The Lance (Creek) Formation is a division of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

(dating to about 69–66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

vertebrate faunas. The Lance Formation is Late Maastrichtian in age ( Lancian land mammal age), and shares much

fauna Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...

with the

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Formation (stratigraphy), formation s ...

of Montana and North Dakota, the

Frenchman Formation The Frenchman Formation is a stratigraphic unit of Late Cretaceous (late Maastrichtian) Geochronology, age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills (C ...

of southwest Saskatchewan, and the lower part of the Scollard Formation of Alberta. The Lance Formation occurs above the ''Baculites clinolobatus'' ammonite marine zone in Wyoming, the top of which has been dated to about 69 million years ago, and extends to the K-Pg boundary, 66 million years ago. However, the characteristic land vertebrate fauna of the Lancian age (which take its name from this formation) is only found in the upper strata of the Lance, roughly corresponding to the thinner equivalent formations such as the Hell Creek Formation, the base of which has been estimated at 66.8 million years old.Lehman, T. M., Mcdowell, F. W., & Connelly, J. N. (2006). First isotopic (U-Pb) age for the Late Cretaceous Alamosaurus vertebrate fauna of West Texas, and its significance as a link between two faunal provinces. Journal of Vertebrate Paleontology, 26(4), 922–928.

Description

The formation is described by W.G. Pierce as thick-bedded, buff-colored sandstone, and drab to green shale. It is Upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

in age. The formation varies in thickness from about 90 m (300 ft.) in

North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...

, to almost 600 m (2,000 ft.) in parts of Wyoming.

Depositional environment

The Lance Formation was laid down by streams, on a coastal plain along the edge of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...

. The

climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...

was subtropical; there was no cold season and probably ample

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

Paleontology

At least tens of thousands of Late Cretaceous vertebrate remains have been recovered from the Lance Formation. Fossils ranging from microscopic elements to extensive bonebeds, with nearly complete, sometimes articulated dinosaur skeletons, have been found. Most other animals known from the formation are freshwater animals, and some are exclusively freshwater forms (for instance, frogs and salamanders). However, marine fossils are also found in the formation, suggesting that the sea was nearby. The bird fauna is mainly composed of

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

s still existing today.

Coelurosaurs

Birds

Other coelurosaurs

An isolated tooth crown of an indeterminate coelurosaur is recovered from the formation.

Ornithischia

Ankylosaurs

Marginocephalians

Ornithopods

Indeterminate lambeosaurinae fossils have been found in the Lance Formation.

Other vertebrates

Other land

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s include

pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

s (e.g. cf. ''

Quetzalcoatlus ''Quetzalcoatlus'' () is a genus of azhdarchid pterosaur that lived during the Maastrichtian age of the Late Cretaceous in North America. The Type (biology), type specimen, recovered in 1971 from the Javelina Formation of Texas, United States, ...

''), crocodiles, champsosaurs, lizards, snakes, turtles, frogs and

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s. Remains of

fishes A fish (: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed ...

and

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

(i.e. '' Nanocuris'') have also been found in the Lance Formation.

References

External links

Passport-In-Time Microvertebrate Fossil Project
{{Chronostratigraphy of Colorado, Mesozoic state=expanded Geology of the Rocky Mountains Cretaceous geology of Wyoming Geologic formations of North Dakota Natural history of Wyoming Natural history of North Dakota Maastrichtian Stage of North America Fluvial deposits Sandstone formations of the United States Shale formations of the United States Siltstone formations of the United States