The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359.2 million years ago, to the beginning of the Permian period, about 299 million years ago. As with most older geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by 5–10 million years.

The Carboniferous is named for the extensive coal beds of that age found in Western Europe. The first third of the Carboniferous is called the Mississippian epoch, and the remainder is called the Pennsylvanian. Conifer trees were introduced in this important and well-known time period.

During this period snakes emerged as well as salamander type amphibians.  Large amphibians roamed the lands now and fresh water fish and sharks were now in abundance. Near the end of this period the first reptiles appeared on land.

A global drop in sea level at the end of the Devonian reversed early in the Carboniferous; this created the widespread epicontinental seas and carbonate depostion of the Mississippian. There was also a drop in south polar temperatures; southern Gondwanaland was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost glaciers.

In the oceans the most important groups are the foraminifera, corals, bryozoa, brachiopods, ammonoids, echinoderms (especially crinoids), and Chondrichthyes (sharks and their relatives).

Many fish inhabited the Carboniferous seas; predominantly Elasmobranchs (sharks and their relatives). These included some, like Psammodus, with crushing pavement-like teeth adapted for grinding the shells of brachiopods, crustaceans, and other marine organisms. Other sharks had piercing teeth, such as the Symmoriida; some, the petalodonts, had peculiar cycloid cutting teeth. Most of the sharks were marine, but the Xenacanthida invaded fresh waters of the coal swamps.

Among the bony fish, the Palaeonisciformes found in coastal waters also appear to have migrated to rivers. Sarcopterygian fish were also prominent, and one group, the Rhizodonts, reached very large size.

Most species of Carboniferous marine fish have been described largely from teeth, fin spines and dermal ossicles, with smaller freshwater fish preserved whole.

Freshwater fishes were abundant, and include the genera Ctenodus, Uronemus, Acanthodes, Cheirodus, and Gyracanthus.

Fossil remains of air-breathing insects, myriapods and arachnids are known from the late Carboniferous, but so far not from the early Carboniferous. Their diversity when they do appear however show that these arthropods were both well developed and numerous.

Among the insect groups are the Syntonopterodea (relatives of present-day mayflies), the abundant and often large sap-sucking Palaeodictyopteroidea, the huge predatory Protodonata (griffinflies), the diverse herbivorous "Protorthoptera", and numerous basal Dictyoptera (ancestors of cockroaches).

Many insects have been obtained from the coalfields of Saarbruck and Commentry, and from the hollow trunks of fossil trees in Nova Scotia. Some British coalfields have yielded good specimens: Archaeoptitus, from the Derbyshire coalfield, had a spread of wing extending to more 35 cm; some specimens (Brodia) still exhibit traces of brilliant wing colours. In the Nova Scotian tree trunks land snails (Archaeozonites, Dendropupa) have been found.

Carboniferous amphibians were diverse and common by the middle of the period, more so than they are today; some were as long as 6 metres, and those fully terrestrial as adults had scaly skin. They included a number of basal tetrapod groups classified in early books under the Labyrinthodontia. These had long bodies, a head covered with bony plates and generally weak or undeveloped limbs.

The largest were over 2 metres long. They were accompanied by an assemblage of smaller amphibians included under the Lepospondyli, often only about 15cm long. Some Carboniferous amphibians were aquatic and lived in rivers (Loxomma, Eogyrinus, Proterogyrinus); others may have been semi-aquatic (Ophiderpeton, Amphibamus) or terrestrial (Dendrerpeton, Hyloplesion, Tuditanus, Anthracosaurus).

One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. These included the earliest Sauropsid reptiles (Hylonomus), and the earliest known Synapsida (Archaeothyris).

These small lizard-like animals quickly gave rise to many descendants. The amniote egg allowed these ancestors of all later birds, mammals and reptiles to reproduce on land by preventing the desiccation, or drying-out, of the embryo inside.

By the end of the Carboniferous period, the reptiles had already diversified into a number of groups, including protorothyridids, captorhinids, aeroscelids, and several families of pelycosaurs.