An international team of scientists led by the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has applied a new method to investigate the diet of the biggest shark that ever livedthe emblematic ‘Otodus megalodon‘. This new method investigates the zinc isotopic composition of the highly mineralized part of the teeth and is particularly useful for deciphering the diet of these animals extinct.
The megalodon lived between 23 and 3.6 million years in the oceans around the world and possibly reached up to 20 meters in length. By comparison, great white sharks The largest today reach a total length of only six meters. Many factors have been discussed to explain gigantism and extinction megalodon, and their diet and feeding competition are often thought to be key factors.
In this study, published in the journal Nature Communications, researchers analyzed the stable isotope ratios of zinc in modern and fossil shark teeth from around the world, including the teeth of modern and fossil megalodon and great white sharks.
This new method allows scientists to investigate an animal’s trophic level, which indicates how high up in the food chain it feeds. Stable isotope analysis of zinc in dental enameloid, the highly mineralized part of teeth, is comparable to nitrogen isotope analysis of dental collagen, the much more established organic tissue of dentin, and is used to assess the degree consumption of animal matter.
However, “on the time scales we investigated, collagen is not conserved and therefore traditional nitrogen isotope analysis is not possible,” explains lead author, Jeremy McCormackresearcher at the Max Planck Institute for Evolutionary Anthropology and the Goethe University of Frankfurt.
“Here we demonstrate, for the first time, that diet-related zinc isotopic signatures are conserved in the highly mineralized enameloid crown of fossil shark teeth.” Thomas Tütkenprofessor at the Institute of Geosciences at the Johannes Gutenberg University.
using this New methodthe team compared the isotopic signature of zinc in teeth of many extinct species early Miocene (20.4 to 16.0 million years ago) and from early pliocene (5.3 to 3.6 million years ago) with those of modern sharks.
“We observed a coherence of the signals of zinc isotopes in analogous fossil and modern taxa, increasing our confidence in the method and suggesting that there may be minute differences in zinc isotope values at the base of marine food webs, a confounder for nitrogen isotope studies. “, Explain Sora Whoprofessor at the University of California Merced.
The researchers then analyzed zinc isotope ratios in early Pliocene megalodon teeth and those of early Miocene Otodus chubutensis sharks, as well as contemporary and modern great white sharks, to investigate the impact that these emblematic species had in the ecosystems from the past and each other.
“Our results show that both the megalodon and its ancestor were really top level predatorswhich fed at the top of their respective food chains –highlights Michael Griffiths, professor at William Paterson University, in the United States–. But what is truly remarkable is that zinc isotope values of shark teeth from early Pliocene North Carolina suggest that the trophic levels of early white sharks they overlap largely with those of the much larger megalodon.
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“These results probably imply at least some overlap in prey taken by both shark species -underlines Kenshu Shimada, professor at DePaul University in Chicago. Although more research is needed, our results seem to support the possibility of a megalodon dietary competition with great white sharks from the early Pliocene.
New isotope methods, such as zinc, offer a unique window into the past. “Our research illustrates the feasibility of using zinc isotopes to investigate the diet and trophic ecology of extinct animals for millions of years, a method that can also be applied to other groups of animals fossilsincluding our own ancestors,” McCormack concludes.