Unearthed: the cannibal sharks of a forgotten age

August 11, 2016, University of Bristol
Unearthed: the cannibal sharks of a forgotten age
Sketch of Orthacanthus, the tri-cuspid tooth of Orthacanthus and a thin section of an Orthacanthus coprolite showing teeth within the black box. Credit: University of Bristol

Scientists have discovered macabre fossil evidence suggesting that 300 million-year-old sharks ate their own young, as fossil faeces of adult Orthacanthus sharks contained the tiny teeth of juveniles.

These fearsome marine predators 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.

The evidence for shark cannibalism comes from distinctive spiral-shaped coprolites (fossil poop) found in the Minto Coalfield of New Brunswick, Canada. The faeces is known to have been excreted by Orthacanthus because this shark had a special corkscrew rectum that makes identification easy. The faeces is packed full of the teeth of juvenile Orthacanthus, confirming that these sharks fed on their own babies. This is called "fillial cannibalism".

PhD candidate in the School of Natural Sciences, Trinity College Dublin, Aodhán Ó Gogáin, made the extraordinary discovery. His findings have just been published today in the journal Palaeontology.

He said: "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 like Orthacanthus preyed on amphibians and other fish, but this is the first evidence that thesesharks also ate the young of their own species."

Professor Mike Benton, University of Bristol, is a co-author of the study. He 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, Royal Holloway University of London is another co-author. He said: "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."

Aodhán Ó Gogáin added: "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."

Explore further: Unraveling the jaw-dropping goblin shark

Related Stories

Unraveling the jaw-dropping goblin shark

August 10, 2016

A research team, led by Emeritus Professor Kazuhiro Nakaya of Japan's Hokkaido University, analyzed world-first footage captured by public broadcaster NHK in which two goblin sharks separately captured prey on a total of ...

Reef sharks prefer bite-size meals

February 22, 2016

Sharks have a reputation for having voracious appetites, but a new study shows that most coral reef sharks eat prey that are smaller than a cheeseburger.

Humans are greater threat to sharks, not the other way around

June 27, 2016

Fans of Shark Week are sinking their teeth into a whole new slate of programming focused on one of the world's most fascinating predators. While Shark Week often delves into the sensational aspects of sharks, Florida International ...

Teeny teeth indicate ancient shark nurseries

September 13, 2011

Fuelled by Hollywood and its vision of Jaws, sharks conjure images of fearsome predators patrolling our seas in search of their next unfortunate victim. It is therefore hard to imagine sharks as relatively small, harmless ...

Recommended for you

Big Agriculture eyeing genetic tool for pest control

October 16, 2018

A controversial and unproven gene-editing technology touted as a silver bullet against malaria-bearing mosquitos could wind up being deployed first in commercial agriculture, according to experts and an NGO report published ...

A selfish gene makes mice into migrants

October 16, 2018

House mice carrying a specific selfish supergene move from one population to another much more frequently than their peers. This finding from a University of Zurich study shows for the first time that a gene of this type ...

Discovery of a simple mechanism for color detection

October 15, 2018

Color vision, consisting of ocular color detection, is achieved with complicated neural mechanisms in the eyes. Researchers from Osaka City University in Japan have found color detection with a simple mechanism in the fish ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.