65-23 Ma

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§Of World Interest

It is estimated that ice began forming in Antarctica 34 million years ago. This caused the oceans to become less acidic. The data suggests that a fall in sea-level had the effect of leaving coral reefs stranded above the high-tide level where they were then eroded by wind and rain. Corals are composed of calcium carbonate - chalk - which has the effect of reducing acidity when dissolved in seawater.

§ Paleogene Period

63 Mya - Dinosaurs go extinct

Mammals become abundant. The first primates appear. Flowering plants become abundant.

The Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a plethora of diverse animals in the wake of the mass extinction that ended the preceding Cretaceous Period. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial and even airborne environments. Birds also evolved considerably during this period changing into roughly-modern forms. Most other branches of life on earth remained relatively unchanged in comparison to birds and mammals during this time period. Some continental motion took place. Climates cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period.

An early primate, believed to be in the human evolutionary tree is Darwinius masillae, found in Germany and believed to be from 47 million years ago. Another fossil from China, Eosimias sinensis, dates to 45 Ma. Aegyptopithecus zeuxis, found in Egypt, dates to 31 Ma.

It is believed by some that an Eocene era fossil found in Germany, dubbed "Ida" is a "missing link" between higher primates such as monkeys, apes, and humans and their more distant relatives such as lemurs. Ida, known as Darwinius masillae, has a unique anatomy. The lemur-like skeleton features primate-like characteristics, including grasping hands, opposable thumbs, clawless digits with nails, and relatively short limbs. Scientists were able to examine fossil evidence of fur and soft tissue and even the remains of her last meal: fruits, seeds, and leaves.

§Divisions

This period consists of the following epochs:

  • Paleocene
  • Eocene
  • Oligocene

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.The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene 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 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.

§ Sources

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