Academics have made a macabre discovery in the Minto Coalfield of New Brunswick, Canada: juvenile shark teeth in the fossilised faeces of an Orthacanthus shark, which roamed the freshwater swamps of Europe and North America 300 million years ago. The grisly remains suggest that the ancient predator ate its own young, behaviour known as “filial cannibalism”. “Orthacanthus was a three-metre-long Xenacanthus shark with a dorsal spine, an eel-like body, and tricuspid teeth. There is already evidence from fossilised stomach contents that ancient sharks like Orthacanthus preyed on amphibians and other fish, but this is the first evidence that these sharks also ate the young of their own species,” says Aodhan Ó Gogáin of Trinity College Dublin, who found the gnashers.
But why? Surely it’s counterintuitive for an animal to eat its offspring? Filial cannibalism may sound brutal, but it has been observed in a wide range of modern species, from cats to primates, and the reasons for it include: removing weaker young (“runts of the litter”), making the most of an easy food source and increasing reproduction rates. Dr Howard Falcon-Lang from Royal Holloway, University of London explains: “We don’t know why Orthacanthus resorted to eating its own young. However, the Carboniferous Period was a time when marine fishes were starting to colonise freshwater swamps in large numbers. 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.”