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The Western Interior Seaway divided across the Dakotas and retreated south towards the Gulf of Mexico. This shrunken and final regressive phase is sometimes called the Pierre Seaway. [1] During the early Paleocene, parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment, submerging the site of present-day Memphis.
Primitive hadrosauromorph. Its only known fossil specimen found appeared to have been washed into the Western Interior Seaway. It is believed to be from Appalachia because it was found closer to the Appalachia side of the sea and is unknown from Laramidia. "Coelosaurus" Upper Cretaceous: omnivore: May be synonymous with Ornithomimus. Its ...
The Western Interior Seaway, was a large inland sea that started to expand in the early Cretaceous period, though geological evidence suggests it started to expand in the late Jurassic period. It existed at its fullest extent from the mid-late Cretaceous period.
Laramidia was an island continent that existed during the Late Cretaceous period (99.6–66 Ma), when the Western Interior Seaway split the continent of North America in two. In the Mesozoic era, Laramidia was an island land mass separated from Appalachia to the east by the Western Interior Seaway.
The Pierre Shale represents a period of marine deposition from the Western Interior Seaway, a shallow continental sea that submerged much of central North America during the Cretaceous. [100] At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachians, some 1,000 kilometers (620 mi) wide. At its deepest, it ...
The presence of young mosasaurs in the formation suggests that mosasaurs were viviparous and gave birth hundreds of miles out to sea, as Niobrara was in the middle of the Western Interior Seaway at the time. [28] Juveniles would likely have been vulnerable to predation by the many large mid-ocean predators present in the ecosystem.
It inhabited the northern Western Interior Seaway, a mild to cool temperate area, dominated by plesiosaurs, hesperornithiform seabirds, and mosasaurs. It may have gone extinct due to the shrinking of the seaway, increased infant mortality rates (in the sea), higher instances of egg and hatchling predation (on land), and a rapidly cooling climate.
Deinosuchus was present on both sides of the Western Interior Seaway. [9] Specimens have been described from 12 U.S. states: Utah, Montana, Wyoming, New Mexico, New Jersey (Marshalltown Formation), Delaware, [35] Georgia, Alabama, Mississippi, Texas, and North & South Carolina (Tar Heel/Coachman & Bladen Formations [36]).