The Mesozoic Era, or the Age of Dinosaurs, spanned roughly 252 to 66 million years ago. During this time, the world’s landmasses underwent a dramatic transformation, starting as a single supercontinent and slowly drifting toward their modern positions. This immense geographic shift was powered by the continuous movement of tectonic plates. The changing continental arrangement profoundly influenced global climate, ocean circulation, and the evolution and distribution of dinosaur species.
The Triassic Period: The Supercontinent Pangea
At the dawn of the Mesozoic Era, around 252 million years ago, all major landmasses were fused into a single, colossal supercontinent called Pangea. This unified landmass stretched nearly from pole to pole, creating a unique global climate system. Due to its sheer size, the interior of Pangea was extremely arid, characterized by a continental climate with hot summers and cold winters.
Coastal regions experienced strong, seasonal monsoonal rains, but the vast center remained a dry desert. The overall global climate was significantly warmer than present, and there were no polar ice caps. This uninterrupted land bridge allowed for the widespread distribution of early dinosaur relatives and other terrestrial life. This led to a relatively homogeneous collection of species, since geographic barriers did not limit movement across the supercontinent.
The Jurassic Period: The Great Rift
The geological stability of the Triassic gave way to massive rifting starting around 200 million years ago, marking the Jurassic Period. The breakup of Pangea began with the opening of rift valleys that eventually became oceans. The first major split occurred along a north-south axis, dividing Pangea into two immense continents: Laurasia (north) and Gondwana (south).
The Tethys Sea began to open and expand between these two emerging landmasses. Simultaneously, the Central Atlantic Ocean began separating northwestern Africa from North America. While Laurasia (North America and Eurasia) remained connected, the southern supercontinent Gondwana (Africa, South America, Antarctica, Australia, and India) began internal fracturing. This division profoundly impacted dinosaur evolution, isolating populations and setting the stage for regional diversification.
The Cretaceous Period: Continents Nearing Their Modern Positions
Continental fragmentation accelerated during the Cretaceous Period (starting 145 million years ago), pushing landmasses toward their modern locations. The most dramatic movements involved the complete breakup of Gondwana. South America pulled away from Africa, progressively opening the South Atlantic Ocean from south to north.
India and Madagascar simultaneously rifted away from Antarctica and Australia, beginning India’s rapid journey northward toward Asia. Rapid seafloor spreading displaced ocean water, contributing to a significant rise in global sea levels. This high sea level caused shallow seas to flood continental interiors, notably in North America. There, the Western Interior Seaway split the continent into Laramidia (west) and Appalachia (east). This immense inland sea acted as a marine barrier, isolating dinosaur populations and driving the evolution of unique regional species.
Decoding the Past: The Evidence for Continental Reconstructions
Scientists reconstruct the Mesozoic world by examining several independent lines of geological and biological evidence. One early observation was the “jigsaw puzzle” fit of the continents, particularly the complementary coastlines of South America and Africa. However, the most compelling evidence comes from the distribution of ancient life.
Fossils of the land-dwelling reptile Lystrosaurus, for example, are found exclusively in Antarctica, India, and South Africa—once adjacent parts of Gondwana. The discovery of identical geological formations and rock strata on now-separated continents further confirms this former connection. Paleomagnetism, the study of the Earth’s ancient magnetic field recorded in rocks, provides quantitative data. Analyzing magnetic signatures in rocks of the same age across different continents showed that the landmasses moved relative to each other, validating the theory of continental drift and plate tectonics.