Because the Miocene is closer to the present day than most other periods of geologic time, it is easier to see the effects of events, and to interpret patterns. Many of the fossil species of this time have close relatives alive today, which can be both good and bad. It is good in that we have living representatives to infer past biology, but bad in that we may be tempted to infer too much from this.
The overall pattern of biological change for the Miocene is one of expanding open vegetation systems (such as deserts, tundra, and grasslands) at the expense of diminishing closed vegetation (such as forests). This led to a rediversification of temperate ecosystems and many morphological changes in animals. Mammals and birds in particular developed new forms, whether as fast-running herbivores, large predatory mammals and birds, or small quick birds and rodents.
Plant studies of the Miocene have focussed primarily on spores and pollen. Such studies show that by the end of the Miocene 95% of modern seed plant families existed, and that no such families have gone extinct since the middle of the Miocene. A mid-Miocene warming, followed by a cooling is considered responsible for the retreat of tropical ecosystems, the expansion of northern coniferous forests, and increased seasonality. With this change came the diversification of modern graminoids, especially grasses and sedges.
In addition to changes on land, important new ecosystems in the sea led to new forms there. Kelp forests appeared for the first time, as did sea otters and other critters unique to those environments. At the same time, such ocean-going mammals as the Desmostylia went extinct.
For specific examples of Miocene communities, visit the Miocene Localities page.
UCMP Special Research: MIOMAP
Utilizing a Geographic Information System (GIS), the MIOMAP project is collecting and analyzing Miocene data from the western United States to examine how major environmental events have affected the diversity of animals in the past.
Find out more about the Tertiary paleontology and geology of North America at the Paleontology Portal.