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Paleocene

From Academic Kids

The Paleocene epoch (65-56 MYA) ("early dawn of the recent") is the first geologic epoch of the Palaeogene period in the modern Cenozoic era. As with most other older geologic periods, the strata that define the epoch's beginning and end are well identified, but the exact date of the end is uncertain.

The Paleocene epoch immediately followed the mass extinction event at the end of the Cretaceous, known as the K-T boundary (Cretaceous - Tertiary), which marks the demise of the dinosaurs. The die-off of the dinosaurs left unfilled ecological niches worldwide, and the name "Paleocene" refers to the "old(er) – new" fauna that arose during the epoch, prior to the emergence of modern mammalian orders in the Eocene.

The K-T boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna, with high Iridium levels. There is also fossil evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but very short-lived climatic change may have occurred in the very early decades of the Paleocene. There are a number of theories about the cause of the K-T extinction event, with most evidence supporting the impact of a 10 km diameter asteroid near Yucatan, Mexico.

The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic, a sudden global change, the Paleocene-Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.

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Contents

Paleocene subdivisions

The Paleocene is usually broken into lower and upper subdivisions. The faunal stages from youngest to oldest are:

Thanetian (58.7 ± 0.2 – 55.8 ± 0.2 MYA)
Selandian (61.7 ± 0.2 – 58.7 ± 0.2 MYA)
Danian (65.5 ± 0.3 – 61.7 ± 0.2 MYA)

Paleocene climate

Temperatures rose during the Paleocene, and the climate was warm and humid world-wide, with subtropical vegetation growing in Greenland and Patagonia. The poles were cool and temperate, North America, Europe, Australia and southern South America were warm and temperate; tropical climates characterized equatorial areas, and North and South of the Equator climates were hot and arid.

See: PaleoMap Project: Paleocene Climate (http://www.scotese.com/paleocen.htm)

Paleocene paleogeography

During the Paleocene, the continents continued to drift toward their present positions. North America, Europe and Asia were still joined in a supercontinent, Laurasia, but Greenland and North American were beginning to separate.

The southern supercontinent Gondwanaland continued to split apart, with Africa, South America, Antarctica and Australia pulling away from each other. Africa was heading north towards Europe, and India began its migration to Asia that would lead to the huge tectonic collision and formation of the Himalayas.

South and North America were still separated by vast equatorial seas. The warm Tethys Ocean continued to dominate the globe.

The inland seas in North America (Western Interior Seaway) and Europe receded and eventually disappeared, making way for new land-based flora and fauna.

Paleocene flora

On land, modern plant species developed. Cacti and palm trees appeared. Paleocene and later plant fossils are generally attributed to modern genera or to closely related taxa.

The warm temperatures world-wide gave rise to thick tropical, sub-tropical and deciduous forest cover around the globe, with ice-free polar regions covered with pine trees, and deciduous forests in the north. Flowering plants (angiosperms), first seen in the Cretaceous, continued to develop and proliferate, and along with them coevolved the insects that fed on these plants and pollinated them.

Paleocene fauna

Mammals

Mammals had first appeared in the Triassic, and developed alongside the dinosaurs, exploiting ecological niches untouched by the larger and more famous Mesozoic animals: in the insect-rich forest underbrush, and high up in the trees. These smaller mammals (as well as birds, reptiles, amphibians, and insects) survived the mass extinction at the end of the Cretaceous, which wiped out the dinosaurs, and mammals diversified and spread throughout the world.

While early mammals were small nocturnal animals with herbivorous and insectivorous diets, the demise of the dinosaurs and the beginning of the Paleocene saw mammals growing bigger, more ferocious, and finally becoming the dominant predators and spreading throughout the world. Ten million years after the death of the dinosaurs, the world was filled with rodent-like mammals, medium sized mammals scavenging in forests, and large herbivorous and carnivorous mammals hunting other mammals, birds, and reptiles.

Paleocene mammals did not yet have specialized teeth or limbs, and are considered primitive, or archaic. It was not until the Eocene, 55 MYA, that true modern mammals developed.

Fossil evidence from the Paleocene is scarce, and there is relatively little known about mammals of the time. Because of their small size, early mammal bones are not well-preserved in the fossil record, and most of what we know comes from fossil teeth (a much tougher substance), and only a few skeletons.

Mammals of the Paleocene include:

Reptiles

Due to the climatic conditions of the Paleocene, reptiles were more cosmopolitian than at present. Among the sub-tropical reptiles found in North America during this epoch are champsosaurs (aquatic reptiles that resemble modern gavials), crocodylians, soft-shelled turtles, palaeophid snakes, varanid lizards, and Protochelydra zangerli (similar to modern snapping turtles).

Examples of champsosaurs of the Paleocene include Champsosaurus gigas, the largest champsosaur ever discovered. This creature was unusual among Paleocene reptiles in that C. gigas begame larger than its known Mesozoic ancestors: C. gigas is more than twice the length of the largest Cretaceous specimens (3m vs. 1.5m). Reptiles as a whole decreased in size after the K-T event. Champsosaurs declined towards the end of the Paleocene and became extinct at the end of the Eocene.

Examples of Paleocene crocodylians are the early eusuchian crocodile Leidyosuchus formidabilis, the apex predator and the largest animal of the Wannagan Creek fauna, and the alligator Wannaganosuchus.

Birds

Birds began to diversify during the epoch, occupying new niches. Most modern bird types had appeared by mid-Cenozoic, including perching birds, cranes, hawks, pelicans, herons, owls, ducks, pigeons, loons, and woodpeckers.

Large carnivorous flightless birds (also called Terror Birds) have been found in late Paleocene fossils, including the fearsome Gastornis in Europe.

Early owl types such as Ogygoptynx and Berruornis appear in the late Paleocene in the U.S. and France respectively.

Paleocene oceans

Warm seas circulated throughout the world, including the poles. The warm oceans gave rise to abundant marine life, including coral reefs. With the demise of marine reptiles at the end of the Cretaceous, sharks became the top predators. The end of the Cretaceous also saw extinctions of the ammonites, and many species of foraminifera.

Marine faunas also came to resemble modern faunas, with only the marine mammals and the Charcharinid sharks missing.

External links

fr:Palocne he:פליאוקן ja:暁新世 nl:Paleoceen

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