The Mesozoic Era and its Three Time Periods

"Discover how the ancient beasts progressed in the three periods of the Mesozoic Era: Triassic, Jurassic, and Cretaceous."

The Mesozoic Era, which was at the time from about 252 million years ago (MYA) to 66 million years ago, is also known as the Age of Dinosaurs. It started around the end-Permian extinction event that wiped out 70% of terrestrial species and 96% of marine life. During this era, life rebounded gradually with the change in the earth’s climate and flora and fauna, leading to new species of lizards and dinosaurs.

Our planet back then was much warmer than it’s now, and there were no ice caps. The three periods of the Mesozoic encompass the Triassic, Jurassic, and Cretaceous periods. Dinosaurs evolved in the Jurassic period but were more diverse in the Jurassic. Let’s find out what life was like during the Mesozoic era and its three periods. 

mesozoic era three periods

Triassic Period

A lot of changes took place in the Triassic period. It began after the worst extinction event of the earth around 252-201 million years ago, called the Permian extinction or the Great Dying. At that time, there were no continents, just one supercontinent called the Pangaea. Even though it was one big landmass, it didn’t have a uniform environment. The northern and southern parts had different vegetation. During the early Triassic, there were no flowering plants and grasses, and the conifers began to spread. In the drier places, there were vast fern prairies.  

Scientists believe that the first dinosaurs appeared around 240 MYA. They were small and bi-pedal, darting across the varied landscape. The first pterosaurs appeared about 228 million years ago. They were flying vertebrates that evolved into huge animals. During this period, the dinosaurs were divided into two main groups, called the Saurischia and the Ornithischia. Some dinosaurs gradually evolved to have large sizes, reaching over nine meters.

Around 201.3 MYA, this Triassic ended with an extinction event ending major terrestrial life except for the crocodiles, dinosaurs, and pterosaurs.

mesozoic era three periods
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Jurassic Period

The second part of the Mesozoic era occurred around 201.3 to 145 million years ago and is called the Jurassic period. During this time, the Pangaea supercontinent split into two: the northern part, called the Laurentia, and the southern, Gondwana. Due to this rift coupled with the rising temperatures, the dinosaurs became dominant and diversified further.

During the early Jurassic, plant life evolved to include ferns, ginkgoes, and conifers. The mid and late Jurassic period saw the emergence of flowering plants, also called angiosperms, though they were rare compared to gymnosperms.

Dinosaurs continued to evolve during this period and became gigantic. There were many titanic sauropods, like the Brachiosaurus and the Seismosaurus. Large predators like the Allosaurus and the Ceratosaurus preyed upon the weaker ones. Dinosaurs further evolved into armored creatures like the Stegosaurus. Pterosaurs continued to be dominant as flying vertebrates. We also see the emergence of the largest marine predators, such as the Temnodontosaurus and the Liopleurodon.

The transition to the Cretaceous period wasn’t without losing some species. During the Jurassic period’s end, several species died out, leading to the next phase of the Mesozoic.

mesozoic era three periods

Cretaceous Period

The Cretaceous period was the last of the Mesozoic era and the longest for the dinosaurs, from 145.5 million years ago to about 65.5 MYA. The two earth landmasses were further divided into continents like we have today but in different positions.

The climate was warm and humid, similar to the Jurassic period. Flora and fauna evolved during this time. There were abundant flowering plants, leading to a surge in the pollinating insect population. Other life forms also diversified, like insects, mammals, and birds. Many birds took flight and joined the pterosaurs during this period.

Dinosaurs, like the hadrosaurs, Triceratops, Dreadnoughtus, and T-rex, were the dominant creatures during the Cretaceous. There were also massive herds of herbivorous ornithischians, like Iguanodon, ceratopsians, and Ankylosaurus.

mesozoic era three periods

End of the Dinosaur Era

At the end of the Cretaceous period, around 66 million years ago, a huge comet or asteroid hit the earth resulting in a sudden mass extinction called the Paleogene (K-Pg) extinction event. It wiped out nearly all life forms on this planet, leading to the end of the Mesozoic era. However, many species survived, like some insects, birds, mammals, angiosperms, and marine life forms like fishes, mollusks, and corals. To know more about the dinosaur extinction, click here.

But what was an end for one era was but a beginning for another. The Cenozoic era began soon after the K-Pg extinction and continues to this day.

Picture of Ekta G

Ekta G


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