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Why did dinosaur species differ on separate continents during the Late Cretaceous?

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Illustration showing various dinosaur species drawn to scale and grouped by geologic era: Late Cretaceous, Early Cretaceous, Jurassic, and Triassic. Dinosaurs range from large species like Brachiosaurus and Tyrannosaurus to smaller ones like Velociraptor and Compsognathus, with a human silhouette included for size comparison. Measurement bars at the bottom indicate 1 meter and 3 feet for scale reference. — dinosaur A selection of dinosaurs grouped by the geologic interval in which they lived.

During the Late Cretaceous Period, dinosaur species differed across continents primarily because of the ongoing breakup of the supercontinent Pangea and the subsequent isolation of landmasses.1

As the Earth's crustal plates moved throughout the Mesozoic Era, the continents drifted apart, creating widening ocean barriers that prevented the migration of land animals. This geographic separation meant that dinosaur populations on different continents were effectively cut off from one another, allowing them to evolve independently. Over time, these isolated groups diversified, waned, and were replaced by new, distinct fauna unique to their specific landmasses.1

By the Late Cretaceous, this process of continental drift had resulted in each continent occupying its own unique geographic position and climatic zone. Consequently, the fossil record reflects these differences, as the fauna on each continent adapted to the specific environmental conditions and evolutionary pressures of their isolated regions.1