The Tyrannosaurus rex, or T. rex, is one of history’s most recognized dinosaurs. Its imposing size and fearsome reputation have cemented its place in popular culture and scientific study.
Where T-Rex Roamed
Tyrannosaurus rex lived in western North America during the Late Cretaceous period, from approximately 72.7 to 66 million years ago. This region was an island continent called Laramidia, separated from eastern North America (Appalachia) by the Western Interior Seaway. The landmass of Laramidia stretched from modern-day Alaska down to Mexico. Fossils of T. rex have been found across a wide expanse, including states like Montana, South Dakota, Wyoming, and Colorado in the United States, and as far north as Alberta and Saskatchewan in Canada.
This extensive geographical distribution suggests T. rex was highly adaptable to different environments within Laramidia. All confirmed T. rex fossils originate from this western portion of the continent.
The World of the Late Cretaceous
The Tyrannosaurus rex habitat during the Late Cretaceous period was warm, humid, and subtropical, significantly warmer than today. Crocodilians and palm trees thrived in this environment, indicating the absence of prolonged freezing temperatures. This period is often described as a “Greenhouse World.”
The landscape where T. rex lived consisted of lush forests, swamps, and coastal plains. These environments were often part of extensive floodplains, laced with broad, shallow river systems that drained into the receding Western Interior Seaway. Vegetation was abundant, including conifers and a diversifying array of flowering plants such as magnolias, sycamores, and roses. This diverse flora supported a rich ecosystem of herbivorous dinosaurs like hadrosaurs and ceratopsians, which served as potential prey for T. rex.
Uncovering Ancient Environments
Paleontologists determine the ancient habitats of dinosaurs like Tyrannosaurus rex by examining the geological formations where fossils are found. The Hell Creek Formation, spanning parts of Montana, North Dakota, South Dakota, and Wyoming, is a prime example, preserving an extraordinary record of Late Cretaceous life. This formation consists of fine-grained sandstones, mudstones, and claystones, indicative of ancient floodplains, rivers, swamps, and coastal areas. The type of sedimentary rock provides clues about the depositional environment, such as the presence of coal seams suggesting swamps, or alternating layers of sand and mud indicating river systems.
Fossilized plant remains, studied through paleobotany and palynology (the study of pollen and spores), offer direct evidence of the flora and climate. For instance, the Hell Creek flora is dominated by flowering plants, with conifers and ferns also present, reflecting the subtropical conditions. Sedimentology, the study of how sediments are formed and deposited, further reveals details about ancient water bodies and landforms. By analyzing the size and type of sediment, scientists can infer the energy levels of ancient environments, such as slow-moving water in lakes or fast-moving rivers. The associated fossilized animals found alongside T. rex, including other dinosaurs, reptiles, amphibians, and fish, provide a comprehensive picture of the food web and overall ecosystem.