The poop's signature twist hints at a corkscrew-shaped anus. The teeth inside hint at something even worse. (Aodhán Ó Gogáin/Trinity College Dublin)

In the summer of 2015 in New Brunswick, Canada, a man picked up a brown and black stone shaped sort of like a tiny pine cone. You or I would have probably flicked it aside, thinking the object was just another pebble. But this man knew what he was doing, and he’d come to the Minto Coalfield for a reason. It was the first place in North America where fossil fuel was mined, dating back to 1639.

Much of this continent’s coal was formed around 300 million years ago during what scientists call the Carboniferous Period. When you dig down and start messing around in coal seams, a lot of other interesting rocks come tumbling out of the earth, too — rocks that are just as old as the clumps of coal. And sometimes those rocks aren’t rocks at all, but coprolites — a fancy word for fossilized poop.

Coprolites can tell us all kinds of things about the ancient world and the creatures that inhabited it. In this case, for instance, Aodhán Ó Gogáin had picked up the scat of a creature with a corkscrew-shaped rectum.

This probably seems like a juvenile thing to focus on. But when you’re trying to understand what life was like hundreds of millions of years before the dinosaurs even existed, you need to make use of every clue available. With that in mind, let’s have a grown-up, totally serious talk about the ancient Earth and the anuses that inhabited it.

Way back when these coprolites were formed, North America would have been hovering over the equator, smashed into the supercontinent known as Pangea. Basically all of the western United States would have been a shallow sea, and swamps would have stretched from Texas to New England.

And in those swamps, there are basically two known creatures that could have produced twisty coprolites like this, says Gogáin, a paleontologist at Trinity College Dublin and lead author of a new study published Thursday in the journal Palaeontology.

One is called Ageleodus, a creature still shrouded in mystery, as we’ve only ever found its teeth. And the other is known as Orthacanthus: a long, lithe-bodied shark that probably would have swum by flexing its body along the length, sort of like how an eel swims or a snake slithers.

“It is thought that Orthacanthus may have evolved these eel-like bodies in order to maneuver between tree roots in coal swamps,” Gogáin says.

Wherever we find evidence of Orthacanthus across North America, we also find a high proportion of coprolites with a telltale twist at the end. Therefore, the idea that Orthacanthus is producing these turds is supported by quantitative data — which is about as hot as the smoking gun gets when you’re peering back through hundreds of millions of years.

But why a corkscrew? Gogáin says it’s a primitive feature that’s been maintained in some sharks. Most other fish, such as the Actinopterygians, do not possess rifled rectums. (Quick note on shark biology: A shark's digestive track actually terminates inside a chamber called the cloaca, which is basically an all-purpose orifice used for both waste and reproduction.) But it’s thought that a corkscrew shape both slows down the passage of poo and also gives the shark more surface area with which to digest its meals.

Increased digestive efficiency is something sharks desperately need, because their intestines are surprisingly short compared with other animals. If you were to unravel an adult human gut, you’d get about 24 feet of viscera. But for a shark of the same size, the intestines would stretch just one foot. Orthacanthus, in other words, would have needed all the surface area it could get.

Gogáin’s coprolites are obviously not the first feces found for this species, but one of them is unique because it contains — wait for it — teeth from another, smaller Orthacanthus. Like its scat, Orthacanthus had pretty recognizable chompers — three-pronged tridents built for seizing prey and never, ever letting go.

The tooth of Orthacanthus. (Aodhán Ó Gogáin/Trinity College Dublin)
The tooth of Orthacanthus. (Aodhán Ó Gogáin/Trinity College Dublin)

That's right: Ol’ corkscrew butt seems to have dabbled in cannibalism. And it gets worse. One of Gogáin’s co-authors, Howard Falcon-Lang, suggests that Orthacanthus may have preyed upon its own young when times were tough.

“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,” Falcon-Lang said in a news release. “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.”

That sounds pretty cold, but far more cuddly looking species have been found to eat their own. Hamsters, for one. And modern sand tiger sharks start eating each other before they even leave their mother’s body, so let’s not judge Orthacanthus too harshly.

In fact, if you want to celebrate this species and the precious poop it left behind, you can visit all of these specimens in person at the New Brunswick Museum in St. John. Just, you know, maybe wash your hands after.

Jason Bittel writes about weird animals for a living. You can find more of his work at his website

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