Everything about The Oligocene totally explained
The
Oligocene epoch is a geologic
period that extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene comes from the Greek ὀλίγος (
oligos, few) and καινός (
kainos, new), and refers to the sparsity of additional modern
mammalian faunas after a burst of
evolution during the
Eocene. The Oligocene follows the
Eocene epoch and is followed by the
Miocene epoch. The Oligocene is the third and final epoch of the
Paleogene period.
The Oligocene is often considered an important time of transition, a link between "[the] archaic world of the tropical Eocene and the more modern-looking
ecosystems of the Miocene."(Haines)
Oligocene Epoch flora change is a global expansion of grasslands, and a regression of tropical (broad leaf) to earth's equatorial belt.
The Oligocene Epoch temperature is a clearly defined notch in a
general temperature decline across the Paleogene Period. Evidence indicates a galactic causal. From 3C321 (NASA, 2007), a Black Hole Quasar was found to emit relativistic ISM particles in a narrow beam at about distances equal to our Sol Galactic core distance. Glaciating (cooling) is a result of ISM Heliosphere reduction and ISM penetration (PCFrisch, 2006). The Oligocene is the Neotectonic cycle of a 220million year planetary equidistant rupture (PER) geologic cycle (Kvet, 1991), extending to 4650Ma (Million years ago). The Oligocene, a biosphere stressed by temperature and perhaps loss of Heliosphere shielding, is understandably an epoch of few new species.
The start of the Oligocene is marked by a major
extinction event that may be related to the impact of a large extraterrestrial object in
Siberia and/or one
near Chesapeake Bay (See
Grande Coupure). The Oligocene-Miocene boundary isn't set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the relatively cooler Miocene.
Subdivisions
Oligocene
faunal stages from youngest to oldest are:
| Chattian or Late Oligocene |
(28.4 ± 0.1 – 23.03 mya) |
| Rupelian or Early Oligocene |
(33.9 ± 0.1 – 28.4 ± 0.1 mya) |
Climate
Climates remained warm, although the slow global cooling that eventualty led to the
Pleistocene glaciations started around the end of the epoch.
Paleogeography
During this period, the continents continued to
drift toward their present positions.
Antarctica continued to become more isolated and finally developed a permanent
ice cap.(Haines)
Mountain building in western
North America continued, and the
Alps started to rise in
Europe as the
African plate continued to push north into the
Eurasian plate, isolating the remnants of
Tethys Sea. A brief marine incursion marks the early Oligocene in Europe. Oligocene marine exposures are rare in North America. There appears to have been a land bridge in the early Oligocene between
North America and
Europe since the
faunas of the two regions are very similar. During sometime in the Oligocene,
South America was finally detached from
Antarctica and drifted north towards
North America. It also allowed the
Antarctic Circumpolar Current to flow, rapidly cooling the continent.
Flora
Angiosperms continued their expansion throughout the world; tropical and sub-tropical forests were replaced by temperate deciduous woodlands. Open plains and deserts became more common.
Grasses expanded from the water-bank habitat in the Eocene and moved out into open tracts; however even at the end of the period it wasn't quite common enough for modern
savanna.(Haines)
In North America, subtropical species dominated with
cashews and
lychee trees present, and temperate trees such as
roses,
beech and
pine were common. The
legumes of the pea and bean family spread, and
sedges,
bulrushes and
ferns continued their ascent.
Fauna
Important Oligocene land faunas are found on all continents except
Australia. Even more open landscapes allowed animals to grow to larger sizes than they'd earlier in the
Paleogene.(Haines) Marine faunas became fairly modern, as did terrestrial
vertebrate faunas in the northern continents. This was probably more as a result of older forms dying out than as a result of more modern forms evolving.
South America was apparently isolated from the other continents and evolved a quite distinct fauna during the Oligocene.
Reptiles were abundant in the Oligocene.
Choristodera, a group of semi-
aquatic,
crocodile-like,
diapsid (
archosauromorph?)
reptiles originated in the
Jurassic, possibly as far back as Late
Triassic. Early in the Oligocene, the Choristodera became extinct, possibly due to climate changes.
Snakes and
lizards did diversify to a degree.
Mammals included:
Brontotherium,
Indricotherium,
Entelodont,
Hyaenodon,
Mesohippus. Elephant-like forms,
Proboscidea, were present.
The Oligocene oceans resembled today's fauna, such as the
bivalves.
The baleen and toothed
cetaceans (whales) just appeared, and their ancestors, the
Archaeoceti cetaceans remained relatively common but their numbers were falling as Oligocene progressed because of climate changes and competition with today's modern cetaceans and the Charcharinid
sharks, which also appeared in this epoch.
Pinnipeds probably appeared near the end of the epoch from a
bear-like or
otter-like ancestor.
Oceans
Oceans continued to cool, particularly around Antarctica.
Further Information
Get more info on 'Oligocene'.
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