The Mesozoic Era

The Mesozoic era also ended with a mass extinction event known as the Cretaceous-Paleogene Extinction Event (with Cretaceous-Paleogene sometimes being shortened to K-Pg or K-T). This extinction event was caused by the impact of a large asteroid around 10km in diameter in the Yucatán peninsula in Mexico, leading to the loss of around 75% of all plant and animal species, including all non-avian dinosaurs. It marked the end of the Mesozoic era and the beginning of the Cenozoic era (the current era). Click here to read our full article on the End-Cretaceous extinction.

Earth during the Mesozoic era looked very different to today, and changed drastically throughout the era. By the beginning of the Triassic period, earlier continents had collided together to form one large, C-shaped supercontinent called Pangea. This was surrounded by one large superocean called Panthalassa.

Around 200 million years ago, at the end of the Triassic/beginning of the Jurassic, Pangea began to break apart into two large continents - Laurasia in the North and Gondwana in the South. These continued to break apart throughout the Jurassic and Cretaceous periods, and by the end of the Cretaceous period they looked somewhat close to the continents we know today - but not in their current positions (this occurred well after the end of the Mesozoic era). As the continents moved apart, plants and animal diversity increased as groups in different areas evolved independently. Dinosaurs across the world during the Triassic and early Jurassic were much more similar than during the Cretaceous period.

Click here to visit the "Ancient Earth" tool which gives you a rotating view of Earth at different times. You can even enter a city/town name to see where you would have lived on Pangea!

During the Triassic, forests were dominated by ferns, ginkgos and conifers - large non-flowering, cone-producing plants with needle-like leaves. Cycads (palm-like plants) appeared towards the end of the Triassic and flourished during the Jurassic - so much that the Jurassic era is sometimes referred to as the "Age of the Cycads". Horsetails were also common undergrowth plants.

Angiosperms (flowering plants) appeared and began to diversify during the Cretaceous, and dominated the landscape by the mid-to-late Cretaceous. Many modern insect groups also evolved at this time. Recent evidence shows that grasses evolved during the Cretaceous, though it is believed that they did not become widespread until well after the end of the Mesozoic.

During the Triassic, the land was dominated by reptiles. The first dinosaurs and mammals also appeared during this time along with ancestral forms of many modern groups including crocodiles, turtles, and lizards. The ocean was teeming with mollusks, corals, urchins, and ammonites (spiral-shelled cephalopods, an extremely successful group that unfortunately went extinct at the end of the Cretaceous period). At the top of the marine food chain were giant marine reptiles such as the long-necked plesiosaurs and dolphin-shaped ichthyosaurs, which preyed on fish and cephalopods like squid. Pterosaurs, the famous flying reptiles, evolved during the late Triassic.

During the Jurassic, dinosaurs flourished and diversified to include huge plant-eaters like Brachiosaurus and Diplodocus, and large carnivores like Allosaurus. The first birds evolved, sharing the skies with Pterosaurs, along with small groups of mammals about the size of a rat. Insects were abundant and included early ancestors of ants, dragonflies, lacewings, grasshoppers, crickets and beetles. Ocean life also flourished and included ichthyosaurs, plesiosaurs, sharks, crocodiles, cephalopods (early forms of squid), ammonites, rays, snails and mollusks. There were also huge numbers of blood-red plankton.

Dinosaurs continued to evolve and diversify during the Cretaceous, and reached their peak sizes. Large sauropods, called titanosaurs, included Argentinosaurus (around 35 m long and weighing 80 tons or more) and Patagotitan (around 30 m long). Large carnivores also appeared including the famous Tyrannosaurus Rex and Giganotosaurus. Bees and butterflies evolved along with snakes. Mammals continued to evolve and diversify and included groups like marsupials and placental mammals. Most of these were small - about the size of modern rabbits - unaware that they would come to dominate the Earth after the mass extinction at the end of the Cretaceous. Towards the end of the Cretaceous period, the oceans were dominated by Mosasaurs after the ichthyosaurs and plesiosaurs went extinct.