This allows for more grazers, such as horses, rhinoceroses,and hippos. Ninety five percent of modern plants existed by the end of this epoch. The coevolution of gritty, fibrous, fire-tolerant grasses and long-legged gregarious ungulates with high-crowned teeth, led to a major expansion of grass-grazer ecosystems, with roaming herds of large, swift grazers pursued by predators across broad sweeps of open grasslands, displacing desert, woodland, and browsers.
The higher organic content and water retention of the deeper and richer grassland soils, with long term burial of carbon in sediments, produced a carbon and water vapor sink. This, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. C4 grasses, which are able to assimilate carbon dioxide and water more efficiently than C3 grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago.
The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO2. Cycads between 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. In the Early Miocene, several Oligocene groups were still diverse, including nimravids, entelodonts, and three-toed horses. Like in the previous Oligocene epoch, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with easily recognizable dogs, bears, raccoons, horses, beaver, deer, camels, and whales, along with now extinct groups like borophagine dogs, gomphotheres, three-toed horses, and semi-aquatic and hornless rhinos like Teleoceras and Aphelops.
The expansion of silica-rich C4 grasses led to worldwide extinctions of herbivorous species without high-crowned teeth. Unequivocally recognizable dabbling ducks, plovers, typical owls, cockatoos and crows appear during the Miocene. Marine birds reached their highest diversity ever in the course of this epoch.
Approximately species of apes lived during this time. They ranged over much of the Old World and varied widely in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived from between 15 to 12 million years ago. In the oceans, brown algae, called kelp, proliferated, supporting new species of sea life, including otters, fish and various invertebrates.
Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera in comparison to only six living genera. This diversification correlates with emergence of gigantic macro-predators such as megatoothed sharks and raptorial sperm whales. Prominent examples are C. Other notable large sharks were C. Crocodilians also showed signs of diversification during Miocene. The largest form among them was a gigantic caiman Purussaurus which inhabited South America.
Another gigantic form was a false gharial Rhamphosuchus, which inhabited modern age India. A strange form Mourasuchus also thrived alongside Purussaurus. This species developed a specialized filter-feeding mechanism, and it likely preyed upon small fauna despite its gigantic size.
The pinnipeds, which appeared near the end of the Oligocene, became more aquatic. Prominent genus was Allodesmus. A ferocious walrus, Pelagiarctos may have preyed upon other species of pinnipeds including Allodesmus. Because marine plants do not preserve well over time, scientists can date kelp only to the Miocene, when animals it supports are known to appear, but it may exist in earlier periods.
The shifting continents, changing climate patterns, and formation of a polar ice cap cause sea levels to drop and inland seas to shrink.
Land routes open between continents, most notably between Africa and Eurasia, and Eurasia and North America. The great diversification of land mammals during the Miocene is due in large part to the formation of land bridges. These routes, which emerge as sea levels drop and inland seas dry out, connect continents previously separated by water. They provide access to new habitats and enable migrating animals to greatly extend their geographic ranges. Routes between Africa, Eurasia, and North America are the primary migratory paths.
The once-great Tethys Ocean no longer divides Africa and Eurasia. Elephants and apes are among the mammals that venture out of Africa and settle in parts of Eurasia, while rabbits, pigs, saber-toothed cats, and modern rhinos move in the opposite direction.
To the north, a dry corridor, the Bering land bridge, connects what are now Siberia and Alaska. Eventually, both elephants and rhinos make their way to North America, perhaps crossing paths with horses on their way to Eurasia. At the close of the Miocene, North America and South America are close enough for some species to cross the narrow dividing waters.
Ground sloths, which had evolved in isolation with other South American species, make their first appearance in the north, while raccoons can be found in the south. The island continent of Australia welcomes visitors from southeast Asia, like rodents, which may travel along the Malaysian island chain to get there.
Surprisingly, the large numbers of "invading" species probably do not force great numbers of native species to extinction. Animals that go extinct in the Miocene more likely do so because they fail to adapt to changes in climate and vegetation. Horses first appeared in the early Eocene as cat-sized herbivores, feeding on leafy vegetation.
As coarse grasses replace this woodland vegetation, however, some horse species evolve larger jaws and deep-rooted teeth with protective enamel. They also evolve larger guts, because grasses are relatively poor in nutrition and must be eaten in higher quantities to compensate.
Grazing horses are larger than their browsing cousins, with longer legs and hooves that enable them to run faster than those with padded feet. They quickly spread from North America to Europe and Asia, and from there to Africa, where some species become today's zebras.
Orangutans, or Asian apes, are modern, tree-dwelling primates, specialized for four-limbed climbing. Australia's early Miocene facts.
Position Australia was isolated from all other continents and had slowly begun to drift northwards. Climate During the early Miocene, northern Australia had a warm, wet climate. It became cooler and drier by the late Miocene. Setting In the early Miocene, New Guinea was a series of islands on the northern edge of the tectonic plate carrying Australia.
A tectonic plate is a large area of the Earth's crust that drifts as one piece over the molten mantle below. From about 15 million years ago, as the Australian plate crumpled up against the South-East Asian plate, larger areas of New Guinea rose above sea level. Vegetation Northern Australia was covered in lush rainforest. The Miocene was a time of enormous richness and variety of plant and animal life in Australia, equal to that found today in the rainforests of Borneo and the Amazon.
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