Neogene Period: A unit of geologic time consisting of the [Miocene] and [Pliocene] Epochs. The Neogene Period follows the [Paleogene] Period and is followed by the [Quaternary] Era. The terms 'Neogene System' and 'Upper Tertiary System' have also been used to describe what is currently called the 'Neogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine granularity of time units as time approaches the present and more information is preserved. By dividing the [Tertiary] Era into two 'PeriodsPeriods' instead of 7 'epochs', the periods are more closely comperable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.
The Neogene Covers roughly 26 Million years. During the Neogene mammals and birds evolved considerably. Most other forms were relatively unchanged. Some continetal motion took place, the most significant event being the connection of North And South America in the late [Pliocene]. Climates cooled somewhat over the duration of the Neogene culminating in continental glaciations in the [Quaternary Era] that follows.