From the beginning of the Triassic, following the end-Permian mass extinction, Earth entered a predominantly warm climatic regime. For much of the Mesozoic, the planet lacked permanent polar ice caps comparable to those of today. Global temperatures were, on average, higher, and polar regions experienced temperate conditions capable of supporting diverse vegetation and fauna.
These conditions persisted and became firmly established during the Jurassic, allowing terrestrial ecosystems to expand into higher latitudes and promoting a broader geographic distribution of many species. During the Cretaceous, particularly in its warmest intervals, this pattern reached some of its thermal maxima, with direct consequences for sea level and the extent of epicontinental seas.
Elevated atmospheric carbon dioxide levels, associated with intense volcanic activity and the planet’s tectonic configuration, played a central role in maintaining these warm conditions. The absence of large ice sheets also contributed to relatively stable sea levels, facilitating the expansion and persistence of shallow marine environments across the continents.
Despite its globally warm character, the Mesozoic climate exhibited pronounced regional variability across its different periods. During the Triassic, when Pangea remained largely united, vast continental interiors experienced arid and extreme conditions, with strong seasonal contrasts.
With the progressive fragmentation of continents beginning in the Jurassic and intensifying during the Cretaceous, climatic patterns became more complex. Latitudinal differences produced more humid and productive zones near the equator, while interior and subtropical regions alternated between arid and more temperate phases.
In many areas, seasons were well defined. Geological evidence indicates recurrent cycles of drought and precipitation, directly influencing vegetation, resource availability, and the adaptive strategies of organisms inhabiting these environments.
The Mesozoic was not a period of continuous climatic stability. During the Late Triassic, the planet experienced major environmental disturbances associated with large-scale volcanism, culminating in the Triassic–Jurassic boundary extinction.
Throughout the Jurassic and Cretaceous, additional episodes of climatic change were linked to shifts in ocean circulation, variations in marine chemistry, and further large volcanic events. In the Late Cretaceous, these environmental stresses accumulated over millions of years prior to the final extinction event.
These episodes did not represent complete resets of life, but rather periods of selective pressure that reorganized existing ecosystems and promoted new evolutionary radiations.
Across all three major periods of the Mesozoic, climate exerted a direct influence on ecosystem structure. Warm and relatively stable long-term conditions supported high levels of primary productivity, sustaining complex food webs from the Jurassic through the Cretaceous.
At the same time, regional climatic variability drove the diversification of adaptive strategies. Different lineages evolved to thrive in humid, arid, coastal, or strongly seasonal environments, resulting in remarkable ecological diversity on both land and sea.
From the Early Triassic to the end of the Cretaceous, Mesozoic climate was closely linked to continental movement, the advance and retreat of seas, and changes in atmospheric composition. Together, these factors created a dynamic environmental framework in which life evolved continuously for nearly 186 million years.
Correctly interpreting the Mesozoic fossil record requires viewing climate as an active component of the planetary system rather than a passive backdrop. It was one of the forces that shaped the Mesozoic world and the forms of life we know today through their fossils.