South American land mammal age

The basic unit of measurement is the first/last boundary statement. This shows that the first appearance event of one taxon is known to predate the last appearance event of another. If two taxa are found in the same fossil quarry or at the same stratigraphic horizon, then their age-range zones overlap.

Background

South America was an island continent for much of the Cenozoic, or the "Age of Mammals". As a result, its mammals evolved in their own unique directions, as Australia and Madagascar still have today.

Paleogeographic timeline

A simplified paleogeographic timeline of South America:

• 66 Ma – South America was connected to both North America and Antarctica. Soon after this point, it lost its connection to North America.
• 66–50 Ma – Tiupampan to Casamayoran - South America was connected to Antarctica which, in turn, was connected to Australia. The Antarctica–Australia connection was lost around the end of this interval or perhaps as much as 15 million years later.
• 50–34 Ma – Casamayoran to Tinguirirican - South America was connected to Antarctica, which was not yet covered by ice.
• 34 Ma – Tinguirirican - South America and Antarctica became detached and glaciations started to form in Antarctica.
• 34–9 Ma – Tinguirirican to Chasicoan - South America had no land connections to any other continent.
• 9–3 Ma – Huayquerian to Chapadmalalan - islands formed between South and North America. A complete Isthmus of Panama most likely formed near the end of this interval, leading to the Great American Biotic Interchange (GABI).
• 3 Ma to present – Uquian to Holocene - the land connection between South and North America is established and migration between the formerly separated continents occurs. Significantly higher rates of extinction due to climatic changes occur in South America compared to North America, resulting in an asymmetrical exchange of species between the continents. North American originating taxa diversify significantly in South America during this period. It was previously believed this asymmetry was due to the main migrational route being from north to south, rather than the opposite way.
• Pleistocene – the glacials and interglacials of the Pleistocene caused drastic eustatic sea level changes, widening and narrowing the land bridge at the 'bottleneck' of Panama. As a side-effect, the vegetation changed during this period of strong climatic changes.
• Late Pleistocene – the earliest humans arrived in South America and settled in various parts of the continent. Evidence for cohabitation with the latest Pleistocene megafauna has been found at multiple locations, such as Monte Verde in coastal Chile and Tibitó on the Altiplano Cundiboyacense in Colombia.