Paleoclimatology
The early part of the Carboniferous was mostly warm; in the later part of the Carboniferous, the climate cooled. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age.
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 deposition 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.
A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea-level drop and the associated unconformity in North America separate the Mississippian period from the Pennsylvanian period. This happened about 320 million years ago, at the onset of the Permo-Carboniferous Glaciation.
Tectonics
The Carboniferous was a time of active mountain-building, as the supercontinent
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| Global paleogeographic reconstruction of the Earth in the late Carboniferous ("Pennsylvanian") period 300 million years ago. (Picture Source) |
There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed - Rheic Ocean (closed by the assembly of South and North America), the small, shallow Ural Ocean (which was closed by the collision of Baltica and Siberia continents, creating the Ural Mountains) and Proto-Tethys Ocean (closed by North China collision with Siberia/Kazakhstania).
Rocks and Coal
Carboniferous rocks in Europe and eastern North America largely consist of a repeated sequence of limestone, sandstone, shale and coal beds, known as "cyclothems" in the U.S. and "coal measures" in Britain. In North America, the early Carboniferous is largely marine limestone, which accounts for the division of the Carboniferous into two periods in North American schemes. The Carboniferous coal beds provided much of the fuel for power generation during the Industrial Revolution and are still of great economic importance.
In eastern North America, marine beds are more common in the older part of the period than the later part and are almost entirely absent by the late Carboniferous. More diverse geology existed elsewhere, of course. Marine life is especially rich in crinoids and other echinoderms. Brachiopods were abundant. Trilobites became quite uncommon. On land, large and diverse plant populations existed. Land vertebrates included large amphibians.
Life in the Carboniferous
Plants
Although Earth's poles
were covered by ice caps, the
equatorial regions of the planet were dominated by vast
swamp
lands during most of the Carboniferous. Early Carboniferous
land plants were very similar to those of the preceding Late
Devonian, but new groups also appeared at
this time.
The main Early Carboniferous plants were the
Equisetales (Horse-tails),
Sphenophyllales
(vine-like plants),
Lycopodiales (Club mosses),
Lepidodendrales (scale trees),
Filicales (Ferns),
Medullosales
(informally included in the "seed
ferns", an artificial assemblage of a number
of early
gymnosperm groups) and
the
Cordaitales. These
continued to dominate throughout the period, but during
late Carboniferous, several other groups,
Cycadophyta (cycads),
the
Callistophytales
(another group of "seed ferns"), and the
Voltziales (related to
and sometimes included under the
conifers), appeared.
The Carboniferous lycophytes of the order Lepidodendrales, which are cousins
(but not ancestors) of the tiny club-moss of today, were huge trees with
trunks 30 meters high and up to 1.5 meters in diameter. These included
Lepidodendron (with its
fruit cone called
Lepidostrobus),
Halonia,
Lepidophloios and
Sigillaria. The roots
of several of these forms are known as
Stigmaria.
The fronds of some Carboniferous ferns are almost identical with those of
living species. Probably many species were
epiphytic (an epiphyte is a plant that grows
upon another plant (such as a tree) non-parasitically or sometimes upon some
other object). Fossil ferns and "seed ferns"
include
Pecopteris,
Cyclopteris,
Neuropteris,
Alethopteris, and
Sphenopteris;
Megaphyton and
Caulopteris were tree
ferns.
The Equisetales included the common giant form
Calamites, with a trunk diameter of 30 to
60 cm and a height of up to 20 meters.
Sphenophyllum was a
slender climbing plant with whorls of leaves, which was probably related
both to the calamites and the lycopods.
Cordaites, a tall plant
(6 to over 30 meters) with strap-like leaves, was related to the cycads and
conifers; the
catkin-like
inflorescence, which bore yew-like berries, is called
Cardiocarpus. These plants were thought to
live in swamps and mangroves. True coniferous trees (Walchia,
of the order Voltziales) appear later in the Carboniferous, and preferred
higher drier ground.
Marine invertebrates
In the oceans the most important
marine invertebrate
groups were the
foraminifera, corals,
bryozoa,
brachiopods,
ammonoids,
hederelloids and
echinoderms (especially
crinoids).
For the first time foraminifera take a prominent part in the marine faunas.
The large spindle-shaped genus
Fusulina and its
relatives were abundant in what is now Russia, China, Japan, North America;
other important genera include
Valvulina,
Endothyra,
Archaediscus, and
Saccammina (the latter
common in Britain and Belgium). Some Carboniferous genera are still extant.
Sponges are known from
spicules
and anchor ropes, and include various forms such as the
Calcispongea
Cotyliscus and
Girtycoelia, and the
genus of unusual colonial
glass sponges
Titusvillia.
Other common fossils of this period include
Gastropods and
Ostracods (a class of
crustacean
zooplankton).
Trilobites are rarer
than in previous periods, represented only by the proetid group.
Amongst the
echinoderms, the
crinoids
were the most numerous. Dense submarine thickets of long-stemmed crinoids
appear to have flourished in shallow seas, and their remains were
consolidated into thick beds of rock. The
blastoids, which
included the
Pentreinitidae and
Codasteridae and
superficially resembled crinoids in the possession of long stalks attached
to the seabed, attain their maximum development at this time.
Fish
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.
Sharks (especially the Stethacanthids)
underwent a major
evolutionary radiation
during the Carboniferous.
It is believed that this evolutionary radiation occurred because the decline
of the
placoderms at the end
of the Devonian period caused many
environmental niches to become unoccupied
and allowed new organisms to evolve and fill these niches.
As a result of the evolutionary radiation carboniferous sharks assumed a
wide variety of bizarre shapes including
Stethacanthus who possessed a flat
brush-like dorsal fin with a patch of
denticles on its top.
Stethacanthus unusual fin may have been used
in mating rituals.
Terrestrial Invertebrates
Late Carboniferous
giant dragonfly-like insect
Meganeura grew to wingspans of 75 cm.
Gigantic
Pulmonoscorpius from the early Carboniferous
reached a length of up to one meter.
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, shows that these arthropods were both well
developed and numerous. Their large size can be attributed to the moistness
of the environment (mostly swampy fern forests) and the fact that the oxygen
concentration in the Earth's atmosphere in the Carboniferous was much higher
than today. (The oxygen concentration in the Earth's atmosphere during the
Carboniferous was 35% whereas the oxygen concentration in earth's current
atmosphere is 21%.) This required less effort for respiration and allowed
arthropods to grow
larger with the up to 2.6 metres long centipede
Arthropleura being the largest known land
invertebrate of all time.
Tetrapods
Carboniferous
amphibians were diverse
and common by the middle of the period, more so than they are today; some
were as long as 6 meters, 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 meters long. They were
accompanied by an assemblage of smaller amphibians included under the
Lepospondyli, often only about 15 cm long.
Some Carboniferous amphibians were aquatic and lived in rivers, while others may have been
semi-aquatic or terrestrial.
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
synapsid (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
amniotes had already diversified into a
number of groups.
End of Reading
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