OLIGOCENE: CHARACTERISTICS, SUBDIVISIONS, GEOLOGY AND FAUNA - GEOGRAFÍA - 2024

The Oligocene was the third and last of the eras that made up the Paleogene period of the Cenozoic Era. It lasted from about 33.9 million years ago to about 23 million years ago, a period during which the planet underwent noticeable changes.

These changes in the planet caused a redistribution of living beings, both plants and animals. Climate played a fundamental role in this process, since it created the ideal conditions for an animal or plant to be able to thrive or not in a specific region.

Oligocene fossil record. Source: Falconaumanni

The Oligocene has been a time that has always fascinated specialists in the area, who have devoted a great deal of time and effort to elucidate the still hidden aspects of this geological stage of the planet.

characteristics

Duration

The Oligocene lasted 11 million years, beginning about 33.9 million years ago and extending until about 23 million years ago.

Reordering the continents

During this time the movement of the continental plates continued, redistributing and occupying positions similar to those they occupy today.

"The age of mammals"

The group of mammals was the one that experienced the greatest diversification and variety during this time. A large number of subdivisions appeared as rodents or canids.

geology

The Oligocene was a time of much orogenic and geological activity. During this time the fragmentation of the supercontinent Pangea continued, whose fragments began their displacement to position themselves in the places they occupy today.

Likewise, in the Oligocene epoch, two orogenic processes took place: the Laramide Orogeny (which began in the Cretaceous) and the Alpine Orogeny.

Laramide Orogeny

It was a very violent orogenic process that caused a great deformation. It resulted in the formation of several mountain ranges that extend across the western tip of North America, from Alaska to Mexico.

The most recognized mountain ranges that formed during the Laramide orogeny are the Rocky Mountains in the United States and the Sierra Madre Oriental in Mexico.

It also resulted in the appearance of several volcanoes, in such a way that in certain places there was a scattering of a large amount of material from volcanic activity.

Alpine Orogeny

It was an orogenic process that had its origin in the movement and collision of some tectonic plates. It is important to remember that this time was of great activity regarding the movement of the continents. In this sense, the collision of three pieces of land (Africa, Cimmeria and the one corresponding to India), with the supercontinent Eurasia.

As in any geological process, the collision of these large land masses resulted in the elevation of certain parts of the terrain, forming various mountain ranges, which are located in the south of the European and Asian continents, and in North Africa..

The only mountain range that belongs to the African continent and that was formed thanks to the Alpine Orogeny is the Atlas mountain range. While the Apennines, the Alps, the Balkans and the Caucasus, among others, were formed on the European continent. And in Asia, the mountain ranges that owe their origin to this geological process are the Himalayas, Hindu Kush and Karakorum.

Tectonic plate movement

The fragmentation of the supercontinent Pangea became more evident with the separation of the fragment that corresponds to South America, which began its slow movement towards the west, to meet North America and form the American continent as it is known today.

Likewise, Antarctica continued its separation from the rest of the continents and deepening the ice cover.

Similarly, according to the conclusions reached by various specialists, during this time the plate corresponding to the African continent collided with Eurasia, as did the fragment that currently corresponds to India.

At the end of this time, the land masses were arranged in much the same way as they are today. The same happens with the oceans, since several of the oceans that separate the continents were already formed today. These include the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean.

Weather

Climatic conditions during the Oligocene were quite extreme, characterized by very low temperatures.

During this time, both Antarctica and Greenland remained covered with ice, as is the case today. Likewise, when Antarctica was completely separated from South America, it caused various maritime currents to circulate completely around it, being the Circumpolar Antarctica one of the most important, since it was responsible for the ice cover of Antarctica, as well as the glacier formation.

This progressive decrease in the temperature of the Earth resulted in a modification of some ecosystems. Coniferous and deciduous forests predominated, which are apt to survive low temperatures.

Lifetime

During the Oligocene the diversification of life continued, both of plants and animals. Despite the climatic conditions being a bit difficult, the organisms knew how to adapt to them and thus survive.

Flora

In the Oligocene, angiosperms (seed-covered plants) began to spread through a large number of habitats, even reaching the dominance that they have today.

At this time, a decrease or regression of tropical forests was observed, which were replaced by herbaceous plants and grasslands. The latter spread to all continents: America, Asia, Europe and Africa.

Herbaceous plants had great evolutionary success and adapted thanks to their own growth characteristics. Herbaceous plants have a continuous growth rate, which never stops.

Likewise, this type of plants had to face the action of grazing animals, which fed on them. However, they were able to survive these and even establish a kind of symbiotic relationship, since this type of animal collaborated with the spreading of seeds through excrement.

In the same vein, legume-type plants such as beans were also developed during this period.

Fauna

In the Oligocene epoch there were many groups of animals that diversified and prospered despite the climatic conditions. Among the groups of animals that expanded during this time are birds, reptiles and mammals.

During this time there were a great variety of birds, as well as reptiles. However, the group that gained the most prominence were mammals. It is important to note that the Cenozoic, to which this time belongs, was known as "the age of mammals."

Mammals

It was one of the most successful animal groups at this time. A large number of new species of mammals appeared: rodents, canids, primates and cetaceans.

Mammals typical of the Oligocene. Source: Heinrich Harder (1858-1935)

Rodents

The order of rodents (rodentia) is the most abundant within the group of mammals. Its distinctive feature is very sharp incisor teeth that have multiple uses, such as biting predators or gnawing on wood (hence its name).

One of the most recognized families of Oligocene rodents was the Eomyidae. These were similar to today's squirrels, with a small body and arboreal habits. Also, some were able to glide from tree to tree.

Primates

Primates are a group of mammals characterized by having five toes on the extremities, an opposable thumb, plantigrade feet (they rely on the entire sole of the foot to move), in addition to a general dental pattern, in which their teeth they are very little specialized.

According to specialists in the area, the primates that could be observed at this time are the lemur and the tarsier.

The tarsier is a small primate, approximately 10 cm. Its characteristic anatomical element is its large eyes, which allow it to adapt its vision in the dark. They are of arboreal habits, which means that they spend a large part of their life suspended in the branches of the trees.

The lemur is a primate that, depending on the subspecies, can vary in size. One of its most outstanding characteristics is its long tail, often longer than the body. They have large eyes, which allow them to see in the dark. They do not distinguish colors, although they can distinguish shapes. They are very sociable animals.

Canids

Animals such as wolves and dogs belong to this group. They are characterized by having a medium-sized body and walk supported on the tips of their fingers.

They are carnivorous. The first specimens of this group appeared in the Eocene and in later times they diversified, having managed to remain until today.

Cetaceans

It is a group of mammals that has managed to adapt to marine life. They are characterized by the fact that their forelimbs have been modified to become fins, while the hindlimbs have disappeared. They have lung respiration, so they must periodically rise to the surface to take air.

Among the cetaceans that inhabited the seas during the Oligocene, we can mention the Aeticetus and the kentriodon, among others.

The largest land mammal

During the Oligocene, the largest land mammal of all time, the Paraceratherium, inhabited. They were approximately 8 meters high and 7 meters long.

They were herbivorous animals, with a very well developed sense of smell. According to the studies carried out, it was not a sociable animal, but with a solitary lifestyle. It is believed that the males tended to fight each other for the attention of the females during mating.

Apparently they fought among themselves clashing their heads, finding this duly protected by the bones of the skull, which was much thicker.

Subdivisions

Source: wikipedia.org

The Oligocene epoch was divided into two ages:

• Rupeliense: it is named after a Belgian river, the Rupel. It stretched from 38 million years ago to 33 million years ago, with a duration of 5 million years.
• Chattian: it was the most recent age of the Oligocene. Its name derives from the "Chatti", an ancient German tribe. It was a quiet age, in which the most relevant events had to do with the intense volcanic activity that was recorded in the west of the North American continent. It had an extension of 5 million years, since it was established 33 million years ago and culminated 28 million years ago.

References

1. Berta A, Sumich J & Kovacs KM. (20119. Marine mammals. Evolutionary Biology. 2nd ed. Califòrnia: Academic Press
2. Cox, C. Barry & Moore, Peter D. (1993): Biogeography. An ecological and evolutionary approach (5th ed.). Blackwell Scientific Publications, Cambridge
3. Donald R. Prothero (1993). The Eocene-Oligocene Transition: Paradise Lost. Columbia University Press
4. Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999
5. Rögl, F. (1997). Paleogeographic Considerations for Mediterranean and Paratethys Seaways (Oligocene to Miocene). Naturhistorisches Museum