Borealopelta

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Borealopelta
Temporal range: Early Cretaceous, Albian
Nodosaur.jpg
The holotype specimen on display at the Royal Tyrell Museum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Thyreophora
Suborder: Ankylosauria
Family: Nodosauridae
Subfamily: Nodosaurinae
Genus: Borealopelta
Brown et al., 2017
Species:
B. markmitchelli
Binomial name
Borealopelta markmitchelli
Brown et al., 2017

Borealopelta (meaning "Northern shield") is a genus of nodosaurid ankylosaur from the Lower Cretaceous of Alberta, Canada. It contains a single species, B. markmitchelli, named in 2017 by Caleb Brown and colleagues from a well-preserved specimen known as the Suncor nodosaur. Discovered at an oil sands mine north of Fort McMurray, Alberta, the specimen is remarkable for being among the best-preserved dinosaur fossils of its size ever found. It preserved not only the armor (osteoderms) in their life positions, but also remains of their keratin sheaths, overlying skin, and stomach contents from the animal's last meal. Melanosomes were also found that indicate the animal had a reddish skin tone.

Contents

Discovery and history

Holotype shown from above Borealopelta dorsal view.png
Holotype shown from above

The holotype specimen was uncovered on March 21, 2011, at the Millennium Mine, an oil sands mine 30 kilometres (19 mi) north of Fort McMurray, Alberta, that is owned and operated by Suncor Energy. [1] It was discovered by a miner, Shawn Funk, who was digging in the bank and noticed the specimen. [2] The Wabiskaw Member sediments (belonging to the Clearwater Formation) were being removed to allow mining of the underlying bitumen-rich sands of the McMurray Formation when an excavator struck the fossil. Noting the unusual nature of the exposed fragments, the operators alerted the Royal Tyrrell Museum of Palaeontology. In accordance with Suncor's mining permit and Alberta fossil law, the specimen became the property of the Alberta government. [1]

On March 23, Royal Tyrrell Museum scientist Donald Henderson and senior technician Darren Tanke were brought to the mine to examine the specimen, which, based on photographs, they expected to be a plesiosaur or another marine reptile, as no land animals had ever been discovered in the oil sands previously. [1] Upon correct identification, which was made on-site by Tanke, Henderson was astonished to learn that it was an ankylosaurian dinosaur and not a marine reptile. The animal had apparently been washed out to sea after death. [3]

After three days of mine safety training, museum staff and Suncor employees began working to recover all pieces of the fossil. Aside from the several pieces broken free, the bulk of the specimen was still embedded 8 metres (26 ft) up a cliff that was 12 metres (39 ft) high. The process took fourteen days in total. [1]

As the major piece of rock containing the fossil was being lifted out, it broke under its own weight into several pieces. Museum staff salvaged the specimen by wrapping and stabilizing the pieces in plaster, after which they were able to successfully transport them to the Royal Tyrell Museum. There, technician Mark Mitchell spent six years removing the adhering rock and preparing the fossil for study, which was sponsored by the National Geographic Society. The species B. markmitchelli was named for him in recognition of his skilled work. [1] [4] [5] The specimen was put on public exhibit on May 12, 2017, as part of the Royal Tyrrell Museum's "Grounds for Discovery" exhibition, along with other specimens discovered via industrial activity. [5]

Description

Restoration Borealopelta NT.jpg
Restoration

Borealopelta was a large dinosaur, measuring 5.5 metres (18 ft) long and weighing 1.3 metric tons (1.4 short tons). The Suncor specimen is remarkable for its three-dimensional preservation of a large, articulated dinosaur complete with soft tissue. While many small dinosaurs have been preserved with traces of soft tissues and skin, they are usually flattened and compressed during fossilization. Similar-looking hadrosaurid "mummies" have a shriveled, desiccated appearance due to their partial mummification prior to fossilization. The Suncor specimen, however, appears to have sunk upside-down onto the sea floor shortly after its death, causing the top half of the body to be quickly buried with minimal distortion. The result is a specimen that preserves the animal almost as it would have looked in life, without flattening or shriveling. [6] [4]

The Suncor specimen preserved numerous closely spaced rows of small armor plates, or osteoderms, lining the top and sides of its broad body. It had a straight tail rather than a tail club, and from the shoulders protruded a pair of long spines, shaped like the horns of a bull. Study of the pigments present in remnants of skin and scales suggest that it might have had a reddish-brown coloration in life, with a countershaded pattern that was used for camouflage. [6] [4]

Classification

Side view of its display case at the museum. Display case at Royal Tyrell Museum.jpg
Side view of its display case at the museum.
Photocomposite and schematic line drawings of the holotype Borealopelta schematics.png
Photocomposite and schematic line drawings of the holotype

Borealopelta was classified by Brown et al. within Nodosauridae. In the phylogenetic analysis conducted by the authors, Borealopelta nested within nodosaurids more derived than Nodosaurus . The completed cladogram was a strict consensus in 480 different trees, each with slightly different results. In both strict consensus and majority rules cladograms Borealopelta nested with Pawpawsaurus and Europelta in a group of Albian nodosaurs, with Hungarosaurus being the next closest taxon. The phylogeny below displays the results of the strict consensus, excluding taxa outside Nodosauridae. [6] [7]

Nodosauridae

Sauroplites scutiger

Mymoorapelta maysi

Dongyangopelta yangyanensis

Gastonia burgei

Gargoyleosaurus parkpinorum

Polacanthus foxii

Peloroplites cedrimontanus

Sauropelta edwardsi

Nodosaurus textilis

Tatankacephalus cooneyorum

Silvisaurus condrayi

Animantarx ramaljonesi

Hungarosaurus tormai

Europelta carbonensis

Pawpawsaurus campbelli

Borealopelta markmitchelli

Struthiosaurus austriacus

Stegopelta landerensis

Panoplosaurus mirus

Edmontonia rugosidens

Edmontonia longiceps

Denversaurus schlessmani

Paleobiology

Comparisons of the size of the bony core and keratinous sheath of the parascapular spine of Borealopelta to modern analogs Keratinous sheaths of Borealopelta and analogues.png
Comparisons of the size of the bony core and keratinous sheath of the parascapular spine of Borealopelta to modern analogs

The discovery that Borealopelta possessed camouflage coloration indicates that it was under threat of predation, despite its large size, and that the armor on its back was primarily used for defensive rather than display purposes. [6] Additionally, the spikes of Borealopelta might have had a dual function as defensive weapons and potential display structures useful in attracting mates and in species recognition. [8]

Diet

Examination of the specimen's stomach contents indicates that ferns were a major part of the animal's diet. The fact that ferns made up the majority of Borealopelta's last meal suggested that it was a highly selective feeder. Roughly six percent of the stomach contents contained charcoal as well, leading to the conclusion that Borealopelta was feeding in an area that was experiencing regrowth after a recent wildfire. Brown and colleagues inferred that the ferns themselves had been halfway through their growing season when ingested, suggesting that the Borealopelta individual ingested them in early or mid-summer, dying only a few hours afterward. [9]

Paleoecology

Specimen from the right side Borealopelta Royal Tyrrell 4.jpg
Specimen from the right side

The Suncor Borealopelta was preserved in the marine sandstones and shales of the Wabiskaw Member of the Clearwater Formation, which were laid down during the Albian stage of the Early Cretaceous period, about 110–112 million years ago. [6] At that time, the region was covered by the Western Interior Seaway, an inland sea that stretched from the Arctic Ocean to the Gulf of Mexico, [4] [10] and the Wabiskaw sediments were being deposited in an offshore marine environment. [6]

The holotype specimen of Borealopelta must have been washed out to sea, perhaps during a flood. Initially, it was thought that it had bloated after death and floated on its back at the surface of the water for weeks before the eventual release of the built-up gases within the trunk region of the carcass at which point it sank. [11] Larramendi and colleagues in 2020 doubted this hypothesis, as ankylosaurians would need a density comparable to modern birds for this to occur which is most certainly not the case; instead, it is thought that the animal was washed out to sea where it drowned after struggling to stay near the surface and then proceeded to sink. [12]

The fact that ankylosaurians are front-heavy is probably what led to the animal being fossilized upside down. It landed on the seabed on its back with enough force to deform the immediately underlying sediments. About 15 centimetres (5.9 in) of sediment settled over the carcass prior to the release of body fluids, as evidenced by fluid-escape structures preserved in the sediments, and the body cavity became filled with sand. A siderite concretion began to form around the carcass shortly after its arrival on the seabed, which prevented scavenging and preserved the body intact, with its scales and osteoderms in their original configuration. [6]

See also

Related Research Articles

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Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the Middle Jurassic, and persisted until the end of the Cretaceous Period. The two main families of Ankylosaurs, Nodosauridae and Ankylosauridae are primarily known from the Northern Hemisphere, but the more basal Parankylosauria are known from southern Gondwana during the Cretaceous.

<i>Nodosaurus</i> Extinct genus of dinosaurs

Nodosaurus is a genus of herbivorous nodosaurid ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found exclusively in the Frontier Formation in Wyoming.

<i>Ankylosaurus</i> Ankylosaurid dinosaur genus from the Late Cretaceous Period

Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.

<i>Minmi paravertebra</i> Ankylosaurian dinosaur genus from early Cretaceous Period

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<i>Edmontonia</i> Extinct genus of dinosaurs

Edmontonia is a genus of panoplosaurin nodosaurid dinosaur from the Late Cretaceous Period. It is part of the Nodosauridae, a family within Ankylosauria. It is named after the Edmonton Formation, the unit of rock where it was found.

<span class="mw-page-title-main">Ankylosauridae</span> Extinct family of dinosaurs

Ankylosauridae is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.

<span class="mw-page-title-main">Nodosauridae</span> Extinct family of dinosaurs

Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia.

<i>Sauropelta</i> Extinct genus of dinosaurs

Sauropelta is a genus of nodosaurid dinosaur that existed in the Early Cretaceous Period of North America. One species has been named although others may have existed. Anatomically, Sauropelta is one of the most well-understood nodosaurids, with fossilized remains recovered in the U.S. states of Wyoming, Montana, and possibly Utah. It is also the earliest known genus of nodosaurid; most of its remains are found in a section of the Cloverly Formation dated to 108.5 million years ago.

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<i>Mymoorapelta</i> Extinct genus of ornithischian dinosaur

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<i>Panoplosaurus</i> Extinct genus of dinosaurs

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<i>Pawpawsaurus</i> Extinct species of reptile

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<span class="mw-page-title-main">Timeline of ankylosaur research</span>

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