Overview and Definition of the Mesozoic Era

The Mesozoic Era is probably the one that people know the best. This has been labeled the “Time of the Dinosaurs”, or the “Time of the Reptiles.”

Mesozoic means “middle life” and comes from the Greek “meso” meaning “between” and zoon” meaning “animal” or “living being.” John Phillips labeled this time period.

This era is broken down into three time periods: the Cretaceous which occurred between 145 and 65 million years ago; the Jurassic which occurred between 145 to 200 million years ago; and the Triassic which occurred between 200 to 250 million years ago.

During the Mesozoic, the Earth’s climate was warmer than it is now. It experienced milder seasons, higher sea levels and no polar ice. This was also a time of great tectonic movement and climate change.

Due to the Permian Extinction, oxygen levels were low at the beginning of the Mesozoic. They fell even lower by the end of the Triassic, which caused more extinction. The level of oxygen did climb during the Jurassic and Cretaceous periods to reach levels near today’s Carbon dioxide began this era at very high levels but they also dropped to reach levels near todays.

The Mesozoic era was the beginning of the breaking apart of Pangea. Before this time, during the late Paleozoic, all the land masses formed one continent, Pangea. During the Mesozoic, Pangea gradually broke apart to form, what is known today as, North America, Africa and India. As the continents moved, the Atlantic began to expand and sea levels were low. They gradually rose to create shallow seas over many of the land masses.

During the Triassic time the climate was dry, leading to arid landmasses. This changed during the Jurassic as warm and moist climates prevailed. As time changed to the Cretaceous, climates became cooler and glaciers began to grow at the poles. Even with the glaciers, the carbon dioxide levels created a warm climate.

There are not very many coal deposits from the early Mesozoic. This is due to the little amount of plant life on the Earth during this time. Plants increased in number when the carbon dioxide levels rose before they fell again.

Some of the Mesozoic plants carried over from the Paleozoic Era. They would adapt to their new environment, as needed, and survived. Flowering plants, or angiosperms, first made an appearance during this time. They were able to aid in the dietary needs of animals and they provided habitats. Angiosperms would make up about 90 percent of all plants by the end of the Mesozoic.

The Mesozoic is probably best known as the Age of the Dinosaurs. The first dinosaurs appeared late in the Triassic period and continued throughout the future periods. Mammals also appeared in the late Triassic; however the dinosaurs would be the larger group in numbers. During the time of the mammals, three new reproductive methods developed: placental mammals, marsupials, and monotremes. Along with dinosaurs and mammals, pterosaurs developed. This group formed numerous species and their population flourished by the Cretaceous. There was also, at this time, the earliest birds.

Large animals also began forming in the oceans, including pelsiosaurs, ichthosaurs, and giant turtles. Along with these came the development of coral reefs in the warmer waters.

Another group of animals which came to the forefront was the insects. As more angiosperms developed, insects began to adapt. Some of the insects that were formed or adapted were ants, flies and grasshoppers.

The Permian Extinction occurred before the Triassic period. During that time 90 to 95 percent of all marine species and 70 percent of all terrestrial vertebrates were wiped out. The Cretaceous-Tertiary extinction marked the end of the Mesozoic. At this event about 50 percent of all genera became extinct.

Even though this era is called the Age of the Dinosaur, it is clear that terrific changes occurred in other areas as well. Some of these changes are with us today.