Sundance Sea
Encyclopedia
The Sundance Sea was an epeiric sea
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
, 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.
--each separated by an erosion
al hiatus
--which advanced and receded from the middle Jurassic
onward. The terrestrial sediments of the Morrison Formation
--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.
The sedimentary rocks which formed in and around the Sundance Sea are often rich in fossils.
s. Gryphaea
was extremely common, and shark
teeth have been found. In addition to fish
, belemnites and to an extent ammonite
s swarmed in shoals
. Crinoid
s and bivalvia
dotted the seafloor. Ophthalmosaurus
, a large ichthyosaur
, swam in the seas using its large, long jaws to catch belemnite 'squid'. Pantosaurus
, a cryptocleid plesiosaur
the size of a seal
, went after the easier-to-catch fish. The largest marine reptile
in the Sundance Sea was Megalneusaurus
, a large pliosaur
similar to Liopleurodon
. 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
s and other Jurassic
terrestrial animals frequented the shores, as evidenced by the Red Gulch Dinosaur Tracksite
near Shell, Wyoming
.
Epeiric Sea
An epeiric sea is a shallow sea that extends over part of a continent.Epeiric seas are usually associated with the marine transgressions of the geologic past, which have variously been due to either global eustatic sea level changes, local tectonic deformation, or both, and are occasionally...
that existed in 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...
during the mid to late 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...
Period of the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Era. It was an arm of what is now the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...
, and extended through what is now western Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
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 transgressionsTransgression (geology)
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water...
--each separated by an erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
al hiatus
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...
--which advanced and receded from the middle 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...
onward. The terrestrial sediments of the 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...
--eroded from rising highlands to the west--were deposited on top of the marine Sundance sediments
Sundance Formation
The Sundance Formation is a western North American sequence of Upper Jurassic age marine shales, sandy shales, and sandstones.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...
as the sea regressed for the last time late in the Jurassic.
The sedimentary rocks which formed in and around the Sundance Sea are often rich in fossils.
Fauna
The Sundance Sea was rich in many types of animalAnimal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s. Gryphaea
Gryphaea
Gryphaea, common name Devil's toenails, is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae.These fossils range from the Jurassic to the Cretaceous periods. They are particularly common in many parts of Britain....
was extremely common, and shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
teeth have been found. In addition to fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, belemnites and to an extent ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
s swarmed in shoals
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
. Crinoid
Crinoid
Crinoids are marine animals that make up the class Crinoidea of the echinoderms . Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 6,000 meters. Sea lilies refer to the crinoids which, in their adult form, are...
s and bivalvia
Bivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
dotted the seafloor. Ophthalmosaurus
Ophthalmosaurus
Ophthalmosaurus is an ichthyosaur of the Middle to Late Jurassic period , named for its extremely large eyes. It had a graceful 6 metre long dolphin-shaped body, and its almost toothless jaw was well adapted for catching squid...
, a large ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
, swam in the seas using its large, long jaws to catch belemnite 'squid'. Pantosaurus
Pantosaurus
Pantosaurus is an extinct genus of plesiosaur from the Late Jurassic of what is now Wyoming. It lived in what used to be the Sundance Sea. It was originally named Parasaurus by Othniel Charles Marsh in reference to Plesiosaurus, but that name was preoccupied, and Marsh changed it...
, a cryptocleid plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
the size of a seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...
, went after the easier-to-catch fish. The largest marine reptile
Marine reptile
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semi-aquatic life in a marine environment.The earliest marine reptiles arose in the Permian period during the Paleozoic era...
in the Sundance Sea was Megalneusaurus
Megalneusaurus
Megalneusaurus is an extinct genus of large pliosaur that lived in the Sundance Sea during the Kimmeridgian, ~156-152 million years ago, in the Late Jurassic....
, a large pliosaur
Pliosaur
Pliosauroidea is an extinct clade of marine reptiles. Pliosauroids, also commonly known as pliosaurs, are known from the Jurassic and Cretaceous Periods. The pliosauroids were short-necked plesiosaurs with large heads and massive toothed jaws. These swimming reptiles were not dinosaurs but distant...
similar to Liopleurodon
Liopleurodon
Liopleurodon is a genus of large, carnivorous marine reptile belonging to the Pliosauroidea, a clade of short-necked plesiosaurs. Two species of Liopleurodon lived during the Callovian stage of the Middle Jurassic Period , while the third, L. rossicus, lived during the Late Jurassic...
. 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
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...
s and other 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...
terrestrial animals frequented the shores, as evidenced by the Red Gulch Dinosaur Tracksite
Red Gulch Dinosaur Tracksite
Red Gulch Dinosaur Tracksite is an assemblage of fossil dinosaur footprints discovered in 1997 on public land near Shell, Wyoming by , a research geologist from the Indiana Geological Survey. The tracks are believed to have been made during the Middle Jurassic Period, 160-180 million years b.p.,...
near Shell, Wyoming
Shell, Wyoming
Shell is an unincorporated community in Big Horn County, Wyoming, United States.The community is named for the abundance of fossil shells located in the area. Nearby exposed formations such as the Cloverly Formation and the Morrison Formation have yielded numerous fossils of dinosaurs and other...
.