Mesozoic Era

The Mesozoic Era is known as the “Age of Reptiles”. Many reptiles were able to survive in the environment created at the end of the Permian era. Crocodiles, snakes, lizards, turtles, and the dinosaurs emerged during the Mesozoic era.   The climate was so warm and tropical that glaciers did not form during this era. The Mesozoic Era is divided into three periods: Triassic, Jurassic, and Cretaceous.

The first mammals evolved during the Triassic period.  These warm blooded animals resemble small rodents.  Dinosaurs evolved from reptiles. They were most likely the fiercest and dominant animals to roam the Earth.  Their ability to lay amniotic eggs on dry land instead of in water like amphibians was a great advantage for dinosaurs. Amniotic eggs contain food and water which allow dinosaurs to leave their eggs as they roam forests full of conifers and cycads. Fossil records indicate that these gymnosperms, woody cone-bearing plants, were very common during the Triassic period. Invertebrates called ammonites, a type of shellfish, are Mesozoic index fossils.

Dinosaurs continued to evolve during the Jurassic period. “Lizard-hipped” and “bird-hipped” dinosaurs emerged. The Brontosaurus was a type of “lizard-hipped” dinosaur. The Stegosaurus was a type of “bird-hipped” dinosaur. Both dinosaurs were herbivores. Reptiles that could fly also evolved during the Jurassic period. The pterosaurs had skin covered wings whereas some dinosaurs had feathers. The Archaeopteryx was one of the early ancestors of birds that exist today. The fossil remains of the small feathered dinosaur indicated that it had reptilian teeth, claws on its wings, and a tail.

The Tyrannosaurus rex was one of the major dinosaurs to dominate the Cretaceous period. It had huge jaws, sharp teeth, and stood up to 6 meters tall. The horned Triceratops, the enormous Apatosaurus, and the duck-billed Hadrosaurs were some other common Cretaceous dinosaurs. The earliest flowering plants, angiosperms, evolved during the Cretaceous period. Maples, oaks, magnolias, and willows were some of the most common types of trees during this period.


A mass extinction occurred at the end of the Cretaceous period. All of the dinosaurs, ammonites, and many large land animals became extinct.  The impact hypothesis suggests that a large meteorite struck the Earth.  The impact of the collision created enough dust to block out the sun’s rays for many years.  Dinosaurs starve and perish when plants die. Scientists have found traces of iridium within the Earth’s crust.  The concentration of iridium is much greater in meteorites compared to Earth’s rocks.  Another hypothesis for the extinction of dinosaurs is volcanic activity.  The movement of tectonic plates may have led to the drastic change in the climate and environment.

There have been several mass extinctions throughout the history of the Earth. One occurred at the end of the Paleozoic Era when nearly 95% of plant and animal life in the seas disappeared. The most famous mass extinction probably happened 65 million years ago when the dinosaurs disappeared. Many other plants and animals became extinct at the same time. Whatever triggered the extinction of the dinosaurs also caused the death of nearly 70% of all the other species on Earth.