The Mesozoic Era lasted 186 million years.
To put that in perspective: the entire evolutionary history of modern humans — from the first Homo sapiens to today — is approximately 300,000 years. The Mesozoic lasted 620 times longer than our entire species has existed.
And throughout almost all of it, the planet was dramatically warmer than it is today.
There were no permanent ice caps. Even the poles supported vegetation during the Mesozoic — not the frozen wastelands we know, but forests and wetlands that experienced cold winters but never the deep glaciation that has characterized so much of Earth's more recent history.
This sustained warmth had consequences for every dimension of life. The warm, CO2-rich atmosphere drove extraordinary plant productivity. Dense forests covered vast areas that would later become deserts. Shallow inland seas spread across the continents, creating productive coastal ecosystems.
Into this world of extraordinary biological richness, the dinosaurs emerged, diversified, and expanded to fill every available ecological niche on land.
For 186 million years, they were the most successful large land animals the Earth has ever produced.
Their era has a name. We live in what came after it.