Scientists Find World’s First ‘Club-Tailed’ Ankylosaurid Dinosaur Footprints in BC Riverbed

Victoria Arbour, a curator of paleontology at the Royal BC Museum, poses beside a stone slab with the fossilized footprints of an ankylosaurid ankylosaur. Courtesy of Royal B.C. Museum

Footprints of the iconic armour-plated dinosaur known as nodosaurid ankylosaurs, which roamed on all fours and lived from the Late Jurassic to Late Cretaceous periods, are scattered throughout the area near Tumbler Ridge, B.C.—but researchers have now discovered new prints unlike any that have emerged before.

According to the research team, this is a first-ever find.

The nodosaurid is, perhaps, dwarfed in notoriety by its distant relative the ankylosaurid ankylosaur, famous for its sledgehammer of a tail, which it swung menacingly to defend itself, presumably shattering the shin bones of many a T-Rex. But although the former (hammer-less) lizard is known to have inhabited these parts, ankylosaurids have not.

Still, the team of paleontologists who examined the unusual impressions believe these belong to exactly that ankylosaurid genus.

“Ever since two young boys discovered an ankylosaur trackway close to Tumbler Ridge in the year 2000, ankylosaurs and Tumbler Ridge have been synonymous,” Charles Helm, scientific adviser at the Tumbler Ridge Museum, said in a press release.

Ankylosaurs are a broader family of dinosaurs that includes both nodosaurids and ankylosaurids.

Nodosaurid footprints have been found across North America in past years. These all have four toes. And, in fact, scientists assign dinosaur footprints species names of their own, so these four-toed footprints belonging to nodosaurids were called Tetrapodosaurus borealis.

The strange thing is that for several years, sets of three-toed prints near Tumbler Ridge were also known to Helm. While the nodosaurid had four toes, the club-tailed ankylosaurid had three. These three-toed prints were later dubbed by the team who extracted and studied them as Ruopodosaurus clava, which means “the tumbled-down lizard with a club/mace,” honouring that mountainous region.

Victoria Arbour, a curator of paleontology at the Royal BC Museum, poses beside a stone slab with the fossilized footprints of an ankylosaurid ankylosaur. Courtesy of Royal B.C. Museum

These novel three-toed prints were deemed about 100–94 million years old, dating to the middle of the Cretaceous Period. That’s unusual because no ankylosaur bones were ever found in North America between about 100 and 84 million years back, leading some to speculate that they'd disappeared from the continent at that time.

That’s now proven false.

Even stranger, no footprints of the mace-wielding ankylosaurid have ever been found anywhere in the world. Until now, that is.

“It is really exciting to now know through this research that there are two types of ankylosaurs that called this region home, and that Ruopodosaurus has only been identified in this part of Canada,” Helm said.

After coming across the strange three-toed tracks, Helm reached out to Victoria Arbour, curator of paleontology at the Royal BC Museum, inviting her to work together, and along with Tumbler Ridge Museum curator Eamon Drysdale and geoscientist Roy Rule, to identify and interpret them.

(Left) Researches extract and airlift slabs of stone with the dinosaur footprints on them; (Right) Victoria Arbour examines the ankylosaurid ankylosaur footprints. Courtesy of Royal B.C. Museum

A relative of the ankylosaurid ankylosaur dinosaur, this image illustrates a Gobisaurus found in China. Courtesy of Royal B.C. Museum/Sydney Mohr

It’s thought that these hefty, plated dinos weighed two to three tons. The menacing tail they wielded possessed what looks like a giant medieval mace. It’s no wonder their feet impressed into the delta lowlands around Peace River, where shallow lakes and heavily vegetated lowlands are constantly carved up by channels.

Images of Ruopodosaurus footprints found near Tumbler Ridge, B.C. Courtesy of Royal B.C. Museum

Photogrammetric images were generated, showing the Ruopodosaurus footprints found near Tumbler Ridge, B.C. Courtesy of Royal B.C. Museum

Stone slabs displaying convex impressions were excavated and lifted by helicopter from several small tributaries, riverbeds, and creeks near Tumbler Ridge. The fossilized specimens were digitally rendered using photogrammetry to produce 3D models for further study. Scientists measured everything: their length and width, free digit length, digit width, stride length, pace length, and pace angulation.

“In order to test the likelihood of different ankylosaur clades as potential trackmakers for these tracks, we conducted several ancestral state reconstructions of the number of pedal digits,” the team wrote in a study about their findings findings recently published in the peer-reviewed Journal of Vertebrate Paleontology.

Aside from having three toes as opposed to four, Tetrapodosaurus footprints typically had longer digits and heels than the novel Ruopodosaurus specimens; the two species also differed in size. Squaring the discovery with fossil records in the Dunvegan and Kaskapau Formations, in northern Alberta and B.C. respectively, where bones of many ankylosaurs have been found before, and also noting the presence of ankylosaur trackmakers in close proximity with the new sets, the team lined up a positive identification.

These novel tracks were pressed by the feet of none other than ankylosaurid ankylosaurs.

Tracks of this charismatic dino have finally been found.

“This study also highlights how important the Peace Region of northeastern B.C. is for understanding the evolution of dinosaurs in North America,“ said Arbour, who led the study. ”There’s still lots more to be discovered.”