In zoology, megafauna are large animals. The most common thresholds to be a megafauna are weighing over 45 kg (99 lb) or weighing over 1,000 kg (2,200 lb). The first occurrence of the term was in 1876. After the Cretaceous–Paleogene extinction event wiped out all non-avian dinosaurs, mammals and other vertebrates experienced an expansion in size. Millions of years of evolution led to gigantism on every major land mass. During the Quaternary extinction event, many species of megafauna went extinct as part of a slowly progressing extinction wave that affected ecosystems worldwide.
The African bush elephant (foreground), Earth's largest extant land mammal, and the Masai ostrich (background), one of Earth's largest extant birds
Baleen whale comparative sizes
Diprotodon optatum
"Megalania" (Varanus priscus),
Late Pleistocene extinctions
The Late Pleistocene to the beginning of the Holocene saw numerous extinctions of predominantly megafaunal animal species, which resulted in a collapse in faunal density and diversity across the globe. The extinctions during the Late Pleistocene are differentiated from previous extinctions by the widespread absence of ecological succession to replace these extinct megafaunal species, and the regime shift of previously established faunal relationships and habitats as a consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. Human impact on megafauna populations is thought to have been driven by hunting ("overkill"), as well as possibly environmental alteration. The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy.
Late Pleistocene in northern Spain, by Mauricio Antón. Left to right: wild horse; woolly mammoth; reindeer; cave lion; woolly rhinoceros
Mural of the La Brea Tar Pits by Charles R. Knight, including sabertooth cats (Smilodon fatalis, left) ground sloths (Paramylodon harlani, right) and Columbian mammoths (Mammuthus columbi, background)
The proportion of extinct large mammal species (more than or equal to 10 kg (22 lb)) in each country during the last 132,000 years, only counting extinctions earlier than 1000 years BP
Giant tapir (Tapirus augustus) restoration