North America: Land mammal fauna. In most of North America, faunal stages are defined according to the land mammal fauna (NALMA). They overlap the borders of the Miocene and Oligocene/Pliocene:Hemphillian(9 - 4.75 mya); includes much of the Early PlioceneClarendonian(11.8 - 9 mya)Barstovian(15.5 - 11.8 mya)Hemingfordian(19 - 15.5 mya)Arikareean(30.5 - 19 mya); includes much of the Oligocene
California sites. Californian sites, which are derived from the former Farallon Plate, provide another sequence which also overlaps with the epoch boundaries:Delmontian(7.5 - 2.9 mya); includes much of the PlioceneMohnian(13.5 - 7.5 mya)Luisian(15.5 - 13.5 mya)Relizian(16.5 - 15.5 mya)Saucesian(22 - 16.5 mya)Zemorrian(33.5 - 22 mya); includes nearly all the Oligocene
Other systems. Yet other systems are used to describe the Miocene stratigraphy of Japan, Australia, and New Zealand.
Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent.
Mountain building took place in Western North America and Europe. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the American Great Plains and in Argentina. India continued to collide with Asia, creating more mountain ranges.
The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish-Arabian region between 19 and 12 mya. Subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis) near the end of the Miocene.
Climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued.
Although a long-term cooling trend was well underway, there is evidence for a warm period during the Miocene when the global climate rivaled that of the Oligocene. The Miocene warming began 21 mya and continued until 14 mya, when global temperatures took a sharp drop. By eight mya, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as seven to eight mya, although the climate for the most part remained warm enough to support forests there well into the Pliocene.
The oceans continue to cool as the poles were transformed into glaciers.
Grasslands appear to have underwent a major expansion as forests fell victim to a generally cooler and drier climate overall. Grasses also diversified greatly into a number of species and also caused a major increase in the biodiversity of large herbivores and grazers, including ruminants (of which modern cattle and deer belong).
Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist.
Mammals. These were also modern, with recognizable wolves, raccoons, horses, beaver, deer, camels, and whales. A plethora of Miocene hominoid (ape) fossils have been found in both Eurasia and Africa, with most of the Middle and Late Miocene hominoids discovered in Eurasia (Smith 2006). It is believed that during the Early and Middle Miocene, African hominoids first immigrated to Eurasia (Smith 2006). Two Miocene fossil hominoids, Dryopithecus and Ouranopithecus, are classified under the family Hominidae (hominids), a taxon that includes the great apes (gorillas, chimpanzees, bonobos, orangutans), as well as humans and extinct relatives of humans, such as Australopithecus (Smith 2006).
Birds. Recognizable crows, ducks, auks, grouses, and owls appear in the Miocene. By the epoch's end, all or almost all modern families are believed to have been present; the few post-Miocene bird fossils that cannot be placed in the evolutionary tree with full confidence are simply too badly preserved instead of too equivocal in character. Marine birds reached their highest diversity ever in the course of this epoch.
Sea life. Brown algae, called kelp, proliferate, supporting new species of sea life, including otters, fish, and various invertebrates. The cetaceans diversified and some modern genera have already appeared, such as the sperm whales. The pinnipeds, who appeared near the end of the Oligocene, are more and more aquatic.
- Geologic time scale
- Begun, D. R. “Miocene fossil hominids and the chimp-human clade.” Science, 257(5078): 1929-1933, 1992.
- Malone, D. “Mechanisms of hominoid dispersal in Miocene East Africa.” Journal of Human Evolution 16(6): 469-481, 1987.
- Ogg, J. Overview of Global Boundary Stratotype Sections and Points (GSSP's) 2004. Retrieved September 17, 2007.
- Rohde, R. A. GeoWhen Database 2005. Retrieved September 17, 2007.
- Smith, J. European Miocene Hominoids: The Missing Link? 2006. Retrieved September 17, 2007.