Borealopelta

Description

Paleontologists estimate Borealopelta to have been between 5 and 6 metres long. Like other ankylosaurs, it had short, thick arms and legs, a wide, squat body, and a moderately long tail. Like other nodosaurs, Borealopelta had a narrow muzzle, spiked armour plates over its neck and shoulders, and no club at the end of its tail. Borealopelta had three bands of six spines running across its neck. Two longer, sword-like spines projected sideways from the shoulders. Bands of armour with much smaller, square-shaped plates ran across the body from its neck to the base of its tail. In the only specimen of Borealopelta discovered to date, the armour is so well preserved, and covers the body so completely, that it is not possible to see the actual skeleton, except for where a few limb bones and back bones are visible as broken edges.

Range and Habitat

The only known specimen of Borealopelta was found in northeastern Alberta from rocks about 112 million years old. These rocks record the presence of an inland sea, the Western Interior Seaway, that lay along the eastern flank of the newly developing Rocky Mountains.

Paleontologists believe that all plant-eating dinosaurs, including nodosaurs like Borealopelta, were strictly land-living animals, living in either forests or on fern meadows (there were no flowering plants such as grasses at that time). Therefore, to find the body of a plant-eating dinosaur preserved in rocks from the bottom of an ancient sea is very unusual. Only a handful of dinosaurs have been discovered in such conditions worldwide.

Reproduction and Development

As there is only one fossilized specimen of Borealopelta, paleontologists do not know much about the animal’s reproduction or development. However, all dinosaurs are thought to have laid eggs in nests, and the parents to have cared for the eggs to some degree.

Diet

One of the exceptional features of the Borealopelta specimen is the preservation of the animal’s last meal. As the fossil was found at sea and far from where the animal lived, paleontologists could not compare the plant remains in the stomach with plant fossils from the surrounding area. Instead, they used plant fossils from Western Alberta to help identify the small, chopped-up remains found within Borealopelta. They discovered that the majority of these remains were ferns.

Unlike the broad muzzles of their close relatives the ankylosaurs, the muzzles of Nodosaurid dinosaurs like Borealopelta are narrow. Among living, large herbivores, those with narrow muzzles (such as deer, cattle, sheep and horses) tend to be selective feeders, while broad-muzzled animals (such as hippopotamuses and elephants) eat a wide variety of plants. Fossil pollen preserves well, and can be used to estimate the diversity of plants in ancient environments. Paleontologists found fossilized pollen in Borealopelta’s stomach and in the rocks around its body. The variety of pollen types in the stomach was much lower than that of the external sample. This evidence supports the idea that the narrow-muzzled Borealopelta ate only a limited number of plants species.

Did you know?
In addition to leaves and stems, paleontologists found fragments of unidentifiable wood in Borealopelta’s stomach, including some that was burnt to charcoal. The high fraction of ferns in the stomach, along with the presence of charcoal, strongly suggests that Borealopelta was feeding in an area that had recently experienced a forest fire. Ferns are among the first plants to colonize areas after fires, and would have been an abundant food source.

Behaviour

The remains of nodosaurs like Borealopelta are rare. This suggests that these animals may have been more solitary than other plant-eating dinosaurs such as the hadrosaurs (duck-billed dinosaurs) and ceratopsians (horned dinosaurs), whose remains are found in great abundance.

Discovery and Naming

The remains of Borealopelta were found by accident. Since the 1970s, there has been mining for bitumen-soaked sand in the area north of Fort McMurray in northeastern Alberta. To reach the bitumen, miners have to dig through a layer rock about 8 m thick. This layer of rock is known as the Clearwater Formation. It was deposited in the shallow sea that covered much of Alberta in the Early Cretaceous period. Prior to the discovery of Borealopelta, two ichthyosaurs and several plesiosaurs, all marine reptiles, were discovered in the Fort McMurray mines. In the spring of 2011 the first dinosaur — Borealopelta— was found in these rocks. Only the front half of the animal was found. Its tail and most of its limbs were scooped away by miners before the fossil was spotted.

The fossil of Borealopelta was encased in a very hard, very heavy, well-cemented layer of rock, almost like the stone coffins that ancient Egyptian pharaohs were buried in. The hardness and thickness of the rock proved to be a blessing and a curse. It prevented seabed scavengers from disturbing the carcass, and the weight of other rocks from squishing Borealopelta’s body flat like most other dinosaur fossils. However, the rock encasing Borealopelta also made preparing the fossil a major challenge. It took one of the Royal Tyrrell Museum’s technicians, Mark Mitchell, 7,000 hours — or 5.5 years — to expose the surface of the animal and its armour. In recognition of his efforts, Mitchell is honoured in the name of the species, Borealopelta markmitchelli. The word pelta is often used in the name of nodosaurian dinosaurs, and means "shield,” while boreas means “north winds” and references the location of the fossil’s discovery.