The History of Life on Earth

The Carboniferous Period is a geologic time period that took place between 360 to 286 million years ago. The Carboniferous Period is named after the rich coal deposits that are present in rock layers from this time period. The Age of Amphibians The Carboniferous Period is also known as the Age of Amphibians. It is the fifth of six geologic periods that together make up the Paleozoic Era. The Carboniferous Period is preceded by the Devonian Period and followed by the Permian Period. The climate of the Carboniferous Period was quite uniform (there were no distinct seasons) and it was more humid and tropical than our present-day climate. The plant life of the Carboniferous Period resembled modern tropical plants. The Carboniferous Period was a time when the first of many animal groups evolved: the first true bony fishes, the first sharks, the first amphibians, and the first amniotes. The appearance of the amniotes is evolutionarily significant because of the amniotic egg, the defining characteristic of amniotes, enabled the ancestors of modern reptiles, birds, and mammals to reproduce on land and colonize terrestrial habitats that were previously uninhabited by vertebrates.   Mountain Building The Carboniferous Period was a time of mountain building when the collision of the Laurussian and Gondwanaland land masses formed the supercontinent Pangea. This collision resulted in the uplifting of mountain ranges such as the Appalachian Mountains, the Hercynian Mountains, and the Ural Mountains. During the Carboniferous Period, the vast oceans that covered the earth often flooded the continents, creating warm, shallow seas. It was during this time that the armored fish that had been abundant in the Devonian Period became extinct and were replaced by more modern fishes. As the Carboniferous Period progressed, the uplifting of landmasses resulted in an increase in erosion and the building of floodplains and river deltas. The increased freshwater habitat meant that some marine organisms such as corals and crinoids died out. New species that were adapted to the reduced salinity of these waters evolved, such as freshwater clams, gastropods, sharks, and bony fish. Vast Swamp Forests Freshwater wetlands increased and formed vast swamp forests. Fossil remains show that air-breathing insects, arachnids, and myriapods were present during the Late Carboniferous. The seas were dominated by sharks and their relatives and it was during this period that sharks underwent much diversification. Arid Environments   Land snails first appeared and dragonflies and mayflies diversified. As the land habitats dried, animals evolved ways of adapting to the arid environments. The amniotic egg enabled early tetrapods to break free of the bonds to aquatic habitats for reproduction. The earliest known amniote is Hylonomus, a lizard-like creature with a strong jaw and slender limbs. Early tetrapods diversified significantly during the Carboniferous Period. These included the temnospondyls and the anthracosaurs. Finally, the first diapsids and synapsids evolved during the Carboniferous. By the middle the Carboniferous Period, tetrapods were common and quite diverse. The varied in size (some measuring up to 20 feet in length). As the climate grew cooler and drier, the evolution of amphibians slowed and the appearance of amniotes lead to a new evolutionary path.