The Mesozoic Era, spanning from approximately 252 to 66 million years ago, was the age of the dinosaurs and a time of profound geological change. Driven by plate tectonics, the continents embarked on a journey of separation, fracturing a single supercontinent into the distinct landmasses we recognize today. This continental drift profoundly influenced global climate, sea levels, and the evolutionary path of the dinosaurs that walked upon them.
The Triassic World and Pangaea
At the dawn of the dinosaur age in the Triassic Period (252 to 201 million years ago), all landmasses were merged into the colossal supercontinent Pangaea, surrounded by the vast superocean Panthalassa. The sheer size of Pangaea created a unique and extreme continental climate, characterized by intense interior deserts and a lack of moderating ocean influences.
Far from the coasts, the interior experienced extreme temperature variations and pervasive aridity, while coastal regions had powerful monsoonal weather patterns. This unified geography meant early dinosaurs, such as the slender, bipedal Coelophysis, could roam across nearly all latitudes without encountering a major oceanic barrier. The connected environment allowed for the rapid and widespread distribution of early dinosaur species.
The Jurassic Rifting of Laurasia and Gondwana
The geological stability of Pangaea began to fracture during the Jurassic Period (201 to 145 million years ago) as the supercontinent started to rift apart. This initial breakup divided the landmass into two primary continents: Laurasia in the north (North America and Eurasia) and Gondwana in the south (South America, Africa, India, Australia, and Antarctica).
The separation coincided with the formation of the Central Atlantic Magmatic Province, a period of massive volcanic activity between North America and Africa. As these two halves pulled away, the proto-Atlantic Ocean began to open as a narrow seaway that gradually widened. The Tethys Sea became a prominent, tropical seaway separating Laurasia from Gondwana.
The Cretaceous: A World of Isolated Continents
The fragmentation accelerated during the Cretaceous Period (145 to 66 million years ago), resulting in a world of increasingly isolated continents. Gondwana continued its breakup, with South America and Africa pulling apart, and India, Australia, and Antarctica drifting toward their current positions. The widening Atlantic Ocean lengthened and deepened, further isolating the landmasses.
Global sea levels rose significantly, flooding low-lying coastal areas and pushing marine waters deep into continental interiors. A prime example is the Western Interior Seaway, a vast, shallow sea that split North America into two distinct, separate landmasses. To the west lay Laramidia, stretching from Alaska to Mexico, while the smaller landmass of Appalachia formed to the east.
How Geography Shaped Dinosaur Evolution
The planet’s shifting geography was a primary driver of dinosaur diversification and speciation throughout the Mesozoic Era. In the early Triassic, the unified landmass allowed for a relatively uniform and widespread fauna, enabling new species to quickly spread across the globe. The initial fragmentation into Laurasia and Gondwana in the Jurassic started the process of “vicariance,” where a species’ population is physically separated by a geographical barrier.
The full isolation of the Cretaceous continents created unique evolutionary pressures. The split of North America by the Western Interior Seaway, for instance, caused dinosaur populations on Laramidia and Appalachia to evolve independently for millions of years, leading to distinct, specialized fauna. This pattern of geographical isolation and subsequent diversification, known as allopatric speciation, produced the specialized dinosaur groups seen just before the end of the Cretaceous Period.