A German-American team of scientists set out to investigate where the megalodon (Otodus megalodon) – the largest shark that has ever existed in the world – occupied in the food chain. The researchers hoped to learn more about the lives of these prehistoric animals. Thanks to the analysis of the remains of megalodon teeth, it turned out that they could compete for food with the 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. For comparison, the largest modern great white sharks (Carcharodon carcharias) grow to just six meters in length.
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. This new method allowed scientists to study the trophic level of megalodons and thus information on the position in the food chain.
They examined the remains of the enamel
The analysis of stable zinc isotopes in enamel, a highly mineralized portion of the teeth, is comparable to the much better known nitrogen isotope analysis in tooth collagen, organic tissue in dentin that is studied to assess the consumption of animal matter. In this case, the method would not be effective.
“The collagen was not preserved during the time period studied, so traditional methods were not feasible,” explained Jeremy McCormack, lead author of the study and researcher at the Institute of Evolutionary Anthropology. Max Planck and the Johann Wolfgang Goethe University in Frankfurt.
‘We have demonstrated for the first time that dietary zinc isotope signatures are preserved in the enamel of shark tooth debris,’ added Thomas Tuetken, professor at the Johannes Gutenberg University Institute of Geosciences in Mainz.
Researchers looked at the remains of animals living 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 noticed some consistency in the results, which increases our confidence in the method and suggests that there may be slight variations in zinc isotope values at the base of marine food webs,” said Sora Kim, 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 megalodon’s ancestors – 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, 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 suggest to a large extent that early white sharks had the same trophic level as much larger megalodons,” he added.
This means that great white sharks and megalodons could exist at the same time and compete with each other for food.
“These results probably suggest at least some overlap between the victims hunted by both shark species,” noted Kenshu Shimada, 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 great sharks,’ he added.
Scientists are happy because the new way of 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 can also be applied to other groups of fossil animals, including our own ancestors, concluded Jeremy McCormack, lead author of the study.
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