A dinosaur graveyard is a rare geological deposit where many fossilized dinosaur remains are concentrated in a small area. These sites offer a unique window into prehistoric ecosystems, providing insights that single fossil finds cannot. The exceptional preservation and abundance of bones make these locations invaluable to paleontologists. Such concentrations are not only uncommon but also provide a detailed snapshot of life and death events from millions of years ago.
How Dinosaur Graveyards Form
The formation of dinosaur graveyards typically involves a combination of natural processes and environmental conditions that lead to the rapid burial and preservation of multiple animals. One common scenario is rapid sedimentation caused by large-scale floods or mudslides, which can quickly engulf and bury carcasses, protecting them from scavengers and decomposition. Volcanic ashfalls also provide rapid burial, encasing animals and preventing decay. These events create anoxic, or low-oxygen, environments around the remains, which significantly slows decomposition by limiting bacterial and other organism activity.
Drought conditions can also contribute to mass mortality events. Animals congregated around shrinking water sources, eventually succumbing to dehydration or becoming trapped in muddy banks. Subsequent burial by sediment, perhaps from seasonal floods, would then preserve these remains. Tar pits or bogs served as natural traps, where animals became stuck and died, with their bones preserved in the anoxic, acidic conditions of the mire. Taphonomy, the study of how organisms decay and become fossilized, helps scientists understand the environmental factors and post-mortem processes that led to the excellent preservation observed in these graveyards.
What Dinosaur Graveyards Reveal
Dinosaur graveyards offer profound insights into the behavior and ecology of prehistoric life. The presence of numerous individuals of the same species at one site often provides compelling evidence of herd behavior or social grouping. For instance, large bone beds featuring dozens or hundreds of individuals from a single species suggest these dinosaurs lived and moved together. Analyzing bone damage and arrangements can also reveal predator-prey interactions or scavenging patterns that occurred before burial.
These sites can also reconstruct ancient ecosystems by showing which species coexisted in a particular environment. The geological layers and sediment types within a graveyard can provide clues about past climates and catastrophic events, such as sudden floods or volcanic eruptions, that dramatically altered the landscape and led to the mass death and burial of animals. In rare instances, exceptional conditions have even led to the preservation of soft tissues, such as skin impressions or muscle fibers, offering details about dinosaur anatomy.
Famous Dinosaur Graveyard Sites
Dinosaur National Monument, located on the border of Utah and Colorado in the United States, is a famous dinosaur graveyard. It showcases a massive wall of exposed dinosaur bones within a former riverbed. Discovered in 1909, this quarry contains thousands of bones from over ten different dinosaur species, including Allosaurus, Camarasaurus, and Stegosaurus, dating back to the Late Jurassic period, approximately 150 million years ago. The site is believed to represent a logjam or sandbar where dinosaur carcasses accumulated during ancient floods, providing a rich assemblage of Morrison Formation fauna.
Ghost Ranch, in northern New Mexico, is another significant site, renowned for its discovery of hundreds of Coelophysis skeletons from the Late Triassic period, around 200 million years ago. Paleontologist Edwin H. Colbert led excavations there in the 1940s, uncovering evidence of mass mortality likely caused by a flash flood that buried a large group of these early predatory dinosaurs. The large number of Coelophysis individuals, including juveniles and adults, offers insights into their growth patterns and potential gregarious behavior.
The Cleveland-Lloyd Dinosaur Quarry in central Utah, part of the Morrison Formation, is unique for its high concentration of carnivorous dinosaur remains, especially Allosaurus. Over 10,000 bones have been excavated from this site, representing at least 70 individual dinosaurs, with approximately 75% belonging to Allosaurus. The conditions of its formation, possibly a mucky bog or predator trap, continue to be debated, but it provides valuable data on Jurassic predators and their environment.