| Sundance Formation | |
| Type: | Geological formation |
| Period: | Callovian |
| Prilithology: | shale |
| Otherlithology: | limestone, sandstone |
| Namedby: | Darton |
| Region: | Western North America |
| Subunits: | Canyon Springs Sandstone Member, Hulett Sandstone Member, Lak Member, Pine Butte Member, Redwater Shale Member, Stockade Beaver (Shale) Member, Windy Hill Sandstone Member |
| Underlies: | Morrison Formation |
| Overlies: | Gypsum Springs Formation |
| Thickness: | Up to 100 m |
| Year Ts: | 1904 |
The Sundance Formation is a western North American sequence of Middle Jurassic to Upper Jurassic age[1] Dating from the Bathonian to the Oxfordian, around 168-157 Ma, It is up to 100 metres thick[2] and consists of marine shale, sandy shale, sandstone, and limestone deposited in the Sundance Sea, an inland sea that covered large parts of western North America during the Middle and early Late Jurassic.
The Sundance Formation underlies the western North American Morrison Formation, the most fertile source of dinosaur fossils in the Americas, and is separated by a disconformity from the underlying Middle Jurassic Gypsum Springs Formation.
The Sundance Formation is known for fossils of an extinct species of marine cephalopod, the belemnite Pachyteuthis densus, as well as several extinct species of oyster, including Deltoideum, Liostrea, and Gryphaea nebrascensis. Other common invertebrates include crinoids, echinoids, gastropods, insects, ostracods, and foraminifera.[3]
Fossil dinosaur 'footprints' on an ancient ocean shoreline are preserved in the formation and protected at the Red Gulch Dinosaur Tracksite, located in the Bureau of Land Management Red Gulch/Alkali National Back Country Byway, near Shell in Big Horn County, Wyoming.[4]
| Genus | Species | Member | Material | Notes | |
|---|---|---|---|---|---|
| Pteraichnus[5] |
|
| Trace fossils | A Pteraichnid belonging to the Pterodactyloidea. | |
| Tatenectes |
|
| A Cryptoclidid Plesiosaur. | ||
| Pantosaurus |
|
| A Cryptoclidid Plesiosaur. | ||
| Megalneusaurus |
|
| A Thallasophonid Pliosaur. | ||
| Baptanodon |
|
| An Ophthalmosaurid Ichthyosaur. | ||
| Plesiosaurus |
| Material now lost.[6] | Possibly a Plesiosaurid Plesiosaur. |
| Genus | Species | Member | Material | Notes | |
|---|---|---|---|---|---|
| Occithrissops |
| An ichthyodectiform | |||
| Caturus |
| A caturid amiiform | |||
| Hybodontiformes |
|
| Teeth | Belongs to a group of shark like cartilaginous fish called the Hybodontiformes. This might either be Hybodus or Asteracanthus.[7] Found in association with Tatenectes. |