A giant megalodon shark may have broken a whale's back in a vicious attack around 15 million years ago, according to a study.
The paper, published in the journal Palaeontologia Electronica, documents an analysis of cetacean vertebrae discovered in Maryland that show signs of compression fracture-trauma that the authors said most likely resulted from a predation attempt by a large predator, such as megalodon, although they also put forward other plausible explanations.
The vertebrae of the cetacean (a group of aquatic mammals that includes whales, dolphins and porpoises) were found in the Calvert geologic formation, which stretches across Maryland, Virginia and Delaware, preserving an abundance of fossils that date back to the Miocene epoch (around 23 million to 5.3 million years ago).
Megalodon (Otodus megalodon) is an iconic shark species-the largest to ever roam Earth's oceans-that scientists think went extinct around 3.6 million years ago. Its earliest remains date back more than 20 million years ago.
This species is considered to be one of the largest and most powerful predators to have ever lived. Some estimates suggest it could have grown to between roughly 50 feet and 60 feet in length, according to the Natural History Museum in London.
A megalodon shark may have been responsible for the breaks in the cetacean bones, according to the authors of the Palaeontologia Electronica, who decided to examine the vertebrae because they were "sufficiently unique," they wrote in the study.
The kind of physical trauma seen in the vertebrae of the cetacean in question is extremely rare, according to the researchers.
"In terms of the fossils we've seen on Calvert Cliffs, this kind of injury is exceedingly rare," Stephen Godfrey, a paleontologist with the Calvert Marine Museum, Maryland, and National Museum of Natural History, told LiveScience.
"The injury was so nasty, so clearly the result of serious trauma, that I wanted to know the backstory."
Godfrey and his colleague Brian Beatty, a researcher with the National Museum of Natural History and New York College of Osteopathic Medicine, decided to conduct CT scans of the vertebrae. These bones came from a cetacean that likely measured around 13 feet in length, although the exact type of whale has not been determined, and the bones may even belong to a dolphin.
The scans revealed that the vertebrae had suffered compression fractures. According to the researchers, the injury was so "severe" that it was likely caused by a large predatory shark, such as megalodon or its close relative Otodus chubutensis-both of which have been found in the region-or a macroraptorial sperm whale of the family Physeteroidea, another apex predator.
Intriguingly, a single megalodon shark tooth was found with the vertebrae, which could strengthen the case that one of these sharks was responsible for the potential attack. But there are several possible explanations, according to the researchers.
Firstly, the tooth could have become embedded in the body of the cetacean as a result of the bite associated with the original trauma. Secondly, the tooth could have been shed by the shark that killed the cetacean. Thirdly, the tooth could have ended up next to the vertebrae simply by chance. And finally, the tooth could have been shed by a shark as it scavenged the carcass of the cetacean after it died.
The authors said there is even a possibility that the trauma seen in the vertebrae was not caused by a predatory attack at all. Instead, it could have resulted from a "massive seizure" triggered by poisoning with toxic algal blooms.
But Godfrey said the most plausible explanation is an attack by a megalodon shark, given the nature of the injuries.
"It's just so over the top in terms of the violence," Godfrey said. "We don't know the full repertoire of predatory techniques that megalodon could have employed, but it's possible that, like living sharks, they ambushed their prey from below." Such an attack could have resulted in the observed injuries.
Despite the severe trauma that the cetacean suffered, the evidence suggests that the animal did not die straight away, and may have survived for a minimum of 6 to 8 weeks based on the signs of healing observed in the bones.
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