The largest shark of all time was longer than a school bus. Known as Otodus megalodon to specialists, but simply megalodon in the seemingly endless schlock films and books the shark has inspired, the extinct fish stretched to sixty feet in length. And possibly more. The legend of the monstrous selachian is so tenacious that even hard-nosed treatments of the Cenozoic chomper feel compelled to mention the myths of modern megalodon of even greater size, or that “the one that got away” may be still out there. When considering a sixty-foot shark, after all, a seventy- or eighty-foot version doesn’t seem that outlandish, and the prospect of a hundred-foot monster is often paired with the ominous statement that "much of the ocean is still unexplored."
But it turns out that the enormous whale-cruncher is quite dead and probably wasn’t quite so gargantuan as previously supposed. Teeth tell the tale.
Most of what we know about Otodus megalodon comes from teeth. The shark’s serrated cutlery fared better at making it into the fossil record than most of the rest of its cartilaginous skeleton – with the exception of the odd vertebrae – and remain the starting point for all things megalodon.
The trouble is that teeth aren’t always the dead giveaways we wish them to be. For example, no one has described a complete tooth set for O. megalodon. Isolated teeth are all we have. No wonder the very name of the shark has shifted back and forth over the years, with different experts preferring Carcharodon, Megaselachus, Carcharocles, and now Otodus, changing what we think this shark looked like. Likewise, the teeth have been of critical importance to megalodon size estimates. By comparing O. megalodon teeth to those of great white sharks, paleoichthyologists have come up with maximum sizes for the prehistoric shark between 60 and 66 feet in total length, with a little wiggle room on either side.
A new study by DePaul University fossil shark expert Kenshu Shimada downsizes megalodon down to a maximum length of fifty feet or less. By looking at how tooth size changes with shark growth, and estimating size based on specific teeth at the front of the jaw, Shimada was able to better constrain the shark’s size.
The largest megalodon teeth in museum collections formed the core of Shimada’s sample. There might be larger teeth held in private collections – megalodon teeth are highly-prized, with exceptionally-large teeth often vanishing into the shady reaches of the commercial fossil market – but museum-held teeth allow other researchers to check each other's measurements and results. And with a celebrity species like megalodon, that's critical. In this case, Shimada specifically looked for large teeth from the very front of the top jaw. These teeth appear to be more reliable for estimating size than those of the front lower jaw, and, after checking that the trend held for great white sharks, Shimada applied the method to O. megalodon.
So, how large was the shark with a tooth over six inches tall? Shimada’s estimates come out to between 46 and a little more than 50 feet in length. Perhaps there were bigger megalodon out there. Shimada notes that there are rumors of larger teeth in private collections, but even these secret specimens – if they are as stupendous as they are said to be – would have belonged to a shark a bit short of the 60-foot mark. “Otodus megalodon can still rank as one of the largest carnivores of all time,” Shimada writes, “even though individuals exceeding [fifty feet in total length] were exceptionally rare.” And if the thought of a downsized megalodon harshes your paleo buzz, consider how little difference ten feet of body length might make if you found yourself in prehistoric waters with such a fish.