The Sundance Sea was an

epeiric sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...

that existed in North America during the mid-to-late Jurassic Period of the Mesozoic Era. It was an arm of what is now the

Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...

, and extended through what is now western Canada into the central western United States. The sea receded when highlands to the west began to rise.

Stratigraphy

The Sundance Sea did not occur at a single time; geological evidence suggests that the Sea was actually a series of five successive marine transgressions—each separated by an erosional

hiatus Hiatus may refer to: * Hiatus (anatomy), a natural fissure in a structure * Hiatus (stratigraphy), a discontinuity in the age of strata in stratigraphy *''Hiatus'', a genus of picture-winged flies with sole member species '' Hiatus fulvipes'' * G ...

—which advanced and receded from the middle Jurassic onward. The terrestrial sediments of the

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock 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, ...

—eroded from rising highlands to the west—were deposited on top of the marine Sundance sediments as the sea regressed for the last time late in the Jurassic.

Fauna

The Sundance Sea was rich in many types of

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

s. '' Gryphaea'' was extremely common, and shark teeth have been found. In addition to fish,

belemnite Belemnitida (or the belemnite) is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most ...

s and to an extent

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish ...

s have been found in sediments from the Sundance Sea.

Crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which ar ...

s and

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

would have dotted the seafloor. ''

Ophthalmosaurus ''Ophthalmosaurus'' (meaning "eye lizard" in Greek) is an ichthyosaur of the Jurassic period (165–150 million years ago). Possible remains from the Cretaceous, around 145 million years ago, are also known. It was a relatively medium-sized ichth ...

'', a large long ichthyosaur, swam in the seas using its large, long jaws to catch belemnite 'squid'. '' Pantosaurus'', a 15-20 foot (4.5-6 m) long cryptoclidid plesiosaur, went after the easier-to-catch fish. The largest marine reptile in the Sundance Sea was '' Megalneusaurus'', a long

pliosaur Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toot ...

similar to ''

Liopleurodon ''Liopleurodon'' (; meaning 'smooth-sided teeth') is an extinct genus of large, carnivorous marine reptile belonging to the Thalassophonea, a clade of short-necked pliosaurid plesiosaurs. ''Liopleurodon'' lived from the Callovian Stage of the M ...

''.Knight WC. 1895 A new Jurassic plesiosaur from Wyoming. ''Science'' 2: 449. Its fossils have been found in Alaska and Wyoming, which were both covered by the Sundance Sea when it was alive. During the periods of recession, dinosaurs and other Jurassic terrestrial animals frequented the shores, as evidenced by the Red Gulch Dinosaur Tracksite near

Shell, Wyoming Shell is a census-designated place (CDP) in Big Horn County, Wyoming, United States. The population was 83 at the 2010 Census. The community is named for the abundance of fossil shells located in the area. Nearby exposed formations such as the ...

References

External links

Map of North America in the middle Jurassic, with the location of the Sundance Sea

Historical oceans Late Jurassic North America Jurassic paleogeography Jurassic Canada Jurassic United States Geology of the Rocky Mountains Jurassic Alberta Jurassic Montana Jurassic geology of Wyoming

Stratigraphy

Fauna

See also

References

External links