Science

When did the dinosaurs roam Earth?

The age of the dinosaurs has fascinated the modern imagination for centuries. Often, we are tempted to think of the era as an ancient time when all our favorite dinosaurs squared off against one another in a battle of survival.

However, dinosaurs ruled Earth for a period spanning hundreds of millions of years, during which world-ending events occurred, and the planet changed in ways that are almost difficult to imagine. Here is a guide to the different time periods during which the dinosaurs roamed the planet.

Mesozoic Era

Illustration of dinosaurs during the Mesozoic Era
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The overall time period in which the dinosaurs lived was known as the Mesozoic Era. The Mesozoic Era lasted 180 million years, from 248 million years ago to 65 million years ago. It was preceded by the Paleozoic era, during which life began to take shape, and was followed by the Cenozoic Era, in which we live.

The Mesozoic Era is divided into three distinct time periods:

  • The Triassic Period – 248 million to 206 million years ago
  • The Jurassic Period – 206 million to 146 million years ago
  • The Cretaceous Period – 146 million to 65 million years ago

During the Mesozoic Era, mountains rose, climates shifted, and life reshaped itself multiple times.

Triassic period

Fossil of a pterosaur
Credit: AKKHARAT JARUSILAWONG/ Shutterstock

The first period of the Mesozoic era was the Triassic period. During this time, all the continents were still connected in one giant super continent, known as Pangaea. Temperatures were warmer and there were no polar ice caps.

The oceans teemed with life during this period. Turtles and fish were common, and the corals developed alongside mollusks and ammonites. Large marine reptiles were present as well, such as the plesiosaurus and ichthyosaurus.

On land, early dinosaurs and mammals evolved, and the first flying reptiles, the pterosaurs, took to the skies. There were no flowering plants or grass present during the Triassic period, but cycads, ferns and ginkgoes grew near water sources such as rivers or streams. Small forests of conifers grew in some parts of Pangaea, but for the most part, inland areas were arid deserts with little or no plant or animal life.

Jurassic period

Illustration of Brachiosaurs
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The Triassic period came to an end with a mass extinction that wiped out over 90 percent of the species on Earth. The animals that survived this event began to repopulate the planet and usher in the Jurassic period.

The Jurassic period was marked by the slow break-up of Pangaea into two smaller landmasses known as Laurasia and Gondwana. When the supercontinent split, new mountains arose in the sea, pushing the sea level up and creating a much wetter, more humid environment.

Ferns and mosses covered much of the ground while the small coniferous forest of the Triassic period expanded to cover wide swaths of the two continents.

Giant dinosaurs ruled the land, the largest of which was the plant-eating Brachiosaurs, which scientists believe could grow to be 80 feet long and 50 feet tall. These large herbivores were hunted by massive carnivores such as the Allosaurus.

The Jurassic period also saw the first birds diverge from the reptile family, and the Archaeopteryx flew above these massive dinosaurs.

Cretaceous period

Skeleton of a Tyrannosaurus Rex
Credit: DavidHCoder/ iStock

During the Cretaceous period, the continents continued to drift apart and end in the locations that we know them today. The climate became both wetter and cooler, resulting in the emergence of the polar ice caps and setting the stage for the glaciers that covered large parts of North America, Europe, and Asia in the following era.

The drifting continents resulted in increased specialization and many new types of dinosaurs. Triceratops and Iguanodon traveled in herds, feasting on the ancestors of the flowers, herbs and broad-leaved trees that populate Earth today.

These massive plant-eating animals were hunted by the famous Tyrannosaurus Rex. Snakes first developed during this time period, as well as crocodiles and turtles. Insects and pterosaurs flew in the air, and the first mammals scurried across the ground.

Despite the proliferation of life during this period, another mass extinction followed a natural disaster at the end of the Cretaceous period. While both reptiles and mammals survived in small numbers, the age of the dinosaurs came to an end.

What’s next?

Earth as viewed from space
Credit: dem10/ iStock

In light of this vast history, do you ever wonder what lies ahead for both Earth and us?