Lance-Formation

The Lance Formation is a lithostratigraphic formation in the U.S. Wyoming. The formation dates back to the late Cretaceous (late Maastrichtian ), so was immediately prior to the Cretaceous - Paleogene extinction event 66 million years ago. The sedimentary rocks of this formation contain one of the best-known Upper Cretaceous faunas. Famous the formation is particular for its dinosaur fossils, including the well-known genera such as Triceratops, Edmontosaurus and Tyrannosaurus.

Structure and lithology

The Lance formation extends over a large part of Wyoming. Their partial over 750 meters in thickness sediments came within about 1.5 million years to deposit. Is named the formation after the village of Lance Creek, Niobrara County.

The sediments of the Lance Formation were deposited at the edge of the Western Interior Seaway, one is then in the center of North America extending flat sea. During the deposition, there was a regression ( the gradual retreat ) of this sea. The dominant rocks are sandstones, pelites and marls that were formed within coastal floodplains. In the lower portions of the formation, there are marginal marine sandstones and shales.

History and fossils

The importance of the formation is in their fossils wealth. The importance of this reference first arose in 1872 out, as Fielding had Bradford Meek and Henry Martyn Bannister discovered a fragmentary dinosaur skeleton in western Wyoming. Fame the formation by John Bell Hatcher, who in the years 1889-1894 numerous vertebrate fossils collected on behalf of paleontologist Othniel Charles Marsh, among other fossils of the horned dinosaur Triceratops. Marsh called the fossil-rich layers Ceratops beds ( Ceratops layers), named after the then applicable ceratopsian genus Ceratops, although Triceratops was the genus most frequently found. The formation was also known under the name of beds Laramie ( Laramie - layers). By 1994 alone, hundreds of Triceratops fossils have been discovered in the central area of the formation in east-central Wyoming, including at least 100 skulls. Important finds include two dinosaur mummies with a ( Trachodon the mummy of 1908 and the Senckenberg mummy of 1910). Due to the continuing erosion of the open-minded to the ground surface rocks are still made ​​new discoveries regularly.

The vertebrate fauna of the formation includes fish, amphibians, Champsosaurier, turtles, squamates, crocodiles, pterosaurs, dinosaurs ( including birds), and mammals with a. Dinosaurs are represented, for example, with the horned dinosaur Triceratops and Torosaurus, the ornithopod Thescelosaurus, Edmontosaurus, the ankylosauruses Ankylosaurus and Edmontonia, the Großtheropoden Tyrannosaurus, as well as the smaller theropods Ornithomimus, Troodon and Dromaeosaurus. A very similar fossil fauna is found in the Hell Creek Formation.