Life on Earth During the Miocene Epoch
During cycles long anterior to the creation of the human race, and while the surface of the globe was passing from one condition to another, whole races of animals–each group adapted to the physical conditions in which they lived–were successively created and exterminated.
— Sir Roderick Impey Murchison
The Miocene Epoch
The word miocene is derived from the Greek words meion (meaning “less”) and kainos (meaning “recent or new”).This epoch was named by geologist Sir Charles Lyell. The name refers to the fact that it has 18% fewer modern sea invertebrates than the Pliocene.The Miocene Epoch was the earliest division of the Neogene Period which occurred million years to 2.6 million years ago. Extending from 23 million to 5.3 million years ago, the Miocene is often divided into:
- Early Miocene (23 - 16 mya)
- Middle Miocene (16 - 11.6 mya)
- Late Miocene (11.6 - 5.3 mya)
In geological terms, the Miocene is often divided into six ages corresponding to the various rock stages discovered. These ages from oldest to youngest are:
North and South America are rich in Miocene deposits. Rich deposits also occur in southern Europe, India, Mongolia, East Africa and Pakistan. The fossil record in Miocene deposits is rich in both terrestrial and marine organisms. In particular, the record of terrestrial evolution, particularly of mammals, is extensive.
The Miocene Epoch is is notable for its prehistoric life which included representatives of most of today's flora and fauna. During the Miocene, the earth was experiencing a continuation of the trend of long term cooling begun in the Eocene epoch. However, its climate was warmer than the Oligocene which preceeded it as well as the following Pliocene. Because the climate first wamed and then cooled during the Miocene period, it is significant that two major ecosystems first appeared:
- kelp forests of the marine ecosystems
- grasslands of the terrestrial ecosystems
Six Ages Of The Miocene Epoch
Time Period (millions of years)
(Middle Miocene Extinction event during this stage)
Climate Change in the Miocene Epoch
A number of factors contributed to climate change during this Epoch.
- Mountain formations in the Americas and Asia altered both air circulation and weather patterns leading to drier conditions.
- Because Antartica separated from South America during the Oligocene, warm, tropical waters mixed little with the cool, polar waters. Antartica froze triggering another global climate cooling.
- Seals and whales evolved in the abundance of organisms which appeared due to the stirring of nutrient rich waters.
- During this period, the oceans receded and inland waters evaporated forming land bridges between continents which allowed waves of animal migration.
- Grasslands dominated and those families adaptive to the harsher conditions survived and evolved such as horses, deer and antelope while those not suited to the new conditions verged on extinction.
The Miocene went through a series of changes resulting in rapid evolution of new flora and fauna and the extinction of many others.
1. 24 million years ago: In the short term, warming and drying occurred.
- Kelp forests and grasslands eventually became the dominant vegetation.
2. 20 million years ago: A period of mountain building occurred.
- The Cascade Mountains of North America, the Andes in South America and the Himalayas of Asia were formed during the Miocene.
- Wind and weather patterns were disrupted changing rainfall patterns.
- Carbon dioxide was removed from the atmosphere due to the erosion of the newly exposed rock which may have esacerbated the global cooling.
- Evolving marine life was supported by communities of large, brown algae that developed into kelp forests.
- These kelp forests support a number of evolving animal groups including sea otters, fish, and invertebrates.
- Inland seas dry out because of shifting continents, changing climate, and the formation of the polar ice cap.
- Sea levels dropped and also inland waters shrank.
- Land bridges formed, most importantly between Africa and Eurasia, as well as Eurasia and North America.
Life in the Miocene Epoch
During the Miocene, the open vegetation systems including deserts, tundra and grasslands were expanding while forests were becoming smaller.
- Studies of spore and pollen samples from this epoch suggest that most modern seed plant families existed by the end of the Miocene.
- A warming trend during the middle Miocene followed by a cooling period was likely responsible for the loss of northern tropical ecosystems, the expansion of coniferous forests in the north and the appearance of definite seasons.
- These changes triggered the evolution and diversification of modern grasses and sedges.
Changes in plant systems triggered morphological changes in animals; therefore, in temperate ecosystems, mammals and birds in particular evolved new forms including:
- fast-running herbivores
- large predatory mamals and birds
- small quick birds
Similar changes occurred in marine ecosystems as kelp forests appeared for the first time in the Miocene.
- Sea otters and other marine organisms adapted to this unique ecosystem evolved in tandem.
- Other marine dwellers not suited to these kelp forests went extinct such as the mammal Desmostylia.
Fauna Of The Miocene EpochClick thumbnail to view full-size
Land Bridges And The Diversification Of Life In The Miocene Epoch
Diversification of life during the Miocene was accelerated due to the appearance of land bridges. Connection of continents once separated by water allowed animals to migrate to new habitats, thus extending their geographic ranges.
- The primary paths of migration were between Africa, North America, and Eurasia.
- The Tethys Ocean, now receded, created a land bridge between Africa and Eurasia.
- Elephants and apes ventured over this land bridge extending their range into Eurasia.
- Rabbits, pigs, saber-toothed cats, and modern rhinos crossed the same bridge from Eurasia into Africa.
- Across the Bering land bridge which connected Siberia and Alaska, rhinos and elephants extended their range even further along while horses made their way from North America into Eurasia.
- At the end of the Miocene, only a narrow corridor of water separated North from South America allowing some animals to cross such as Ground Sloths which had evolved in the isolation in South America.
- Racoons crossed the same narrow waterway, making their way from North to South America.
- The island continent, Australia, gains immigrant species from southeast Asia, including rodents which may have travelled along the Malaysian island chain in order to expand their range.
- It does not appear that the migration of these invading species forced native species to extinction.
- Rather, it appears that changing climate and vegetation were the cause of most Miocene extinctions.
Notable Life During the Miocene Epoch
prehistoric horses of North America
Hypohippus, Merychippus, Hipparion
camels and deer
golden age of apes and hominids of Africa and Eurasia
Gigantopithecus, Dryopithecus, Sivapithecus
enormous Argentavis (200 pds)
North American and Eurasian
enormous Osteodontornis (50 pds)
Pelagornis (75 pds)
most other bird families present
South American Purussaurus, Australian Quinkana, Indian Rhamphosuchus
snakes, turtles, lizards
Sites of Significant Miocene Fossils
San Joaquin California is locatied within the Monterey Formation, a vast area of marine deposits rich in fossils from the Miocene Epoch.
The Villavieja Formation located around this area is also rich in Miocene fossils.
The Alcoota Fossil Beds in Australia are notable for the occurrence of well-preserved, rare, Miocene vertebrate fossils
Editors of Encyclopedia Britannica. Britannica Online Encyclopedia. Miocene Epoch. November 2011.
Editors of PBS. Evolution: A Journey into Where We're From and Where We are Going. Change: Deep Time - The Cenozoic Era: (248 mya - present) - Miocene Epoch
Polly, David and Dave Smith et al. University of California Museum of Paleontology. The Miocene Epoch. June 2010.
Strauss, Bob. About.com Dinosaurs. The Miocene Epoch (23-5 Million Years Ago). 2012.
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