Bearpaw Formation | |
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Stratigraphic range: Campanian-Maastrichtian, | |
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 |
Thickness | Up 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 |
Region | Alberta, Saskatchewan, Montana |
Country | Canada, United States |
Extent | Northern Montana to central Alberta and southern Saskatchewan |
Type section | |
Named for | Bear Paw Mountains, Montana |
Named by | Hatcher 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]
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]
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]
Color key
| Notes Uncertain or tentative taxa are in small text; |
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 from the Bearpaw Formation | ||||||
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Genus | Species | Location | Member | Material | Notes | Images |
Brachylophosaurus [7] | Indeterminate [7] | |||||
Daspletosaurus | ||||||
Edmontonia [7] | Indeterminate [7] | |||||
cf. Kritosaurus | "Nearly complete skull and postcranium." [9] | A hadrosaurid | ||||
Prosaurolophus [7] [10] | P. maximus [10] | Three juvenile specimens [10] | A Saurolophinae hadrosaurid, also known from the Dinosaur Park and Two Medicine Formations | |||
Stegoceras [7] | Indeterminate [7] | |||||
Plesiosaurs from the Bearpaw Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Member | Material | Notes | Images |
Albertonectes [11] | A. vanderveldei | Alberta | A complete, well-preserved postcranial specimen, missing only the skull. | An elasmosaurid plesiosaur. Albertonectes has the longest neck of any known plesiosaur. | ||
Nakonanectes [12] | N. bradti | Montana | A nearly complete skeleton including the skull. | A small elasmosaurid plesiosaur with an unusually short neck. | ||
Terminonatator [13] | T. ponteixensis | Saskatchewan | A partially articulated incomplete skeleton, including a skull. | An elasmosaurid plesiosaur. | ||
Dolichorhynchops [14] | D. herschelensis | Saskatchewan | An incomplete skeleton | One of the latest known polycotylids. | ||
Mosasaurs from the Bearpaw Formation | ||||||
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Genus | Species | Location | Member | Material | Notes | Images |
Mosasaurus [15] | M. missouriensis | Alberta and Montana | Several specimens, including a near complete skeleton with stomach contents | A large mosasaurine mosasaur. | ||
M. conodon | Saskatchewan | A large mosasaurine mosasaur. | ||||
Prognathodon [16] | P. overtoni | Alberta | Several exceptionally preserved specimens | A large mosasaurine mosasaur. | ||
Plioplatecarpus [17] | P. primaevus | Saskatchewan | A widespread genus of plioplatecarpine mosasaur. | |||
P. peckensis | Montana | |||||
Tylosaurus [18] | T. saskatchewanensis | Saskatchewan | A single semi-complete skeleton | A large tylosaurine mosasaur. | ||
Turtles from the Bearpaw Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Member | Material | Notes | Images |
Nichollsemys | N. baieri | Alberta | Known from skulls | A basal chelonioid sea turtle. | ||
A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätte. It is also applied to brecciated and stalagmitic deposits on the floor of caves, which frequently contain osseous remains.
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.
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.
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.
The Lance (Creek) Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas. The Lance Formation is Late Maastrichtian in age, and shares much fauna with the Hell Creek Formation of Montana and North Dakota, the Frenchman Formation of southwest Saskatchewan, and the lower part of the Scollard Formation of Alberta.
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.
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.
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It was laid down during the same time period as portions of the Two Medicine Formation of Montana and the Oldman Formation of Alberta. It is an historically important formation, explored by early American paleontologists such as Edward Drinker Cope, who named several dinosaurs from scrappy remains found here on his 1876 expedition. Modern work has found nearly complete skeletons of the hadrosaurid Brachylophosaurus.
The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller.
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).
The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from Pembina Valley in Canada to New Mexico.
The Milk River Formation is a sandstone-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern Alberta, Canada. It was deposited in near-shore to coastal environments during Late Cretaceous time. Based on uranium-lead dating, palynology and stratigraphic relationships, deposition occurred between ~84.1 and 83.6 Ma.
The Wapiti Formation is a geological formation of the Western Canada Sedimentary Basin in northwestern Alberta, and northeastern British Columbia, Canada. Its deposition spanned the time interval from the lower Campanian through to the upper Maastrichtian, between approximately 80 and 68 Ma. It was named by G.M. Dawson in 1881, presumably for exposures along the lower part of the Wapiti River and downstream along the Smoky River in Alberta.
The St. Mary River Formation is a geologic formation of Late Cretaceous age of the Western Canada Sedimentary Basin in southwestern Alberta and northwesternmost Montana. It was first described from outcrops along the St. Mary River by George Mercer Dawson in 1883, and it takes its name from the river.
The Aguja Formation is a geological formation in North America, exposed in Texas, United States and Chihuahua and Coahuila in Mexico, whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation. Fossil palms have also been unearthed here.
Continuoolithus is an oogenus of dinosaur egg found in the late Cretaceous of North America. It is most commonly known from the late Campanian of Alberta and Montana, but specimens have also been found dating to the older Santonian and the younger Maastrichtian. It was laid by an unknown type of theropod. These small eggs are similar to the eggs of oviraptorid dinosaurs, but have a distinctive type of ornamentation.
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.
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.