Morrison Formation

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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, siltstone, and limestone, and is known for its rich fossil beds, which have yielded a diverse array of dinosaur species.

Geology

The Morrison Formation dates to the late Jurassic period, approximately 156 to 146 million years ago. It is primarily composed of fluvial (river and stream) deposits, with some lacustrine (lake) and floodplain deposits. The formation is named after the town of Morrison, Colorado, where the first fossils were discovered.

Paleontology

The Morrison Formation is renowned for its dinosaur fossils, including some of the most iconic species such as Allosaurus, Apatosaurus, Diplodocus, and Stegosaurus. The formation has also yielded fossils of other vertebrates, invertebrates, and plants, providing a comprehensive view of the ecosystem during the late Jurassic.

Dinosaur Fauna

• Allosaurus - A large theropod dinosaur, one of the top predators of its time.
• Apatosaurus - A massive sauropod dinosaur, known for its long neck and tail.
• Diplodocus - Another large sauropod, characterized by its long, whip-like tail.
• Stegosaurus - A herbivorous dinosaur, easily recognizable by its plated back and spiked tail.

Other Fauna

In addition to dinosaurs, the Morrison Formation has produced fossils of other reptiles, amphibians, fish, and mammals. Notable finds include early mammals like Docodon and various species of turtles and crocodiles.

Stratigraphy

The Morrison Formation is divided into several members, which vary in thickness and composition across different regions. These members include:

• Salt Wash Member - Characterized by sandstone and mudstone, rich in dinosaur fossils.
• Brushy Basin Member - Known for its colorful mudstones and abundant fossilized remains.
• Windy Hill Member - Contains a mix of sandstone and mudstone, with fewer fossils.

Significance

The Morrison Formation is one of the most studied geological formations in the world due to its rich fossil content. It provides critical insights into the late Jurassic period, including the diversity of life, paleoecology, and the climatic conditions of the time.

Related Pages

• Jurassic
• Dinosaur
• Fossil
• Geology of the United States
• Paleontology