The Sundance Sea was an epeiric sea that existed in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the mid-to-late

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Period of the

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 ...

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 oceanic divisions. It spans an area of approximately and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, ...

, and extended through what is now western

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

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

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

al hiatus—which advanced and receded from the middle

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, siltston ...

—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 animals. '' Gryphaea'' was extremely common, and

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

teeth have been found. In addition to

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

belemnite Belemnitida (or belemnites) is an extinct order (biology), order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous (And possibly the Eocene). Unlike squid, belemnites had an internal skeleton that made up the cone ...

s and to an extent

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

s have been found in sediments from the Sundance Sea.

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

s and

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

would have dotted the seafloor. ''

Ophthalmosaurus ''Ophthalmosaurus'' (Greek ὀφθάλμος ''ophthalmos'' 'eye' and σαῦρος ''sauros'' 'lizard') is a genus of ichthyosaur known from the Middle-Late Jurassic. Possible remains from the earliest Cretaceous, around 145 million years ago, a ...

'', a large long

ichthyosaur Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

, 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 The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

, went after the easier-to-catch fish. The largest

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including mari ...

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''.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,

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s and other

terrestrial animals frequented the shores, as evidenced by the Red Gulch Dinosaur Tracksite near Shell, Wyoming.

References

External links

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

Jurassic Sea Monsters
, ''Discover'' magazine

, Alaska Museum of Natural History 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