Healed Bone Gives Away Prehistoric Shark Bite

Of all the jaws to have evolved in their roughly 440 million year old history, few were as formidable as those of the enormous Carcharocles megalodon. The shark’s razor-toothed maw is what has made the extinct fish a regular star of pulp novels, b horror movies, and even basic cable hoaxes. Science backs up the shark’s reputation. In 2008, based on estimates from the study of a great white shark’s biting abilities, biomechanics expert Stephen Wroe and colleagues calculated that C. megalodon really did have a terrible bite – a crushing chomp between 24,000 and 41,000 pounds, depending on the position of prey in the 50-foot shark’s mouth.

But since C. megalodon forever disappeared from the world’s oceans as long ago as 3 to 4 million years before the present, we’ll never get to see those jaws in action. Images brought to life by science, special effects, and the darker parts of our imaginations are the closest we’ll get. Still, despite our temporal distance from the shark, there are damaged fossils that may testify to the predatory prowess of C. megalodon and help us envision the destruction this superpredator was capable of.

In the collections of Maryland’s Calvert Marine Museum, there  is a curious piece of whalebone. A damaged rib, found in the spoil pile of a North Carolina phosphate mine, the fossil bears a trio of ugly pathological bumps that look like osteological zits. Together, the lesions outline a 3-4 million year old bite.

Calvert Marine Museum paleontologist Robert Kallal and his coauthors described the specimen in a 2012 International Journal of Osteoarchaeology study.  Even though the rib fragment wasn’t found in place, the researchers pointed out that the identity of the fossil as part of a baleen whale narrows down the age of the specimen. At the locality where the shard was picked up, baleen whale remains are only found in the 3-4 million year old Pliocene rock of the Yorktown Formation. From the anatomy of the bone and the site’s fossil roster, the best candidate for the owner of the rib might be an ancient humpback whale.

That the rib was damaged by a predator, and not disease or some other cause, is clear from the spacing of the lesions. “Evenly spaced bony protrusions such as those preserved in [the whale rib fragment] are not known to occur naturally on mammalian ribs,” Kallal and colleagues observed, but the lesions are consistent with the bite of a carnivorous creature. And at this time in Earth history, there were several marine predators capable of inflicting the damage seen on the whale rib.

Whoever the predator was, they were not successful. The whale’s rib does not show sharp tooth slashes or fresh crushes, but healed bone. The whale survived the encounter. Still, the shape and arrangement of the wounds give away the presence of a large predator that attacked the whale’s flank. The space between each lesion is about 2.3 inches, which best matches a very large great white shark – bigger than has been found at the site before – or a young C. megalodon, fossils of which have been found at the locality. (Kallal and collaborators note that some kind of sperm whale could have created the damage, although they doubt this because the lesions are laid out in a crescent pattern that better matches the mouth of a shark.)

So who bit the whale? We may never know for sure. Healed bite wounds will only take us so far. But the rib fragment could bear the marks of a young C. megalodon with unrealistic predatory ambitions. The piece hardly stands alone. Other damaged whale bones support the idea that C. megalodon regularly fed upon – if not hunted – the large whales of their day, the chief confounding factor being that the tooth marks left in the aftermath of a successful hunt will look no different than those of a scavenger who shows up late to a carcass.

Even though distinguishing between hunting and scavenging in any single case of a tooth-sliced bone is often impossible, the fossils of marine mammals found in the same deposits as C. megalodon often bear awful bite damage. It’d be unreasonable to assume that all these cases represent either hunting or scavenging alone. The great prehistoric shark certainly did both, equipped with frightening jaws adapted for the dirty work of cutting through skin, blubber, muscle, and bone.

References:

Kallal, R., Godfrey, S., Ortner, D. 2012. Bone reactions on a Pliocene cetacean rib indicate short-term survival of predation event. International Journal of Osteoarchaeology. 22: 253-260

Wroe, S., Huber, D., Lowry, M., McHenry, C., Moreno, K., Clausen, P., Ferrara, T., Cunningham, E., Dean, M., Summers, A. 2008. Three-dimensional computer analysis of white shark jaw mechanics: how hard can a great white bite? Journal of Zoology. 276, 4: 336-342