Mesozoic Era: The Age of Reptiles

lizard illustration cretaceous period
New research suggests that reptiles that lived during the Dinosaur age were hard-hit. Here, the carnivorous lizard Palaeosaniwa chases a pair of young Edmontosaurus while the snake Cerberophis and the lizard Obamadon look on.
Credit: Carl Buell

During the Mesozoic, or "Middle Life" Era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth. The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles.

Basic Facts

The era is divided up into the Triassic, the Jurassic, and the Cretaceous periods. The Triassic Period, from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs, the Jurassic Period, from about 200 million to 145 million years ago, ushered in birds and mammals, and the Cretaceous Period, from 145 million to 66 million years ago is known for some of its iconic dinosaurs.

The period saw the breakup of the massive supercontinent Pangaea into the seven continents we have today, although they were in very different locations at the end of the era. During the Mesozoic Era, Antarctica was not at the South Pole and was not covered in ice.

Plants and animals

The Mesozoic Era began soon after a massive extinction that wiped out 90 percent of the known species on the planet. Life slowly rebounded, eventually giving way to a flourishing diversity of animals. Massive lizards such as Iguanodon and iconic dinosaurs such as Tyrannosaurus rex and Triceratops dominated the landscape.

Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the Era, but they became much more abundant during the Mesozoic. Flowering plants would not emerge until the late Cretaceous Period. The lush plant life during the Mesozoic Era provided plenty of food, allowing the biggest of the dinosaurs to grow up to 100 tons.


Earth during the Mesozoic Era was much warmer than today. It was so warm, in fact, that none of the polar ice caps existed.

During the Triassic Period, Pangaea still formed one massive supercontinent. Without much coastline to moderate the continent's interior temperature, Pangaea experienced through major temperature swings and was covered in large swaths of desert.

The Jurassic Period saw a rise in sea levels, which flooded coastal regions and hastened the breakup of the supercontinent. With more coastline, many areas experienced warmer, more stable temperatures and a wetter climate.

By the Cretaceous Era, carbon dioxide levels in the atmosphere would rise, trapping the planet's heat. As a result, the planet was hotter — possibly up to 18 degrees Fahrenheit (10 degrees Celsius) warmer. In fact, some scientists believe the period was so hot that large swaths of equatorial oceans were too warm to support sea life.

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