A German-American team of scientists set out to find out where the megalodon (Otodus megalodon) — the largest shark to ever exist in the world — was in the food chain. The researchers hoped to learn more about the life of these prehistoric animals. Analyzing the remains of megalodon teeth showed that they could compete for food with the great white sharks (Carcharodon carcharias) known to us.
Megalodons lived from about 23 to 3.6 million years ago. They inhabited the oceans around the world and were probably up to 20 meters long. In comparison, the largest modern great white sharks (Carcharodon carcharias) grow to only six feet tall.
In the study, scientists analyzed the ratio of stable zinc isotopes in the tooth remains of prehistoric sharks and compared the results with data from modern white sharks. With this new method, scientists were able to study the trophic level of megalodons and thus information about their position in the food chain.
They examined the remains of the enamel
The analysis of stable zinc isotopes in enamel, a highly mineralized part of the teeth, is comparable to the much better known nitrogen isotope analysis in dental collagen, organic tissue in dentin that is being studied to assess the consumption of animal material. In this case, the method would not be effective.
“The collagen was not preserved over the time period studied, so traditional methods were not feasible,” explains Jeremy McCormack, the study’s lead author and researcher at the Institute of Evolutionary Anthropology. Max Planck and the Johann Wolfgang Goethe University in Frankfurt.
“We have shown for the first time that dietary zinc isotope signatures are preserved in the enamel of shark tooth remains,” added Thomas Tuetken, a professor at the Johannes Gutenberg University Institute of Geosciences in Mainz.
Researchers looked at the remains of animals that lived in the early Miocene (about 20.4 to 16.0 million years ago) and the early Pliocene (about 5.3 to 3.6 million years ago). Then they compared them with data on modern sharks.
“We noted some consistency in the results, which increases our confidence in the method and suggests that there may be slight variations in zinc isotope levels at the base of marine food webs,” said Sora Kim, a professor at the University of California, Merced.
At the top of the food chain
Next, scientists analyzed the ratio of zinc isotopes in the teeth of the ancestors of the megalodon – a species Otodus chubutensis, who lived in the early Miocene. They then compared these results with information obtained from examining the teeth of modern sharks.
– Our results show that both the megalodon and its ancestor were indeed apex predators [a więc znajdującymi się na szczycie łańcucha pokarmowego – przyp. red.] said Michael Griffiths, a professor at William Paterson University in New Jersey. “But what was really remarkable is that the early Pliocene North Carolina shark tooth zinc isotope values strongly suggest that early white sharks had the same trophic level as much larger megalodons,” he added.
This means great white sharks and megalodons can coexist and compete with each other for food.
“These results probably suggest at least some overlap between the victims that both shark species prey on,” noted Kenshu Shimada, a professor at DePaul University in Chicago. “While additional research is needed, our results seem to confirm the possibility of megalodon food competition with early Pliocene large sharks,” he added.
Scientists are happy because the new way of doing research can make it much easier to learn about the past.
– Our method illustrates the possibility of using zinc isotopes to study the diet and trophic ecology of extinct animals over millions of years. It could also be applied to other groups of fossil animals, including our own ancestors, concluded Jeremy McCormack, the study’s lead author.
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