Tuesday, July 5, 2022

Megalodon extinction may have been aided by great white sharks

Using zinc isotopes, scientists investigated the diet of the megalodon, the largest shark to have ever lived.

Diet is a crucial trait of an animal’s lifestyle and ecology. Likewise, the diet of extinct fossil animals can hold clues to their lifestyle, behavior, evolution, and, ultimately, extinction. Although, it’s quite difficult to study an animal’s diet after millions of years due to the poor preservation of chemical dietary indicators in organic material on these timescales.

Using a newly developed method, an international team of scientists led by the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, investigated the diet of the most giant shark ever existed, the iconic Otodus megalodon.

Otodus megalodon, more commonly known as the megalodon, lived between 23 and 3.6 million years ago in oceans around the globe. Estimates suggest it grew between 15 and 20 meters in length, three times longer than the largest recorded great white shark.

In this study, scientists discussed several factors to explain the gigantism and extinction of megalodon- including its diet and dietary competition, often considered vital factors.

The new method allows scientists to investigate an animal’s trophic level, indicating how far up an animal’s food chain feeds. Scientists found the zinc isotope composition of the highly mineralized part of teeth. Zinc stable isotope analysis of tooth enameled, the highly mineralized part of teeth, is comparable to much more established nitrogen isotope analysis of tooth collagen, the organic tissue in tooth dentine, which is used to assess the degree of animal matter consumption.

Lead author Jeremy McCormack, a researcher at the Max Planck Institute for Evolutionary Anthropology and the Goethe-University Frankfurt, said, “However, on the timescales we investigate, collagen is not preserved, and traditional nitrogen isotope analysis is therefore not possible. Here, we demonstrate, for the first time, that diet-related zinc isotope signatures are preserved in the highly mineralized enameloid crown of fossil shark teeth.”

Using their method, scientists compared the tooth zinc isotope signature of multiple extinct Early Miocene (20.4 to 16.0 million years ago) and Early Pliocene (5.3 to 3.6 million years ago) species with those of modern sharks.

Sora Kim, a professor from the University of California Merced, said, “We noticed a coherence of zinc isotope signals in fossil and modern analog taxa, which boosts our confidence in the method and suggests that there may be minimal differences in zinc isotope values at the base of marine food webs, a confounding factor for nitrogen isotope studies.”

The scientists then looked at the zinc isotope ratios in megalodon teeth from the Early Pliocene, as well as those in earlier megatooth sharks, Otodus chubutensis, from the Early Miocene, and contemporaneous and modern great white sharks, to see how these iconic species impacted past ecosystems and each other.

Michael Griffiths, professor at William Paterson University, said, “Our results show that both megalodon and its ancestor were apex predators, feeding high up their respective food chains. But what was truly remarkable is that zinc isotope values from Early Pliocene shark teeth from North Carolina suggest largely overlapping trophic levels of early great white sharks with the much larger megalodon.”

Kenshu Shimada, professor at DePaul University, Chicago, said, “These results likely imply some overlap in prey hunted by both shark species. While additional research is needed, our results appear to support the possibility for a dietary competition of megalodon with Early Pliocene great white sharks.”

McCormack said“New isotope methods such as zinc provide 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 over millions of years, a method that can also be applied to other groups of fossil animals, including our ancestors.”

Journal Reference:

  1. McCormack, J., Griffiths, M.L., Kim, S.L. et al. Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes. Nat Commun 13, 2980 (2022). DOI: 10.1038/s41467-022-30528-9
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