A new study conducted by researchers at the University of Cambridge showed that megalodons, also known as megatooth sharks, the largest sharks to have ever lived, were apex predators operating at the peak of the prehistoric food webs more than any other marine predators in history. The findings were published in Science Advances.
How big are the Megalodon sharks?
Megalodon sharks went extinct about 3 million years ago. They were three times bigger than contemporary great white sharks – “about the size of a city bus,” according to the study. The researchers made the discovery by examining nitrogen isotopes in the shark’s gigantic teeth, which can be bigger than a human hand. It was from their teeth that the Megatooth sharks got their name.
How long did the Megalodon sharks exist?
Megatooth sharks only emerged after the dinosaurs went extinct. They ruled the waters until about three million years ago, despite the fact that some kinds of sharks had lived for more than four hundred million years before the dinosaurs.
According to Emma Kast, who conducted the research at Princeton University, “Megalodon and the other megatooth sharks were absolutely enormous carnivores that ate other predators, and Megalodon went extinct only a few million years ago. We typically think of the largest species as filter feeders or herbivores rather than predators, including blue whales, whale sharks, elephants, and diplodocuses.
The prehistoric marine food webs
Kast and other Princeton University scientists used nitrogen traces trapped in shark tooth enamel to determine the trophic levels (trophic level of an organism is its position in a food chain) of the ancient predators. They discovered undeniable proof that Megalodon and some of its ancestors lived at the top of the prehistoric food chain or trophic level. According to the researchers, Megalodon sharks must have consumed other predators and predators of predators in a complex food web because their trophic signature is so high.
“The relationship between humans and the marine environment would be significantly impacted if Megalodon existed in the present seas, remarked co-author and Dusenbury Professor of Geological and Geophysical Sciences at Princeton, Danny Sigman.
The researchers were able to plot the relationship between trophic level and size using information from a collection of fossil shark teeth from various eras. Kast also compiled a collection of tens of thousands of contemporary marine organisms during the initial lockdowns, which he compared with the new fossil record.
Kast, Sigman, and his team examined nitrogen isotopes in the shark teeth, which can be used as a time machine to decipher an organism’s place in the food chain to draw inferences about the prehistoric marine food web.
Nitrogen-15
Ecologists have long understood that an organism’s trophic level increases with the amount of nitrogen-15 that it contains. But the minuscule levels of nitrogen that have been preserved in the enamel of the teeth of these prehistoric predators have never before been quantified by scientists.
The new research proved difficult since even the largest tooth has a thin enamel coating and only a minuscule trace of nitrogen, necessitating highly precise work. In order to extract, purify, concentrate, and transfer the gas to a specialized stable isotope ratio mass spectrometer, they required specially designed, automated nitrous oxide preparation equipment.
The researchers discovered that the Megalodon’s teeth contained high concentrations of the isotope nitrogen-15, which suggested that many of these sharks consumed only top predators, which in turn consumed other huge carnivores, much like polar bears and orcas do today.
The nitrogen found in water or air is turned into nitrogen from the tissues of many algae, plants, and other species at the bottom of the food chain. Organisms that feed on them subsequently absorb the nitrogen into their own bodies and preferentially excrete more nitrogen-14 than nitrogen-15, which is heavier isotope of nitrogen.
Hence, nitrogen-15 accumulates in organisms as they move up the food chain. Based on this theory, Sigman and his team have spent years creating techniques to identify nitrogen isotopes in an organism’s cells, revealing their place in prehistoric food chains in the process.
Other researchers have already applied the technique to samples up to 15,000 years old and are geologically recent. However, the soft tissue required for nitrogen analysis is rarely maintained, even in older living animals.
Shark’s teeth
Sharks do not have bones, and their cartilage-based skeletons add more to the complications. But sharks possess an invaluable entryway into the fossil record: teeth. Teeth are more easily preserved than bones since they are covered in enamel, a rock-hard substance that is extremely resistant to most decomposing bacteria.
“Teeth are designed to be both physically and chemically resistant in order to survive in the highly chemically reactive mouth environment – and to break down food that may have hard components,” according to Sigman. Each shark produces thousands of teeth over the course of its lifetime due to continual tooth production and loss.
“One of the most common types of fossils in the geologic record is the shark teeth,” Sigman explains. Their teeth are so abundant and well-preserved that the nitrogen signatures in the enamel can be used to measure position in the food chain, whether the tooth fell off a shark’s mouth yesterday or millions of years ago.
“You must be highly skilled and ready to take a lot of risks to get these. The best sample can only be discovered at the ocean’s bottom, despite the fact that you can locate little shark teeth on the coast,” said Griffiths. Teeth have been gathered by Marty and Harry from various locations.
Kast plans to decode ancient food webs
Kast, a Fellow at Trinity Hall, intends to reproduce the procedure for other organisms in order to recreate their hierarchical structure within an ecosystem. She explained that they needed samples as their technique has the ability to unravel ancient food webs.
“I’d want to find a museum or repository with a collection of various fossil types that depict an environment at a specific point in time, ranging from otoliths to forams near the base of the food web, or inner ear bones, from various types of fish to teeth from marine mammals, as well as shark teeth. The same nitrogen isotope analysis would allow us to piece together the history of an ancient ecosystem.
