Baby teeth in fossilized poop reveal cannibal shark

BRISTOL, England, Aug. 11 (UPI) -- Scientists recently found dozens of baby Orthacanthus shark teeth in ancient coprolites -- fossilized feces -- deposited by adult Orthacanthus sharks. The evidence suggests the prehistoric freshwater shark cannibalized its young.

The evidence is pretty clear. There's no mistaking the juvenile teeth or the owner of the coprolites. Orthacanthus possessed spiral-shaped rectums, making their ancient waste deposits quite distinctive.

The 300 million-year-old evidence was recovered from the Minto Coalfield of New Brunswick, Canada. Europe and North America once boasted vast, oil-rich jungles near the equator. Orthacanthus swam the swampy waters that dotted these so-called "coal forests."

"Orthacanthus was a three-meter-long xenacanth shark with a dorsal spine, an eel-like body, and tricusped teeth," researcher Aodhán Ó Gogáin, a postdoctoral candidate at Trinity College Dublin, said in a news release. "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."

Ó Gogáin is the lead author of a new paper on the discovery, published this week in the journal Paleontology. He likens the ancient shark to the modern bull shark -- both preferring to navigate back and forth between inland waters and shallow coastal seas.

"We don't know why Orthacanthus resorted to eating its own young," said study co-author Howard Falcon-Lang, a researcher at the Royal Holloway University of London. "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," Falcon-Lang concluded.