Dinosaur bones are fossilized structures where the original organic material has been replaced by minerals, turning them into rock. Finding these ancient remnants is rare, as most organisms decay completely after death. Only a tiny fraction of the dinosaurs that ever lived were preserved. This rarity means that specific geological areas across the globe have become crucial sites for paleontologists, offering windows into prehistoric ecosystems.
The Conditions Necessary for Fossil Preservation
The preservation of a dinosaur’s skeleton requires rapid burial, which isolates the remains from oxygen and scavengers before decay can begin. This quick covering is often provided by environments with high sedimentation rates, such as riverbeds, floodplains, and lake bottoms.
A carcass settling in a lowland floodplain is quickly covered by fine-grained silt or mud carried by floodwaters. Over vast spans of time, the weight of overlying sediment compresses the material into sedimentary rock, the only rock type that typically holds fossils. Dissolved minerals in groundwater then seep into the bone, replacing the original structure with stable minerals like quartz or calcite, a process known as permineralization.
North America’s Rich Fossil Record
The western United States and Canada contain some of the most concentrated dinosaur fossil sites in the world. One of the most productive areas is the Late Jurassic Morrison Formation, a vast rock unit stretching across states like Wyoming, Colorado, and Utah. This formation, deposited between 162 and 145 million years ago, was once a lush, semi-arid environment crisscrossed by rivers and floodplains.
The Morrison Formation is famous for its enormous long-necked sauropods, including Apatosaurus, Brachiosaurus, and Diplodocus. It is also the primary source for plated dinosaurs like Stegosaurus and the carnivorous theropod Allosaurus.
Further north, the Hell Creek Formation, spanning Montana, North Dakota, and South Dakota, captures the end of the Cretaceous Period, approximately 66 million years ago. This region represents an ancient coastal floodplain environment characterized by swamps and low-lying forests. The Hell Creek Formation is recognized as the source of nearly all specimens of Tyrannosaurus rex and Triceratops. Remains of Triceratops are statistically the most common large dinosaur found, with T. rex being the second most common.
Discoveries Across the Southern Continents
The continents of the Southern Hemisphere, once part of the ancient supercontinent Gondwana, offer a distinct and significant fossil record. South America, particularly Argentina and Brazil, has yielded some of the oldest definitive dinosaur fossils, dating back 245 to 230 million years ago. Early forms like Herrerasaurus and Eoraptor from Argentina provide insights into the initial diversification of dinosaurs.
The later Cretaceous record in these southern lands is dominated by unique fauna that evolved separately from their northern counterparts. Large sauropods, such as the titanosaur Argentinosaurus, represent some of the largest land animals ever discovered. The Southern Hemisphere was also home to the abelisaurids, a group of short-faced, muscular carnivores like Carnotaurus from Argentina.
Discoveries across Africa, such as the remains of the abelisaurid Chenanisaurus, further illustrate the distinct ecosystem of Gondwana. Evidence like matching three-toed theropod footprints found in both Brazil and Cameroon confirms a land connection existed between the two continents as they began to drift apart about 120 million years ago.
Asia and Europe’s Unique Contributions
Asia, specifically the Gobi Desert region of Mongolia and China, is renowned for the exceptional quality of its fossil preservation. The arid conditions and unique sedimentary layers of the Gobi have preserved delicate features and entire scenes of prehistoric life. The Flaming Cliffs, or Bayanzag, are a famous site where the first nests of dinosaur eggs were discovered in the 1920s, providing evidence of dinosaur brooding behavior.
Discoveries in the Gobi include iconic fossils such as the “Fighting Dinosaurs,” a Velociraptor and Protoceratops locked in combat, and specimens of feathered dinosaurs that show the evolutionary link to modern birds.
Europe holds a significant place in the historical context of dinosaur research. The earliest scientifically recognized dinosaur fossils were found there, marking the beginning of the field of paleontology. Discoveries in England, such as those of Megalosaurus and Iguanodon in the early 19th century, were the first to establish the concept of giant, extinct reptiles. Germany’s Solnhofen limestone is famous for its fine-grained layers that preserved the exquisite details of Archaeopteryx, a feathered creature often considered a transitional link between dinosaurs and birds.