SCIENTISTS HAVE DISCOVERED macabre fossil evidence suggesting that sharks who lived 300 million years ago ate their own young.

TCD researchers, led by 25-year-old Aodhán Ó Gogáin, found ‘fossil poop’ of prehistorica adult orthacanthus sharks which contained the tiny teeth of juveniles.

These fearsome marine predators, which existed before the age of dinosaurs, used protected coastal lagoons to rear their babies.

But it seems they also resorted to cannibalising them when other food sources became scarce.

Three hundred million years ago, Europe and North America lay on the equator and were covered by steamy jungles, the remains of which are now compacted into coal seams.

The top predators of these so-called ‘coal forests’ were not land animals, but huge sharks that hunted in the oily waters of coastal swamps.

Aodhán Ó Gogáin, a PhD candidate at Trinity’s School of Natural Sciences, made the extraordinary discovery.

Image of a thin-section through an Orthacanthus coprolite, or poop fossil, with a black box indicating the tooth of the shark's own offspring.

“It is a brilliant feeling making this discovery and being able to contribute to a field I am passionate about,” the 25-year-old told TheJournal.ie.

“I did my Masters over in Bristol, and someone had already collected some specimens of the shark poop.

I eventually went over there to Canada and collected some new samples in the field, and we cut through the sections and found a baby shark’s tooth.

Aodhán, from Glasnevin, is currently researching tetrapods found in Kilkenny in the 1800s.

The fossil evidence for shark cannibalism was found in distinctive spiral-shaped coprolites (fossil poop) found by Aodhán and others in the Minto Coalfield of New Brunswick, Canada.

Corkscrew

The poop is known to have been excreted by Orthacanthus because this shark had a special corkscrew rectum that makes identification easy.

The poop is packed full of the teeth of juvenile Orthacanthus, confirming that these sharks fed on their own babies – a phenomenon known as “fillial cannibalism”.

Ó Gogáin’s findings have just been published in the journal Palaeontology. He added: 

Orthacanthus was a three-metre-long xenacanth shark with a dorsal spine, an eel-like body, and tricusped 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.

Orthacanthus was probably a bit like the modern day bull shark, 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 colonisation of inland freshwater environments.

“It’s such a privilege to work with such influential palaeontologists as my co-authors.”

Eating its own young

A co-author of the study, Professor Mike Benton of the University of Bristol, said: “As palaeontologists cannot observe predator-prey relationships directly in the way that a zoologist can, they have to use other methods to interpret ancient food webs.

One method is by probing the contents of coprolites [fossil poop] as we have done here.

Dr Howard Falcon-Lang of the Royal Holloway University of London is another co-author. He said:

We don’t know why Orthacanthus resorted to eating its own young.

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.

The Minto Coalfield in Canada, where the fossils were discovered, was the first place in North America where settlers mined coal in the early 17th Century.

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