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Oligocene Epoch
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What is the Oligocene Epoch?
The Oligocene Epoch is a division of the Paleogene Period, which occurred from 33.9 million to 23 million years ago. It is further divided into the Rupelian and Chattian ages/stages. The name Oligocene means "epoch of few recent forms," because fewer modern animals originated during this time.
During the Oligocene epoch, grasslands expanded, forested regions dwindled, and tropical vegetation grew along the Tethyan Sea. Modern groups of carnivores and herbivores became diverse, and the largest land mammal, Indricotherium, appeared in Asia.
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When did the Oligocene Epoch occur?
The Oligocene Epoch occurred from 33.9 million to 23 million years ago, marking the third and final epoch of the Paleogene Period. It is further divided into the Rupelian and Chattian ages. The name Oligocene comes from Greek, signifying the "epoch of few recent forms," due to the limited number of modern animals that originated during this time. The Oligocene was preceded by the Eocene Epoch and followed by the Miocene Epoch, the Neogene Period's first epoch.
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How is the Oligocene Epoch identified in geochronology?
The Oligocene Epoch, part of the Paleogene Period, spans from 33.9 million to 23 million years ago and is identified in geochronology through various methods.
- Index Fossils Index fossils are crucial for defining geologic time scale boundaries and correlating strata. A good index fossil is easily recognizable, abundant, widely distributed geographically, and has a short time range. In marine strata, single-celled Protista and ammonoids are commonly used, while mammals are widely used in terrestrial sediments of the Cenozoic Era.
- Isotope Stratigraphy This method analyzes variations in isotopes of oxygen, carbon, and strontium in layered limestone beds to identify changes in climate and erosion patterns. Ratios of isotopes such as oxygen (^{18})O to (^{16})O and carbon (^{13})C to (^{14})C indicate colder or warmer intervals, while strontium isotopes (^{87})Sr to (^{86})Sr indicate periods of increased erosion.
- Radioactive Measurements Absolute dating through radioactive measurements confirms the relative order of strata defined by fossils. The rhenium-osmium method is used to study mantle-crust evolution and the origin of ore deposits.
- Faunal Succession The relative age of a fossiliferous rock is indicated by the types of fossils it contains. The unique fauna of each geologic history interval associates a given fossiliferous rock with that particular interval.
- Key Beds Volcanic ash layers serve as key beds for correlation due to their distinctiveness, wide distribution, rapid deposition, and suitability for radiometric dating.
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What significant climate changes happened during the Oligocene Epoch?
During the Oligocene Epoch, which spanned from 33.9 million to 23 million years ago, significant climate changes occurred, including a global temperature decline that started in the middle and late Eocene and accelerated rapidly across the Eocene-Oligocene boundary, initiating continental-scale glaciation in Antarctica. A continental ice sheet developed in Antarctica during the Oligocene Epoch, persisting until a rapid warming event took place 27 million years ago.
The cooler oceans of the early Oligocene may have been more productive than oceans of the late Eocene. At the boundary between the Eocene and Oligocene epochs (33.9 million years ago), Antarctic Bottom Water (AABW) began to form, resulting in greatly decreased bottom-water temperatures in both the Pacific and Atlantic oceans.
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What types of plants and animals lived during the Oligocene Epoch?
During the Oligocene Epoch, which spanned from 33.9 million to 23 million years ago, grasslands expanded while forested regions dwindled, and subtropical climates existed in many areas.
Animals
Terrestrial vertebrate faunas were diverse and abundant across North America, Europe, Africa, and Asia. Modern groups of carnivores and herbivores became diverse and abundant. The largest land mammal of all time, Indricotherium (a giant hornless rhinoceros), lived in Asia, and the first mastodons appeared in Egypt. In North America, primitive horses evolved, including three-toed forms such as Mesohippus and Miohippus. Primitive beavers also appeared. The earliest apelike form, Parapithecus, is known from Oligocene deposits in Egypt, which also have yielded remains of several kinds of Old World monkeys. The earliest New World monkeys are known from late Oligocene deposits in South America.
Plants
Tropical vegetation flourished along the borders of the Tethyan Sea. Warm, swampy conditions prevailed over much of what is now Germany, and extensive deposits of lignite coal were formed.
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How did the Oligocene Epoch influence the development of later life on Earth?
The Oligocene Epoch, lasting from 33.9 million to 23 million years ago, significantly shaped the development of later life on Earth. During this epoch, grasslands expanded while forested regions dwindled, and modern groups of carnivores and herbivores became diverse and abundant.
The similarities among early Oligocene vertebrate faunas across the northern continents suggest animal interchange, though later faunas became more provincial. The epoch saw the appearance of early pigs and peccaries in Europe, the spread of bats, and the evolution of primitive horses like Mesohippus and Miohippus in North America. Additionally, the earliest apelike form, Parapithecus, emerged in Egypt during this time.
Climatic cooling and drying trends during the Oligocene also led to the expansion of grassland ecosystems and the diversification of grazing mammals.
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Oligocene Epoch, third and last major worldwide division of the Paleogene Period (65.5 million to 23 million years ago), spanning the interval between 33.9 million to 23 million years ago. The Oligocene Epoch is subdivided into two ages and their corresponding rock stages: the Rupelian and the Chattian. It followed the Eocene Epoch and was succeeded by the Miocene Epoch, the first epoch of the Neogene Period. The term Oligocene is derived from Greek and means the “epoch of few recent forms,” referring to the sparseness of the number of modern animals that originated during that time.
In western Europe the beginning of the Oligocene was marked by an invasion of the sea that brought with it new mollusks characteristic of the epoch. Marine conditions did not exist for long, however, and brackish and freshwater conditions soon prevailed. This cycle of marine transgression, followed by the establishment of brackish and then freshwater environments, was repeated during the Oligocene. Sediments on the floor of the ancient Tethyan Sea, which covered part of Eurasia during the Oligocene, were deformed early in the development of the European Alps.
Oligocene climates appear to have been temperate, and many regions enjoyed subtropical climatic conditions. Grasslands expanded and forested regions dwindled during this time, while tropical vegetation flourished along the borders of the Tethyan Sea. Warm, swampy conditions prevailed over much of what is now Germany, and extensive deposits of lignite coal were formed.
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A prominent group of Oligocene marine organisms were the foraminiferans, protists similar to amoebas but bearing a complex, often calcareous test, or shell. Among the especially prominent foraminiferans were the nummulites (large, lens-shaped foraminiferans). Other marine forms were essentially modern in aspect. Terrestrial invertebrate life was abundant and diverse. Stream and lake deposits on the Isle of Wight in England contain the remains, often well preserved, of termites and other insects. In the Baltic, many forms of Oligocene insects, including butterflies, bees, ants, and spiders, are preserved in amber.
Oligocene terrestrial vertebrate faunas are diverse and abundant and are known from North America, Europe, Africa, and Asia. The vertebrates of the northern continents possess an essentially modern aspect that is more a result of the extinction of archaic vertebrates at the close of the Eocene Epoch than the appearance of new forms. The similarities between the various early Oligocene vertebrate faunas of the northern continents suggests a relatively free interchange of animals, but later Oligocene faunas show a greater degree of provincialism. Early pigs and peccaries first appeared in Europe during the early Oligocene and reached North America late in the epoch. Bats became more widespread during the Oligocene and at least locally abundant; their droppings in caves contributed to the formation of extensive phosphate deposits that are now economically significant in many areas.
Throughout the epoch, modern groups of carnivores and herbivores became diverse and abundant. The largest land mammal of all time, Indricotherium (a sort of giant hornless rhinoceros), is known from Asia, and the first mastodons are known from Egypt. In North America, primitive horses were evolving, including three-toed forms such as Mesohippus and Miohippus. Primitive beavers also appeared late in the Oligocene.
The earliest apelike form, Parapithecus, is known from Oligocene deposits in Egypt, which also have yielded remains of several kinds of Old World monkeys. The earliest New World monkeys are known from late Oligocene deposits in South America. During the Oligocene, South America was isolated from Central and North America, and a unique mammalian fauna developed there. Remarkably, many South American mammals of the Oligocene exhibit extreme parallelism in adaptation to forms that are found elsewhere in the world and to which they are not closely related.
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