MIOCENE: CHARACTERISTICS, SUBDIVISIONS, GEOLOGY, FLORA AND FAUNA - BIOLOGY - 2025

The Miocene was one of the two eras that made up the Neogene period. It lasted 8 million years, during which a large number of events occurred at the climatic, biological and orogenic levels.

During the Miocene, the climate experienced certain fluctuations, beginning with low temperatures, and then slowly rising. During half the season, optimal warm temperatures were reached, which led to the successful development of certain animals and plants.

Miocene fossil. Source: I, porshunta

Likewise, it was a time when the various groups of animals that coexisted on the planet were able to expand and diversify. Such was the case with mammals, birds, and reptiles and amphibians. All this is known because there is an important fossil record of the specimens that inhabited the Earth at that time.

General characteristics

Duration

The Miocene was an epoch that began 23 million years ago and ended 5 million years ago, for an approximate duration of 8 million years.

Changes at the orogenic level

During the Miocene, orogenic activity was quite intense, since the growth of various mountain ranges occurred. In some very specific places the emergence of new mountains brought important consequences, such as the Messinian salt crisis.

The age of mammals

There are fossil records that a great variety of mammals existed in this era, of all sizes and dietary predilections. It is the group of animals that experienced the greatest development and diversification.

Divisions

The Miocene was divided into six ages of variable duration but which together spanned 18 years of the planet's geological history.

geology

During the Miocene epoch, intense activity was observed from the geological point of view, as the continents continued their unstoppable movement, thanks to continental drift, almost to occupy the place they have today.

Even, for some specialists, already at that time the planet practically had the configuration that it has today.

Likewise, during this time the collision of the north of the African continent with the area where Turkey and the Arabian peninsula currently settle. This was a momentous event, as it resulted in the closure of one of the seas that had existed until then, the Paratetis.

Previously, the collision of what is now India with Eurasia had already occurred, a process that led to the formation of the Himalayan mountain range. However, during the Miocene the Indian movement had not ceased, but remained, pressing against the Asian region. This caused the Himalayan mountains to continue to grow and form.

Specifically in the geographical area of ​​the Mediterranean, there was a great orogenic activity, showing the records collected that important mountains were raised there during this time.

This uplift of great mountains originated an event known as the Messinian salt crisis.

Messinian saline crisis

As its name indicates, it occurred at the end of the Messinian, the last age of the Miocene epoch. It consisted in the systematic and progressive isolation of the Mediterranean Sea from the Atlantic Ocean. This occurred thanks to the great orogenic activity that occurred in that geographical area.

This activity resulted in the formation of two important mountain ranges: the Betic mountain ranges, in the Iberian Peninsula and the Rif mountain range, in northern Morocco.

If you look at a map of the area, you can see that between the Iberian Peninsula and North Africa, especially Morocco, the space is really narrow. This is known as the Strait of Gibraltar, which is just 14 kilometers long.

Well, during the Messinian, the Strait of Gibraltar was closed, with which the Mediterranean Sea was losing volume until finally it dried up, leaving an extensive saline as a residue.

As reliable proof of the aforementioned, there is a finding made a few years ago, which consisted of a thick layer (2 km thick) of salt on the bottom of the seabed.

Causes

According to those who have studied this phenomenon, the main cause was tectonic activity in the area, which caused the raising of a kind of natural barrier that prevented the flow of water from the Atlantic Ocean.

Likewise, it has also been estimated that at this time the sea level decreased, which resulted in the formation of a kind of barrier between the Mediterranean Sea and the Atlantic Ocean, such as an isthmus, which contributed to the physical isolation of the space. occupied by the Mediterranean Sea.

This remained so until the next epoch (Pliocene).

Existing water bodies during the Miocene

During this time there were practically all the oceans that exist today. These include:

• Pacific Ocean: as today, it was the largest and deepest ocean. It was located between the extreme east of Asia and the extreme west of America. Some of the islands it contains today had already emerged, others had not.
• Atlantic Ocean: it was between the continents of America and Africa and Europe. It was formed during the fragmentation of Pangea, specifically from the lands that correspond to the continents Africa and South America. As they moved away, the space between them filled with water, giving rise to this ocean.
• Indian Ocean: had the same current position. from the east coast of Africa to Australia. It covered all that vast space.

Weather

The climate during the early Miocene was characterized by low temperatures. This was a consequence of the wide expansion of ice at both poles, which began in the previous epoch, the Eocene. This resulted in some environments acquiring arid conditions, as they were not able to retain moisture.

However, this did not hold true for long, since towards the middle of the Miocene there was a considerable and significant increase in ambient temperature. This phenomenon was baptized by specialists as the Miocene Climate Optimum.

During the Miocene Climate Optimum, ambient temperatures rose gradually, believed to be as much as 5 ° C above current temperatures. Thanks to this, a temperate-type climate developed over almost the entire planet.

Likewise, it is important to remember that during this time mountain ranges of great importance developed, with mountains and high peaks. This played a very important role in the climate after the Miocene Climate Optimum, since thanks to this, rainfall greatly decreased.

As the Miocene progressed, a large percentage of the planet acquired a dry climate. Consequently, the extent of the forests was diminished, while the tundras and deserts expanded.

At the level of the south pole, there were many glaciers at the beginning of the time, however, with the passing of time the ice sheet on the Antarctic continent increased until it completely covered it.

Flora

Many of the life forms, both plants and animals that were present in the Miocene, are preserved today as an important part of the great diversity of ecosystems on the planet.

During the Miocene, a significant decrease in the extension of forests and jungles was observed, due to the climatic changes caused. Because at a certain point in time the rainfall became scarce, the plants had to adapt to these changes as well.

This is how herbaceous plants and others that are also small and resistant to long periods of drought, such as chaparral, begin to dominate. Likewise, during this time angiosperms, which are seed-covered plants, flourished.

Herbaceous

Herbaceous plants are plants whose stems are not woody, but flexible and green in color. Its leaves are also green. They are generally small in size and some reach a medium height.

If they present flowers, they are in a terminal position, generally in groups or clusters. They are very versatile plants, as they can adapt to environmental conditions, despite being hostile. Regarding the life span, theirs is one year, although of course, there are exceptions.

Chaparrales

In reality, the chaparral is a type of biome in which a particular type of vegetation known as chaparros is found. These are woody-stemmed shrubs that are capable of surviving extreme environmental conditions. Likewise, in the chaparral there are also other types of plants, such as cacti and bushes.

Fauna

The dominant group during the Miocene epoch were mammals, which became highly diversified. From small mammals like the group of rodents, to large mammals like some marine ones.

Likewise, the group of birds also experienced a great expansion, being able to find fossils of specimens all over the planet.

Land mammals

Many land mammals walked the Earth during the Miocene epoch. These include:

Gomphotherium (extinct)

It was a large mammal (3 meters) that inhabited mainly the territories of Eurasia. He belonged to the group of proboscideans. Among its characteristic features we can mention two pairs of fairly long and resistant fangs, which were used to search for its food, which was made up of tubers and roots.

Amphicyon

It is also extinct. It had the appearance of an animal intermediate between the dog and the bear. Its body was compact, featuring four thick limbs and a long tail that was also quite strong.

It had specialized teeth for the carnivorous diet it had. It was quite large, it could measure up to 1 meter in height, two meters in length and have an approximate weight of more than 200 kg. Its main habitat was in North America.

Skeleton of an Amphicyon. Source: Clemens v. Vogelsang from Liechtenstein, via Wikimedia Commons

Merychippus

This animal is also extinct. It belonged to the equidae family. It was relatively small (89 cm). It was characterized by having three fingers on each extremity, of which one was covered with a hoof.

In addition, according to the specialists, it was grouped in herds, which moved through the land, grazing. It was very similar to today's horses and zebras.

Astrapotherium

It is extinct. It was a fairly large animal, as it could measure up to 3 meters and weigh 1 ton. The characteristics of its teeth allow to infer that it was a herbivore.

Its limbs were of average size and allowed it to move through marshy and dry terrain. According to the fossil records, it lived in South America, mainly near the Orinoco River.

Megapedetese

It belonged to the order of rodents. It was small in size, weighed 3 kg and could measure up to 14 cm in height. His body resembled that of a hare. It had very powerful and developed hind limbs, while the front limbs were very small. He was on a herbivorous diet.

Aquatic mammals

In the seas the fauna also diversified, being the group of mammals one of the main ones. Here the ancestors of the current whales had their origin.

Brygmophyseter

It belonged to the group of cetaceans, specifically the odontocetes (dentate). It is believed that the specimens reached a length of up to 14 meters. It was of carnivorous habits, being its favorite foods fish, squid and even other cetaceans.

Cetotherium

From a physical point of view, this mammal was quite similar to the whales that sail the seas today. They were quite large animals. According to fossil records, they could reach lengths of between 12 and 14 meters. They did not have beards, so they did not feed through water filtration.

Birds

Within the group of birds, there were large specimens that reached a great development during the Miocene.

Andalgalornis

It mainly inhabited the South American continent. It could measure up to 1.5 meters. Anatomically, its strongest feature was its legs, which allowed it to move very quickly. It also had a fairly resistant beak with which it could effectively capture its prey.

Kelenken

It was part of the so-called "birds of terror" that inhabited during the Miocene. It is estimated that it could measure up to 4 meters and weigh approximately 400 kg. Its beak had an average length of 55 cm. It had strong limbs that allowed it to chase and capture its prey.

Reptiles

In the Miocene there was also a great range of reptiles:

Stupendemys

It is believed that it inhabited northern South America, since its fossils have only been found there. It has been the largest freshwater turtle so far. It was about 2 meters long. It was carnivorous, its preferred prey being amphibians and fish.

Purussaurus

It was similar to crocodiles today. Large (up to 15 meters in length), it could even weigh several tons. His body was covered with a kind of armor that was impenetrable.

It was carnivorous, with teeth over 20 cm long, ideal for capturing its prey and not losing it. Its habitat was mainly aquatic, since due to its large size, it was quite slow to move on land.

Representation of a Purussaurus. Source: Nobu Tamura (http://spinops.blogspot.com), from Wikimedia Commons

Divisions

The Miocene is divided into six ages:

• Aquitanian: with a duration of three million years
• Burdigaliense: 5 million years
• Langhiense: 2 million years
• Serravaliense: 2 million years.
• Tortonian: 4 million years
• Messinian: 2 million years.

References

1. Cox, C. Barry & Moore, Peter D. (1993): Biogeography. An ecological and evolutionary approach (5th ed.). Blackwell Scientific Publications, Cambridge
2. Emiliani, C. (1992) Planet Earth: Cosmology, Geology, and the Evolution of Life and Environment. Cambridge: Cambridge University Press.
3. Herber, T., Lawrence, K., Tzanova, A., Cleaveland, L., Caballero, R. and Kelly, C. (2016). Late Miocene global cooling and the rise of modern ecosystem. Nature geoscience. 9. 843-847.
4. Peterson, J. (2018) Climate of the Miocene period. Obtained from: sciencing.com
5. Van Andel, T. (1985), New Views on an Old Planet: A History of Global Change, Cambridge University Press