The terms Neogene System (formal) and upper Tertiary System (informal) describe the rocks deposited during the Neogene Period.
The Neogene traditionally ended at the end of the Pliocene epoch, just before the beginning of the Quaternary Period; many time scales show this division. However, there is a movement amongst geologists (particularly Neogene Marine Geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly Quaternary Terrestrial Geologists) insist the Quaternary to be a separate period of distinctly different record. The somewhat confusing terminology and disagreement amongst geologists on where to draw what hierarchical boundaries, is due to the comparatively fine divisibility of time units as time approaches the present, and due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and reflecting many more environments, than the slightly older geological record. By dividing the Cenozoic era into three (arguably two) periods (Paleogene, Neogene, Quaternary) instead of 7 epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras.
The International Commission on Stratigraphy ICS has proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.588 Ma., namely the start of the Gelasian. The International Union for Quaternary Research (INQUA) has counterproposed that the Neogene and the Pliocene end at 2.588 Ma., that the Gelasian be transferred to the Pleistocene, and the Quaternary be recognized as the third period in the Cenozoic, citing the key changes in Earth's climate, oceans, and biota that occurred 2.588 Ma. and its correspondence to the Gauss-Matuyama reversal.
The Neogene covers roughly 23 million years. During the Neogene Mammals and Birds evolved considerably. Most other forms were relatively unchanged. Some continental 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 sub-era (or period, in some time scales) that follows, and that saw the dawn of Homo Sapiens.