300-Million-Year-Old Shark Was a Cannibal

Photo Credit: WikiMedia Commons/Nobu Tamura

Some 300 million years ago, a shark species did something that had yet to be documented: It ate the young of its own kind.

The shark, Orthacanthus, was a top marine predator of its day. Thanks to a lump of its fossilized poo found in a famous coal field in New Brunswick, Canada, Trinity College PhD candidate Aodhán Ó Gogáin was able to examine what it ate.

That turned out to be juvenile Orthacanthus. The ancient fecal specimen was full of the youngins' teeth, confirming cannibalism.

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Orthacanthus was eel-like and grew to just under 10 feet (3 meters) long. While prior research had shown that it ate other fish and amphibians, "this is the first evidence that these sharks also ate the young of their own species," Ó Gogáin said in a statement.

(In case you're wondering how Ó Gogáin knew that the poo came from an Orthacanthus, it's because the shark had a distinctive "corkscrew" rectum that ... "makes identification easy," as a press release gently put it. See the spiral-shaped sample below.)

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The scientists aren't sure yet exactly what drew the sharks to eat their young, but they have some ideas, beginning with a shifting food supply.

The shark lived in a time when Europe and North America were humid jungle landscapes close to the equator. Orthacanthus terrorized the coastal swamps of the period, but in that era the push was on to expand into freshwater further inland, with marine fish beginning to colonize freshwater swamps.

"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," study co-author Howard Falcon-Lang, of Royal Holloway University of London, told the BBC.

"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 said in a statement.

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"Orthacanthus was probably a bit like the modern day bull shark," said Ó Gogáin, "in that it was able to migrate backwards and forwards between coastal swamps and shallow seas. This unusual ecological adaptation may have played an important role in the colonization of inland freshwater environments."

Findings on the ancient shark's cannibalism have been published in the journal Palaeontology.

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