Miocene Epoch

Miocene Epoch, epoch of the Cenozoic Era of the geological timescale, and also the series of rocks formed during this time which lasted between about 24 and 5 million years ago. It is the older of the two epochs of the Neogene Period, succeeding the Oligocene (the youngest epoch of the Palaeogene Period) and preceding the Pliocene. The ending “-cene”, meaning “recent” (in reference to modern life), denotes the proportion of fossils that occur in each Cenozoic epoch that are still living today. Miocene, meaning “less recent”, alludes to the intermediate nature of Miocene fossils.

Many important physical and biological features of the modern Earth emerged during the Miocene. Climatically, it is the time of transition from the Greenhouse Earth of the Cretaceous and Palaeogene, to modern Ice-house conditions. Although there was a notable warming during the Early Miocene, this was followed by a very rapid cooling as the Antarctic ice-cap expanded dramatically. The great seaway, Tethys, which stretched from the Caribbean through to the Indian Ocean, and onwards to the western margins of the Pacific, was severed by closure of two former “gateways”. In the Middle East, Arabia collided with south-west Asia, disconnecting the Mediterranean from the Indian Ocean; and in the Indonesian region, Australia collided with south-east Asia giving rise to the large mountainous archipelagos of the Indo-West Pacific. Northward movement of Africa against Europe caused the most recent of the main mountain folding events in the Alps, but to the north and east large areas of Eurasia were flooded by shallow seas (Paratethys). Towards the end of the Miocene however, the Mediterranean, which had become isolated from other seas, temporarily dried up, the so-called Messinian Salinity Crisis.

Uplift of other main mountain belts already in existence (Himalaya, and the Cordilleras of the Americas), continued. Widespread uplift led to greatly increased rock erosion, which affected the carbon dioxide balance in the atmosphere and contributed to climatic cooling and expansion of Antarctic ice. Also significant was the widening of the ocean passage between Australia and Antarctica, leading to the development of a circumglobal current system in the southern oceans, cutting off Antarctica from warmer currents elsewhere.

On land, climatic cooling was accompanied by great vegetational changes, with many areas of thick forests giving way to increasing areas of grasslands, or to mosaics of woodlands and grasslands. The continued insularity of South America and Australia was reflected by their endemic marsupials, and by endemic sloths and their relatives in South America. Global spread of grassland was accompanied by adaptive radiations of grazing animals within herbivore groups, particularly among hoofed mammals, notably of bovids (sheep, antelopes, cattle, and their relatives), while horses evolved from browsers to grazers. Apes are Miocene and African in origin, later spreading into Eurasia, presumably following the Middle East closure of Tethys. Other important groups that originated in the Miocene include elephants, hyenas, and bears. Antlered deer, rhinoceroses, and giraffes diversified in the Old World, and raccoons and their relatives diversified in North America. In the air, the largest known flying (condor-like) bird has been found as a fossil in Argentina.

The largest known carnivorous shark roamed the seas, and whales developed their modern dorsal blow-holes. Many shallow marine invertebrates diversified in response to increasing areas of shelves and coastlines in the Indo-West Pacific region. Initially, coral reefs and warm-water limestones reached a far greater extent than at any time since, and the two main circumtropical marine provinces of today (Atlantic and Indo-Pacific) emerged in response to the closure of Tethys in the Middle East.