Solving a 150-Year-Old Fossil Mystery From the Canadian Arctic

In the summer of 1859, Captain Sherard Osborn of the British Royal Navy stood on Cameron Island, Nunavut, looking at his boots. He and crew had been sent there to determine the fate of HMS Erebus and HMS Terror, two ships that had been lost a decade earlier as part of the ill-fated Franklin expedition. As he kicked over some loose stones, he noticed a bone-shaped fragment that fit neatly into his palm. For whatever reason, he decided to pocket the specimen. Little did he know that the fossil’s true identity—much like the location of the ships that Osborn was searching for—would remain a mystery for another 150 years.

“I’m sure he just thought it was an interesting-looking rock,” says Hans Sues, Curator of Vertebrate Paleontology at the Smithsonian National Museum of Natural History. Sues is the author of a new paper in the Canadian Journal of Earth Sciences that aims to finally answer the question of where the creature that left Osborn’s fossil fits into the tree of life.

Sues explains that even though Royal Navy sailors were not necessarily well-versed in the sciences, they would often pick up items to be identified by experts back home. “Minerals, rocks, fossils, interesting biological specimens, you name it,” he says. “They really vacuumed the place!”

In a detailed account of the voyage published by Osborn’s boss, Captain Francis McClintock, the fossil bone was recorded as belonging to an ichthyosaur, an ocean-dwelling reptile somewhat similar in appearance to modern-day dolphins. Sues says that’s wrong, but understandable. “In the south of England, there are a lot of ichthyosaur fossils, so lots of people from the British Isles were familiar with them,” he says. “It makes sense that they would jump to that conclusion, but it looks completely different from that.”

The first scientific description of the fossil didn’t appear until 1875, the same year Osborn died. Its author, the Scottish physician and naturalist Andrew Leith Adams, identified it as a cervical vertebra, a bone found in the neck. However, while confirming its reptilian origin, Adams wasn’t confident enough to say what kind of reptile it was, calling it simply “saurian”. The name he proposed, Arctosaurus osborni, translates roughly as “Arctic-dwelling reptile found by Captain Osborn.”

To be fair, identifying a creature by a single, incomplete neck bone is a tricky business at the best of times, and paleontology was still a relatively new science in the 19th century. But that didn’t stop others from speculating. Over the next century and a half, Arctosaurus became a kind of odd sock of the paleontological world: some researchers classified it as an early relative of crocodiles, others as a dinosaur. At least one thought it was a turtle, though Sues thinks “they probably should have known it wasn’t”.

Sues himself first saw a cast of the fossil in the 1970s, at the Natural History Museum in London, U.K. As a Canadian paleontologist and an expert in the Triassic period, the geological era to which Arctosaurus belongs, Sues was fascinated by the specimen and wanted to learn more. Eventually, he was given a copy of the cast by a friend. Unfortunately, by that time Sues was busy with other projects, so he filed it away to examine in detail at a future date.

Last year, Sues was working on Triassic fossil found in the eastern U.S. that suddenly reminded him of Arctosaurus. He still had the cast, but decided to take the next step and look for the original specimen. He wrote to Nigel Monaghan, Keeper of Geology at the National Museum of Ireland in Dublin, where it had been stored for more than a century. A few weeks later, he had the fossil in his hands, and was able to conduct a detailed analysis, including a full 3D scan.

“This is great example of why institutional collections exist,” says Jim Gardner, an associate editor for the Canadian Journal of Earth Sciences. Gardner knows whereof he speaks: the Royal Tyrrell Museum of Palaeontology, where he works, holds more than 160,000 specimens. “Fossils and other natural history objects are the primary data for our work. Without repositories, the specimens are at risk of being lost after they were first described. In this case, that would have left us unable to solve the mystery.”

So what is Arctosaurus? In the paper, Sues suggests that it belongs to a group called Allokotosauria. “It’s a group that includes a whole bunch of really strange-looking, plant-eating reptiles that lived during the Triassic,” he says. That means that Arctosaurus lived on land, not in the water, and was probably about five to six feet long, including a longish neck and tail. “The kind of lizard you might compare it to today would be a green iguana,” says Sues.

It also means that Arctosaurus was not a dinosaur, but would have lived alongside them, competing with the herbivorous ones for food and trying to avoid becoming a meal for the carnivorous ones. Sadly, Arctosaurus left no descendents; the allokotosaurians did not survive the mass extinction at the end of the Triassic period. The dinosaurs did, and went on to dominate the earth for the next 140 million years.

More than a century and a half after its discovery, Sues hopes the new paper has finally found a home in the tree of life for Arctosaurus osborni. If so, it would mirror the search for the Franklin expedition that started it all off: though Osborn and McClintock’s company found a lifeboat and a number of graves, they never located the original ships. It wasn’t until 2014 that a team of Canadian researchers located the wreck of the HMS Erebus, and the HMS Terror wasn’t found until last fall.

But while Arctosaurus is the first—and so far the only—Triassic land animal to be found in the Canadian Arctic, it will not likely be the last. “There’s so much stuff up there, and so many different kinds of rock formations,” says Sues. “They may have early dinosaurs in them, or precursors of mammals. It could be a real treasure trove.”