Illustration by Timothy Scheirer

Carcharocles megalodon strikes again!

Traces of ancient shark attack preserved in a fossil whale bone

Biology News

Whale bone fossil showing three tooth marks from a large shark, probably Carcharocles megalodon.

Fossil tooth of Carcharocles megalodon from the Atacama Desert, Chile (Miocene). Ruler is marked in centimeters.

The specimen is described in the article entitled "Bone Reactions on a Pliocene Cetacean Rib Indicate Short-Term Survival of Predation Event" published in the International Journal of Osteoarchaeology. It was coauthored by Robert Kallal and Stephen Godfrey of the Calvert Marine Museum in Solomons, Maryland, and Donald Ortner of the Smithsonian's National Museum of Natural History.

Three tooth marks on the rib indicate the whale was once severely bitten by a strong-jawed animal. Judging by the 6 centimeter spacing between tooth marks, scientists believe the attacker was the huge shark, Carcharocles megalodon (pronounced "kar-KAR-uh-kleez MEG-uh-luh-don").

Scientists know the whale survived because "most of the fossil fragment is covered with a type of bone known as woven bone, which forms rapidly in response to localized infection," explains Ortner, an authority on the effect of disorders on skeletal tissue. "Biomechanically woven bone is not very strong. The body eventually remodels it into compact bone, but it takes time." CT scans reveal evidence of inflammation in the bone marrow consistent with infection.

The presence of the woven bone indicates the healing was incomplete and the whale died, the scientists estimate, between two and 6 weeks after the attack. The whale's death may have been unrelated to its infection and injury, Ortner says. "We don't know why it died."

Based on the curvature of the shark's jaw, as indicated by the arc of the impressions of its teeth, the scientists believe the shark was between four and eight meters long (not big for Carcharocles).

In the realm of paleontology, "only a handful of fossils show these kinds of interactions," Godfrey explains. "There are lots of bite marks on fossils showing where the animal died and its carcass was scavenged. This fossil is one of a very few examples that shows a trauma clearly attributed to another animal, yet also shows the victim survived the event."

"One certainly doesn't expect to find evidence of animal behavior preserved in the fossil record, but this fossil shows just that, a failed predation," says Godfrey, who discovered the fossil. "The shark may have gone away with a mouthful, but it didn't kill the whale"