Studying poop shows ancient shark ate its own young

An ancient group of sharks living approximately 300 million years ago were cannibalistic and would even devour their own young, according to fossil evidence collected as part of research detailed in Thursday’s edition of Palaeontology.

Lead author Aodhán Ó Gogáin, a Ph. D. student in the Trinity College Dublin School of Natural Sciences, and his colleagues studied coprolites (or fossilized feces) of adult Orthacanthus sharks and found that they contained tiny teeth belonging to young members of their own species.

Orthacanthus sharks, the study authors explained, lived in coastal swamps along the equator and used protected lagoons to raise their offspring – but when food started to become scarce, they did not hesitate to cannibalize their own young in order to obtain much-needed sustenance.

“Orthacanthus was a three-metre-long xenacanth shark with a dorsal spine, an eel-like body, and tricusped teeth,” Ó Gogáin explained in a statement. “There is already evidence from fossilized 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.”

Why bother eating your own young?

Ó Gogáin’s team found evidence of shark cannibalism in unusual spiral-shaped coprolites found in the Minto Coalfield of New Brunswick. Because of the shape of the fossilized dung, they were able to link it to Orthacanthus, as the shark possessed a unique corkscrew-shaped rectum.

In-depth analysis of the coprolites found they contained many fossilized teeth belonging to juvenile Orthacanthus, confirming that the creatures engaged in fillial cannibalism (which is just a fancy way of saying they would eat their own young). This discovery is not unprecedented, since as BBC News noted, modern-day bull sharks are also know to consume their own offspring.

“We don’t know why Orthacanthus resorted to eating its own young,”  co-author Dr. Howard Falcon-Lang of Royal Holloway University of London said. “However, the Carboniferous Period was a time when marine fishes were starting to colonize 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.”

He added that filial cannibalism is “relatively unusual,” telling BBC News. “We generally find it in rather stressed ecosystems, where for whatever reason, food is running scarce. Obviously it’s evolutionarily a bad move to eat your own young unless you absolutely have to… Part of this story, we think, is that during this invasion of fresh water, sharks were cannibalizing their young in order to find the resources to keep on exploring into the continental interiors.”

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Image credit: Alain Beneteau 

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