Thursday, December 18, 2008

The Mesozoic : The age of dinosaurs

The breakup of Pangea

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 dinosours (as well as the Mesozoic). The Mesozoic era is divided into three geologic periods;
  • Triassic (245-208 m.a)
  • Jurassic (208-146 m.a)
  • Cretaceous (146-65 m.a)
The Mesozoic was the time of the beginning of the breakup of Pangea about 225-200 m.a, eventually fragmenting that supercontinent into the modern continents that what we have today. This break had profound consequences for living things, as had the earlier formation of Pangea 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 advent 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 cycadeiods, conifers and gingkgoes. Flowering plants finally appreared about 140 m.a and have risen to 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 anf flying reptiles and ammonites. The causes of this extinction have long been speculated on and are not presently conclusively settled.

1 comment: