Judith River Group

The Judith River Group ( eng. Judith River Group ) is a sequence of sedimentary rocks of the Late Cretaceous ( Campanian ), which is open in western North America. This group is an important reference for dinosaur fossils - including part of the Dinosaur Provincial Park in Alberta to this rock unit, one of the richest sites for dinosaur fossils around the world. The Judith River Group in Alberta is sometimes called the Belly River Group ( Belly River Group eng. ), often also referred to as Judith River Wedge. The name is derived from the Judith River, a river in Montana. The Judith River Group is divided into three to four geological formations - in the Foremost Formation, Oldman Formation and the Dinosaur Park Formation ( eng. Dinosaur Park Formation) in Alberta and Saskatchewan in Canada and in the Judith River Formation in the central northern Montana. Foremost is the lowest and oldest layer, while the Dinosaur Park Formation is the uppermost and youngest layer. The Judith River Formation in Montana equal to the Oldman Formation in Canada, both formations form the middle layer of the Judith River Group.

Geological History

Since the mid- Cretaceous North America was one arm of the sea, the Western Interior Seaway, divided into two halves. In the Campanian, the rise of the Rocky Mountains began by lara mix orogeny, causing the estuary to the east and south was pushed back. The Judith River Group was deposited on the west coast of Meerarms; the deposits show a wide range of different ecosystems at different places and times due to fluctuating sea level. There were marine habitats in coastal areas, coastal wetlands, deltas and lagoons, as well as the great flood plains, from which the most dinosaur fossils. The flood plains were traversed by large rivers that flowed from the mountains into the estuary - these rivers brought the sediment with it, the form next to the Judith River Group and the Two Medicine Formation. The flood levels provided space for a rich flora and fauna - but periodic droughts repeatedly led to mass extinctions, as can be seen at many bonebeds in the Judith River Formation and also in the Two Medicine Formation. Periodic Vulkanausbrücke in the west covered the region with ash and led to further mass extinctions, soil enriched with nutrients but for future plant growth. These pockets allow researchers also precise radiometric dating of rock layers. However, before 73 million years, the sea again spread to the west and north, and the entire region was covered by the Bearpaw Lake, today form the marine deposits, the Bearpaw Formation in western North America.

Fossil finds

The Judith River Group is home to a wide variety of vertebrate fossils. Among other things, the remains of fish such as sharks, rays, sturgeon, gars and others remained intact even be found aquatic amphibians and reptiles, including frogs, salamanders, turtles, crocodiles and Champsosaurus. Terrestrial lizards such as rail lizards, skinks, iguanas and Stealth were also discovered. Pterosaur ( Pterosauria ) from the family of Azhdarchidae and neornithe birds like Apatornis dominated the sky. Furthermore, there were enantiornithe birds like Avisaurus and 20 species of mammals from the groups of Multituberculaten, marsupial and higher mammals.

So far, more than 40 different dinosaur species have been discovered, the majority originates from the Dinosaur Park Formation of Dinosaur Provincial Park. Known genera among theropods include the unspecified classifiable Coelurosaurier Paronychodon and Ricardoestesia that Ornithomimosaurier Dromiceiomimus, Ornithomimus and Struthiomimus that Caenagnathiden Chirostenotes, Elmisaurus and Caenagnathus, troodontids and Dromeosauriden as Troodon, Saurornitholestes and Dromaeosaurus, indefinable Avimimiden and Therizinosauroideen discoveries as well as the tyrannosaurids, Gorgosaurus and Daspletosaurus with a. The bird Beck dinosaur ( Ornithischia ) are also abundantly represented: Ankylosauriden as Euoplocephalus and Nodosauriden as Edmontonia and Panoplosaurus, Pachycephalosaurier as Gravitholus, Ornatotholus, Pachycephalosaurus, Stegoceras and Hanssuesia, ceratopsians are known as Leptoceratops, Anchiceratops, Centrosaurus, Chasmosaurus, Styracosaurus and Monoclonius and Hadrosauriden as Brachylophosaurus, Gryposaurus, Prosaurolophus, Corythosaurus, Lambeosaurus and Parasaurolophus.