Pleistocene rewilding is the advocacy of the reintroduction of descendants of Pleistocene megafauna, or their close ecological equivalents. An extension of the conservation practice of rewilding, which involves reintroducing species to areas where they became extinct in recent history (hundreds of years ago or less).

Towards the end of the Pleistocene era (roughly 13,000 to 10,000 years ago), nearly all megafauna of Europe, as well as South, Central and North America, dwindled towards extinction, in what has been referred to as the Quaternary extinction event. With the loss of large herbivores and predator species, niches important for ecosystem functioning were left unoccupied. In the words of the biologist Tim Flannery, "ever since the extinction of the megafauna 13,000 years ago, the continent has had a seriously unbalanced fauna". This means, for example, that the managers of national parks in North America have to resort to culling to keep the population of ungulates under control.

Paul S. Martin (originator of the Pleistocene overkill hypothesis) states that present ecological communities in North America do not function appropriately in the absence of megafauna, because much of the native flora and fauna evolved under the influence of large mammals.

Ecological and evolutionary implications

Research shows that species interactions play a pivotal role in conservation efforts. Communities where species evolved in response to Pleistocene megafauna (but now lack large mammals) may be in danger of collapse. Most living megafauna are threatened or endangered; extant megafauna have a significant impact on the communities they occupy, which supports the idea that communities evolved in response to large mammals. Pleistocene rewilding could "serve as additional refugia to help preserve that evolutionary potential" of megafauna. Reintroducing megafauna to North America could preserve current megafauna, while filling ecological niches that have been vacant since the Pleistocene.
Deuda pleistocene debt by serchio25

All of the planned species that will be introduced to North America.

Possible fauna for reintroduction

The Pleistocene rewilding project aims at the promotion of extant fauna and the reintroduction of extinct genera in the southwestern United States. Native fauna are the first genera for reintroduction. The Bolson tortoise was widespread during the Pleistocene era, and continued to be common during the Holocene epoch until recent times. Its reintroduction from northern Mexico would be a necessary step to recreate the soil humidity present in the Pleistocene, which would support grassland and extant shrub-land and provide the habitat required for the herbivores set for reintroduction. However, to be successful, ecologists will support fauna already present in the region.
Wild new america

North America in 500 years after people.

The pronghorn, which is extant in most of the US southwest after almost becoming extinct, is a candidate for the revival of the ancient ecosystem. The pronghorn are native to the region, which once supported large numbers of the species and extinct relatives from the same genus. It would occupy the more arid and mountainous ecosystems within the assigned area.

The plains bison numbered in the millions during the Pleistocene era, until European settlers drove them to near-extinction in the late 19th century. The bison has made a recovery in many regions of its former range, and is involved in several local rewilding projects across the Midwestern United States.
Rewilding north america plains by serchio25

Great Plains in 500 years after people.

Bighorn sheep and mountain goats are already present in the surrounding mountainous areas and therefore should not pose a problem in rewilding more mountainous areas. Reintroducing extant species of deer to the more forested areas of the region would be beneficial for the ecosystems they occupy, providing rich nutrients for the forested regions and helping to maintain them. These species include white-tailed and mule deer.

Herbivorous species considered beneficial for the regional ecosystems include the collared peccary, a species of New World wild pig that was abundant in the Pleistocene. Although this species (along with the flat-headed and long-nosed peccaries) are extinct in many regions of North America, their relatives survive in Central and South America and the collared peccary can still be found in southern Arizona and Texas.

The horse, which is today extant as the mustang is, in fact, a native species reintroduced by the Spanish in the 15th century. Horses originated in North America and spread to Asia via the Ice Age land bridge, but became extinct in their evolutionary homeland alongside the mammoth and ground sloth. The Pleistocene grasslands of North America were the birthplace of the modern horse, and by extension the wild horse. The only remaining species of wild horse is a part of the prairie ecosystem and grazes alongside bison. The plains were home to an equid resembling a zebra, called the Hagerman horse; this could be represented by grant's zebra or Grevy's zebra. It would be introduced into the Great Plains from Africa as part of the project. The mountainous region was also once home to the extinct Yukon wild horse, whose close relative (the onager) survives in central Asia today, and can be reintroduced to boost biodiversity in the more arid regions of the rewilding area.

Alongside the wild horse, camels evolved in the drier regions of North America. Proof of this can be seen in the camelids of South America: the llama, alpaca, guanaco and vicuna. North America, therefore, links the South American camelids with those of the Old World (the dromedary and Bactrian camel). Pleistocene rewilding suggests that the closest relatives of the North American species of camel (Camelops) be reintroduced. The best candidates would be the dromedary for the arid desert regions and the guanaco and/or vicuna in the arid mountain regions, but there have been suggestions of breeding and wilding the fertile hybrid camelids (cama).

During the Pleistocene, two species of tapir existed in North America: the California and Florida tapirs. They became extinct at the end of the Pleistocene era, but their relatives survive in South America. The mountain tapir would be an excellent choice for rewilding humid areas, such as those near lakes and rivers. The mountain tapir is the only extant non-tropical species of tapir.

During the Pleistocene, large populations of Proboscideans lived in North America, such as the Columbian mammoth and the American mastodon. The mastodons all became extinct at the end of the Pleistocene era, as did the mammoths of North America. However, an extant relative of the mammoth is the Asian elephant. It now resides only in tropical southeastern Asia, but the fossil record shows that it was much more widespread, living in temperate northern China as well as the Middle East (an area bearing an ecological similarity to the southwestern United States). The Asian elephant is, therefore, a good candidate for the Pleistocene rewilding project. It would probably best be suited to occupy the same humid areas as the tapir, as well as dense forest regions where it would cause soil regeneration and control the spread of forests. Meanwhile, the African elephant may be the best extant candidate to refill the niche left empty with the extinction of the mastodon.

During the Pleistocene era, North, Central and South America were populated with a group of large animals that moved north as part of the Great American Interchange caused by the junction of the North and South American continents. Today, species such as the ground sloth and glyptodon are extinct, although a few "dwarf" species of sloth survived in remote Caribbean-island forests until a few thousand years ago. Their close relatives, the tree sloths and armadillos, are a remnant of this once-diverse group of mammals. The reintroduction of armadillos (such as the nine-banded armadillo and the giant armadillo) could help regenerate soils in the arid and prairie regions of the rewilding project.

Pleistocene America boasted a wide variety of dangerous carnivores (most of which are extinct today), such as the short-faced bear, saber-toothed cats (e.g. Homotherium), the American lion, dire wolf, American cheetah and (possibly) the terror bird. Some carnivores and omnivores survived the end of the Pleistocene era and were widespread in North America until Europeans arrived, such as grizzly bears, mountain lions, jaguars, grey and red wolves, bobcats, and coyotes. The African cheetah would make a great choice for rewilding, keeping the population of pronghorns in check. Jaguars could be reintroduced back to North America to control populations of prey animals. Some of the larger cats such as the African lion could act as a proxy for the Pleistocene American lion, they could be introduced to keep the numbers of herds of American bison in check.

Back then, there were also native new world monkeys of North America. Some species including capuchin monkeys, spider monkeys, and/or squirrel monkeys could be reintroduced to warm and humid parts of North America, including Florida, etc, to fill the niche left behind by the native monkeys.

Recreating a lost ecosystem

In order for a functioning and balanced ecosystem to exist, there must be carnivores that prey on the herbivores. In the mountains, the reintroduction of the mountain lion is necessary to keep mountainous herbivores, such as the camelids, asses and mountain goats, under control.

In the forest surrounding them, the reintroduction of the jaguar (which roamed much of southwestern America until early 20th century) will control the populations of animals such as deer, tapirs and peccary. Alongside the jaguar will be the grizzly bear, an omnivore that was once distributed across North America but now survives only in the far north of the US and much of western and northwestern Canada. In heavily forested areas, the Siberian tiger and dhole will be introduced to control the populations of deer, wild asses, camels, bighorns, and mountain goats.

The terror birds' closest living relatives are the much smaller seriemas. Ecologically, the seriema is the South American counterpart of the secretary bird.

In arid regions, the Old World cheetah could be introduced to control the population of pronghorn, the fastest-running herbivore on earth (it can run so fast because it was once hunted by the American cheetah). The American cheetah was more closely related to the mountain lion, but evolved in a similar way to the Old World cheetah (an example of convergent evolution).

Reintroduced into its ancient environment, the grey wolf will spread across all ecosystems and compete for prey with all other predators; it may once again be seen hunting camels in arid regions, and bison on the grassy prairies of the Great Plains.

The final (and most-controversial) aspect of the rewilding project is the reintroduction of lions to the American southwest. Whilst many consider the lion to be strictly an African species, this was not always true. The lion was, in fact, one of the most widespread of all megafauna (certainly of the carnivores). The lion once ranged from Africa through Pleistocene Europe and Asia, across Beringia and down through North America to Argentina in South America. A relict remnant of that distribution across the world is still found in India, where the Asiatic lion still survives in a small sanctuary in the Gir Forest National Park. In Europe and northern Asia it existed as the cave lion, and in the Americas as the American lion. The American lion once hunted in prides across the grasslands of Pleistocene North America, taking down bison and wild horses as their African equivalents take down wildebeest and zebra. The reintroduction of lions is, however, the end of a long line of reintroductions, and will only have realistic prospects of occurring if all goes well with the others first.

The Pleistocene parks idea was first suggested for Arctic and South American ecosystems, and was less publicized. Mauro Galetti suggested that several plant species in South America lost their major megafauna seed dispersers at the end of the Pleistocene. Secondary seed dispersal, water and indigenous people were responsible for maintaining the seed-dispersal process over the past 10,000 years. Therefore, rewilding South American savannas will establish lost seed-dispersal services and also control unburned vegetation (due to a lack of megaherbivores). Brazilian savannas burn and release tons of carbon dioxide to the atmosphere yearly. Asian elephants, horses, llamas and other large mammals may be used to control fires.


The reintroduction of Bolson tortoise, equids (mustangs and burros) and camelids (dromedary) has already begun. Muskoxen roam areas of Europe and Asia last grazed during Rome's heyday, and bison herds thrive in subarctic Canada and Alaska. As of 2011, there are no active plans to reintroduce more exotic megafauna, such as elephants, cheetahs or lions, due to the controversial nature of these reintroductions.

The southwestern United States and the Brazilian savanna are the most suitable parts of North and South America where Pleistocene rewilding could be implemented. Besides fencing off large land tracts, a natural setting would be maintained, in which predator-prey dynamics would take their course uninterrupted. The long-term plan is for an "ecological history park encompassing thousands of square miles in economically depressed parts of the Great Plains".

The Bolson tortoise will expand its prehistoric population and thrive in places like Texas. Feral horses will be encouraged to breed and multiply, and will be proxies for extinct equids. Camelids (of the genera Camelus, Lama, and Vicugna) will serve as proxies for the approximately six extinct camel species in North America. The African cheetah will serve for the American cheetah, while the African lion will serve for the American lion. The elephant species will represent the five species of mammoth, mastodon, and gomphothere which thrived in North America.

Other animals that can be used for the project might include: mountain tapir, Baird's tapir, and South American tapir (formerly part of a widespread Holarctic family); Saiga antelope (a Pleistocene resident of the Alaskan steppe, now found only in Central Asia); Capybara (which had its relatives that lived in North America); and the dhole (which thrived throughout North America and Eurasia during the Pleistocene). Scientific evidence points to the Siberian tiger crossing the Bering Strait into Alaska during the Pleistocene.


The main criticism of the Pleistocene rewilding is that it is unrealistic to assume that communities today are functionally similar to their state 10,000 years ago. Opponents argue that there has been more than enough time for communities to evolve in the absence of mega-fauna, and thus the reintroduction of large mammals could thwart ecosystem dynamics and possibly cause collapse. Under this argument, the prospective taxa for reintroduction are considered exotic and could potentially harm natives of North America through invasion, disease, or other factors.

Opponents of the Pleistocene rewilding present an alternative conservation program, in which more recent North American natives will be reintroduced into parts of their native ranges where they became extinct during historical times. Another way of rewilding Americas, Asia, etc. is by using de-extinction, bringing extinct species back to life through cloning.

Pleistocene rewilding in North America

Already Introduced

  • Bolson tortoise
  • California condor (has been introduced to sites, where it is only known from the Pleistocene and reported by rare, unconfirmed sightings in historic times)
  • Mustang (feral horses roam North American grasslands and can count as proxies for extinct horses)

Expanding populations

  • Albatrosses, petrels, and relatives
  • Amargosa pupfish
  • American alligator
  • American badger
  • American beaver
  • American bison
  • American coot
  • American crocodile
  • American mice and rats
  • American white pelican
  • Anhinga
  • Antelope squirrel
  • Auk
  • Axolotl
  • Bat
    • Common vampire bat
    • Florida bonneted bat
    • Gray bat
    • Hairy-legged vampire bat
    • Hoary bat
    • Indiana bat
    • Lesser long-nosed bat
    • Mexican long-nosed bat
    • Mexican long-tongued bat
    • Townsend's big-eared bat
    • White-winged vampire bat
  • Bear
    • American black bear
    • Grizzly bear
    • Polar bear
  • Bighorn sheep
  • Black-footed ferret
  • Bobcat
  • Brown pelican
  • Canada lynx
  • Caribou
  • Coati
  • Cormorant
  • Cottontail rabbit
  • Cougar
  • Coyote
  • Dall sheep
  • Desert tortoise
  • Eagle
    • Bald eagle
    • Golden eagle
  • Elk
  • Fox
    • Arctic fox
    • Gray fox
    • Kit fox
    • Red fox
    • Swift fox
  • Frigatebird
  • Gannets and boobies
  • Gila monster
  • Gophers
  • Grebe
  • Ground squirrels
  • Groundhog
  • Hares
  • Hellbender
  • Heron
    • Bare-throated tiger heron
    • Boat-billed heron
    • Cattle egret
    • Great egret
    • Great blue heron
    • Green heron
    • Large bitterns
    • Little blue heron
    • Reddish egret
    • Small bitterns
    • Snowy egret
    • Tricolored heron
    • Yellow-crowned night heron
  • Ibis
    • American white ibis
    • Scarlet ibis
    • White-faced ibis
  • Kangaroo mouse
  • Kangaroo rat
  • Kirtland's warbler
  • Lemming
  • Loach minnow
  • Loon
  • Marmot
  • Mole
  • Eastern mole
  • Star-nosed mole
  • Moose
  • Mountain beaver
  • Mountain Goat
  • Mule deer
  • Musk ox
  • Muskrat
  • Nine-banded armadillo
  • North American porcupine
  • Otter
    • North American river otter
    • Sea otter
  • Owl
    • Burrowing owl
    • Northern spotted owl
    • Great horned owl
  • Pika
    • American pika
    • Collared pika
  • Pinniped
    • Bearded seal
    • California sea lion
    • Grey seal
    • Guadalupe fur seal
    • Harbor seal
    • Harp seal
    • Hooded seal
    • Northern elephant seal
    • Northern fur seal
    • Ribbon seal
    • Ringed seal
    • Spotted seal
    • Steller sea lion
    • Walrus
  • Prairie dog
  • Pronghorn
  • protected gull species
  • Raccoon
  • Red-cockaded woodpecker
  • Roseate spoonbill
  • Salamander
    • Mole salamander
    • Small-mouth salamander
    • Spotted salamander
    • Tiger salamander
  • Salmon
    • Chinook salmon
    • Chum salmon
    • Coho salmon
    • Sockeye salmon
  • Skimmer
  • Skua
  • Skunk
    • Hog-nosed skunk
    • Hooded skunk
    • Spotted skunk
    • Stink badger
    • Striped skunk
  • Tern
  • Tree squirrels
  • Virginia opossum
  • Vole
  • Waterfowl
    • American wigeon
    • Barnacle goose
    • Barrow's goldeneye
    • Black-bellied whistling duck
    • Black scoter
    • Blue-winged teal
    • Brant goose
    • Bufflehead
    • Cackling goose
    • Canada goose
    • Canvasback
    • Common eider
    • Common goldeneye
    • Common merganser
    • Emperor goose
    • Fulvous whistling duck
    • Gadwall
    • Greater scaup
    • Greater white-fronted goose
    • Green-winged teal
    • Harlequin duck
    • Hooded merganser
    • King eider
    • Lesser scaup
    • Long-tailed duck
    • Mallard
    • Masked duck
    • Muscovy duck
    • Mute swan
    • Northern pintail
    • Northern shoveler
    • Red-breasted merganser
    • Redhead
    • Ring-necked duck
    • Ross's goose
    • Ruddy duck
    • Smew
    • Snow goose
    • Spectacled eider
    • Steller's eider
    • Surf scoter
    • Trumpeter swan
    • Tundra swan
    • West Indian whistling duck
    • White-cheeked pintail
    • White-faced whistling duck
    • White-winged scoter
  • West Indian manatee
  • Whale
    • Atlantic spotted dolphin
    • Atlantic white-sided dolphin
    • Beaked whales
    • Beluga whale
    • Blue whale
    • Bowhead whale
    • Bryde's whale
    • Clymene dolphin
    • Common bottlenose dolphin
    • Common minke whale
    • Dall's porpoise
    • Dwarf sperm whale
    • False killer whale
    • Fin whale
    • Fraser's dolphin
    • Gray whale
    • Harbour porpoise
    • Humpback whale
    • Killer whale
    • Long-beaked common dolphin
    • Long-finned pilot whale
    • Melon-headed whale
    • Narwhal
    • North Atlantic right whale
    • North Pacific right whale
    • Northern right whale dolphin
    • Pacific white-sided dolphin
    • Pantropical spotted dolphin
    • Pygmy blue whale
    • Pygmy killer whale
    • Pygmy sperm whale
    • Risso's dolphin
    • Rough-toothed dolphin
    • Sei whale
    • Short-beaked common dolphin
    • Short-finned pilot whale
    • Sperm whale
    • Spinner dolphin
    • Striped dolphin
    • White-beaked dolphin
  • Wild Turkey
  • Wolf
    • Grey wolf
    • Red wolf
  • Whooping crane
  • Wood stork
  • Wolverine

Species that became extinct in the historic past that would be reintroduced

  • Collared peccary (extinct in many regions of North America, can still be found in southern Arizona and Texas)
  • Jaguar (roamed much of southwestern United States until early 20th century, there is a possibly breeding population in Arizona and the bootheel of New Mexico)
  • Jaguarundi (once found in most of Southwestern United States, they can still be found in Southern Texas)
  • Margay (fossil record showed that margays once lived in Southwestern North America, only to be last seen in Texas in 1852)
  • Ocelot (extinct in most of southwestern United States, there are possible breeding populations in Arizona and Texas)

Considered to be reintroduced as ecological proxies

  • African bush elephant (as a proxy for the extinct Imperial Mammoth and Stegomastodon)
  • African cheetah (as a proxy for the extinct American cheetah, the extinct natural predator of the pronghorn)
  • African lion (as a proxy for the extinct American lion)
  • African wild dog (as a proxy for the extinct Amphicyon)
  • Asian elephant (as a proxy for the extinct Columbian mammoth)
  • Baird's tapir (as a proxy for the extinct Tapirus veroensis)
  • Brazilian tapir (as a proxy for the extinct Tapirus copei and the Tapirus veroensis)
  • Black Rhinoceros (as a proxy for the extinct Brontotherium)
  • Capybara (as a proxy for the extinct Neochoerus)
  • Chacoan peccary (as a proxy for the extinct long-nosed peccary)
  • Colocolo opossum (as a proxy for the extinct mice-like marsupials of North America)
  • Commerson's dolphin (as a proxy for the extinct Denebola and Semirostrum)
  • Common opossum (as a proxy for the extinct species of North American opossum)
  • Derby's woolly opossum (as a proxy for the extinct relatives of a modern Virginia opossum)
  • Dhole (fossil record indicates that the species also occurred in North America, with remains being found in Beringia and Mexico)
  • Dromedary camel (as a proxy for the extinct camelops)
  • Dugong (fossil record shows that dugongs lived in Florida, suggesting they might also have lived in seas off the coast of North American areas, South America, and Asia)
  • European bison (as a proxy for the prehistoric bison species)
  • Freshwater crocodile (as a proxy for the extinct Thecachampsa)
  • Giant anteater (as a proxy for the extinct ground sloth species)
  • Giant armadillo (as a proxy for the extinct Glyptotherium)
  • Gracile capuchin monkey (as a proxy for the prehistoric monkeys which were native to North America)
  • Guanaco (as a proxy for the extinct Palaeolama)
  • Indian Rhinoceros (as a proxy for the extinct Brontotherium and Subhyracodon)
  • Mountain tapir (as a proxy for the extinct Tapirus californicus)
  • Onager (as a proxy for the extinct species of North American horses/asses)
  • Plains zebra (as a proxy for the extinct species of North American horse/zebra)
  • Robust capuchin monkey (as a proxy for the prehistoric monkeys which were native to North America)
  • Saiga antelope (if saved from extinction, they could be reintroduced back to North America)
  • Seriema (as a proxy for the extinct Buteogallus daggetti)
  • Siberian tiger (as a proxy for the extinct Smilodon)
  • Spider monkey (as a proxy for the prehistoric monkeys which were native to North America)
  • Spotted hyena (as a proxy for the extinct Chasmaporthetes)
  • Squirrel monkey (as a proxy for the prehistoric monkeys which were native to North America)
  • Vicuña (as a proxy for the extinct Hemiauchenia)
  • Water opossum (as a proxy for the extinct amphibious opossums of North America)
  • White-eared opossum (as a proxy for the extinct species of North American opossum)
  • White-lipped peccary (as a proxy for the extinct flat-headed peccary)
  • White Rhinoceros (as a proxy for the extinct Brontotherium)
  • West Indian Manatee (fossil record shows that manatees lived in not just Florida, but also other parts of North America (including California), and South America)

Species that could be brought back through De-Extinction

  • American mastodon
  • Caribbean monk seal
  • Carolina parakeet
  • Chendytes (it Is possible that some of the remains of Chendytes could still have DNA, if true, this species could hopefully be brought back to life and be reintroduced to its native homeland)
  • Dusky seaside sparrow
  • Giant ground sloth
  • Glyptotherium
  • Golden toad (Costa Rica and Caribbean Islands only)
  • Great auk
  • Guadeloupe amazon (Costa Rica and Caribbean Islands only)
  • Heath hen
  • Imperial woodpecker
  • Ivory billed woodpecker
  • Jefferson's ground sloth
  • Labrador duck
  • Nesophontes (Caribbean islands only)
  • Passenger pigeon
  • Shasta ground sloth
  • Steller's sea cow
  • Steppe bison
  • Woolly mammoth

Life After People

If the Pleistocene rewilding in North America had already happened, this time in 1990's and 2000's instead of the future, what will happen to the introduced wildlife in North America?

1 second after people

People disappeared.

1 day after people

Power grids fail.

1 week after people

The tapirs, camels, guanacos, vicunas, monkeys, lions, tigers, feral horses, wild (not feral) dogs (including dholes and African wild dogs), wisents, African elephants, Asian elephants, giant anteaters, giant armadillos, saiga antelopes, seriemas, peccary, manatees, dugongs, mammoths, mastodons, glyptodons, ground sloths, passenger pigeons, and nonnative possums in North America have started to spread from their introduced lands.

1 month after people

Despite the competition from invasives such as wild boars and many others, which aren't supposed to live in North America, peccaries and other recently introduced and reintroduced species continued to thrive, even in life after people.

1 year after people

Tapirs, peccaries, elephants, camelids, and others are now seen in abandoned cities, towns, urban and suburbs, and other human settlements of North America after their former rulers are gone.

10 years after people

Human settlements are starting to be replaced by grasslands, forests, and other native lands, allowing the tapirs, camelids, peccaries, elephants, and others to spread even further into more land areas.

1,000 years after people

In 1,000 years after people disappeared, all human settlements look like forests with some remaining buildings, while all animals that were part of the Pleistocene rewilding project had somehow survived, because they had adapted to the new ecosystem and have adapted to deal with the competition from native species and invasive species. Fortunately, non of the animals that are part of the Pleistocene Rewilding has negative impact to North America, they actually have a positive impact to all of the environments of North America. Lots of large Megafuana are back roaming North America.

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