The Rancholabrean Land Mammal Age (RLB) occurred in the late Pleistocene, incorporating at least the Wisconsin Glaciation and possibly the preceding interglacial ('Sangamon'). The RLB is defined based on the occurrence of Bison. The first occurrence (arrival time) of Bison is not well established and is still debated. A conservative approach toward the RLB includes: (1) restricting the RLB to faunas south of 55°. N latitude in North America, (2) defining the RLB by the earliest arrival of Bison south of this latitude, (3) placing the best-corroborated arrival time of Bison (therefore the beginning of the RLB) between approximately 210 and 160. ka, and (4) the end of the RLB is marked by the extinction of mainly large mammals as an event or process culminating at approximately 11 radiocarbon ka BP. RLB faunas contain a wealth of information including amphibians, reptiles, birds, and mammals, but clearly the most is known about the latter. Glacial climate regimes forced species into communities that do not occur today (nonanalog or disharmonious scenarios). The debate about the terminal RLB extinctions continues with the cause either being (1) overkill due to the arrival of the First Americans, or (2) the climatic and environmental defragmentation of biotic communities.

The Rancholabrean Land Mammal Age (RLB) occurred in the late Pleistocene, incorporating at least the Wisconsin Glaciation and possibly the preceding interglacial ('Sangamon'). The RLB is defined based on the occurrence of Bison. The first occurrence (arrival time) of Bison is not well established and is still debated. A conservative approach toward the RLB includes: (1) restricting the RLB to faunas south of 55°. N latitude in North America, (2) defining the RLB by the earliest arrival of Bison south of this latitude, (3) placing the best-corroborated arrival time of Bison (therefore the beginning of the RLB) between approximately 210 and 160. ka, and (4) the end of the RLB is marked by the extinction of mainly large mammals as an event or process culminating at approximately 11 radiocarbon ka BP. RLB faunas contain a wealth of information including amphibians, reptiles, birds, and mammals, but clearly the most is known about the latter. Glacial climate regimes forced species into communities that do not occur today (nonanalog or disharmonious scenarios). The debate about the terminal RLB extinctions continues with the cause either being (1) overkill due to the arrival of the First Americans, or (2) the climatic and environmental defragmentation of biotic communities.