An ancient species of shark called Orthacanthus engaged in filial cannibalism, a behavior that happens when adults of the species feasted on their own young.
The Orthacanthus sharks lived about 300 million years ago in the coastal swamps of modern-day North America and Europe, which were once surrounded by hot jungles.
In a paper published in the journal Palaeontology, researchers reported that they found juvenile shark teeth in the fossilized poop of these sharks that were found in a coal field in Canada.
The findings show that the animal, a top marine predator of its time, ate its kind.
Researchers were certain that the fossilized poo called coprolite belong to these sharks because of the fecal matter's unusual shape. The teeth were also confirmed to belong to the same species.
"These sharks have very distinctive tricuspid teeth, where they have little tusks coming up from the tooth," said study researcher Aodhan ó Gogáin, from the University of Bristol.
Earlier research has shown that the eel-like shark ate other fish and other amphibians but the new findings provide the first evidence that they also ate the juveniles of their own species.
Although scientists are not exactly certain as to what drove the sharks to eat their young, they have some ideas. The marine animal, for instance, may have resorted to cannibalism to keep themselves from getting hungry when there is shortage of food supply.
The animal lived during the period when marine fish started to colonize freshwater locations, which caused significant reduction in the shark's food supply. The shark terrorized the coastal swamps but there was a push to expand into freshwater inland as marine fish start to colonize the freshwater swamps.
Researchers think that the Orthacanthus was like the modern-day bull shark capable of migrating back and forth between coastal swamps and shallow seas, an ecological adaptation that has possibly played a role in the colonization of inland freshwater environments.
"It's possible that Orthacanthus used inland waterways as protected nurseries to rear its babies, but then consumed them as food when other resources became scarce," said study author Howard Falcon-Lang, from the Royal Holloway University of London.
During their invasion of the fresh water, the sharks likely cannibalized their young to serve as resources needed for exploring into the interiors of the continent, said Falcon-Lang.
"Orthacanthus, may have practised filial cannibalism in coastal nurseries because its heteropolar coprolites contain juvenile xenacanthid teeth," the researchers wrote in their study published on Aug. 11.
