Biology : Semester II


IntroductionSection 1 | Section 2 | Section 3 | Section 4 | Section 5

  Section Four:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 | Part 11

Biology : The Age of Dinosaurs : Part One

The Mesozoic Era: The Age of Dinosaurs

The Mesozoic era covers the time between two great extinctions: the Permian extinction that closed the Paleozoic era, and the Cretaceous extinction that ended the reign of the dinosaurs (as well as the Mesozoic era). The Mesozoic era is divided into three geologic periods, the Triassic ( 245-208 million years ago), the Jurassic (208-146 million years ago), and the Cretaceous (146-65 million years ago).

During the Mesozoic the breakup of Pangaea began about 225-200 million years ago. Eventually the supercontinent would fragment into the modern continents. This breakup had profound consequences for living things, as had the earlier formation of Pangaea during the later Paleozoic. The breakup continues today!

Mesozoic seas saw a rise and spread of another iteration of the cephalopods, the ceratites, eventually to be replaced by the ammonites. Coral reefs, which had been decimated by the Carboniferous extinction returned to prominence with the evolution of new groups of reef-building animals and algae. Modern bony fish evolved and began to compete with the ammonites as swimming predators.

Terrestrial animals saw the rise of major groups of tetrapods: dinosaurs and mammals and the later evolution of birds. Tetrapods took to new environments in the air as well as a secondary return to the waters. Forests took on an increasingly modern look, with the evolution of cycads and cycadeoids, conifers and ginkgoes. Flowering plants finally appeared about 140 million years ago and have since become the dominant floral component of many areas of the planet.

The Mesozoic ended with the great mass extinction that eliminated nearly 75% of all species, including dinosaurs, swimming and flying reptiles, and ammonites. The causes of this extinction have long been speculated on and are not presently conclusively settled.

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