Megalodon. The name alone inspires awe: A massive shark capable of swallowing a human whole that formerly controlled the world's waters. Such a beast must have been terrifying, based on the teeth and vertebrae that have survived the 3.6 million years since it became extinct.
It was one of the world's most massive carnivores... Even yet, there is one predator alive today that may have dragged the gigantic megalodon (Otodus megalodon) to its death: the great white shark (Carcharodon carcharias).
According to new study, the two creatures lived at the same time, implying that the great white shark may have contributed to the megalodon's extinction simply by sharing the same biological niche - living in the same areas and hunting the same prey.
Now, a new study has reached the same conclusion using a different parameter — the zinc isotope ratios in the animals' teeth. This adds to the evidence that great whites played a role in the megalodon's death through drowning.
"We reveal that dietary zinc signatures are preserved in fossil shark tooth enameloid over deep geologic time and are robust recorders of each species' trophic level. We observe significant zinc differences among the Otodus and Carcharodon populations implying dietary shifts throughout the Neogene in both genera," wrote a team led by geoscientist Jeremy McCormack of the Max Planck Institute for Evolutionary Anthropology in Germany.
"Notably, Early Pliocene sympatric C. carcharias and O. megalodon appear to have occupied a similar mean trophic level, a finding that may hold clues to the extinction of the gigantic Neogene megatooth shark."
It's not as difficult as you would think to figure out what ancient people and animals ate, especially if their teeth have been preserved. Shark teeth are pretty much all we have because their cartilaginous bones aren't preserved in the fossil record.
How it works is as follows. In any given environment, organisms will take up combinations of isotopes. When a toothed creature consumes those creatures, the isotopes are absorbed as well. Scientists may utilize some of these isotopes to substitute calcium phosphate in the muncher's teeth and bones, allowing them to better understand their diet.
We don't know what megalodons and great white sharks ate because we don't know what they ate. However, investigations of zinc isotope ratios in ancient, paleontological marine mammal bones show that the greater an organism's trophic level — that is, the position it holds in the food chain – the lower the zinc isotope ratios.
However, very little research had been done on non-mammalian marine animals, so McCormack and his team set out to fill that gap.
They built a database of zinc isotope ratios in the teeth of 20 extant shark species, including several that live in aquariums. They also got isotope ratios from 13 ancient species, including megalodon, for comparison. They were able to determine the trophic level of each species using this information.
Then they compared megalodon teeth to great white shark teeth, and this is where things start to get interesting.
The two species coexisted, albeit not smoothly, during the early Pliocene, an age that spanned from 5.33 million to 2.58 million years ago. Their zinc isotope ratios indicate that they were fighting for resources at the same trophic level.
Megalodon, which flourished from 23 million years ago until the middle of the Pliocene, died out approximately 3.6 million years ago. It's improbable that great white sharks, who preyed on megalodons, were the only cause of their extinction, but it's becoming increasingly likely that lesser species had a substantial part.
"The extinction of Otodus megalodon could have been caused by multiple, compounding environmental and ecological factors, including climate change and thermal limitations, the collapse of prey populations and resource competition with Carcharodon carcharias and possibly other taxa not examined here," the researchers wrote.
"In general, our study demonstrates [zinc isotope ratios] to be a powerful, promising tool to investigate the trophic ecology, diet, evolution, and extinction of fossil marine vertebrates."
Future research on the strange ancient sharks' massive teeth may give more insight on how they lived and died long ago.
Meanwhile, make friends with an orca if you're worried about a shark so ravenous that it may help destroy megalodon.
