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The Mesozoic begins: the Triassic period

The Mesozoic begins: the Triassic period


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This intermediate age in the geological history of the Earth lasted about 185 million years. The Mesozoic or Secondary Era is the time of terrible lizards, dinosaurs.

The Mesozoic began 251 million years ago and ended 66 million years ago. At the beginning of this geological era all the continents or islands of the previous period (Permian, in the Paleozoic Era) had gathered in a single gigantic continent that we call Pangea, that is, all the land.

There were no major orogenic movements. Pangea fragmented and the continental masses moved slowly towards their current positions. The main folds occurred in the western slope of America, the Rocky Mountains in the north and the Andes in the South.

The weather, which remained very warm, favored the evolution and diversity of life. The Earth was dominated by huge conifers, so its appearance, from space, should be much greener than today. Among the animals they appeared and, in the end, the famous ones were extinguished dinosaurs.

Large groups of animals such as trilobites, graptolites and armored fish disappeared during the Mesozoic Era. Vertebrates were developed, especially reptiles, so the Secondary Era is also called the Age of Reptiles or Age of Dinosaurs. Mammals, birds and angiosperm plants, with showy flowers, also appeared.

He Mesozoic It is divided into three periods: Triassic, Jurassic and Cretaceous. On this page we focus on the first.

The Triassic: dinosaurs arrive

This geological period extended from about 251 to 201 million years ago. Its beginning and its end coincide with two very important extinctions: the mass extinction of the Permian-Triassic and that of the Triassic-Jurassic.

The Triassic is characterized primarily by the appearance of the famous dinosaurs. The first were small, bipeds and carnivores. Throughout the period they diversified, coming to dominate the entire planet and cause the extinction of some more primitive animals.

The continents Africa and South America were together, with a magmatic activity on the border of the two continents. Throughout the Triassic the supercontinent Pangea began to dismember. As the earth's crust stretched, large blocks sank, creating basins.

The weather was warm and somewhat drier, which favored the formation of deserts. In addition, as Pangea was very extensive, the interior areas were far from the marine influence and, therefore, had well marked seasons, with icy winters and scorching summers.

In the driest north, Laurasia, the evergreen trees, conifers and ginkgos dominated. In the somewhat more humid south, Gondwana, large forests of gigantic ferns and huge conifers formed.

Among the invertebrates, the insects were represented by the first species to experience a complete metamorphosis, going through the larva, pupa and adult phases. In the seas there were belemnites similar to squid, ammonites, crustaceans, molluscs, bivalves, gastropods and corals.

The Triassic marks the appearance of the first true mammals, but little is known about their physiology. Some small reptiles, such as pterosaurs (winged lizards in Greek), they developed membranes in their legs with which they learned to plan increasing distances. They had hot blood and a body covered with hair. And no, they were not dinosaurs.

75% of the invertebrate species disappeared in a mass extinction at the end of the Cretaceous, the last of the three Mesozoic periods that, with the Jurassic, we will see on the next page.

Discover more:
• The Mesozoic Era according to Wikipedia
• Origin and evolution of mammals
• The mass extinction of the Triassic-Jurassic


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The Paleozoic: Devonian, Carboniferous, PermianThe Mesozoic: Jurassic and Cretaceous