Oligocene
The
Oligocene epoch is a geologic
period of time that extends from about 34 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
oligos (few) and
ceno (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
Palaeogene 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)
The start of the Oligocene is marked by a major
extinction event that may be related to the impact of large extraterrestrial object in
Siberia and/or near
Chesapeake Bay. The Oligocene-Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the relatively cooler Miocene.
Oligocene
faunal stages from youngest to oldest are:
Chattian>| (28.4 ± 0.1 – 23.03 MYA) | | Rupelian | (33.9 ± 0.1 – 28.4 ± 0.1 MYA) |
Climates remained warm, although the slow global cooling that eventualty led to the
Pleistocene glaciations started around the end of the epoch.
See also:
PaleoMap Project: OligoceneDuring 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. 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 as the
faunas of the two regions are very similar.
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 was not 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 common. The
legumes of the pea and bean family spread, and
sedges,
bulrushes and
ferns continued their ascent.
Important Oligocene land faunas are found on all continents except
Australia. Even More open landscapes allowed animals to grow to larger sizes than they had 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.
Mammals
Brontotherium,
Indricotherium,
Enteledont,
Hyaenodon,
MesohippusReptiles
Peltosaurus
Birds
Sea Life
bivalves
Oceans continued to cool, particularly around Antarctica.
* Haines, Tim;
Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999)
* Ogg, Jim; June, 2004,
Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
*
BBC Changing Worlds: Oligocene*
Paleos: Oligocene*
UCMP Berkley Oilgocene Page*
Prehistoric Pictures, in the Public Domain*
Oligocene Leaf Fossils*
Olicgocene Fish Fossils*
PaleoMap Project
