The Late Triassic period represents a distinct geological epoch spanning approximately 237 to 201.4 million years ago. This interval marks the final third of the Triassic Period, the earliest division of the Mesozoic Era. Preceded by the Middle Triassic and followed by the Early Jurassic, the Late Triassic was a time of significant change.
Earth’s Configuration
During the Late Triassic, Earth’s landmasses were amalgamated into the supercontinent Pangea, a vast C-shaped landmass covering about a quarter of the planet’s surface. This configuration profoundly influenced global climate patterns. The interior of Pangea experienced hot, arid conditions with extensive deserts, due to its distance from oceanic moisture.
Despite the aridity, strong seasonal monsoons occurred over large areas, particularly in coastal regions. Temperature differences between the equator and the poles were less extreme than today, and there was no polar ice. Towards the end of the Triassic, Pangea began to rift apart, leading to the separation of northern Laurasia (North America and Eurasia) from southern Gondwana (South America, Africa, India, Antarctica, and Australia). This rifting shaped the climate and environment.
Emergence of Dominant Life
The Late Triassic was a time for the evolution and diversification of various life forms. Early dinosaurs, though not yet fully dominant, began to appear and diversify during the Carnian age. They emerged in a world where crurotarsan archosaurs, such as phytosaurs and rauisuchians (relatives of modern crocodilians), were prominent terrestrial vertebrates. Dinosaurs gradually started to displace these groups, adapting to the arid climate.
Early mammals also appeared, characterized by their small size and likely nocturnal habits. Though less prominent than dinosaurs, their presence marked an evolutionary step. In the skies, pterosaurs, the first flying vertebrates after insects, began to take flight. These early flying reptiles diversified into various environments.
The oceans were home to diverse marine reptiles. Ichthyosaurs were abundant. Plesiosaurs, with their long necks, also diversified, alongside other marine reptile groups. Plant life on land was dominated by conifers and cycads, which became widespread across both hemispheres.
The End-Triassic Extinction
An extinction event marked the boundary between the Late Triassic and the Early Jurassic. This event, known as the End-Triassic Extinction, led to the demise of about 76% of all marine and terrestrial species and about 20% of all taxonomic families. Marine life was severely impacted, with significant losses among corals, bivalves, and brachiopods, and the complete disappearance of conodonts.
The leading scientific explanation for this extinction is massive volcanic activity associated with the Central Atlantic Magmatic Province (CAMP). As Pangea began to rift apart, immense volumes of lava, along with gases like carbon dioxide and sulfur, were spewed into the atmosphere. This sudden release of greenhouse gases resulted in rapid global warming and ocean acidification.
The environmental changes, including ocean poisoning and reduced calcium carbonate availability due to acidification, caused widespread biodiversity loss. On land, many large amphibians and non-dinosaurian reptiles perished. The End-Triassic Extinction cleared ecological niches, allowing surviving dinosaurs to expand and become the dominant terrestrial animals in the subsequent Jurassic Period.