Bearpaw Formation

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Bearpaw Formation
Stratigraphic range: Campanian-Maastrichtian, 75–72  Ma
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Bearpaw-Horseshoe Canyon.jpg
Contact (red arrow) between the underlying marine shales of the Bearpaw Formation and the coastal Horseshoe Canyon Formation.
Type Geological formation
Unit of Montana Group
Underlies Horseshoe Canyon Formation, St. Mary River Formation, Eastend Formation, and others
Overlies Dinosaur Park Formation,
Judith River Formation
ThicknessUp to 350 meters (1,150 ft) [1]
Lithology
Primary Shale, claystone
Other Siltstone, sandstone, concretionary beds
Location
Coordinates 48°15′0″N109°30′0″W / 48.25000°N 109.50000°W / 48.25000; -109.50000 (Bearpaw Formation)
Region Alberta, Saskatchewan, Montana
Country Canada, United States
ExtentNorthern Montana to central Alberta and southern Saskatchewan
Type section
Named for Bear Paw Mountains, Montana
Named byHatcher and Stanton, 1903 [2]

The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous (Campanian) age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear Paw Mountains in Montana. [2] It includes a wide range of marine fossils, as well as the remains of a few dinosaurs. It is known for its fossil ammonites, some of which are mined in Alberta to produce the organic gemstone ammolite. [3]

Contents

Lithology and depositional environment

Bearpaw shale being excavated to recover ammonites for ammolite production. Ammolite mining.jpg
Bearpaw shale being excavated to recover ammonites for ammolite production.

The formation was deposited in the Bearpaw Sea, which was part of the Western Interior Seaway that advanced and then retreated across the region during Campanian time. [4] It is composed primarily of dark grey shales, claystones, silty claystones and siltstones, with subordinate silty sandstones. It also includes bedded and nodular concretions (both calcareous and ironstone concretions) and thin beds of bentonite. As the seaway retreated toward the southwest, the marine sediments of the Bearpaw became covered by the deltaic and coastal plain sediments of the overlying formations. [1] [5] [6]

Relationship to other units

The Bearpaw Formation conformably overlies the Dinosaur Park Formation of the Belly River Group in central Alberta, and the Judith River Formation in the plains to the east and Montana. It is overlain by the Horseshoe Canyon Formation in central Alberta; by the Blood Reserve Formation and the St. Mary River Formation in southern Alberta; by the Eastend Formation in southern Saskatchewan; and by the Fox Hills Formation in Montana. To the east, it merges into the Pierre Shale. [1]

Fauna

Color key
Taxon Reclassified taxonTaxon falsely reported as presentDubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
A specimen of Placenticeras ammolite from the Bearpaw Formation. Ammolite from Placenticeras fossil ammonite, Alberta.jpg
A specimen of Placenticeras ammolite from the Bearpaw Formation.

The Bearpaw Formation is famous for its well-preserved ammonite fossils. These include Placenticeras meeki , Placenticeras intercalare, Hoploscaphites , and Sphenodiscus , the baculite Baculites compressus and the bivalve Inoceramus , some of which are mined south-central Alberta to produce the organic gemstone ammolite. [3]

Other fossils found in this formation include many types of shellfish, bony fish, sharks, rays, birds, and marine reptiles like mosasaurs such as Prognathodon overtoni and Plioplatecarpus peckensis, plesiosaurs such as Dolichorhynchops herschelensis , Albertonectes and Nakonanectes , and sea turtles. Dinosaur remains have occasionally been discovered, presumably from carcasses that washed out to sea. [7] [8]

Dinosaurs

Dinosaurs from the Bearpaw Formation
GenusSpeciesLocationMemberMaterialNotesImages
Brachylophosaurus [7] Indeterminate [7]
Brachylophosaurus Brachylophosaurus NT.png
Brachylophosaurus
Daspletosaurus
Daspletosaurus Daspletosaurus torosus steveoc.jpg
Daspletosaurus
Edmontonia [7] Indeterminate [7]
Edmontonia Edmontonia dinosaur.png
Edmontonia
cf. Kritosaurus "Nearly complete skull and postcranium." [9] A hadrosaurid
Kritosaurus Kritosaurus BW.jpg
Kritosaurus
Prosaurolophus [7] [10] P. maximus [10] Three juvenile specimens [10] A Saurolophinae hadrosaurid, also known from the Dinosaur Park and Two Medicine Formations
Prosaurolophus Prosaurolophus Maximus.jpg
Prosaurolophus
Stegoceras [7] Indeterminate [7]
Stegoceras Stegoceras validum.jpg
Stegoceras

Plesiosaurs

Plesiosaurs from the Bearpaw Formation
GenusSpeciesLocationMemberMaterialNotesImages
Albertonectes [11] A. vanderveldeiAlbertaA complete, well-preserved postcranial specimen, missing only the skull.An elasmosaurid plesiosaur. Albertonectes has the longest neck of any known plesiosaur.
Albertonectes Fossil vertebrae.jpg
Albertonectes
Nakonanectes [12] N. bradtiMontanaA nearly complete skeleton including the skull.A small elasmosaurid plesiosaur with an unusually short neck.
Terminonatator [13] T. ponteixensisSaskatchewanA partially articulated incomplete skeleton, including a skull.An elasmosaurid plesiosaur.
Dolichorhynchops [14] D. herschelensisSaskatchewanAn incomplete skeletonOne of the latest known polycotylids.

Mosasaurs

Mosasaurs from the Bearpaw Formation
GenusSpeciesLocationMemberMaterialNotesImages
Mosasaurus [15] M. missouriensisAlberta and MontanaSeveral specimens, including a near complete skeleton with stomach contentsA large mosasaurine mosasaur.
Mosasaurus missouriensis TMP 2008.036.0001.jpg
Mosasaurus missouriensis
M. conodonSaskatchewanA large mosasaurine mosasaur.
Mosasaurus conodon MOR 006 (1).jpg
Mosasaurus conodon
Prognathodon [16] P. overtoniAlbertaSeveral exceptionally preserved specimensA large mosasaurine mosasaur.
Prognathodon overtoni Tyrrell mosasaur.jpg
Prognathodon overtoni
Plioplatecarpus [17] P. primaevusSaskatchewanA widespread genus of plioplatecarpine mosasaur.
Plioplatecarpus PlioplatecarpusDB.jpg
Plioplatecarpus
P. peckensisMontana
Tylosaurus [18] T. saskatchewanensisSaskatchewanA single semi-complete skeletonA large tylosaurine mosasaur.
Tylosaurus Tylosaurus nepaeolicus NT.png
Tylosaurus

Turtles

Turtles from the Bearpaw Formation
GenusSpeciesLocationMemberMaterialNotesImages
Nichollsemys N. baieriAlbertaKnown from skullsA basal chelonioid sea turtle.
Nichollsemys Turtle skull fossil.jpg
Nichollsemys

Related Research Articles

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<i>Maiasaura</i> Extinct genus of reptiles

Maiasaura is a large herbivorous saurolophine hadrosaurid ("duck-billed") dinosaur genus that lived in the area currently covered by the state of Montana and the province of Alberta, Canada, in the Upper Cretaceous Period, about 76.7 million years ago. Maiasaura peeblesorum is the state fossil of Montana.

<i>Xiphactinus</i> Extinct genus of fishes

Xiphactinus, colloquially referred to as the X-fish, is an extinct genus of large predatory marine bony fish that lived during the late Albian to the late Maastrichtian. The genus grew up to 5–6 metres (16–20 ft) in length, and superficially resembled a gargantuan, fanged tarpon.

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

Montanoceratops is an extinct genus of small ceratopsian dinosaur that lived approximately 70 million years ago during the latter part of the Cretaceous Period in what is now Montana and Alberta. Montanoceratops was a small sized, moderately-built, ground-dwelling, quadrupedal herbivore, that could grow up to an estimated 2.5 m (8.2 ft) in length and 170 kg (370 lb) in body mass.

<span class="mw-page-title-main">Lance Formation</span> Geological formation in the United States

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<span class="mw-page-title-main">Dinosaur Park Formation</span> Uppermost member of the Belly River Group geologic unit in Alberta, Canada

The Dinosaur Park Formation is the uppermost member of the Belly River Group, a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 76.5 and 74.4 million years ago. It was deposited in alluvial and coastal plain environments, and it is bounded by the nonmarine Oldman Formation below it and the marine Bearpaw Formation above it.

The Oldman Formation is a stratigraphic unit of Late Cretaceous age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was named for exposures along the Oldman River between its confluence with the St. Mary River and the city of Lethbridge, and it is known primarily for its dinosaur remains and other fossils.

<span class="mw-page-title-main">Two Medicine Formation</span> Geological formation in Montana, United States and Alberta, Canada

The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between 83.5 ± 0.7 Ma and 70.6 ± 3.4 Ma, during Campanian time. It crops out to the east of the Rocky Mountain Overthrust Belt, and the western portion of this formation is folded and faulted while the eastern part, which thins out into the Sweetgrass Arch, is mostly undeformed plains. Below the formation are the nearshore deposits of the Virgelle Sandstone, and above it is the marine Bearpaw Shale. Throughout the Campanian, the Two Medicine Formation was deposited between the western shoreline of the Late Cretaceous Interior Seaway and the eastward advancing margin of the Cordilleran Overthrust Belt. The Two Medicine Formation is mostly sandstone, deposited by rivers and deltas.

<span class="mw-page-title-main">Judith River Formation</span> Fossil-bearing geologic formation in Montana, part of the Judith River Group

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<span class="mw-page-title-main">Horseshoe Canyon Formation</span> Geological formation in Canada

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<i>Dolichorhynchops</i> Extinct genus of reptiles

Dolichorhynchops is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing the species D. osborni and D. herschelensis, with two previous species having been assigned to new genera. Specimens of D. osborni have been found in the early Coniacian to early Campanian rocks, while those of D. herschelensis have been found in the late Campanian to early Maastrichtian rocks. Dolichorhynchops was a prehistoric marine reptile. Its Greek generic name means "long-nosed face". While typically measuring about 3 metres (9.8 ft) in length, the largest specimen of D. osborni is estimated to have a total body length more than approximately 4.3 metres (14 ft).

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<span class="mw-page-title-main">St. Mary River Formation</span> Geologic formation in western Canada

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<i>Albertonectes</i> Extinct genus of reptiles

Albertonectes is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous Bearpaw Formation of Alberta, Canada. It contains a single species, Albertonectes vanderveldei. Albertonectes is the longest elasmosaur, and more generally plesiosaur, known to date both in neck and total body length.

<i>Nakonanectes</i> Extinct genus of reptiles

Nakonanectes bradti is an elasmosaurid plesiosaur of the late Cretaceous found in 2010 the state of Montana in the United States. It is one of the most recently known elasmosaurids to have lived in North America. Unlike other elasmosaurids, it has a relatively short neck.

References

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  15. Takuya Konishi; Michael Newbrey; Michael Caldwell (2014). "A small, exquisitely preserved specimen of Mosasaurus missouriensis (Squamata, Mosasauridae) from the upper Campanian of the Bearpaw Formation, western Canada, and the first stomach contents for the genus". Journal of Vertebrate Paleontology. 34 (4): 802–819. doi:10.1080/02724634.2014.838573. S2CID   86325001.
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  18. Jiménez-Huidobro, P.; Caldwell, M.W.; Paparella, I.; Bullard, T.S. (2018). "A new species of tylosaurine mosasaur from the upper Campanian Bearpaw Formation of Saskatchewan, Canada". Journal of Systematic Palaeontology. 17 (10): 1–16. doi:10.1080/14772019.2018.1471744. S2CID   90533033.