Bearpaw Formation
Stratigraphic range:Campanian-Maastrichtian,75–72 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Contact (red arrow) between the underlying marine shales of the Bearpaw Formation and the coastalHorseshoe 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
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 /48.25000; -109.50000 (Bearpaw Formation)
Region	Alberta,Saskatchewan,Montana
Country	Canada,United States
Extent	NorthernMontana tocentral Alberta and southernSaskatchewan
Type section
Named for	Bear Paw Mountains,Montana
Named by	Hatcher and Stanton, 1903[2]

TheBearpaw Formation, also called theBearpaw Shale, is ageologic formation ofLate Cretaceous (Campanian) age. Itoutcrops in the U.S. state ofMontana, as well as theCanadian provinces ofAlberta andSaskatchewan, and was named for theBear Paw Mountains in Montana.^[2] It includes a wide range of marinefossils, as well as the remains of a fewdinosaurs. It is known for its fossilammonites, some of which are mined in Alberta to produce theorganic gemstoneammolite.^[3]

The formation was deposited in the Bearpaw Sea, which was part of theWestern Interior Seaway that advanced and then retreated across the region duringCampanian time.^[4] It is composed primarily of dark greyshales,claystones, silty claystones andsiltstones, with subordinate siltysandstones. It also includes bedded andnodularconcretions (bothcalcareous andironstone concretions) and thin beds ofbentonite. 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 theDinosaur Park Formation of theBelly River Group in central Alberta, and theJudith River Formation in the plains to the east and Montana. It is overlain by theHorseshoe Canyon Formation in central Alberta; by theBlood Reserve Formation and theSt. Mary River Formation in southern Alberta; by theEastend Formation in southern Saskatchewan; and by theFox Hills Formation in Montana. To the east, it merges into thePierre Shale.^[1]

The Bearpaw Formation is famous for its well-preserved ammonite fossils. These includePlacenticeras meeki,Placenticeras intercalare,Hoploscaphites, andSphenodiscus, thebaculiteBaculites compressus and thebivalveInoceramus, some of which are mined south-central Alberta to produce theorganic gemstone ammolite.^[3]

Other fossils found in this formation include many types ofshellfish,bony fish,sharks,rays, birds, and marine reptiles likemosasaurs such asPrognathodon overtoni andPlioplatecarpus peckensis,plesiosaurs such asDolichorhynchops herschelensis,Albertonectes andNakonanectes, andsea turtles.Dinosaur remains have occasionally been discovered, presumably from carcasses that washed out to sea.^[7][8]

Dinosaurs from the Bearpaw Formation
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]	ASaurolophinaehadrosaurid, also known from theDinosaur Park andTwo 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.	Anelasmosauridplesiosaur.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 knownpolycotylids.

Mosasaurs from the Bearpaw Formation
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 largemosasaurinemosasaur.
	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 ofplioplatecarpine mosasaur.
	P. peckensis	Montana
Tylosaurus[18]	T. saskatchewanensis	Saskatchewan		A single semi-complete skeleton	A largetylosaurine mosasaur.

Turtles from the Bearpaw Formation
Genus	Species	Location	Member	Material	Notes	Images
Nichollsemys	N. baieri	Alberta		Known from skulls	A basal chelonioidsea turtle.

Bony fish from the Bearpaw Formation
Genus	Species	Location	Member	Material	Notes	Images
Dercetis	D. magnificus	Alberta		2 articulated specimens	Adercetidaulopiform.[19]
Ursichthys	U. longiparietalis	Alberta		Partial skeleton, recovered within aMosasaurus specimen.	Anichthyotringoid aulopiform.[20]

• Geologic formations of Saskatchewan
• Cretaceous Alberta
• Cretaceous Montana
• Cretaceous Saskatchewan
• Western Canadian Sedimentary Basin
• Campanian Stage
• Geologic formations of Alberta
• Geologic formations of Montana
• Upper Cretaceous Series of North America

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• Short description matches Wikidata
• Coordinates on Wikidata