North America holds a remarkable record of dinosaur life, offering a window into prehistoric ecosystems. The continent’s vast geological formations preserve fossilized remains, revealing an incredible diversity of dinosaurs that once roamed its ancient landscapes. These discoveries span millions of years, from the earliest appearances of these creatures to their eventual disappearance.
Triassic Dinosaurs
The earliest reliable evidence of dinosaurs in North America dates back to the Late Triassic Period, 225 million years ago. These initial dinosaurs were generally smaller and less varied than their later relatives. Many were lightly built, bipedal carnivores that moved swiftly across the land.
One example of an early North American dinosaur is Coelophysis, a slender meat-eater about 2 meters (6 to 8 feet) long. Fossils of Coelophysis have been found in places like the Chinle Formation in Arizona. Dinosaurs during this time were not the dominant animals; instead, crocodile-like reptiles and other groups were more prominent.
Jurassic Dinosaurs
The Jurassic Period saw an increase in the size and diversity of North American dinosaurs. The Late Jurassic, around 155 to 145 million years ago, is well-represented by fossils from the Morrison Formation, a source of dinosaur remains found across several U.S. states like Colorado, Utah, and Wyoming. This environment featured floodplains and forests of conifers and ferns.
Large, long-necked herbivores, known as sauropods, were prominent during this time. Species such as Apatosaurus, Diplodocus, Brontosaurus, and Brachiosaurus roamed the continent. These massive plant-eaters could reach large sizes, with some sauropods being the largest land animals to have ever lived. Alongside them, large carnivorous theropods like Allosaurus were the primary predators. Allosaurus measured 8.5 meters (28 feet) in length and likely preyed on the abundant sauropods and armored dinosaurs like Stegosaurus.
Cretaceous Dinosaurs
The Cretaceous Period, from 145 to 66 million years ago, marked the peak of dinosaur diversity in North America before their extinction. During this time, the continent was sometimes divided by an inland seaway, influencing the distribution of land-dwelling dinosaurs. The western part of North America, then an island continent called Laramidia, supported many well-known species.
Tyrannosaurus rex were present in western North America during the Late Cretaceous, 72.7 to 66 million years ago. T. rex was a bipedal carnivore with a large skull, powerful jaws, and serrated teeth capable of crushing bone. It could reach lengths of up to 13 meters (43 feet) and weigh between 5.5 and 10 metric tons. Herbivores included the horned Triceratops, recognized by its large frill and three prominent horns. Triceratops could grow to about 9 meters (30 feet) long and weigh between 5,450 and 7,260 kilograms (12,000 to 16,000 pounds).
Hadrosaurs, or “duck-billed” dinosaurs, were abundant and diverse, with Edmontosaurus being one of the largest and most common. Edmontosaurus could reach lengths of 12 to 15 meters (39 to 49 feet) and weighed several metric tons, often living in herds. Armored dinosaurs like Ankylosaurus provided defense against predators with their bony plates and tail clubs. Ankylosaurus, found in western North America, was a large, quadrupedal herbivore 6 to 8 meters (20 to 26 feet) long and weighing up to 8 metric tons. Its body was covered in bony plates and had a heavy tail club for defense.