Otodus megalodon, a megatooth shark that lived between 23 and 3.6 million years ago, was not a fast swimmer, but it had a mega-appetite explaining its gigantism, according to an analysis of the shark’s placoid scales from the Late Miocene of Japan.
Tiny placoid scales of Otodus megalodon compared to a tip of a 0.5-mm mechanical pencil lead on the bottom right corner. Image credit: Kenshu Shimada / DePaul University.
Otodus megalodon is commonly portrayed as a gigantic, monstrous shark in novels and films.
Although the species was indeed quite gigantic, the maximum possible length is thought to be about 15 m.
The animal’s biology was previously based largely on its gigantic teeth and vertebrae.
Inferred to be partially warm-blooded or regionally endothermic, the shark was traditionally assumed to be an active fast swimming shark.
However, the new study reveals that Otodus megalodon’s placoid scales are not equipped with narrowly-spaced ridges or ‘keels’ characteristic of fast-swimming sharks.
“Our big scientific findings come from ‘tiny evidence’ as small as grains of sand,” said DePaul University’s Professor Kenshu Shimada.
Otodus megalodon. Image credit: J.J. Giraldo.
In their study, Professor Shimada and colleagues examined placoid scales found in the rock matrix surrounding a previously described associated tooth set of Otodus megalodon from the Late Miocene of Japan.
“This led my research team to consider Otodus megalodon to be an ‘average swimmer’ with occasional bursts of faster swimming for prey capture,” Professor Shimada said.
The new study also leads to a new paradox: although strong support for the presence of regional endothermy in Otodus megalodon exists based on a recent study, the question was how the fossil shark expended the high level of metabolic heat resulting from its warm-bloodedness without being an active swimmer.
Upon reviewing the literature, the authors noticed another possible function of endothermic body physiology that had been neglected in the biological context of Otodus megalodon — i.e., facilitating digestion as well as absorbing and processing nutrients.
“It suddenly made perfect sense,” Professor Shimada said.
“Otodus megalodon must have swallowed large pieces of food, so it is quite possible that the fossil shark achieved the gigantism to invest its endothermic metabolism to promote visceral food processing.”
The findings were published in the journal Historical Biology.
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Kenshu Shimada et al. Tessellated calcified cartilage and placoid scales of the Neogene megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), offer new insights into its biology and the evolution of regional endothermy and gigantism in the otodontid clade. Historical Biology, published online June 23, 2023; doi: 10.1080/08912963.2023.2211597
