Footprints of armored dinosaurs with clubbed tails found for the first time

Dinosaur fossils often steal the spotlight, but sometimes, tracks and footprints can tell an even deeper story. Ancient ankylosaur tracks, recently discovered in Canada, have rewritten a chapter of dinosaur history.

These newly discovered tracks belong to a group of armored dinosaurs known for their tail clubs called ankylosaurids. Yet, no one had ever seen their footprints before.

Researchers working in British Columbia and Alberta uncovered the fossilized prints in mid-Cretaceous rock formations. The discovery includes multiple trackways of a new ichnospecies, Ruopodosaurus clava.

This finding offers long-sought confirmation that ankylosaurid dinosaurs, known for their weaponized tails, roamed North America far earlier than previously recorded.

The research, published in the Journal of Vertebrate Paleontology, highlights just how much a footprint can reveal. From foot structure to group behavior, and even evolutionary timelines, these impressions bridge gaps in the fossil record and expand our understanding of dinosaur diversity.

Armored ankylosaur dinosaur tracks

Ankylosaurs are famous for their tank-like bodies and low-slung frames. They fall into two main groups: nodosaurids and ankylosaurids.

Nodosaurids had four toes and flexible tails. Ankylosaurids, however, carried club-like tails and walked on three-toed feet.

Until now, paleontologists had only found four-toed ankylosaur tracks in North America. These belonged to Tetrapodosaurus borealis, a widely documented ichnospecies linked to nodosaurid dinosaurs.

The discovery of three-toed tracks with associated five-fingered forelimb impressions was new – and important.

The name Ruopodosaurus clava means “tumbled-down lizard with a club,” which is a nod to both its clubbed tail and the mountainous terrain of Tumbler Ridge.

The armored dinosaur tracks date back around 100 million years to the Cenomanian stage of the Late Cretaceous. They came from two formations – the Dunvegan and the basal Kaskapau. Both represent wet deltaic environments that supported lush vegetation and slow-moving waterways.

Well-preserved dinosaur footprints

The most complete specimen, TRMF 2023.09.002, was found beside the Wolverine River. It preserves a left manus and a pair of feet, with all digits clearly impressed.

Other tracks were recovered from sites like Bullmoose Creek and Everlasting Creek – each offering a unique snapshot of these animals‘ movements.

The prints differ sharply from other dinosaur tracks. The three toes of the hindfoot are wide, blunt, and either triangular or U-shaped.

The forefoot shows five spread-out digits in a crescent shape. The stride patterns, toe shapes, and narrow walking stance support the identification of ankylosaurids.

“While we don’t know exactly what the dinosaur that made Ruopodosaurus footprints looked like, we know that it would have been about 5–6 meters long, spiky and armored, and with a stiff tail or a full tail club,” said Victoria M. Arbour, a vertebrate palaeontologist at the University of Victoria.

Dinosaur fossil record in North America

These footprints bridge a long-standing gap in the North American fossil record. No ankylosaurid bones have been found in this region between 100 and 84 million years ago.

For decades, researchers thought ankylosaurids had disappeared from the continent during this time, only to return later from Asia.

But the tracks tell a different story. They show that ankylosaurids were very much present in mid-Cretaceous ecosystems. They coexisted with nodosaurids, as both Ruopodosaurus and Tetrapodosaurus prints appear in the same rock layers.

Dr. Charles Helm, who co-authored the study, had observed these unusual three-toed tracks near Tumbler Ridge for years.

He eventually brought Arbour into the project to confirm their significance. This collaboration paid off with the identification of a new species and the rewriting of an evolutionary timeline.

“Ever since two young boys discovered an ankylosaur trackway close to Tumbler Ridge in 2000, ankylosaurs and Tumbler Ridge have been synonymous,” Helm enthused.

“It is really exciting to 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.”

Revealing 3D models and skin prints

Beyond visual observations, the researchers used photogrammetry to create detailed 3D models of the dinosaur tracks. These helped confirm the unique features of Ruopodosaurus. Some track surfaces also revealed faint skin impressions, providing rare textural data on ankylosaur feet.

Trackway measurements showed consistent stride lengths, narrow gait, and outward toe rotation. This matched well with ankylosaurid hip and limb anatomy.

Although these dinosaurs had wide bodies, their legs were positioned more vertically, resulting in a surprisingly narrow trackway.

Comparative studies ruled out other possible candidates. Stegosaurs, ceratopsians, and iguanodonts either lacked the right foot shape or had different forelimb anatomy. Only ankylosaurids possessed the correct combination of a three-toed foot and a five-digit hand.

Bone and stone evidence

While skeletal remains from this time are rare, a few bone fragments support the presence of ankylosaurids.

Vertebrae and ossicles found in the same formations share more in common with ankylosaurids than nodosaurids. These hints, paired with the new tracks, paint a clearer picture of mid-Cretaceous dinosaur diversity.

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

The size of the prints suggests the animals were about 120 cm tall at the hip. That’s slightly smaller than some nodosaurids, whose prints measure up to 50 cm. This difference hints at niche separation or varied ecological roles among the armored dinosaurs.

A region rich in dinosaur tracks

The Peace Region continues to be a goldmine for track-based discoveries. Past finds include tyrannosaurid trails, giant crocodylian traces, and even the largest bird footprints from the Mesozoic in North America.

Ruopodosaurus joins this growing list, adding a new dimension to our understanding of dinosaur evolution.

These armored dinosaur tracks, formed in mud and preserved by time, offer more than just direction. They tell us who walked here, how they moved, and how long they remained. In a land where bones are rare, the ground carries the memory of ancient giants.

The study is published in the Journal of Vertebrate Paleontology.

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