Dinosaur-Bearing Rock Formations
Dinosaur-bearing rock formations are geological structures that consist of layers of sediment or rock, known as strata, which contain fossils of dinosaurs and other prehistoric life. These formations vary globally and can include different types of sediment such as shale, sandstone, and limestone. They are essential for paleontological studies, as the fossilized remains help researchers understand the diversity and evolution of dinosaurs. Each formation may be subdivided into smaller units called members, which often have specific fossil sites, sometimes referred to as "bone beds." Notable formations, like the Morrison Formation in North America and the Nemegt Formation in Mongolia, are famous for their rich fossil deposits and historical significance in paleontology.
Discoveries in these formations have been pivotal; for instance, the Bone Wars of the late 1800s led to significant finds in the American West. Ongoing research in various regions, including Asia and Africa, is continuously reshaping our understanding of dinosaur biology, behavior, and evolution. Discoveries from formations such as the Jiufotang Formation in China have provided insights into the links between dinosaurs and modern birds, illustrating the importance of these geological formations in unraveling the history of life on Earth.
Dinosaur-Bearing Rock Formations
Introduction
A geologic formation is defined in paleontology as a collection of one or more layers of sediment or rock (strata) that share certain defining characteristics. A formation may be partially defined by the types of fossils found within the layers, in addition to the type and color of rock and other sediment. Dinosaur-bearing rock formations have been found around the world and may contain a variety of different types of sediment, including shale, sandstone, limestone, and volcanic deposits. Formations are divided into smaller units called members, each of which may contain a number of fossil sites, sometimes called “bone beds.”
A few geologic formations have become famous for the number and quality of dinosaur fossils found there or for their role in paleontological history. Formations are usually discovered by paleontologists or geologists, but a number have been discovered by accident, such as during the course of unrelated mining or excavation projects. Once a productive site is located, paleontologists and amateur fossil hunters flock to the new venue in hopes of making a pivotal discovery. Fossil sites in North America and Europe have been thoroughly explored, but the discovery of new fossils from formations in Asia and Africa has had a major impact on paleontology in the twenty-first century.
Key Terms
Bone Wars: The Bone Wars were a period of intense competition between fossil hunters Edward Drinker Cope and Othniel Charles Marsh that took place in the fossil beds of the American West in the late 1800s. The Bone Wars led to the discovery of a large number of dinosaur fossils.
Cretaceous Period: The final period in the Mesozoic, the Cretaceous stretched from approximately 145 to 66 million years ago.
Geological Formation: An aggregation of strata with similar properties occurring across a certain geographical area. Related formations are often placed together in “groups” and each formation can be divided into “members.”
Jurassic Period: The middle portion of the Mesozoic stretching from 201 to 145 million years ago.
Radiometric Dating: Also called radioisotopic dating, radiometric dating is a method of measuring the age of a rock based on the decay of radioactive isotopes found within minerals.
Relative Dating: System for estimating the relative age of sedimentary samples based on the observation that newer layers of sediment are generally deposited on top of older layers.
Stratum: Layer of sedimentary rock that can be distinguished from layers above or below it by certain characteristics, including the color, type of rock, and types of particles found within the layers.
Triassic Period: The period at the beginning of the Mesozoic that included the emergence of dinosaurs, dating between 252 and 201 million years ago.
Key Players
Barnum Brown: While working for the American Museum of Natural History in 1902, Brown discovered the first Tyrannosaurusrex fossil from bone beds in the Montana portion of the Hell Creek Formation. Brown is considered by many paleontologists to be one of the greatest fossil collectors in history. He amassed so many fossils in the early twentieth century that paleontologists are still cataloging and describing his discoveries in the twenty-first century.
Earl Douglass: Early twentieth-century paleontologist Earl Douglass was one of the first to study the Utah portions of the Morrison Formation. In 1909, while working for the Carnegie Museum, Douglass discovered the first fossils of what was eventually the most complete Apatosaurus skeleton known to science. In 1915, Douglass's dinosaur quarry was renamed Dinosaur National Monument and preserved by the National Park Service as a historic site.
Halszka Osmólska: Osmólska was a twentieth-century Polish paleontologist who participated in a groundbreaking series of expeditions to the Nemegt Formation in Mongolia. In publications including Protoceratopsidae (Dinosauria) of Asia (1975) and Pachycephalosauria: A New Suborder of Ornithischian Dinosaurs (1974), Osmólska provided a significant contribution to the paleontological view of Cretaceous Asia. Fossils uncovered by Osmólska and colleagues helped to develop a new understanding of the evolution of horned dinosaurs, the ornithischian order, and the evolution of birds in the Cretaceous.
Dong Zhiming: Paleontologist Dong Zhiming is one of China's (and the twentieth century's) most prominent paleontologists, often called the world's greatest dinosaur hunter. Zhiming has participated in the discovery of a variety of dinosaurs in China's Jurassic Dashanpu Formation. Among his major contributions to the field, Dong put forth the theory that the primitive Archaeoceratops, an early horned dinosaur genus, crossed from Asia to North America where the group diversified into a variety of species.
History
Historically, paleontologists searched for fossils in a sporadic manner, excavating sites that had been exposed by erosion, water, or mining, often in mountainous, lake, ocean, or river areas, as well as those sites of revealed by accidental discovery, usually by amateurs. Fossils are most often found in sedimentary rock, such as sandstone, limestone, shale, siltstone, mudstone, and dolostone. Paleontologists and stratigraphers (geologists who study straitified rocks) search for certain kinds of rock--ancient lake beds, rivers, and floodplains—places where creatures would have congregated for water or food and where sediment would have collected and preserved them after death as fossils.
As formations are explored and uncovered, the characteristics of good fossil-bearing rock are better understood, providing scientists with the information to more efficiently identify formations likely to contain fossil sites.
Formations in the Northern Hemisphere
The Morrison Formation covers a total of 1.5 million square kilometers (579,153 sq mi) from New Mexico to Canada and consists largely of sandstone, mudstone, and limestone. Radiometric dating indicates that the formation was deposited in the Late Jurassic. The Morrison Formation was a focal point of the Bone Wars in the 1870s, resulting in the discovery of hundreds of species. The discovery of the first complete specimen of Apatosaurus (then called Brontosaurus) by paleontologist Earl Douglass led to the establishment of Dinosaur National Monument, a national historic site preserving one portion of the formation.
Dinosaur Provincial Park in Alberta, Canada, covers 80 square kilometers (30.8 sq mi) comprising three distinct formations (Dinosaur Park, Oldman, and Bearpaw) from the Late Cretaceous. Digging in the park began in the 1880s, and since then, scientists working in the park have unearthed more than 40 dinosaur species, representing virtually every major dinosaur group and including a number of well-known genera, such as Dromaeosaurus, Centrosaurus, Edmontonia, Struthiomimus, Chirostenotes, and Lambeosaurus.
The Hell Creek Formation, covering portions of Montana, South and North Dakota, and Wyoming, consists of rich shale and sandstone deposited at the end of the Cretaceous, when a shallow sea covered much of North America. A variety of important species have been uncovered from Hell Creek beds, including Tyrannosaurusrex, which was discovered by paleontologist Barnum Brown in 1902. Other important genera from the Hell Creek Formation include Triceratops, Troodon, and Ornithomimus.
The Nemegt Formation, in Mongolia's Gobi Desert, was discovered in 1948 and has become one of the most productive fossil sites in Asia. A scarcity of radioisotope evidence forces scientists to date Nemegt fossils using relative dating, and most evidence suggests that the Nemegt beds come from the Late Cretaceous period, around 70 million years ago. A number of prominent paleontologists have worked on Nemegt fossil beds, including Polish paleontologist Halszka Osmólska and Mongolian native Rinchen Barsbold, who conducted some of the first fossil digs in the site. Numerous important species have been uncovered from Nemegt beds, including Avimimus,Homocephale, and the unusual herbivore Therizinosaurus.
The Dashanpu Formation, in China's Sichuan Province, was discovered in the early 1970s during an expedition to drill for petroleum deposits. Chinese paleontologist Dong Zhiming began studying fossils from the area in the late 1970s and was instrumental in convincing the Chinese government to protect Dashanpu dig sites from further oil prospecting. Strata from the formation have been dated to 167 to 170 million years ago, during the Middle Jurassic period. A number of species have been uncovered from Dashanpu, including Gasosaurus (named in honor of the petroleum expedition that uncovered the fossils), Datosaurus, Dashanpusaurus, and Sinraptor.
Formations in the Southern Hemisphere
The Tendaguru Formation in Tanzania was explored by German paleontologists Werner Janensch and Edwin Hennig between 1909 and 1913, unearthing 100 full skeletons and a variety of partial fossils. Tendaguru consists mainly of shale and marine sandstone from the Late Jurassic period where paleontologists have found a number of large sauropod species, including Brachiosaurus and Barosaurus, as well as unusual stegosaur species, such as Kentrosaurus, and a few theropod species, including Ceratosaurus. Tendaguru has remained a major area of research into the twenty-first century.
The Ischigualasto Formation in northwestern Argentina, at the border of Chile, includes more than 600 square kilometers (231.6 sq mi) of varied sediment deposited in the Triassic. Fossil hunters first began searching Ischigualasto in the 1950s, resulting in the discovery of numerous new species, including the small predators Herrerasaurus and Eoraptor. Fossils from Ischigualasto have helped to refine the paleontological understanding of dinosaur origins in the Triassic, and the fossils from Ischigualasto bone beds are among the best-preserved Triassic fossils ever discovered.
The Los Colorados Formation is also in northwestern Argentina. Los Colorados has yielded several tetrapods from the Late Triassic, notably Riojasaurus, Fasolasuchus, Pseudherperosuchus, Hemiprotosuchus, and others. The Coloradisaurus, named after the formation it was found in, was identified by J. F. Bonaparte in 1978.
Current Research and Implications
Dinosaur formations are yielding a wealth of information that not only point to new genera and species, but also shift the way scientists think about previous assumptions. Based on these discoveries, scientists are developing new theories about how dinosaurs bore their weight and carried their bodies, the function of features such as horns and armor, and biological processes such as reproduction, migration, and evolution.
In 2011, paleontologists in Africa reported on the remains of a previously unknown sauropod from Angola, dubbed Angolatitan, the first fossil discovery from the Itombe Formation of the mid-Cretaceous. Paleontologists hope that further examination of this primitive dinosaur helps to refine current thinking about the later evolution of the sauropods.
Similarly, scientists recently found a previously unknown species of a stegosaurid, Miragaia, which was the first of its kind unearthed from the Sobral Formation, a Middle Jurassic formation in Portugal. Miragaia was the first dinosaur uncovered from the Sobral, raising the question of just how many other specimens remain obscured in understudied formations around the world.
Some of the most revolutionary recent discoveries in paleontology came from expeditions to the Jiufotang Formation in China, an Early Cretaceous fossil assemblage studied intensely in the late 1990s and the early 2000s. In 2007, researchers discovered a specimen of dinosaur named Sinosauropteryx. Sinosauropteryx is closely related to modern birds, and its discovery gave new insight into the development of feathers. A variety of other dinosaurs closely related to birds have been found at the Jiufotang site, making it one of the most productive formations of the twenty-first century.
The Hanson Formation of Antarctica, containing Middle Jurassic sediment, wasn’t explored until the early 1990s. Expeditions in 2004 and 2006 discovered the remains of sauropod dinosaurs that survived millions of years after sauropods disappeared from other formations around the world. Because of the discoveries, paleontologists are reexamining their ideas about the evolution and spread of sauropods.
In 2019, Lokiceratops was discovered in the Badlands of Montana, part of the Hell Creek Formation. The newly discovered dinosaur is the largest dinosaur from the family of centrosaurines ever found in North America. Excavated from the same sight as four other dinosaur species, the discovery offers insight into the biodiversity of the area at the time.
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