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The name "Carboniferous" reflects the most famous attribute of the Carboniferous period: the massive swamps that cooked, over tens of millions of years, into today's vast reserves of coal and natural gas. However, the Carboniferous period (350 to 300 million years ago) was also notable for the appearance of new terrestrial vertebrates, including the very first amphibians and lizards. The Carboniferous was the second-to-last period of the Paleozoic Era (542-250 million years ago), preceded by the Cambrian, Ordovician, Silurian, and Devonian periods and succeeded by the Permian period.
Climate and geography. The global climate of the Carboniferous period was intimately linked with its geography. During the course of the preceding Devonian period, the northern supercontinent of Euramerica merged with the southern supercontinent of Gondwana, producing the enormous super-supercontinent Pangea, which occupied much of the southern hemisphere during the ensuing Carboniferous. This had a pronounced effect on air and water circulation patterns, with the result that a large portion of southern Pangea wound up covered by glaciers, and there was a general global cooling trend (which, however, didn't have much effect on the coal swamps that covered Pangea's more temperate regions). Oxygen made up a much higher percentage of the earth's atmosphere than it does today, fueling the growth of terrestrial megafauna, including dog-sized insects.
Terrestrial Life During the Carboniferous Period
Amphibians. Our understanding of life during the Carboniferous period is complicated by "Romer's Gap," a 15-million-year stretch of time (from 360 to 345 million years ago) that has yielded virtually no vertebrate fossils. What we do know, however, is that by the end of this gap, the very first tetrapods of the late Devonian period, themselves only recently evolved from lobe-finned fish, had lost their internal gills and were well on their way toward becoming true amphibians. By the late Carboniferous, amphibians were represented by such important genera as Amphibamus and Phlegethontia, which (like modern amphibians) needed to lay their eggs in water and keep their skin moist, and thus couldn't venture too far onto dry land.
Reptiles. The most important trait that distinguishes reptiles from amphibians is their reproductive system: the shelled eggs of reptiles are better able to withstand dry conditions, and thus don't need to be laid in water or moist ground. The evolution of reptiles was spurred by the increasingly cold, dry climate of the late Carboniferous period; one of the earliest reptiles yet identified, Hylonomus, appeared about 315 million years ago, and the giant (almost 10 feet long) Ophiacodon only a few million years later. By the end of the Carboniferous, reptiles had migrated well toward the interior of Pangea; these early pioneers went on to spawn the archosaurs, pelycosaurs, and therapsids of the ensuing Permian period (it was the archosaurs that went on to spawn the first dinosaurs nearly a hundred million years later).
Invertebrates. As noted above, the earth's atmosphere contained an unusually high percentage of oxygen during the late Carboniferous period, peaking at an astounding 35 percent. This surplus was especially beneficial to terrestrial invertebrates, such as insects, which breathe via the diffusion of air through their exoskeletons, rather than with the aid of lungs or gills. The Carboniferous was the heyday of the giant dragonfly Megalneura, the wingspan of which measured up to two and a half feet, as well as the giant millipede Arthropleura, which attained lengths of almost 10 feet!
Marine Life During the Carboniferous Period
With the extinction of the distinctive placoderms (armored fish) at the end of the Devonian period, the Carboniferous isn't especially well-known for its marine life, except insofar as some genera of lobe-finned fish were closely related to the very first tetrapods and amphibians that invaded dry land. Falcatus, a close relative of Stethacanthus, is probably the best-known Carboniferous shark, along with the much bigger Edestus, which is known primarily by its teeth. As in preceding geologic periods, small invertebrates like corals, crinoids, and arthropods were plentiful in the Carboniferous seas.
Plant Life During the Carboniferous Period
The dry, cold conditions of the late Carboniferous period weren't especially hospitable to plants--which still didn't prevent these hardy organisms from colonizing every available ecosystem on dry land. The Carboniferous witnessed the very first plants with seeds, as well as bizarre genera like the 100-foot-tall club moss Lepidodendron and the slightly smaller Sigillaria. The most important plants of the Carboniferous period were the ones inhabiting the large belt of carbon-rich "coal swamps" around the equator, which were later compressed by millions of years of heat and pressure into the vast coal deposits we use for fuel today.