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Cambrian

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Cambrian
542-488 mya
Era: Paleozoic
Preceded by Ediacaran
Followed by Ordovician

The Cambrian was the first period of the Paleozoic era of the Phanerozoic eon. The Cambrian period occurred around 542-488 million years ago. Major events include the appearance of hard body parts and the first chordates, brachiopods, and trilobites. Large and distinctly fossilizable complex multi-cellular lifeforms became more common in the Cambrian period than they had been in previous periods, such as the Ediacaran and the Cryogenian, due to an event known as the Cambrian explosion. This event occurred around 530-520 million years ago and resulted in the appearance of all modern phyla, except the bryozoans which appeared later in the Ordovician, as well as many extinct phyla and odd animals that are not closely related to modern animals

Contents

Subdivisions

The Cambrian period is the first period of the Phanerozoic era. The Cambrian period began after the end of the final period of the Neoproterozoic era known as the Ediacaran period. The Cambrian period is subdivided into three smaller epoch's the Early Cambrian Middle Cambrian and the Furongian (also known as Late Cambrian , Merioneth or Croixan). These epochs are in turn divided into smaller units known as Faunal Stages which are based on corresponding series of rocks that contain similar groups of fossils (such as the Atdabanian ,Tommotian and the Mayan).

Early Cambrian

The Archaeocyatha were sessile marine organisms that thrived in the tropical and sub tropical waters of the Early Cambrian epoch and were the earth's very first reef builders.
Parapeytoia was a possible early Anomalocarid (or a relative of the Anomalocarids) that lived in the early Cambrian epoch around 530 million years ago. It was one of the few Anomalocarids to posses legs.

The Early Cambrian was the first epoch of the Cambrian period. The Early Cambrian occurred between 542 million years ago and 513 million years ago. The Early Cambrian was a time of extreme change in both life on earth (Such as the Cambrian explosion) and in the geological land scape (such as the breakup of the Ediacaran supercontient pannotia). Abundant simple worm traces appeared to be common during during the Earliest Cambrian and in the late Ediacaran period but however they were soon followed by a set of small primitive shelled fossils known as the Small Shelly Fauna who thrived in the latest Ediacaran and the earliest Cambrian (or also known as the Manykian stage) the Small Shelly Fauna were eventually replaced by a more complex group of fossils known as the Tommotian fauna the relationship between modern fauna and the Tommotian fauna is not well known but however the Tommotian fauna quickly went extinct and were replaced by more modern fauna in the Cambrian explosion which followed the disappearance of the Tommotian fauna. The Cambrian explosion resulted in the appearance of most modern phyla as well as many extinct ones. The Ediacarian supercontient pannotia broke up during the Early Cambrian around 540 million years ago which resulted in the formation of the smaller Cambrian continents such as Laurentia, Baltica and Siberia. The shallow oceans of the Early Cambrian formed a hospitable environment for life which allowed light to reach aquatic plants more easily which allowed aquatic plants to increase in size and expand into new locations and allowed coral reefs to evolve and expand into wide belts that extended for of hundreds, or even thousands of kilometers along the coasts in the Cambrian period.

Middle Cambrian

The Middle Cambrian is the second epoch of the Cambrian period. The middle Cambrian epoch lasted from 513 to 501 million years ago. The odd fossils of Burgess Shale thrived during the Middle Cambrian epoch and the Anomalocarids and trilobites became abundant during during the middle Cambrian. Due to sea spreading corral reefs and and other habitats were being destroyed which may have spurred on the diversification and development of larger and more mobile organisms such as the
Trilobites such as Asaphiscus wheeleri were common in the middle and the late Cambrian.
ancient predatory arthropods known as the Anomalocarids which could reach lengths as long as 2 meters (6 feet). Some paleontologists and geologists such as Andrew Parker have suggested that many key groups of animals evolved the the eye during the Cambrian period (although the eye itself appeared much earlier in the Ediacaran period in an early arthropod known as Bomakellia kelleri) furthermore Andrew Parker and other paleontologists and geologists that have suggested that many key groups of animals evolved the the eye during the Cambrian period also suggest that the Evolution of the eye caused an increase in intelligence in Cambrian fauna because vision requires more intelligence than most other senses.

Furongian

The Furongian (also known as the Late Cambrian) was the final epoch of the Cambrian that occurred around 501 million years ago to and 488.3 million years ago. Groups that thrived earlier in the Middle Cambrian such as Trilobites, brachiopods and Anomalocarids continued to thrive in the Furongian and trilobites proliferated during the Furongian ,Furongian trilobites serve as index fossils which help identify the start and end of the Furongian epoch. Mollusks also became more diverse and new groups such as the Graptolites and the conodonts who were small micro predators that may have been early chordates also appear during the Furongian epoch. The conodonts are mostly known from the remains of their fossilised teeth. Conodonts went extinct in the Late Triassic around 228 and 199.6 million years ago when the first mammals appeared. The last confirmed members of the Ediacaran biota disappeared during this time around 500 million years ago but however these organisms were already extremely rare before the Furongian epoch.

life in the Cambrian

Burrows thought to be produced by the same animal that made Climactichnites trackways, late Cambrian, central Wisconsin.
File:Cambrianlife.jpg
An artist's conception of Cambrian life

Life in the Cambrian period underwent a massive Evolutionary radiation between 520 and 530 million years ago known as the Cambrian explosion. The Cambrian explosion and early Cambrian life in general was marked by the appearance of the ancestors of most modern phyla of animals.

Furthermore the first possible tracks on land were made during late Cambrian time. One of the tracks was Climactichnites, which may have been made by a primitive slug-like animal that crawled over the beaches to obtain food. Another late Cambrian track was Protichnites, which was made by the walking activity of an early arthropod. That arthropod, which may have been either a euthycarcinoid or aglaspidid, may have been ancestral to the eurypterids, which became common in the Silurian period, and to the horseshoe crabs. The names Climactichnites and Protichnites are assigned to the trace fossils only rather than the unknown animals that made them. Trilobites appeared and became successful during the Cambrian period and may have descended from organisms such as Spriggina that somewhat resembled trilobites and lived in the earlier Ediacaran period. The first recognizable trilobites such as Fallotaspis appeared in the early Cambrian. Trilobites reached their highest level of diversity in the middle Cambrian ,Ordovician and the Silurian period and declined through the rest of the Paleozoic era. Although chordates may have evolved earlier in the Ediacaran and true fish evolved later in the following Ordovician period, the first identifiable chordates are lancelet-like organisms that appeared in the Cambrian (such as Myllokunmingia fengjiaoa and Haikouichthys).

Primitive cephalopods and marine snails also appeared during the Cambrian period along with other extinct mollusk clades - however mollusks were generally rare during the Cambrian and only became abundant in the Ordovician period. The shelled protozoans known as the foraminifers first appeared during the Cambrian although they reached their peak level of diversity much later in the Carboniferous era which spans from 359 to 299 million years ago. Sponges, echinoderms and the soft-bodied echiurians, which were carnivorous worm-like creatures, also were important groups during the Cambrian period.

Image of the first complete Anomalocaris fossil found, residing in the Royal Ontario Museum

The largest Cambrian animals known were the predatory arthropods known as the Anomalocarids. The Anomalocarids averaged at 60 cm (or 2 feet) although one genus, Anomalocaris, could reach lengths as long as 2 m (6 ft 8 in).[1]. The fossil record shows trilobite exoskeletons with large pieces taken out of them which provides evidence that the Anomalocarids prayed on smaller arthropods such as trilobites. The Anomalocarids were very well adapted to their environment and some species of Anomalocarids existed for 30 million years with very little or no change. The Anomalocarids may have descended from an early ediacaran arthropod known as Bomakellia kelleri which also was the earliest animal with sight and eyes and may also have been a relative or ancestor of the trilobites.

It is thought that plants and fungi did not exist on land yet - however the molecular clock suggests that land plants appeared around 700 million years ago in the Cryogenian period of the Neoproterozoic era and fungi began to colonise the land around 1 billion years ago in the tonian period of the neoproterozoic era. Green algae became diverse during the Cambrian and would eventually give rise to land plants during the Ordovician period.

Paleogeography

File:Cambrianmap.JPG‎
A picture of earth in the Cambrian period around 514 million years ago.

Cambrian continents are thought to be the result of the breakup of the late Ediacaran supercontient pannotia which existed from 600 to 540 million years ago. Laurentia, Baltica and Siberia became independent continents in the Cambrian due to the breakup of the Cryogenian and Ediacaran supercontinent known as Pannotia. The rate of continental drift during the Cambrian period would have been abnormally high. Cambrian climates are thought to have been warmer than the climates of the previous Ediacaran and Cryogenian periods which experienced (or began shortly after) the worldwide ice age snowball earth. There was no ice at the poles during the Cambrian. The Cambrian oceans were shallow, warm and widespread compared to the cooler and deeper oceans of the previous Ediacaran period. Most of the southern hemisphere was covered by a large ocean known as Panthalassa although many minor oceans such as Proto-Tethys Ocean, Iapetus Ocean, and Khanty Ocean also existed and expanded during this time mostly in the northern hemisphere.

External links

Paleozoic era
Cambrian Ordovician Silurian Devonian Carboniferous Permian

See also

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