The Pleistocene is the name for the geological epoch which started approximately 1,808,000 years ago and ended 11,550 years ago. The most geologically significant aspect of the Pleistocene is that it represented the continuation of a cooling period which began several tens of millions of years ago and continues to this day.
Throughout the Pleistocene were numerous ice ages, with ice sheets covering large parts of Eurasia and North America. Glaciers extended as far south as Hamburg, Germany, London, England, and Chicago in the United States. The Bering straight was passable for long periods of time, called the Bering land bridge. This allowed the intermixing of Old World and New World species, including the migration of humans to the Americas.
The animals of the Pleistocene were largely the same as today, with a few dozen exceptions. The exceptions, of course, are what makes the topic interesting.
Animals unique to the Pleistocene include cave bears (short-faced bears), mammoths and mastodons (relatives of modern elephants), saber-toothed cats with fangs as long as swords, ferocious dire wolves, huge ground sloths, and relatives of armadillos called Glyptodons, which were the size of a Volkswagon Beetle. Many of these have been preserved the La Brea Tar Pits in Los Angeles as well as hundreds of other fossil sites worldwide.
In South America and Australia were flightless birds larger than men, such as Phorusrhacos, sometimes called “Terror Birds”. In Australia there were also carnivorous kangaroos, giant wombats such as Diprotodon, the Marsuipial Lion, and massive snakes and lizards. A giant lizard, megalania, would have been easily able to slay sheep and is the closest thing to a dragon seen on Earth since the age of the dinosaurs.
In general, the adaptive conditions of the Pleistocene favored size, which allowed animals to better retain body heat. As such, these large organisms have been dubbed the Pleistocene megafauna.
Other important Pleistocene animals are the early homonids, such as the genus Paranthropus, and humanity’s ancestors or relatives Homo habilis, Homo floresiensis, Homo erectus, Homo neanderthalis, and Homo heidelbergensis. Homo floresiensis and Homo neanderthalis went extinct the most recently, with signs of the former existing as recently as 12,000 years ago.
Most of the Pleistocene megafauna went extinct between 20,000 and 10,000 years ago. This can very likely be attributed to human hunting, a theory known as overkill. There is various evidence for this, such as the fact that megafauna in North America went extinct only when our ancestors crossed the Bering land bridge. Another theory blames a so-called hyperdisease, a terrible disease which affected many different species, though this has less support than the overkill theory.