Miocene

Miocene
Scotese, Christopher R.; Vérard, Christian; Burgener, Landon; Elling, Reece P.; · CC BY 4.0 · source
Name	Miocene
Color	Miocene
Time start	23.03
Time end	5.333
Caption map	Paleogeography of the Miocene (~20 Ma)
Timeline	Miocene
Celestial body	earth
Usage	Global (ICS)
Timescales used	ICS Time Scale
Chrono unit	Epoch
Strat unit	Series
Timespan formality	Formal
Lower boundary def	Base of magnetic polarity chronozone C6Cn.2n; first appearance of the planktonic foraminiferan Paragloborotalia kugleri
Lower gssp location	Lemme-Carrosio section, Carrosio, Italy
Lower gssp date	1996
Upper boundary def	First appearance of the planktonic foraminiferan Truncorotalia truncatulinoides
Upper gssp location	Monte San Nicola section, Gela, Sicily, Italy
Upper gssp date	2000
Upper boundary acceptance	2000
Lower gssp acceptance	1996

Miocene. The Miocene is a major epoch of the Neogene period within the Cenozoic era, spanning from approximately 23.03 to 5.333 million years ago. It followed the Oligocene and preceded the Pliocene, representing a critical interval of global cooling, continental uplift, and the modernization of terrestrial ecosystems. This epoch witnessed the expansion of grasslands, the diversification of many mammalian families, and the early evolution of the Hominidae family, setting the stage for later human ancestors.

Etymology and definition

The term "Miocene" was coined by the eminent Scottish geologist Charles Lyell, derived from the Greek words *meiōn* (less) and *kainos* (new), meaning "less recent" in reference to its position in the fossil record containing a smaller proportion of modern species than the subsequent Pliocene. Its formal boundaries were later defined by the International Commission on Stratigraphy using biostratigraphic markers, specifically the first appearance of the foraminiferan Paragloborotalia kugleri at its base and the first appearance of Truncorotalia truncatulinoides at its top. The Global Boundary Stratotype Section and Point (GSSP) for its start is located at Lemme-Carrosio in Italy, while its end is defined at Monte San Nicola in Sicily.

Climate and geography

The global climate during the early Miocene was relatively warm, a phase sometimes termed the Miocene Climatic Optimum, but a long-term cooling trend commenced in the middle Miocene, culminating in the expansion of the East Antarctic Ice Sheet around 14 million years ago. This cooling was driven by factors including the closure of the Tethys Ocean and the uplift of major mountain ranges like the Himalayas and the Andes, which altered global atmospheric circulation. Geographically, continents approached their modern positions; the connection between North America and South America had not yet formed, but the Tethys Seaway closed as Africa collided with Eurasia, while the Mediterranean Sea experienced dramatic drying events known as the Messinian salinity crisis near the epoch's end.

Flora and fauna

Terrestrial ecosystems were dominated by the rapid spread of C4 grasses, leading to the expansion of savannas and steppes at the expense of forests, particularly in regions like the Great Plains of North America and parts of Africa. This "grassland revolution" drove the evolution of ungulates with high-crowned hypsodont teeth for grazing, including diverse families of rhinoceroses, chalicotheres, and the three-toed horse Merychippus. Predators like the "bear-dog" Amphicyon and early sabre-toothed cats such as Machairodus were apex carnivores. Marine life included the giant shark Megalodon, early dolphins, and the seal-like Desmostylia.

Paleoenvironmental changes

Significant paleoenvironmental shifts were driven by tectonic activity and climatic feedback loops. The uplift of the Tibetan Plateau intensified the Asian monsoon system, while the formation of the Antarctic Circumpolar Current thermally isolated Antarctica, reinforcing its glaciation. In Europe and Asia, the gradual restriction of the Paratethys Sea created vast, seasonally arid basins. These changes are recorded in deep-sea oxygen isotope records from sites like Ocean Drilling Program cores and in continental fossil assemblages, such as those from the Siwalik Hills in Pakistan and the John Day Fossil Beds in Oregon.

Significance in human evolution

The Miocene is the epoch during which the Hominidae (great ape) family diverged from other catarrhine primates, with key fossils found across Africa and Eurasia. Early members of the human lineage, such as Proconsul from early Miocene sites in Kenya and Dryopithecus from Europe, were arboreal. The later Miocene saw the emergence of the first likely members of the Homininae subfamily, including Samburupithecus and Nakalipithecus, with the split between the lineages leading to modern gorillas, chimpanzees, and humans occurring near its end, as suggested by genetic studies and fossils like Sahelanthropus tchadensis from Chad.

Category:Miocene Category:Geological epochs Category:Neogene