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The Giant Prehistoric Shark O. Megalodon was even longer than previously thought

New research by an international team, including Birkbeck researcher Dr Charlie Underwood, has demonstrated that the iconic and gigantic fossil shark Otodus megalodon (Meg or Megalodon of popular culture) was even longer than previously thought. Study of a fossilised vertebral column has shown that this monstrous animal was not shaped like a scaled -up version of a great white shark, but was instead, longer, slimmer and a slower swimmer. It's now known to have rivaled the sperm whale as the longest, and potentially heaviest, macropredator that has ever lived.

Tooth of Otodus megalodon. These teeth reach over 15 cm high.

The huge, triangular, teeth of the extinct shark Otodus megalodon are amongst the most iconic of fossils, being the remains of a huge shark that lived in oceans worldwide until its extinction about 3.6 million years ago. The teeth were clearly not just for show: rocks containing these teeth also commonly include bones of whales which have gauges and scratches that match the teeth of this shark showing that it hunted and ate whales. But other than the teeth, there are few fossils on which to base a reconstruction; with just minute scales, some vertebrae and some fragments of jaws, as the cartilage-based skeleton of sharks does not fossilise well.

As O. megalodon teeth have a similar overall shape to those of the modern great white shark (although far larger and more robust) it was once thought these sharks were closely related. It is now known that the ancestors of these two sharks diverged over 55 million years ago and the tooth shape was acquired by convergent evolution. In addition, the great white is the only living large shark (over 1000kg) that feeds on marine mammals, so it was considered a good analogue. As a result, reconstructions of O. megalodon have generally considered it as a huge great white, although scaling up from the largest teeth would give a maximum length of maybe 20 metres, three times that of any great white.

Discovery of fossils of a vertebral column of O. megalodon allowed this reconstruction to be tested. The initial study assumed the fossil was nearly complete, and concluded that the body shape was short and spindle-shaped, like a great white.  However, this new study re-examined the material and concluded that a number of vertebrae were missing, the start of the tail was incorrectly positioned and that no allowance was made for bones being crushed. Correcting for these errors gave a reconstructed length of O. megalodon as considerably, maybe up to 20%, longer, but also slimmer. In addition, scales of O. megalodon are not the same shape as those of the great white, and would not have given as streamlined a skin.

The conclusions of this are that O. megalodon was longer and probably slimmer than previously thought, potentially reaching 25 metres long. With this longer and more flexible body, O. megalodon would have hunted whales by chasing them in open water, similar to the way tiger sharks hunt turtles today, and it would not have been a fast-accelerating ambush predator like the modern great white.

Further Information

The results of this study were published in Palaeontologia Electronica.

Find out more about research and study in the School of Natural Sciences.

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