Royal Tyrrell Museum of Palaeontology
Borealopelta mitchelli found its way back into the sunlight in 2017, millions of years after it died. This armored dinosaur is so magnificently preserved that we can see what it looked like in life. Nearly all of the animal—the skin, the armor that covers its skin, the spikes along its side, most of its body and legs, even its face—survived fossilization. It is, according to Dr. Donald Henderson, curator of dinosaurs at the Royal Tyrrell Museum, a once-in-a-billion find.
Beyond its remarkable preservation, this dinosaur is an important key to understanding aspects of Early Cretaceous ecology and shows how this species may have lived within its environment. Since its remains were discovered, scientists have studied its anatomy, armor, and even what it ate in its final days, uncovering unexpected new insight into an animal that went extinct approximately 100 million years ago.
down by the sea
borealopelta it is a nodosaur, a type of four-legged ankylosaur with a straight tail instead of a tail club. Its discovery in 2011 in an ancient marine environment was a surprise, since the animal was terrestrial.
A terrestrial megaherbivore preserved on an ancient seabed is not as rare as one might think. A number of other ankylosaurs have been preserved in this way, although not as well as borealopelta. Scientists suspect that his body may have been carried from a river to the sea in a flood; it may have floated upside down on the surface for a few days before sinking to the depths of the ocean.
It would have been kept on the surface by what is known as “swelling and floating”, since the accumulation of postmortem gases would keep it afloat. Modeling done by Henderson indicates that his heavy armor would have caused him to roll onto his back, a position he suspects may have prevented ocean predators from scavenging through his corpse.
Once the gases that kept it floating were expelled, borealopelta he sank to the bottom of the ocean, landing on his back.
“We can see that it was submerged in water more than 50 meters deep because it was preserved with a particular mineral called glauconite, which is a green phosphate mineral. And it only forms in colder temperatures in water deeper than 50 meters,” explained Dr. Henderson.
He also told Ars that this environment likely discouraged waste collection as well, saying: “It was probably a region where [long-necked] plesiosaurs and big fish did not like to go. It was too cold and too dark. [there was] nothing to eat. And there were very few trace fossils in the sediments around it. So there weren’t a lot of worms, crustaceans, bivalves and other things in there to digest it anymore. It was just a good set of conditions on the seabed that had very low biological activity that led to that preservation.”
Unmet expectations
But none of this was known when the animal was discovered. Although it is not entirely uncommon to find dinosaur remains in marine environments, it is not very common either. Henderson and Darren Tanke, also from the Royal Tyrrell Museum, entered the site anticipating that they would excavate an ancient marine reptile.
The two had inquired about fossil discoveries at other open pit mines within the province. However, this was his first visit to Suncor, a mine in northeastern Alberta, Canada. Everything about this mine is huge. Massive machinery is constantly on the move, scooping rock, sand and gravel from the surrounding cliffs while other teams clean it up, all with the goal of uncovering the deeper oil sands for fuel.
“It’s just unbelievable, the scale of the place,” Dr. Henderson said. “And it works 24 hours a day, 365 days a year.”
Despite the pace of operations, one shovel operator in particular, Shawn Funk, noticed something after pulling a large chunk out of the cliff. It was thanks to him and various people within Suncor that operations in that area were stopped and Royal Tyrrell was notified.
