The Carboniferous period is a geologic period that extends from 359 to 299 million years ago. It gets its name from the huge oil and gas deposits left by decaying plant matter throughout this period. The Carboniferous, about 60 million years in duration, is among the longest of the geologic periods, exceeded in length by only the 80 million-year-long Cretaceous.
The Carboniferous is the first entire period during which there was abundant terrestrial life, including numerous plants, arthropods, and amphibians. The earliest sauropsids (reptiles) and synapsids (ancestors of mammals) evolved during the middle of the Carboniferous, about 420 million years ago. Both of them resembled small lizards in appearance. These species would fossilize when they got trapped in decaying tree stumps and couldn't find their way out.
The bark fiber lignin first evolved just before the Carboniferous. These early trees make such extensive use of bark, that the "bark" was actually most of the tree, making up 80-95% of the tree's volume, with traditional wood making up the rest. It is thought that the large carbon deposits created during the Carboniferous (which fueled the Industrial Revolution) were from two causes — first, that bacteria and animals capable of effectively breaking down lignin hadn't evolved yet, and extensive low-lying forests and swamps from low sea levels during the middle of the period.
Although numerous diverse amphibians existed during the beginning of the period, including amphibians larger than men, terrestrial fauna was mostly dominated by arthropods such as insects. The oxygen levels were so great during the Carboniferous that arthropods could grow to gigantic sizes. Two of the most spectacular examples were the 0.3–2.6 m (1–8.5 feet) myriapod (relative of millipedes and centipedes) Arthropleura, the largest terrestrial invertebrate ever, and the griffinflies, order Protodonata (relatives of dragonflies), with wingspans up to 75 cm (2.5 feet), the largest flying invertebrates ever. Arthropleura had a mixed diet that would have included a ton of plants a year, while griffinflies were predators, eating other insects and even small amphibians, in a reversal of modern species roles.
The shallow oceans were populated by a variety of fish and invertebrate species, especially brachiopods (a phyla of filter-feeders that superficially resemble bivalves) and crinoids (echinoderms called sea lilies). The deep seas of the Devonian disappeared as the poles glaciated and water was withdrawn from the oceans. Marine life was recovering from a 15-million-year-long series of extinctions that wiped out about three-quarters of marine species, including important fish groups like placoderms. During the middle of the Carboniferous, there was another minor extinction event. Like the Permian after it, the Carboniferous was not a great time for marine genera, and much of the action was happening on the land.