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Paleogene
 
 
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The Paleogene (alternatively Palæogene) is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic
Cenozoic

The Cenozoic Era...
 era. Lasting 42 million years, the Paleogene is most notable as being the time in which it is theorized that mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s evolved
Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
 from relatively small, simple forms into a plethora of diverse animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s in the wake of the mass extinction that ended the preceding Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 Period.






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The Paleogene (alternatively Palæogene) is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic
Cenozoic

The Cenozoic Era...
 era. Lasting 42 million years, the Paleogene is most notable as being the time in which it is theorized that mammal
Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s evolved
Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
 from relatively small, simple forms into a plethora of diverse animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s in the wake of the mass extinction that ended the preceding Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 Period. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
, specialized terrestrial and even airborne environments. Bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s also evolved considerably during this period changing into roughly-modern forms. Most other branches of life
Life

Life is a characteristic of organisms that exhibit certain biological processes such as chemical reactions or other events that results in a transformation....
 on earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 remained relatively unchanged in comparison to birds and mammals during this period. Some continental motion
Plate tectonics

Plate tectonics describes the large scale motions of Earth's lithosphere. The theory encompasses the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, understood during the 1960s....
 took place. Climate
Climate

Climate encompasses the temperatures, humidity, atmospheric pressure, winds, rainfall, atmospheric particle count and numerous other Meteorology elements in a given region over long periods of time, as opposed to the term weather, which refers to current activity of these same elements....
s cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period.

This period consists of the Paleocene
Paleocene

The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65.5 ? 0.3 Mega-annum to 55.8 ? 0.2 Ma . It is the first epoch of the Palaeogene Period in the modern Cenozoic era ....
, Eocene
Eocene

The Eocene Geologic time scale is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era....
, and Oligocene
Oligocene

The Oligocene is a geologic epoch of the Paleogene Geologic Timescale and extends from about 33.9 million to 23 million years before the present....
 Epochs. 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
Paleocene-Eocene Thermal Maximum

The Paleocene/Eocene boundary, , was marked by the most rapid and significant climatic disturbance of the Cenozoic. A sudden global warming event, leading to the Paleocene-Eocene Thermal Maximum , is associated with changes in oceanic and atmospheric circulation, the extinction of numerous deep-sea benthos foraminifera, and a major turnover...
, 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.The Paleogene follows the Cretaceous Period and is followed by the Miocene
Miocene

The Miocene is a Geologic time scale of the Neogene period and extends from about 23.03 to 5.33 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified but the exact dates of the start and end of the period are uncertain....
 Epoch of the Neogene
Neogene

The Neogene is a Geologic time scale#Terminology starting 23.03 ? 0.05 million years ago and lasting either until today or ending 2.588 million years ago with the beginning of the Quaternary....
 Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary
Tertiary

The Tertiary is a a term for a Geologic time scale#Terminology 65 million to 1.8 million years ago. The Tertiary covered the time span between the superseded Secondary period and an out-of-date definition of the Neogene#Controversy....
 Period into two periods instead of five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.