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''Borealopelta'' (meaning "Northern shield") is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
of nodosaurid
ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order 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. ...
from the Lower Cretaceous of
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...
. 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 Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ...
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.


Discovery and history

The holotype specimen was uncovered on March 21, 2011, at the Millennium Mine, an oil sands mine north of Fort McMurray, Alberta, that is owned and operated by Suncor Energy. It was discovered by a miner, Shawn Funk, who was digging in the bank and noticed the specimen. The Wabiskaw Member sediments (belonging to the Clearwater Formation) were being removed to allow mining of the underlying
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...
-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. 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 Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. The earliest marine reptile mesosaurus (not to be confused with mosasaurus), arose in the Permian period during ...
, as no land animals had ever been discovered in the oil sands previously. 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. 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 up a cliff that was high. The process took fourteen days in total. 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 National Geographic Society (NGS), headquartered in Washington, D.C., United States, is one of the largest non-profit scientific and educational organizations in the world. Founded in 1888, its interests include geography, archaeology, ...
. The species ''B. markmitchelli'' was named for him in recognition of his skilled work. 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.


Description

''Borealopelta'' was a large dinosaur, measuring long and weighing . 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 A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
. 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. The Suncor specimen preserved numerous closely spaced rows of small armor plates, or osteoderms, lining the top and sides of its broad body. 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.


Classification

''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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
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 ''Pawpawsaurus'', meaning "Pawpaw Lizard", is a nodosaurid ankylosaur from the Cretaceous (late Albian) of Tarrant County, Texas, discovered in May 1992. The only species yet assigned to this taxon, ''Pawpawsaurus campbelli,'' is based on a ...
'' 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.


Paleobiology

The discovery that ''Borealopelta'' possessed camouflage coloration indicates that it was under threat of
predation Predation is a biological interaction In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or o ...
, despite its large size, and that the armor on its back was primarily used for defensive rather than display purposes. 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.


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.


Paleoecology

The Suncor ''Borealopelta'' was preserved in the marine
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...
s and
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...
s of the
Wabiskaw Member The Clearwater Formation is a stratigraphic unit of Early Cretaceous (Albian) age in the Western Canada Sedimentary Basin in northeastern Alberta, Canada. It was first defined by R.G. McConnell in 1893 and takes its name from the Clearwater River ...
of the Clearwater Formation, which were laid down during the Albian stage of the
Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145  Ma to 100.5 Ma. Geology Pr ...
period, about 110–112 million years ago. At that time, the region was covered by the
Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient se ...
, an inland sea that stretched from the
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...
to the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...
, and the Wabiskaw sediments were being deposited in an offshore marine environment. The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...
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. Doubt has been cast on 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. 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 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 Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium an ...
concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...
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
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinc ...
s in their original configuration.


See also

* Timeline of ankylosaur research * 2017 in archosaur paleontology


References


External links

*
Adrift at sea in the Early Cretaceous – the Fort McMurray armoured dinosaur
(video) – Donald Henderson for Royal Tyrrell Museum Speaker Series, 2012 {{Portal bar, Dinosaurs, Cretaceous, Canada Cretaceous Canada Fossils of Canada Paleontology in Alberta Nodosaurids Early Cretaceous dinosaurs of North America Fossil taxa described in 2017 Ornithischian genera