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Bite marks on a now-extinct dolphin reveal that it was killed by an enormous shark that bit, shook and bled its victim to death 4 million years ago, according to a study in the latest issue of the journal Palaeontology.
The shark measured over 13 feet long.According to the Universita di Pisa's Giovanni Bianucci, who led the study: "the skeleton lay unstudied in a museum in Torino for more than a century, but when I examined it, as part of a larger study of fossil dolphins, I noticed the bite marks on the ribs, vertebrae and jaws. Identifying the victim of the attack was the easy part - it's an extinct species of dolphin known as Astadelphis gastaldii- working out the identity of the killer called for some serious detective work, as the only evidence to go on was the bite marks."
Bianucci called in fossil shark expert Walter Landini.
"The smoothness of the bite marks on the ribs clearly shows that the teeth of whatever did the biting were not serrated, and that immediately ruled out some possibilities," Landini said. "We simulated bite marks of the potential culprits and, by comparing them with the shape and size of the marks on the fossils, we narrowed it down to Cosmopolitodus hastalis."
Tell-tale teeth from this shark were also found near the dolphin, providing additional evidence. The size of the bite marks on the victim also enabled the researchers to estimate the overall length of the shark.
"The deepest and clearest incisions are on the ribs of the dolphin" says Bianucci, "indicating the shark attached from below, biting into the abdomen. Caught in the powerful bite, the dolphin would have struggled, and the shark probably detached a big amount of flesh by shaking its body from side to side. The bite would have caused severe damage and intense blood loss, because of the dense network of nerves, blood vessels and vital organs in this area. Then, already dead or in a state of shock, the dolphin rolled onto its back, and the shark bit again, close to the fleshy dorsal fin."
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