Americas

=== Ecology ===
North America and South America began to develop a shared population of flora and fauna around 2.5&nbsp;million years ago, when [[continental drift]] brought the two continents into contact via the [[Isthmus of Panama]]. Initially, the exchange of biota was roughly equal, with North American genera migrating into South America in about the same proportions as South American genera migrated into North America. This exchange is known as the [[Great American Interchange]]. The exchange became lopsided after roughly a million years, with the total spread of South American genera into North America far more limited in scope than the spread of North American genera into South America.<ref>{{cite journal | title = Ecogeography and the Great American Interchange | last = Webb | first = S. David | journal = Paleobiology | volume = 17 | pages = 266–280 | number = 3 | year = 1991 | publisher = Paleontological Society | jstor=2400869| doi = 10.1017/S0094837300010605 | bibcode = 1991Pbio...17..266W | s2cid = 88305955 }}</ref>