The Oligocene ( symbol O < sub > G </ sub >) is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present ( to ).

The formation of the San Andreas Fault system occurred fairly recently during the Oligocene Period between 34 million and 24 million years ago.

Going further back in time, the Late Eocene or Early Oligocene ( some 34 million years ago ) Filholornis from France has also been considered " proof " of a link between the Hoatzin and the gamebirds.

The family was widespread and successful from the Oligocene ( 34 million years ago ) through the Miocene ( about 5 million years ago ), but has remained almost unchanged over that time and remains as an example of primitive ruminant form.

During the Oligocene, about 34 – 23 Ma, these woodlands were replaced by a mosaic of southern beech ( Nothofagus ) and conifer-dominated woodlands and tundra as the climate continued to cool.

This episode of mountain building, known as the Alpine orogeny, occurred mostly during the Oligocene ( 34 to 23 million years ago ( mya )) and Miocene ( 23 to 5. 3 mya ) epochs.

They most likely originated in West Gondwana and are 67 – 107 million years old, so the oldest split could relate to the break-up of Gondwana in the middle Eocene to late Oligocene, 45 – 24 million years ago, and reached their current distribution by multiple intercontinental dispersal events.

The end is set at a major extinction event called the Grande Coupure ( the " Great Break " in continuity ) or the Eocene – Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay.

Although no mass extinctions of marine diatoms have been observed during the Cenozoic, times of relatively rapid evolutionary turnover in marine diatom assemblages occurred near the Paleocene – Eocene boundary and at the Eocene – Oligocene boundary.

Since the late Oligocene, the Iberian plate has been moving as part of the Eurasian plate, with the boundary between Eurasia and Africa situated along the Azores – Gibraltar fracture zone.

The first Apis bees appear in the fossil record at the Eocene – Oligocene ( 23-56 Mya ) boundary, in European deposits.

A piece of a carpometacarpus supposedly from Oligocene rocks near Lusk, Wyoming was described as Gaviella pusilla, but this handbone also shows some similarities to the plotopterids which were flightless wing-propelled divers and if these are apomorphic would make an unconvincing member of the Gaviidae ( though it still could be a small-winged gaviiform in an – as of yet undescribed – family " Gaviellidae "): while the carpometacarpus in Gavia is somewhat convergent to that of wing-propelled divers, enabling the wings to be used as rudders for quick underwater turns, Colymboides still had an unspecialized plesiomorphic hand.

True grebes suddenly appear in the fossil record in the Late Oligocene or Early Miocene, around 23 – 25 mya.

*† Electrophrynus ( 1 species ; Late Oligocene – Early Miocene )

Hoazinavis is an extinct genus of early hoatzin from Late Oligocene and Early Miocene ( about 24 – 22 mya ) deposits of Brazil.

In line with the other 3 main lineages of cracids ( chachalacas, true guans, and the Horned Guan ), mt and nDNA sequence data indicates that the curassows diverged from their closest living relatives ( probably the guans ) at some time during the Oligocene, or c. 35 – 20 mya ( Pereira et al.

The earliest sperm whale fossils are known from the late Oligocene – about 25 million years ago, with an ancestry tracing back from the latest Eocene before diverging from the remainder of the Odontocetid line, leading to the dolphins, and porpoises.

The area is also important in the field of paleontology ; it contains deposits of Pierre Shale formed on the seafloor of the Western Interior Seaway, evidence of the marine Cretaceous – Paleogene boundary, and one of the largest deposits of fossils of extinct mammals from the Oligocene epoch.

* Nephrops maoensis – Oligocene or Miocene, Dominican Republic

* Nephrops aequus – Oligocene or Miocene, Dominican Republic

The fossilised forest was formed during the Late Oligocene to Lower – Middle Miocene, by the intense volcanic activity in the area.

Recent molecular evidence suggests that pinnipeds evolved from a bearlike ancestor about 23 million years ago during the late Oligocene or early Miocene epochs, a transitional period between the warmer Paleogene and cooler Neogene period .< ref >

During the Eocene (~ 55. 8 — 33. 9 Ma ) and Oligocene (~ 33. 9 — 23 Ma ), the Appalachian Mountains began to uplift and the erosion rate increased enough to fill the Gulf Trough with quartz sands, silts, and clays via rivers and streams.

The earliest known fossil of Diprotodontia dates back to the Late Oligocene ( 23. 03mya-28. 4mya ), and the earliest identifiable species is Hypsiprymnodon bartholomaii from the Early Miocene.

The only known fossils of this genus are those of Anopheles ( Nyssorhynchus ) dominicanus contained in Dominican amber from the Late Eocene ( 40. 4 to 33. 9 Mya ) and Anopheles rottensis contained in German amber from the Late Oligocene ( 28. 4 to 23. 0 Mya ).

Fossils of bristle-mouth fishes show that the genus was already distinct in the Late Oligocene, more than 23 million years ago.

However few fossils have been found, of the Menyanthaceae-Asteraceae clade in the Oligocene, about 29 Mya.

The earliest and most primitive branch of the Canidae was the Hesperocyoninae lineage, which included the coyote-sized Mesocyon of the Oligocene ( 38-24 Mya ).

Fossil pollen are known Laurelia attributed to the middle Oligocene of New Zealand.

Baltic amber or succinite ( historically documented as Prussian amber ) is found as irregular nodules in marine glauconitic sand, known as blue earth, occurring in the Lower Oligocene strata of Sambia in Prussia ( in historical sources also referred to as Glaesaria ).

Published estimates of the onset of the Antarctic Circumpolar Current vary, but it is commonly considered to have started at the Eocene / Oligocene boundary.

The family Balaenopteridae is believed to have diverged from the other families of the suborder Mysticeti as long ago as the middle Oligocene.

The Cenozoic is divided into three periods: The Paleogene, Neogene, and Quaternary ; and seven epochs: The Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.

The surviving tropical population of primates, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Faiyum depression southwest of Cairo, gave rise to all living species — lemurs of Madagascar, lorises of Southeast Asia, galagos or " bush babies " of Africa, and the anthropoids: platyrrhine or New World monkeys, catarrhines or Old World monkeys, and the great apes, including humans.

The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya Rift Valley, dated to 24 million years ago.

The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch.

It is called menilite because it was first described from Ménilmontant ( Paris ), France, where it occurs as concretions within bituminous early Oligocene Menilite shales.

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 ecosystems of the Miocene.

The start of the Oligocene is marked by a notable extinction event ; the replacement of European fauna with Asian fauna, except for the endemic rodent and marsupial families called the Grande Coupure.

The Oligocene-Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer late Oligocene and the relatively cooler Miocene.

Puerto Rico is composed of Cretaceous to Eocene volcanic and plutonic rocks, which are overlain by younger Oligocene to recent carbonates and other sedimentary rocks.

Deeper alluvial strata, overlying Precambrian basement rock, Eocene alluvial deposits from a shallow Laramide depression, the Blanco Basin Formation ; and Oligocene ash and lava flows associated with the Conejos Formation, is the Santa Fe formation, mixed alluvium and lava outflows from the San Juan volcanic field to the west ; later strata comprise the Alamosa formation, alternating layers of sand, gravel, and clay.

The fossil record of birds in Australia is patchy ; however, there are records of the ancestors of contemporary species as early as the Late Oligocene.

The first sedimentation layer in Leon County is the Oligocene Suwannee Limestone in the southeastern part of the county as stated by the United States Geological Survey and Florida Geological Survey.

The land that is Orange County was part of the first land to emerge from below the Early Oligocene sea 33. 9 — 28. 4 million years ago and is known as Orange Island.