The Carboniferous is a time period in Earth's history that is part of the Paleozoic era. It lasted about 60 million years, from the end of the Devonian period, 358.86 million years ago, to the start of the Permian period, 298.9 million years ago. It is the fifth period of the Phanerozoic eon. In North America, the Carboniferous is often divided into two separate periods: the earlier Mississippian and the later Pennsylvanian.
The name "Carboniferous" means "coal-bearing," from the Latin words carbō ("coal") and ferō ("to carry"). It refers to the many coal beds that formed during this time. The term was first used in 1822 by geologists William Conybeare and William Phillips, who studied rock layers in Britain.
During the Carboniferous, both land animals and plants were well developed. Four-limbed vertebrates, which evolved from lobe-finned fish in the previous Devonian period, developed five fingers and toes during this time. This period is sometimes called the Age of Amphibians because early amphibians, such as temnospondyls, became the main land vertebrates. Amniotes, including synapsids (a group that includes modern mammals) and sauropsids (a group that includes modern reptiles and birds), first appeared in the late Carboniferous. Insects, especially flying insects, and other land arthropods, such as arachnids and myriapods, also experienced major evolutionary changes. Large forests and swamps covered much of the land, which later turned into the coal beds seen in rock layers today.
The second half of the Carboniferous saw ice ages, low sea levels, and mountain formation as continents collided to form Pangaea. A minor extinction event, called the Carboniferous rainforest collapse, happened at the end of the period due to climate changes. Atmospheric oxygen levels were not always high throughout the Carboniferous. They started low and reached as high as 25–30% during the period.
Etymology and history
The development of a Carboniferous time-based rock layer scale began in the late 1700s. The word "Carboniferous" was first used as an adjective by Irish geologist Richard Kirwan in 1799. Later, in 1811, John Farey Sr. used it in a heading titled "Coal-measures or Carboniferous Strata." Originally, four rock layers were linked to the Carboniferous, listed from bottom to top: Old Red Sandstone, Carboniferous Limestone, Millstone Grit, and Coal Measures. In 1822, William Conybeare and William Phillips grouped these layers into a formal Carboniferous unit. In 1835, Phillips named this group the Carboniferous System. Later, the Old Red Sandstone was reclassified as part of the Devonian period.
Similar rock layer patterns in the British Isles and Western Europe led to a shared European timescale. The Carboniferous System was divided into two main parts: the lower Dinantian, where limestone was deposited, and the upper Silesian, where sandstone and other rock types were formed. The Dinantian was further split into the Tournaisian and Viséan stages. The Silesian was divided into the Namurian, Westphalian, and Stephanian stages. The Tournaisian stage matches the length of the International Commission on Stratigraphy (ICS) stage, but the Viséan stage is longer, extending into the lower Serpukhovian.
North American geologists recognized similar rock layers but divided them into two systems instead of one. These systems are the lower Mississippian, rich in limestone, and the upper Pennsylvanian, which includes sandstone and coal layers. In 1953, the United States Geological Survey officially recognized these two systems. In Russia, British and Russian geologists in the 1840s divided the Carboniferous into Lower, Middle, and Upper series based on Russian rock layers. By the 1890s, these became the Dinantian, Moscovian, and Uralian stages. The Serpukhovian was later proposed as part of the Lower Carboniferous, and the Upper Carboniferous was split into the Moscovian and Gzhelian stages. The Bashkirian stage was added in 1934.
In 1975, the ICS officially approved the Carboniferous System, including the Mississippian and Pennsylvanian subsystems from North America, the Tournaisian and Viséan stages from Western Europe, and the Serpukhovian, Bashkirian, Moscovian, Kasimovian, and Gzhelian stages from Russia. After the Carboniferous System was formally approved, terms like Dinantian, Silesian, Namurian, Westphalian, and Stephanian were no longer used. However, the latter three terms are still commonly used in Western Europe.
Geology
Stages can be defined globally or regionally. For global stratigraphic correlation, the ICS approve global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) that marks the lower boundary of the stage. Only the boundaries of the Carboniferous System and three stage bases are defined by global stratotype sections and points because of the complexity of the geology. The ICS subdivisions from youngest to oldest are as follows:
The Mississippian was proposed by Alexander Winchell in 1870 and named after the widespread exposure of lower Carboniferous limestone in the upper Mississippi River valley. During the Mississippian, a marine connection existed between the Paleo-Tethys and Panthalassa through the Rheic Ocean, leading to the global spread of marine life and allowing widespread correlations using marine biostratigraphy. However, few Mississippian volcanic rocks exist, making radiometric dating difficult.
The Tournaisian Stage is named after the Belgian city of Tournai. It was introduced in scientific literature by Belgian geologist André Dumont in 1832. The GSSP for the base of the Carboniferous System, Mississippian Subsystem, and Tournaisian Stage is located at the La Serre section in Montagne Noire, southern France. It is defined by the first appearance of the conodont Siphonodella sulcata in the evolutionary lineage from Siphonodella praesulcata to Siphonodella sulcata. This was approved by the ICS in 1990. However, in 2006, further study found Siphonodella sulcata below the boundary and Siphonodella praesulcata and Siphonodella sulcata together above a local unconformity. This means the evolution of one species to the other, which defines the boundary, is not clearly visible at the La Serre site, making precise correlation difficult.
The Viséan Stage was introduced by André Dumont in 1832 and named after the city of Visé, Liège Province, Belgium. In 1967, the base of the Viséan was officially defined as the first black limestone in the Leffe facies at the Bastion Section in the Dinant Basin. These changes are now thought to be caused by environmental factors rather than evolutionary changes, so this location is not used for the GSSP. Instead, the GSSP for the base of the Viséan is located in Bed 83 of the sequence of dark grey limestones and shales at the Pengchong section, Guangxi, southern China. It is defined by the first appearance of the fusulinid Eoparastaffella simplex in the evolutionary lineage Eoparastaffella ovalis–Eoparastaffella simplex and was approved in 2009.
The Serpukhovian Stage was proposed in 1890 by Russian stratigrapher Sergei Nikitin. It is named after the city of Serpukhov, near Moscow, and currently lacks a defined GSSP. The Viséan-Serpukhovian boundary coincides with a major period of glaciation. The resulting sea level fall and climate changes caused marine basins to become disconnected and led to the isolation of marine life along the Russian margin. This means changes in marine life were environmental rather than evolutionary, making wider correlation difficult. Work is ongoing in the Urals and Nashui, Guizhou Province, southwestern China, to find a suitable site for the GSSP. The proposed definition for the base of the Serpukhovian is the first appearance of the conodont Lochriea ziegleri.
The Pennsylvanian was proposed by J.J. Stevenson in 1888 and named after the widespread coal-rich strata found across the state of Pennsylvania. The closure of the Rheic Ocean and the formation of Pangea during the Pennsylvanian, along with widespread glaciation across Gondwana, caused major climate and sea level changes. These changes limited marine life to specific geographic areas, reducing the ability to correlate boundaries globally. Extensive volcanic events linked to the assembly of Pangea made radiometric dating more feasible compared to the Mississippian.
The Bashkirian Stage was proposed by Russian stratigrapher Sofia Semikhatova in 1934 and named after Bashkiria, the former Russian name for the republic of Bashkortostan in the southern Ural Mountains of Russia. The GSSP for the base of the Pennsylvanian Subsystem and Bashkirian Stage is located at Arrow Canyon in Nevada, US, and was approved in 1996. It is defined by the first appearance of the conodont Declinognathodus noduliferus. Arrow Canyon was part of a shallow, tropical seaway stretching from Southern California to Alaska. The boundary is within a cyclothem sequence of transgressive limestones and fine sandstones, and regressive mudstones and brecciated limestones.
The Moscovian Stage is named after shallow marine limestones and colorful clays found around Moscow, Russia. It was first introduced by Sergei Nikitin in 1890. The Moscovian currently lacks a defined GSSP. The fusulinid Aljutovella aljutovica can be used to define the base of the Moscovian across the northern and eastern margins of Pangea, but it is limited in geographic range, making it unsuitable for global correlations. The first appearance of the conodonts Declinognathodus donetzianus or Idiognathoides postsulcatus has been proposed as a boundary marker, with potential sites in the Urals and Nashui, Guizhou Province, southwestern China, being considered.
The Kasimovian is the first stage in the Upper Pennsylvanian. It is named after the Russian city of Kasimov and was originally included in Nikitin’s 1890 definition of the Moscovian. It was first
Palaeogeography
During the Carboniferous period, tectonic plates moved more quickly as the supercontinent Pangea formed. The continents arranged themselves in a nearly circular shape around the opening Paleo-Tethys Ocean, with the large Panthalassic Ocean beyond. Gondwana covered the south polar region. To its northwest was Laurussia. These two continents slowly collided to form the core of Pangea. To the north of Laurussia lay Siberia and Amuria. To the east of Siberia, Kazakhstania, North China, and South China formed the northern edge of the Paleo-Tethys, with Annamia located to the south.
The Central Pangean Mountains formed during the Variscan–Alleghanian–Ouachita mountain-building process. Today, their remains stretch over 10,000 km from the Gulf of Mexico in the west to Turkey in the east. This process happened because of a series of collisions between Laurussia, Gondwana, and the Armorican terrane group (which includes parts of modern-day Central and Western Europe, including Iberia) as the Rheic Ocean closed and Pangea formed. This mountain-building process began in the Middle Devonian and continued into the early Permian.
The Armorican terranes separated from Gondwana during the Late Ordovician. As they moved north, the Rheic Ocean closed in front of them, and they began colliding with southeastern Laurussia in the Middle Devonian. This Variscan mountain-building event involved complex collisions, changes in rock structure, volcanic activity, and large-scale deformation between these terranes and Laurussia, continuing into the Carboniferous.
During the mid-Carboniferous, the South American part of Gondwana collided with Laurussia’s southern edge, causing the Ouachita mountain-building event. Faulting between Laurussia and Gondwana extended east into the Appalachian Mountains, where early changes in the Alleghanian mountain-building event were mostly strike-slip movements. When the West African part of Gondwana collided with Laurussia during the Late Pennsylvanian, compression in the Alleghanian event shifted to the northwest.
The Uralian mountain-building event is a north–south trending folded and thrust belt that forms the western edge of the Central Asian Orogenic Belt. This event began in the Late Devonian and continued, with some pauses, into the Jurassic. From the Late Devonian to early Carboniferous, the Magnitogorsk island arc, located between Kazakhstania and Laurussia in the Ural Ocean, collided with the passive margin of northeastern Laurussia (Baltica craton). The boundary between the island arc and the continent formed the Main Uralian Fault, a major structure over 2,000 km long. The island arc fully attached to Laurussia by the Tournaisian, but subduction of the Ural Ocean continued until the Bashkirian, when the ocean closed and continental collision began. Strike-slip movement along this zone shows the collision was oblique. Deformation continued into the Permian, and during the late Carboniferous and Permian, the region was intruded by granites.
The Laurussian continent formed when Laurentia, Baltica, and Avalonia collided during the Devonian. At the start of the Carboniferous, some models show it near the equator, while others place it further south. Either way, the continent moved northward, reaching low latitudes in the northern hemisphere by the end of the period. Moist air from the Paleo-Tethys Ocean rose over the Central Pangean Mountains, causing heavy rain and creating a tropical wetland environment. Thick coal deposits formed in the cyclothem layers that dominated the Pennsylvanian sedimentary basins linked to the growing mountain-building belts.
Subduction of the Panthalassic oceanic plate along its western edge caused the Antler mountain-building event in the Late Devonian to Early Mississippian. Further north, slab roll-back starting in the Early Mississippian led to the splitting of the Yukon–Tanana terrane and the opening of the Slide Mountain Ocean. Along the northern edge of Laurussia, the collapse of the Late Devonian to Early Mississippian Innuitian mountain-building event led to the formation of the Sverdrup Basin.
Much of Gondwana was located in the southern polar region during the Carboniferous. As the plate moved, the South Pole shifted from southern Africa in the early Carboniferous to eastern Antarctica by the end of the period. Glacial deposits across Gondwana show multiple ice centers and long-distance ice movement. The northern to northeastern edge of Gondwana (northeast Africa, Arabia, India, and northeastern West Australia) was a passive margin along the southern edge of the Paleo-Tethys, with cyclothem deposits including coal swamps in Western Australia during warmer times. The Mexican terranes along the northwestern Gondwana edge were affected by the subduction of the Rheic Ocean but were not impacted by continental collision. They became part of the active Pacific margin. The Moroccan edge experienced widespread dextral strike-slip deformation, volcanic activity, and rock changes linked to the Variscan mountain-building event.
Towards the end of the Carboniferous, extension and rifting along the northern edge of Gondwana caused the Cimmerian terrane to break away during the early Permian, opening the Neo-Tethys Ocean. Along the southeastern and southern edge of Gondwana (eastern Australia and Antarctica), northward subduction of Panthalassa continued. Changes in plate movement led to the early Carboniferous Kanimblan mountain-building event. Volcanic activity from continental arcs continued into the late Carboniferous and connected with the developing proto-Andean subduction zone along the western edge of South America.
Shallow seas covered much of the Siberian craton in the early Carboniferous. As sea levels dropped in the Pennsylvanian and the continent moved north into temperate zones, coal deposits formed in the Kuznetsk Basin. The northwest to eastern edges of Siberia were passive margins along the Mongol-Okhotsk Ocean, with Amuria on the far side. From the mid-Carboniferous, subduction zones with volcanic arcs developed along both edges of the ocean.
The southwestern edge of Siberia was a long-lasting and complex mountain-building region. The Devonian to early Carboniferous Siberian and South Chinese Altai mountain-building complexes formed above an east-dipping subduction zone. Further south, the Zharma-Saur arc developed along the northeastern edge of Kazakhstania. By the late Carboniferous, all these
Climate
The Carboniferous climate was shaped by the Late Paleozoic Ice Age (LPIA), the longest and most widespread cold period in Earth’s history. This ice age lasted from the Late Devonian to the Permian (365 to 253 million years ago). Temperatures began to drop during the late Devonian, with a brief period of ice forming near the end of the Famennian stage and the Devonian–Carboniferous boundary, before a warm period called the Early Tournaisian Warm Interval. Later, lower levels of carbon dioxide (CO₂) in the atmosphere, caused by the burial of organic material and widespread lack of oxygen in the oceans, led to cooling and glaciers forming near the South Pole. During the Visean Warm Interval, glaciers shrank and moved toward the proto-Andes in Bolivia and western Argentina, as well as mountain ranges in southeastern Brazil and southwest Africa.
The main phase of the LPIA (about 335 to 290 million years ago) began in the late Visean, as the climate cooled and CO₂ levels dropped. This period was marked by a global drop in sea levels and large gaps in rock layers that formed over millions of years. During this time, ice expanded from up to 30 centers across mid- to high latitudes of Gondwana, including regions in eastern Australia, northwestern Argentina, southern Brazil, and central and southern Africa.
Isotope records suggest that the drop in CO₂ levels was caused by tectonic activity, such as increased weathering of the growing Central Pangean Mountains, which affected rainfall and water flow. The closing of an oceanic passage between the Rheic and Tethys oceans in the early Bashkirian also changed ocean currents and heat patterns, contributing to cooling.
Warmer periods with less ice occurred during the Bashkirian, late Moscovian, and latest Kasimovian to mid-Gzhelian, as shown by the absence of glacial sediments, the presence of deposits from melting ice, and rising sea levels.
In the early Kasimovian, there was a short but intense period of glaciation, with CO₂ levels dropping as low as 180 parts per million (ppm). This ended quickly when CO₂ levels rose rapidly to about 600 ppm, causing a warmer climate. This sudden increase may have been due to volcanic activity or less burial of organic matter on land.
The LPIA reached its peak near the Carboniferous–Permian boundary. Glacial deposits found in South America, western and central Africa, Antarctica, Australia, Tasmania, the Arabian Peninsula, India, and the Cimmerian blocks show that ice sheets covered large areas of southern Gondwana, reaching sea level. At this time, the erosion of mafic rocks in the Central Pangean Mountains caused CO₂ levels to drop to as low as 175 ppm, remaining below 400 ppm for 10 million years.
Temperatures during the Carboniferous reflected the phases of the LPIA. At the coldest point, the Permo-Carboniferous Glacial Maximum (299–293 million years ago), the global average temperature was about 13°C (55°F), with tropical temperatures around 24°C (75°F) and polar temperatures near -23°C (-10°F). During the warmer Early Tournaisian Warm Interval (358–353 million years ago), the global average temperature was about 22°C (72°F), with tropical temperatures around 30°C (86°F) and polar temperatures about 1.5°C (35°F). Overall, the average temperature during the Ice Age was about 17°C (62°F), with tropical temperatures around 26°C and polar temperatures about -9°C (16°F).
Scientists use several methods to estimate past oxygen levels, such as studying charcoal from wildfires, gas trapped in salt crystals, the burial of organic carbon and pyrite, carbon isotopes in organic material, isotope balance calculations, and computer models. Some methods, like gas inclusions in salt, show specific moments in time, while others, like the charcoal record, cover longer periods. For example, the increasing amount of charcoal from wildfires during the Carboniferous suggests oxygen levels rose above 21%. Salt gas inclusions from sediments dated 337–335 million years ago estimate oxygen levels in the Visean to about 15.3%, though with large uncertainties. Pyrite records suggest oxygen levels started at around 15% early in the Carboniferous, rose to over 25% during the Pennsylvanian, and dropped below 20% by the end. While exact numbers vary, all models show oxygen levels increased from 15–20% at the start of the Carboniferous to 25–30% during the period. This rise was not steady but included peaks and troughs due to changing climate conditions. The effect of these oxygen levels on the size of arthropods and other life during the Carboniferous remains a topic of scientific discussion.
Changes in climate also affected sediment patterns. In the warm Early to Middle Mississippian, carbonate rocks formed across shallow continental slopes in Laurussia and North and South China (called carbonate ramps), and salt deposits formed near the coasts of Laurussia, Kazakhstania, and northern Gondwana.
By the late Visean, cooling limited carbonate production to depths less than 10 meters, forming flat-topped carbonate shelves. By the Moscovian, the growth and retreat of ice sheets led to the deposition of alternating layers of carbonate and siliciclastic rocks on continental platforms and shelves.
Seasonal melting of glaciers created near-freezing waters near the edges of Gondwana, as seen in glendonite (a type of calcite formed in glacial water) found in shallow marine sediments.
The grinding of siliciclastic rocks by glaciers across Gondwana and the Central Pangean Mountains produced large amounts of fine silt. Wind carried this silt to form widespread loess deposits across equatorial Pangea.
The main phase of the LPIA was a time of reduced marine biodiversity, with many species disappearing. However, recent studies suggest that rapid climate and environmental changes during this time led to an increase in species diversity as life adapted to new conditions.
Climate changes also caused repeated shifts in Laurasian tropical forests between wetland and seasonally dry environments. During the Kasimovian glacial interval, wetland forests changed, with tree-like lycopods and other wetland plants declining, and biodiversity dropping. These changes were linked to CO₂ levels falling below 400 ppm. Though called the Carboniferous rainforest collapse, this event involved the replacement of one type of rainforest with another, not the complete loss of rainforests.
Across the Carboniferous–Permian boundary, a sharp drop in CO₂ levels and
Geochemistry
As the continents came together to form Pangea, the growth of the Central Pangean Mountains caused more weathering and the buildup of carbonate sediments on the ocean floor. At the same time, the way continents were spread across the ancient tropics allowed large areas of land to support tropical rainforests. These two factors helped remove more carbon dioxide from the atmosphere, which lowered global temperatures, raised ocean pH, and caused the Late Paleozoic Ice Age. The formation of the supercontinent also changed how the seafloor spread, reducing the length and volume of mid-ocean ridge systems.
During the early Carboniferous period, the ratio of magnesium to calcium in seawater began to increase. By the Middle Mississippian, aragonite seas replaced calcite seas. The amount of calcium in seawater is controlled by ocean pH, and as pH increased, calcium levels decreased. At the same time, more weathering added more magnesium to the ocean. Magnesium is removed from seawater and calcium is added along mid-ocean ridges where seawater interacts with newly formed rock. The shorter mid-ocean ridge systems further increased the Mg/Ca ratio. The Mg/Ca ratio in the seas also affects how marine organisms build their shells. During the Carboniferous, aragonite seas favored organisms that produced aragonite, such as sponges and corals, which were the main reef builders at the time.
The strontium isotope ratio (Sr/Sr) in seawater reflects a mix of strontium from two sources: continental weathering, which has a high Sr ratio, and mantle sources like mid-ocean ridges, which have a lower Sr ratio. Sr/Sr values above 0.7075 mean continental weathering was the main source of strontium, while values below 0.7075 indicate mantle sources were more important.
Sr/Sr values changed throughout the Carboniferous but remained above 0.7075, showing that continental weathering was the main source of strontium. During the Tournaisian, Sr/Sr was about 0.70840. It decreased during the Visean to 0.70771, then increased during the Serpukhovian to the lowermost Gzhelian, where it stabilized at 0.70827. It later decreased to 0.70814 at the Carboniferous-Permian boundary. These changes show how weathering and sediment supply from the growing Central Pangean Mountains affected the oceans. By the Serpukhovian, rocks like granite were uplifted and exposed to weathering. The drop in Sr/Sr near the end of the Carboniferous suggests less continental weathering due to drier conditions.
Unlike Mg/Ca and Sr/Sr ratios, which are similar worldwide, δO and δC values in fossils can vary by region. Carboniferous δO and δC records show differences between the open waters of South China and the shallow seas of Laurussia. These differences are due to changes in seawater salinity and evaporation rates in shallow seas compared to open oceans. However, large-scale trends can still be identified. δC values rose quickly from about 0‰ to 5–7‰ during the Early Mississippian and stayed high through the Late Paleozoic Ice Age (3–6‰) into the early Permian. Similarly, δO values increased steadily as the climate cooled.
Both δC and δO records show major global changes (called excursions) during the Carboniferous. A mid-Tournaisian positive δC and δO excursion lasted 6–10 million years and was linked to a 6‰ increase in organic matter δN, a drop in carbonate δU, and a rise in carbonate-associated sulfate δS. These changes suggest lower atmospheric CO2 due to more organic matter burial and widespread ocean anoxia, which cooled the climate and started glaciation.
The Mississippian-Pennsylvanian boundary positive δO excursion happened at the same time as global sea level drops and glacial deposits in southern Gondwana, showing climate cooling and ice accumulation. The rise in Sr/Sr before the δO excursion suggests cooling was caused by increased continental weathering from the Central Pangean Mountains and the effects of mountain-building on rainfall and water flow, not by organic matter burial. δC values varied more regionally, and it is unclear if there was a positive δC excursion or a return to previous levels.
During the early Kasimovian, a short (<1 million year) and intense glacial period ended suddenly as atmospheric CO2 levels rose rapidly. Tropical regions became drier, and tropical rainforests shrank, as shown by the loss of coal deposits from this time. This reduced productivity and organic matter burial, increasing atmospheric CO2. These changes were recorded by a drop in δC values and a smaller decrease in δO values.
Life
During the Early Carboniferous period, land plants were similar to those of the Late Devonian, but new groups also appeared. The main plants included Equisetales (horse-tails), Sphenophyllales (scrambling plants), Lycopodiales (club mosses), Lepidodendrales (scale trees), Filicales (ferns), Medullosales (a group of early seed plants), and Cordaitales. These plants remained common throughout the period, but by the Late Carboniferous, new groups such as Cycadophyta (cycads), Callistophytales (another group of seed plants), and Voltziales also appeared.
The Lepidodendrales, a type of lycophyte, were large trees with trunks up to 30 meters tall and 1.5 meters wide. Examples include Lepidodendron, Anabathra, Lepidophloios, and Sigillaria. Their roots, called Stigmaria, grew in the outer layer of the tree instead of the inner part, which helped support the tree. The Cladoxylopsids were large trees that were ancestors of ferns and first appeared in the Carboniferous.
Some Carboniferous ferns had fronds that looked very similar to those of modern ferns. Many species likely grew on other plants. Fossil ferns and seed plants include Pecopteris, Cyclopteris, Neuropteris, Alethopteris, Sphenopteris, Megaphyton, and Caulopteris.
The Equisetales included Calamites, a tall plant with trunks 30 to 60 cm wide and up to 20 meters tall. Sphenophyllum was a climbing plant with leaves arranged in circles, possibly related to both Calamites and lycopods.
Cordaites was a tall plant with strap-like leaves, related to cycads and conifers. It had structures called Cardiocarpus that produced seeds. These plants likely lived in wetland areas. True conifer trees, like Walchia, appeared later and grew in drier areas.
In the oceans, marine invertebrates included Foraminifera, corals, Bryozoa, Ostracoda, brachiopods, ammonoids, hederelloids, microconchids, and echinoderms (especially crinoids). Brachiopods and fusilinid foraminifera became more common during the Visean stage, while cephalopods and conodonts declined. This event was called the Carboniferous-Earliest Permian Biodiversification Event. Foraminifera, such as Fusulina, Valvulina, Endothyra, Archaediscus, and Saccammina, were widespread. Some Carboniferous species still exist today. The first true priapulids appeared during this time.
Microscopic shells of radiolarians were found in cherts from the Culm of Devon and Cornwall, as well as in Russia, Germany, and other regions. Sponges included forms like Cotyliscus, Girtycoelia, Chaetetes, and Titusvillia. Corals, both reef-building and solitary, included rugose (e.g., Caninia, Corwenia), heterocorals, and tabulate (e.g., Chladochonus, Michelinia) types. Conularids, such as Conularia, were also common.
Bryozoa, like Fenestella, Polypora, and Archimedes, were abundant. Brachiopods included productids, some as large as 30 cm wide, and others like Chonetes. Other common brachiopods were athyridids, spiriferids, rhynchonellids, and terebratulids. Inarticulate brachiopods included Discina and Crania. Many species had wide distributions with minor differences.
Annelids, such as
Extinction events
During the first 15 million years of the Carboniferous period, few land-based fossils were found. Scientists have long debated whether this lack of fossils is due to poor preservation or a real event. Recent research suggests that oxygen levels in the air dropped, which may have caused an ecological collapse. This event led to the disappearance of Devonian fish-like labyrinthodonts and the rise of more advanced amphibians, such as temnospondylians and reptiliomorphans, which became common in Carboniferous land ecosystems.
Before the Carboniferous period ended, a major extinction event occurred. On land, this is known as the Carboniferous rainforest collapse. Large tropical rainforests disappeared quickly as the climate changed from hot and wet to cool and dry. This shift was likely caused by heavy glaciation and falling sea levels. The new climate was unsuitable for rainforests and their animals. Rainforests shrank into small, isolated areas surrounded by dry land. Towering lycopsid forests, which had a mix of different plants, were replaced by less diverse forests dominated by tree ferns.
Amphibians, which were the main vertebrates at the time, suffered greatly during this event, with many species lost. Reptiles, however, survived better because they had key adaptations, such as hard-shelled eggs and scales, which helped them retain water more effectively than amphibians.