The Sundance Formation is a western North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

n sequence of Upper Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 age marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

s, sandy shales, and sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

s.

The Sundance Formation underlies the western North American Morrison Formation

Morrison Formation

The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...

, the most fertile source of dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

 fossils in the Americas, and is separated by a disconformity

Unconformity

An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...

 from the underlying Upper Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 Chugwater Formation

Chugwater formation

The Chugwater Formation is a mapped bedrock unit consisting primarily of red sandstone, in the states of Wyoming, Montana, and Colorado in the USA...

 red beds

Red beds

Red beds are sedimentary rocks, which typically consist of sandstone, siltstone, and shale that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of...

. The Sundance Formation is known for fossils of an extinct species of marine cephalapod, Belemnites densus

Belemnoidea

Belemnoids are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. Like them, the belemnoids possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length, and no tentacles...

.

Pterosaurs

Pterosaur Pterosaur Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight... s of the Summerville Formation
Taxa	Presence	Description	Images
Ichnogenus: Pteraichnus Pteraichnus Pteraichnus is an ichnogenus that has been attributed to pterosaurs. It has been found in, among other units, the Lower Jurassic Aztec Sandstone.... P. stokesi	Found in Wyoming at the Alcova/Grey Reef Reservoir, Seminoe Reservoir, and Bighorn Canyon National Recreation area. Found in Wyoming, at the ichnospecies' type locality.	Alcova/Grey Reef Reservoir and Seminoe Reservoir housed at University of Wyoming, Laramie. Alcova/Grey Reef Reservoir specimens are also housed at Tate Museum, Casper College. Specimens housed at University of Wyoming, Laramie.

Belemnoids

Belemnoids of the Summerville Formation
Taxa	Presence	Description	Images
Genus: Belemnites B. densus