Illustration of two sparring megalodonsClarence Shoe Schumaker, Courtesy of the Calvert Marine MuseumSeveral fossil teeth from the giant predatory shark Otodus megalodon show scratch marks that could only have been made by members of their own species, suggesting that thelargest sharks of all time may have fought by sparring with their jaws.Between 23 and 3.6 million years ago, megalodon, which may have grown up to 24 metres long, swam the worlds oceans. Now, Stephen Godfrey at the Calvert Marine Museum in Maryland and his colleagues have studied four teeth from fossil sites in North and