The Morrison Formation
The wall of bones known as Carnegie Quarry, located at Dinosaur National Monument, is an inspiration to visitors from all over the world. This rocky graveyard is made of pebbly sandstone of the Morrison Formation, a remarkable body of rock which allows scientists to time travel 150 million years in the past, to the real life Jurassic Park.
The Morrison Formation is a distinct unit of sedimentary rocks that spans a large geographic portion of the Western United States. The sandstones and mudstones that constitute the steep beds of the quarry at Dinosaur National Monument are included in the Morrison Formation. Generally, the Morrison Formation has a distinct appearance of bright and multicolored sandstones, siltstones and mudstones, which give it the appearance of a toned down rainbow.
The Morrison Formation has hosted over a century of paleontological excavations, including the “Bone Wars”, a bitter feud between the crews of late 19th century paleontologists Edward Drinker Cope and Othniel Charles Marsh, who would try to name new species of extinct vertebrates at a blistering pace.
The Morrison Formation is not only home to bones, but a seven million year record of the what the world was like during the Late Jurassic, 150 million before humans would encounter these revolutionary rainbow rocks. Clues can be deciphered from the rocks which indicate what the dinosaur graveyard was like and allows for a sense of time travel back into the real Jurassic Park.
The Modern Morrison
The ecosystem of the Morrison Formation has an uncanny resemblance to the modern Serengeti in Africa. The Morrison featured a diverse fauna of large vertebrates, topographically low terrain, with meandering rivers, floodplains, lakes, and a semi-arid climate with strong seasonality. The Serengeti serves as a striking modern analog, minus the dinosaurs. However, numerous comparisons and speculations also been made between the two ecosystems animals.Sauropod behaviors, such as herding and grazing, are even often compared to those of elephants, and the diversity of carnivorous theropods give resemblance to the predatory partitioning of lions, leopards, and cheetahs.
A diversity of some of the largest terrestrial herbivores to walk the earth lived in the Morrison ecosystem, the sauropod dinosaurs.
The Morrison represents an expansive depositional basin consisting of meandering rivers, floodplains, wetlands, freshwater and saline lakes, and sand dunes. The source of erosion, and origination of sediment, for the Morrison basin were areas of tectonic uplift (mountains) on the western edge of North America, much like the modern Cascade Range
Studies of Jurassic oxygen isotopes have revealed information about the climate of the Morrison basin. These studies indicate the region had a large watershed with primary precipitation originating in the highlands to the west of the Morrison basin. Groundwater played a significant role in supplying the water for the streams, lakes, and rivers of the Morrison. The Morrison may have been subject to seasonal rainstorms that caused flooding, but the contributions by groundwater and surface water were much more significant (Turner and Peterson, 2004).
These include the classic genera Diplodocus, Apatosaurs, and Barosaurs. This diversity most likely reflected niche partitioning among these giant sauropod dinosaurs, some adapted to eating the tall, herbaceous foliage associated with a riparian environment. Others were most likely adapted to shorter vegetation associated with the floodplain, including aquatic plants called charophytes (Turner and Peterson, 2004). Medium sized herbivores also occupied the Morrison ecosystem, ornithischian dinosaurs such a Stegosaurs and Camptosaurus, as well as small herbivores like Dryosaurus.
The Morrison ecosystem also contained a diversity of carnivorous theropod dinosaurs, such as Allosaurus, Torvosaurus, Stokesosaurus, Marshosaurus, and Ceratosaurus. Allosaurus is the most common theropod in the Morrison Formation
Although renowned for its large vertebrate fossils, the Morrison ecosystem also contained numerous small vertebrates.Modern excavation efforts have revealed a diversity of small theropod dinosaurs in the Morrison Formation, such as Koparion, a troodontid genus known from a single tooth (Chure, 1994). An array of fossil frogs, salamanders, lizards, and snakes has been accompanied a diversity of crocodyliforms and turtles. The Morrison has revealed a diversity of mammals as well, mostly identified from teeth. Mammalian tooth structure is very complex, and extremely useful in taxonomic identification.
There Morrison has also produced a diverse record of invertebrates. The Carnegie Quarry itself contains beds lined with unionids, a group of freshwater clams. The Morrison also contains fossils of crustaceans and snails. When observing trace fossils, or observable evidence in the rock record of biotic behavior, an even wider diversity of life appears. The Morrison contains trace fossils such as crayfish burrows and social insect nests.
Although the Morrison Formation generally lacks complete plant fossils, much of the floral ecology had been reconstructed with fossilized pollen grains and fragmentary remains (Turner and Peterson, 2004). The Morrison Formation contains a variety of gymnosperm (evergreen) fossil plant material, including conifers such as pines and araucaria (“monkey puzzle trees”), as well as ginkgos and cycads. Ferns, horsetails and mosses were the likely undergrowth of the large gymnosperms (Chure et. al., 1998). Also represented in the Morrison are the trace fossils of fungi.
The Gem of the Late Jurassic
The Morrison Formation provides an unprecedented record of a complete biota of the Late Jurassic. While the fossil record in these rocks typically favors large vertebrates, a more complete picture has been pieced together, revealing a complete, diverse, and interconnected ecosystem. The Morrison is not only home to iconic giant dinosaurs, but the perfect ecological analog for paleontologists studying the Late Jurassic around the world.