even before they were born, with embryos apparently eating their unhatched siblings while still in the womb.

A new study, published Wednesday in the peer-reviewed journal Scientists progress, relies on a new type of evidence to make a startling claim: the most powerful megalodons sat higher in their ancient food webs than any predator alive today. In an enthusiastic paper published alongside the research paper, paleobiologists Nicholas D. Pyenson and Paul L. Koch state that the new data “suggests that many individual megatooth sharks had a diet composed entirely of high-level carnivores which themselves ate other large carnivores, like polar bears and killer whales do today.”

Since many of the large marine carnivores that could have prepared delicious meals are relatively recent arrivals (in evolutionary terms), it seems likely that smaller megalodons were on the menu. “Cenozoic marine food webs may have been dominated by giant cannibals,” they write.

Interesting engineering spoke with paleoecologist Dr Emma Kast, the study’s lead author, to learn more about the research and find out if the megalodon really was as fearsome as everyone says.

This interview has been edited for length and clarity.

Interesting engineering: Why are teeth so important to understanding megalodon?

Emma Kast: When we look at ancient sharks, we only have to rely on the fossil record, and we usually only have their teeth. That’s because unlike us, they don’t really have bones. Their entire skeleton is made of cartilage, like your nose. It doesn’t keep very well in the fossil record.

Essentially everything we know about megalodon and its ancestors comes from these gigantic teeth in the fossil record. You look at one of these teeth and it’s just beautiful. You wonder what they ate. That was really the starting point for this whole study: what the hell were these guys doing? What were they eating?

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IE: What does a megalodon tooth look like?

Kast: My God, I wish I had one on my desk. They are the size of a hand and are triangular. They have serrations on the side, like a bread knife, which is amazing. They’re millions of years old, and they still have the details to preserve those serrations.

IE: Are they found all over the world?

Kast: Yes, they are found all over the world. There are excellent articles from a researcher named Catalina Pimiento assessing how they are distributed across the world. They were truly like a global species.

For this article, we looked at a few different places. We have a decent number of teeth from North Carolina, a few teeth from Japan, and a few teeth from other places – everything we could get our hands on.

IE: How did modern scientists make sense of the huge triangular teeth found all over the world?

Kast: Until now, all we really knew about them was by looking at the shape of the tooth and asking, “What does this morphology mean in terms of what it was doing?” We took this leap into geochemistry by measuring the composition of teeth and wondering what that tells us about their diet. It’s really a change in terms of what we can investigate.

IE: What have the researchers learned from the shape of the teeth?

Kast: The megalodon had these triangular teeth with jagged edges, and what people think is that they have these teeth because they needed to tear everything they ate. So people think this shape means they are eating sea mammals. In contrast, sand tiger sharks, which tend to eat fish, have these very sharp, almost toothpick-like teeth. This is the level of information that you can get from the form alone.

IE: What kind of prey would have been available to predators living between 20 and 3 million years ago, when megalodons lived?

Kast: In the modern ocean, we have a good understanding of what the food web looks like. We can go out and observe species interactions, and we can do things like look at stomach contents and see what certain animals are eating. Many of us can probably visualize in our minds that you have some kind of plankton at the bottom of your food web. Then you could have small fish, medium sized fish. Then you get close to big fish, like tunas and sharks, which eat those fish. And at the very top we have things like killer whales and great white sharks, which eat small marine mammals and large fish. It’s a bit like the image we have of the modern ocean.

Then if we go back in time to the Miocene – that’s 23 million years ago to 5 million years ago, or so – when megalodon was swimming, what we know about food webs also found in the fossil record. So what kind of fossilized bones, teeth, shells and other things do you find? We know who was there, but integrating these ancient animals into a food web is difficult because you need additional information about who ate whom. That’s what we’re looking for, really. Who eats these giant sharks? What was their diet? Where exactly were they located in the food webs of these ancient oceans?

IE: How can you tell who’s eating who by looking at those teeth?

Kast: What we were looking for is called the isotope ratio of nitrogen. There are two facts that will help understand how it works. The first is therefore that nitrogen is the nutrient that all animals must draw from their diet. So all the nitrogen in our body – or in the shark’s body – comes from their food. The other thing is that nitrogen has these two isotopes. I consider them flavors of the same thing. There are 15 nitrogen and 14 nitrogen. Animals generally retain flavor 15 nitrogen a little better than 14 nitrogen.

So if you combine those two facts, what ends up happening is that as you move up the food web, you get progressively more 15 nitrogen versus 14 nitrogen at each stage. A very small fish would have a low 15-nitrogen to 14-nitrogen ratio. And at the very top of the food web, you would have a pretty high ratio of 15 nitrogen to 14 nitrogen.

IE: So when an animal consumes nitrogen, it proliferates throughout its body, including the teeth?

Kast: The short answer is yes. These ratios are certainly influenced by physiology and metabolism. There may be complicated details overlapping, but the general picture is that yes, then the isotope ratio that is in the tooth reflects the isotope ratio of the whole animal. And that gives you an idea of ​​its position in the food web.

IE: What did you find looking at these ratios in the teeth of megalodon?

Kast: The ratios are incredibly high! That’s the title: super high nitrogen isotope ratios, which means megalodon was at that very high position on the food web. To be a bit quantitative, if we make some assumptions, this actually tells us that if you go back to this modern food web that I described, the megalodon would actually be sitting above our top marine predators.

If we imagine killer whales and great whites at the top of the food web, the megalodon would actually be above them, and above them twice: two positions higher in the food web. We predict extraordinarily high trophic levels and high positions in the food web, from these very high values.

IE: Higher than any predator alive today?

Kast: Yes, it’s really extraordinary. That means a lot of questions because if they’re really two positions higher, that means there’s some sort of gap between the two. What were they eating? It couldn’t be killer whales or great whites or equivalent species.

IE: Because the ratios are too high?

Kast: Yes, they are too high. One thing to say here is that there is actually a wide spread. Some individuals – some teeth – have more moderate values ​​and then extraordinarily high values. On average, they are about two positions higher. If they ate things like killer whales and great whites, they would just be one position higher. There are a few possible explanations that are cool, but we can’t really tell which one or the other. [is more accurate].

Perhaps there are extinct marine mammals that have filled this gap. There are raptor sperm whales (they are like toothed whales) that could have been at a fairly high trophic level. We just don’t know what their position in the food web would have been. There may be other extinct species that we have not yet reviewed that can fill this gap. They might also have done some crazy stuff like cannibalism, which tends to push you up the food web because if you eat yourself, your diet is higher in nitrogen.

These are possibilities that we do not yet know about.

IE: At each step of the food chain, a lot of energy is lost, isn’t it? Does this mean that the total energy input must have been much higher in the Miocene ocean?

Kast: I love that question because that’s what I think about the most with it. Sure, it’s really cool that megalodons were at this very high position in the food web, but it raises a lot of questions in terms of the overall ecology of the ancient oceans that allowed megalodon to exist.

I don’t know if that might indicate — and it’s certainly just a hypothesis — some productivity differences at the bottom of the food web, differences that provide a lot more energy at the very top. Or maybe there is something different in the way the food web is structured. So if you think of the food web as a triangle, could the triangle have been more pointed for some reason?

Knowing more about this megatooth shark could tell us more about past ecosystems.