The Judith River Formation is a

fossil 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 preserved ...

-bearing geologic formation in

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

, and is part of the Judith River Group. It dates to the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

, 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 MontanaSullivan, R.M. and Lucas, S. G. (2006). "The Kirtlandian land-vertebrate "age"–faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." Pp. 7-29 in Lucas, S. G. and Sullivan, R.M. (eds.), ''Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35''. and the Oldman Formation 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 ...

. It is an historically important formation, explored by early American

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

s such as

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy intereste ...

, who named several dinosaurs from scrappy remains found here on his 1876 expedition (such as '' Monoclonius''). Modern work has found nearly complete skeletons of the hadrosaurid '' Brachylophosaurus''.

Lithology

The Judith River Formation is composed of mudstone,

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

and

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 ...

Coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

beds,

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...

and coquinas are also observed. Judith River Formation exposure-2

Relationship with other units

The Judith River Formation conformably overlies the

Claggett Formation The Claggett Shale is a geological formation in Montana whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (2004). "Dinosaur distribution ...

and

Pakowki Formation The Pakowki Formation is a stratigraphical unit of Campanian age in the Western Canadian Sedimentary Basin. It takes the name from Pakowki Lake, and was first described in outcrop along the Pakowki Coulee by D.B. Dowling in 1916.Dowling, D.B., ...

. It is overlain by the Bearpaw Formation. It is equivalent to the

Belly River Formation The Belly River Group is a stratigraphical unit of Late Cretaceous age in the Western Canadian Sedimentary Basin. It takes the name from the Belly River, a tributary of the Oldman River in southern Alberta, and was first described in outc ...

in the southern Canadian Rockies foothills, the

Lea Park Formation The Lea Park Formation is a stratigraphical unit of Late Cretaceous age in the Western Canadian Sedimentary Basin, Canada. It takes the name from the settlement of Lea Park, Alberta, located north-west of Lloydminster on the banks of the No ...

in central Alberta and the

Wapiti Formation 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 Maast ...

in the northwestern plains.

Sub-divisions

Judith River Formation, Upper Missouri Breaks National Monument

The Judith River Formation is divided into four members, the Parkman Sandstone Member, the McClelland Ferry Member, the Coal Ridge member, and the Woodhawk Member. The McClelland Ferry Member (78.7-76.3 Ma) is believed to be equivalent to the Oldman Formation, with the Coal Ridge Member (76.3-75.3 Ma) equivalent to the Dinosaur Park Formation.

Fauna

Faunal list follows a review published by Ashok Sahni in 1972 unless otherwise noted.Sahni, A. (1972). "The vertebrate fauna of the Judith River Formation, Montana." ''Bulletin of the AMNH'', v. 147 article 6: 321-415.

Amphibians

There are three potential species of discoglossid frogs. Hip bones, possibly representing a North American member of the European spadefoot toad family are also known from the formation.

Bony fish

Cartilaginous fish

Ornithischian dinosaurs

Choristoderes

Crocodilians

Lizards

Theropod dinosaurs

Turtles

References

{{Western Canadian Sedimentary Basin, Central_Plains=yes Campanian Stage Cretaceous Montana Cretaceous geology of South Dakota Stratigraphy of Alberta