As if producing poop with a spiral structure wasn’t weird enough, it turns out that the ancient sharks that defecated them were also partial to snacking on their own young. Researchers have found that the fossilized feces of a long extinct species of shark was packed with the teeth of their pups, giving them an insight into how these animals lived.
The creatures that produced the perplexing poop are called Orthacanthus sharks. Looking more like modern day eels than sharks, the animals had a long dorsal fin that ran down its back and a long spine growing from the back of its skull. The adults could reach up to an impressive 3 meters (10 feet) in length, making them the top predators of the tropical coastal swamps and rivers in which they lived. And due to one slightly bizarre physical occurrence – a corkscrew rectum – palaeontologists are easily able to identify their unique spiral-shaped poop.
The swamps in which they lived have since been turned to coal, and it was in these deposits in North America that the fossil poop hiding a grisly secret was discovered. Packed full of tiny teeth distinctive to the sharks, the remains provided definitive proof of the creatures hunting habits. “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 Aodhán Ó Gogáin, who made the finding of the teeth in the poop, and published the results in the journal Palaeontology.
Interestingly, the behavior displayed by the ancient sharks is replicated by modern species that inhabit similar environments. Bull sharks, for example, live in coastal swamps and shallow seas, and are also known to eat their young when given the chance or the situation pushes them to. Modern sharks are known to eat a wide variety of prey – even their own siblings while still in the womb – but it is important to have solid evidence for this sort of behavior in extinct species.
“Orthacanthus was probably a bit like the modern day bull shark, in that it was able to migrate backward and forwards between coastal swamps and shallow seas,” explains Ó Gogáin. “This unusual ecological adaptation may have played an important role in the colonisation of inland freshwater environments.” This was a period in which marine fishes were beginning to colonize freshwater habitats in large numbers.
It might also suggest that the sharks living in the swamps 300 million years ago were going through some sort of food shortage. This is because rather than just preying on all ages of their own kind, the ancient sharks have been found to be specifically targeting their young, something known as ‘filial’ cannibalism. This, the authors suggest, is often a sign that the animals are going through some sort of environmental stress, as ordinarily, it would not make evolutionary sense to consume your own young.