If the serrated sharp teeth of a killer shark invaded the dreams of millions of movie buffs across the world 45 years ago when acclaimed director Steven Spielberg released his cult Hollywood film Jaws, the scientifically inaccurate The Meg refreshed those memories in 2018 by telling a story about a 75ft prehistoric shark, the Megalodon. So much for fiction, and now it is time to cut to reality. To date only the length of the legendary giant shark Megalodon had been estimated but, a new study led by the University of Bristol and Swansea University has revealed the size of the rest of its body, including fins as large as an adult human.
There is a grim fascination in determining the size of the largest sharks, but this can be difficult for fossil forms where teeth are often all that remain. Today, the most fearsome living shark is the Great White, at over 6m (20ft) long, which bites with a force of two tonnes. Its fossil relative, the big tooth shark Megalodon, lived from 23 to around 3mn years ago, was over twice the length of a Great White and had a bite force of more than 10 tonnes. The fossils of the Megalodon are mostly huge triangular cutting teeth bigger than a human hand.
Jack Cooper, who has just completed the MSc in Palaeobiology at the University of Bristol’s School of Earth Sciences, and colleagues from Bristol and Swansea used a number of mathematical methods to pin down the size and proportions of this monster, by making close comparisons to a diversity of living relatives with ecological and physiological similarities to Megalodon. The project was supervised by shark expert Dr Catalina Pimiento from Swansea University and Professor Mike Benton, a palaeontologist at Bristol. Dr Humberto Ferrón of Bristol also collaborated. Their findings have been published the other day in the journal Scientific Reports.
Previously the fossil shark, known formally as Otodus megalodon, was only compared with the Great White. Jack and his colleagues, for the first time, expanded this analysis to include five modern sharks. Dr Pimiento said: “Megalodon is not a direct ancestor of the Great White but is equally related to other macropredatory sharks such as the Makos, Salmon shark and Porbeagle shark, as well as the Great White. We pooled detailed measurements of all five to make predictions about Megalodon.”
Professor Benton added: “Before we could do anything, we had to test whether these five modern sharks changed proportions as they grew up. If, for example, they had been like humans, where babies have big heads and short legs, we would have had some difficulties in projecting the adult proportions for such a huge extinct shark. But we were surprised, and relieved, to discover that in fact that the babies of all these modern predatory sharks start out as little adults, and they don’t change in proportion as they get larger.”
As Jack Cooper said, this meant, the researchers could simply take the growth curves of the five modern forms and project the overall shape as they get larger and larger – right up to a body length of 16m. The results suggest that a 16m long Otodus megalodon likely had a head round 4.65m long, a dorsal fin about 1.62m tall and a tail around 3.85m high. This means an adult human could stand on the back of this shark and would be about the same height as the dorsal fin.
The reconstruction of the size of Megalodon body parts represents a fundamental step towards a better understanding of the physiology of this giant, and the intrinsic factors that may have made it prone to extinction.
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