Scientists can learn about the lifestyle, behaviour, and evolution of fossil extinct animals by studying their diet. They can also obtain information about how the animal became extinct. However, it is 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. An international team of scientists have recently applied a new method to investigate the diet of the largest shark to have ever existed, the iconic Otodus megalodon. Using the new method, the scientists investigated the zinc isotope composition of the highly mineralised part of teeth. The method proves to be particularly helpful to understand the diet of these extinct animals.
The study, describing the findings, was recently published in the journal Nature Communications.
Comparison Between Megatooth Shark And Modern Great White Sharks
Otodus megalodon is a Megatooth shark, and is more commonly known as megalodon. It lived between 23 and 3.6 million years ago in oceans around the globe and possibly reached as large as 20 metres in length. The largest great white sharks which exist today reach a total length of only six metres. Diet and dietary competition are often thought of as key factors determining the gigantism and extinction of megalodon.
The researchers carefully analysed modern and fossil shark teeth around the globe, including the teeth of megalodon and modern and fossil great white sharks. They measured the ratios of the stable isotopes of zinc in the teeth.
The Researchers Investigated The Positions Of Ancient Sharks In Food Chain
The scientists were able to investigate an animal's trophic level, which shows how far up the food chain an animal feeds. Enameloid, which is the highly mineralised part of teeth, was analysed as part of the study. Analysis of the stable isotopes of zinc in tooth enameloid is similar to the analysis of nitrogen isotopes in tooth collagen, which is the connective tissue in tooth dentine. The technique is used to assess the degree of animal matter consumption.
In a statement released by Max Planck Society, Jeremy McCormack, the lead author on the paper, said that collagen is not preserved on the timescales the researchers investigate. Therefore, traditional isotope analysis is not possible.
Thomas Tutken, another author on the paper, said researchers demonstrated for the first time that diet-related zinc isotope signatures are preserved in the highly mineralised enameloid crown of fossil shark teeth.
Teeth Of Extinct Sharks Compared With Those Of Modern Sharks
The scientists used the new technique to compare the tooth zinc isotope signature of multiple extinct Early Miocene and Early Pliocene species with those of modern sharks. The Early Miocene era occurred 20.4 to 16 million years ago while the Early Pliocene epoch occurred 5.3 to 3.6 million years ago. Sora Kim, another author on the paper, said the researchers noticed a connection between zinc isotope signals in fossils and modern analog taxa. This suggests that there may be minimal differences in isotope values at the base of marine food webs.
The scientists also analysed the zinc isotope ratios in megalodon teeth from the Early Pliocene and those in earlier Megatooth sharks, such as the Otodus chubutensis, from the Early Miocene. They also analysed the zinc isotope ratios in the teeth of modern great white sharks to investigate the impact the iconic species had on past ecosystems and on each other, the study said.
Trophic Levels Of Early Great White Sharks Overlapped Those Of Megalodon
Michael Griffiths, a senior author on the paper, said the results show that both megalodon and its ancestor were indeed apex predators, and were high up in their respective food chains. He added that the zinc isotope values from Early Pliocene shark teeth from North Carolina suggest that the trophic levels of early great white sharks overlapped those of the much larger megalodon.
Kenshu Shimada, another author on the paper, said the results likely imply at least some overlap in prey hunted by both shark species. He added that the findings of the study appear to support the possibility for dietary competition of megalodon with Early Pliocene great white sharks.