Megatooth sharks, the largest sharks that have ever existed, were also the greatest apex predators ever measured, according to a new Princeton study According to a new Princeton study, ancient megatooth sharks – the largest sharks ever known — were apex predators at the greatest level ever record
Megalodons are known only from the teeth they left behind. Here, a megalodon tooth is compared to a great white shark tooth. Each inch of tooth corresponds to about 10 feet of length: 20 feet for the 2-inch great white shark tooth and 60 feet for the 6-inch megalodon tooth. Encased in rock-hard enamel, teeth are more easily preserved than bones, let alone a shark’s cartilage skeleton.
While sharks of various types have lived for more than 400 million years, long before the dinosaurs went extinct, these megatooth sharks emerged after the dinosaurs died out and controlled the waters until about 3 million years ago. “Ocean food webs do tend to be longer than the grass-deer-wolf food chain of land animals because you start with such small organisms,” said Kast, now at the University of Cambridge, who wrote the first iteration of this research as a chapter in her dissertation. “To reach the trophic levels we’re measuring in these megatooth sharks, we don’t just need to add one trophic level — one apex predator on top of the marine food chain — we need to add several onto the top of the modern marine food web.
One way to tuck in an extra trophic level or two is cannibalism and several lines of evidence point to that in both megatooth sharks and other prehistoric marine predators.Without a time machine, there’s no easy way to recreate the food webs of extinct creatures; very few bones have survived with teeth marks that say, “I was chewed on by a massive shark.”
A few plants, algae, and other species at the bottom of the food web have mastered the knack of turning nitrogen from the air or water into nitrogen in their tissues. Organisms that eat them then incorporate that nitrogen into their bodies, and critically, they preferentially excrete more of nitrogen’s lighter isotope, N-14, than its heavier cousin, N-15.
“When you look in the geologic record, one of the most abundant fossil types are shark teeth,” said Sigman. “And within the teeth, there is a tiny amount of organic matter that was used to build the enamel of the teeth — and is now trapped within that enamel.” The analysis requires a custom-built, automated nitrous oxide preparation system that extracts, purifies, concentrates, and delivers the gas to a specialized stable isotope ratio mass spectrometer.
As Kast was quarantined at home, she painstakingly built up a record with more than 20,000 marine mammal individuals and more than 5,000 sharks. She wants to take things much further. “Our tool has the potential to decode ancient food webs; what we need now is samples,” said Kast.
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