The megalodon – aka megatooth shark, Otodus megalodon – was a mighty beast that once roamed the ancient oceans. They were larger than any other predatory sharks at the time, reaching a whopping 16 meters (52 feet). For comparison, the current biggest predatory fish in the ocean are female whale sharks, averaging 4.5 meters (15 feet).
Unfortunately for them (but fortunately for many marine animals), the megalodon went extinct 3.6 million years ago. In a new study published in Science Advances, scientists revealed that the megalodon occupied the highest trophic level (the position of an organism in a food web) than any other ocean predator, living or extinct.
But why is determining the trophic level of extinct animals important?
“Trophic level is a fundamental characteristic of animals – determining the trophic level of extinct animals can tell us about its place in the ecosystem, and may help us understand the evolution and extinction of specific animals.” Dr Emma Kast, lead author of the study told IFLScience.
“On a more broad scale, determining the trophic level of extinct animals can also help us to understand the ecology of ancient ecosystems overall. For example, the super high trophic level of the megalodon may indicate that food chains were longer millions of years ago. How and why would this past ecosystem be able to sustain such a high trophic level predator? These are exciting questions we can start to answer.”
It has previously been difficult for scientists to determine the trophic level of long-extinct species using the methods for the extant animals, so the megalodon’s trophic level could not be determined… before this study, that is.
Animals require nitrogen from their diet, and the nitrogen isotope composition of animal tissues is a well-used tool to identify the trophic levels in modern ecosystems. The ratio of nitrogen-15 (d15N) and nitrogen-14 (d14N) can be used to determine trophic levels, as at higher trophic level, animals acquire more nitrogen-15 from their food.
“Nitrogen isotopes have been used on ancient marine animals before, but only over the past 10,000 - 100,000 years. As just one example, Feranec et al. 2021 measured the d15N of fossil bone collagen that was approximately 12,000 years old and found an Arctic food web structure that was similar to today.” Kast told IFLScience.
“Beyond these timescales, collagen is not usually preserved. Instead of collagen, we targeted organic matter inside biominerals, which can be preserved on much longer timescales. Our study is the first time that the enameloid-bound organic matter d15N approach has been applied to fossil sharks, and more broadly is the first time we have been able to use d15N to reconstruct the trophic level of a marine animal on million year timescales.”
When this technique was applied to fossilized megalodon teeth, the ratio was a lot higher than the levels in orcas, modern white sharks, and polar bears.
The data also suggested that the Cenozoic marine food chains were two steps longer than they are in the present day. The megalodon may have fed on nursing mammal pups, and could have even cannibalized smaller megalodon sharks.
However, there was a wide range of nitrogen levels in the different teeth samples that the scientists analyzed – this indicates that not every large individual was at the top of the food chain.
There is exciting research planned for this team.
“There is lots more interesting work to be done! On the one hand there is still lots to learn about the megalodon, for example we only looked at teeth from adults in this study, but we would be interested to see if the juveniles have very different diets, like the white shark does today. We are also excited to apply this type of mineral-bound d15N approach to other animals in the fossil record to build up our understanding of food webs in the past.” Kast told IFLScience.