Researchers have discovered that ancient sharks hunted all prey, including other shark species, based on four rare fossils.
In four separate findings, researchers and amateur fossil hunters uncovered the spines of extinct shark species. All four spines were marked with bite marks from sharks, and two of them still had sharp teeth embedded in them. This series of discoveries is significant because shark skeletons are made of cartilage, which rarely fossilizes.
Simulation of ancient sharks engaging in cannibalism. (Photo: Tim Scheirer).
The new findings indicate that millions of years ago, ancient sharks preyed on each other along the eastern coast of the United States. “Sharks have been hunting each other for millions of years, but such interactions are rarely documented due to the scarcity of preserved cartilage,” said Victor Perez, co-author of the study and assistant curator of paleontology at the Calvert Marine Museum in Solomons, Maryland.
For decades, researchers have been aware of cannibalistic behavior among sharks. This behavior is common among living shark species, including goblin sharks, megamouth sharks, basking sharks, mako sharks, and great white sharks. In fact, juvenile sharks often consume their siblings while still in their mother’s womb.
Ancient sharks have left bite marks on numerous prehistoric animals, such as the bones of marine mammals, ray-finned fish, and reptiles, even on pterosaurs, flying reptiles that lived during the age of dinosaurs. However, evidence of sharks attacking their own kind is extremely rare. The oldest evidence of cannibalism among sharks dates back to the Devonian period (419.2 to 358.9 million years ago), when a shark known as Cladoselache consumed another shark, and the remains of the prey became fossilized in its stomach.
In a study published on December 7 in the journal Acta Palaeontologica Polonica, the research team examined three shark fossils found in the Calvert Cliffs along the Maryland coast from 2002 to 2016, and a fourth fossil from a phosphate mine in North Carolina dating back to the 1980s. All fossils date from the Neogene period (23.03 to 2.58 million years ago), a time when the largest shark species in history, megalodon (Otodus megalodon), roamed the oceans. However, the megalodon is not related to these attacks.
Unlike solid bones, shark cartilage is soft tissue made up of tiny hexagonal prisms, which quickly disintegrate after the animal dies. The four preserved fossils are centra, the vertebrae that form the spine. According to Perez, the centra contain more heavily calcified cartilage, making them better preserved than other bone parts. Researchers are unclear whether the bite marks resulted from an active attack or scavenging behavior. However, one fossil from Maryland has two 4 cm long teeth protruding from it, indicating that the shark survived the encounter.
Analysis of the bones reveals that the victim belonged to the class Chondrichthyes, which includes 282 species still living today, such as bull sharks, tiger sharks, and hammerhead sharks. Based on its shape, the fossil with two embedded teeth belongs to the family Carcharhinidae. The remaining tooth may have come from a shark of the genus Carcharhinus or Negaprion.
Another specimen from Maryland also appears to belong to the family Carcharhinidae, showing bite marks from several attackers, possibly including skates, rays, or bony fish. The third specimen may belong to the genus Galeocerdo, with the only living species today being the tiger shark (G. cuvier). The embedded tooth and the circular bite marks on the specimen indicate that all centra bones were bitten very hard.
