The
QuaternaryThe Quaternary period is the youngest of three periods of the Cenozoic era in the geologic time scale of the ICS. It follows after the Neogene period, spanning 2.588 +/- 0.005 million years ago to the present...
epoch saw the
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
s of numerous predominantly larger species, many of which occurred during the transition to the Holocene epoch in what is termed the Holocene extinction. Among the main causes hypothesized by paleontologists are the spread of
diseaseA disease or medical condition isan abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs...
, natural
climate changeClimate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
, and
overkillOverkill is the use of excessive force or action that goes further than is necessary to achieve its goal.-Nuclear weapons:Overkill is especially used to refer to a destructive nuclear capacity exceeding the amount needed to destroy an enemy....
by
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s, which appeared during this epoch. The overkill theory, or Blitzkrieg Hypothesis has been discredited by most scientists as improbable. A variant of this last possibility is the second-order predation hypothesis, which focuses more on the indirect damage caused by overcompetition with nonhuman predators.
The Pleistocene or Ice Age extinction event
The Ice Age extinction event is characterised by the extinction of many large mammals weighing more than 40 kg. In
North AmericaNorth America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...
around 33 of 45
generaIn biology, a genus is a taxonomic unit used in the classification of living and fossil organisms. The term comes from Latin genus "descent, family, type, gender" , cognate with – genos, "race, stock, kin" ..In addition, genus is a taxonomic rank in the hierarchy In biology, a genus (plural:...
of large mammals became extinct, in
South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
46 of 58, in
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
15 of 16, in
EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
7 of 23, and in Subsaharan Africa only 2 of 44. The extinctions in the
AmericasThe Americas, or America, are lands in the Western hemisphere or New World, comprising the continents of North America and South America with their associated islands and regions. America may be ambiguous in English, as it is more commonly used to refer to the United States of America...
entailed the elimination of all the larger (over 100 kg) mammalian megafaunal species of South American origin, including those that had migrated north in the
Great American InterchangeThe Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
. Only in South America and Australia did the extinction occur at family taxonomic levels or higher.
There are two main hypotheses concerning the Pleistocene extinction:
- The animals died off due to climate change
Climate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
: the retreat of the polar ice capA polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of...
.
- The animals were exterminated by humans: the "prehistoric overkill hypothesis" (Martin, 1967).
There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of sudden extinctions of
Australian megafaunaAustralian megafauna are a number of large animal species in Australia, often defined as species with body mass estimates of greater than 30 kilograms, or equal to or greater than 30% greater body mass than their closest living relatives...
. Biologists note that comparable extinctions have not occurred in
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
and
SouthSouth Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries on the west and the east...
or
Southeast AsiaManila
Bangkok
Ho Chi Minh City
Kuala Lumpur
Singapore
Yangon
Bandung
Hanoi
Surabaya
Taichung
Kaohsiung
Medan|-|}...
, where the fauna evolved with hominids. Post-glacial megafaunal extinctions in Africa have been spaced over a longer interval.
Evidence supporting the prehistoric overkill hypothesis includes the persistence of certain island megafauna for several millennia past the disappearance of their continental cousins.
Ground slothsThe ground sloths of the genus Megalocnus were among the largest of the Caribbean ground sloths, with individuals estimated to have weighed up to 90 kilos when alive. Two species are known, M. rodens of Cuba, and M. zile of Hispaniola. Subfossils of M...
survived on the
AntillesThe Antilles refers to the islands forming the greater part of the West Indies in the Caribbean Sea...
long after North and South American ground sloths were extinct. The later disappearance of the island species correlates with the later colonization of these islands by humans. Similarly, woolly mammoths died out on remote
Wrangel IslandWrangel Island is an island in the Arctic Ocean, between the Chukchi Sea and East Siberian Sea. Wrangel Island lies astride the 180° meridian. The International Date Line is displaced eastwards at this latitude to avoid the island as well as the Chukchi Peninsula on the Russian mainland...
7,000 years after their mainland extinction.
Steller's sea cowsSteller's sea cow is a large extinct sirenian mammal. Formerly abundant throughout the North Pacific, its range was limited to a single, isolated population on the uninhabited Commander Islands by 1741 when it was first described by Georg Wilhelm Steller, chief naturalist on an expedition led by...
also persisted off the isolated and uninhabited Commander Islands for thousands of years after they vanished from continental shores of the north Pacific.
An alternative to the theory of human responsibility is
severalThe Younger Dryas impact event or Clovis comet hypothesis refers to the hypothesized large air burst or earth impact of an object or objects from outer space that initiated the Younger Dryas cold spell about 12,900 BP calibrated ....
controversial
hypothesesAlexander Tollmann's bolide, proposed by Kristen-Tollmann and Tollmann in 1994, is a hypothesis presented by Austrian geologist Dr. Alexander Tollmann, suggesting that one or several bolides struck the Earth at 7640 BCE , with a much smaller one at 3150 BCE...
claiming that the extinctions resulted from bolide impact(s). However, such hypotheses would predict an instantaneous, regional extinction(s), and thus cannot account for the planet-wide species losses that occurred over an interval of thousands of years.
Eurasia
(40,000-10,000 years ago)
- Woolly mammoth
The woolly mammoth , also called the tundra mammoth, is an extinct species of mammoth. This animal is known from bones and frozen carcasses from northern North America and northern Eurasia with the best preserved carcasses in Siberia.This mammoth species was first recorded in deposits of the...
- Woolly rhinoceros
The woolly rhinoceros is an extinct species of rhinoceros native to the northern steppes of Eurasia that lived during the Pleistocene epoch and survived the last glacial period...
- Irish Elk
The Irish Elk or Giant Deer , was a species of Megaloceros and one of the largest deer that ever lived. Its range extended across Eurasia, from Ireland to east of Lake Baikal, during the Late Pleistocene. The latest known remains of the species have been carbon dated to about 7,700 years ago...
- Scimitar cat
- Cave lion
The cave lion also known as the European or Eurasian cave lion, is an extinct subspecies of lion known from fossils and multiple examples of prehistoric art.-Physical characteristics:...
- Cave bear
The Cave Bear was a species of bear which lived in Europe during the Pleistocene and became extinct at the beginning of the Last Glacial Maximum about 27,500 years ago....
- Cave hyena
The Cave Hyena is an extinct subspecies of spotted hyena native to Eurasia, ranging from Northern China to Spain and into the British Isles...
- Steppe Wisent
The Steppe Bison or steppe wisent was a bison found on steppes throughout Europe, Central Asia, Beringia and North America during the Quaternary...
- Giant Ostrich
The Giant Ostrich is an extinct species of ratite bird from the Late Pliocene to the Early Pleistocene of Georgia.-References:*National Geographic *...
- Neanderthals, survived until about 24,000 years ago in the Iberian peninsula.
Mediterranean Islands
(by 9000 years ago)
- pygmy hippos of Cyprus
The Cyprus Dwarf Hippopotamus or Cypriot Pygmy Hippopotamus is an extinct species of hippopotamus that inhabited the island of Cyprus until the early Holocene....
(Phanourios minutus), CreteThe Cretan Dwarf Hippopotamus or Hippopotamus creutzburgi is an extinct hippopotamus. It lived during the Pleistocene on Crete.Two subspecies have been named: Hippopotamus creutzburgi creutzburgi and the smalller Hippopotamus creutzburgi parvus.Bones of the Cretan dwarf hippo were found by Dorothea...
(Hippopotamus creutzburgi), MaltaHippopotamus melitensis is an extinct hippopotamus. It lived during the Pleistocene on Malta. The absence of predators led to the dwarfing of the hippos. The majority of findings of this species are known from the Għar Dalam, a cave on Malta famous for its Pleistocene fossil deposits.-See also:*...
(H. melitensis) and SicilyHippopotamus pentlandi is an extinct hippopotamus. It lived during the Pleistocene on Sicily. It was the smallest of the dwarf hippos known from the Mediterranean of the Pleistocene weighing in at 320 kg.-See also:* Maltese Hippopotamus...
(H. pentlandi)
- the Balearic Islands cave goat (Myotragus balearicus
Myotragus balearicus , also known as the Balearic Islands Cave Goat, a species of the subfamily Caprinae which lived on the islands of Majorca and Minorca until its extinction around 5,000 years ago...
) of Majorca and MinorcaMinorca or Menorca is one of the Balearic Islands located in the Mediterranean Sea belonging to Spain. It takes its name from being smaller than the nearby island of Majorca....
- Dwarf elephant
Fossil remains of dwarf elephants have been found on the Mediterranean islands of Cyprus, Malta , Crete, Sicily, Sardinia, the Cyclades Islands and the Dodecanese Islands. Other islands where dwarf elephants have been found are Sulawesi, Flores, Timor and other islands of the Lesser Sundas...
s of Cyprus (Elephas cypriotes), SicilySicily is the largest island in the Mediterranean Sea. It is an autonomous region of Italy. Several much smaller islands surrounding it are considered to be part of Sicily....
, MaltaMalta , officially the Republic of Malta , is a densely populated developed European country in the European Union. The Southern European island nation is an archipelago that includes the inhabited islands of Malta, Gozo and Comino, along with a number of smaller, uninhabited islands...
(E. falconeriElephas falconeri is an extinct Siculo-Maltese species of elephant closely related to the modern Asian elephant. In 1867 George Busk had proposed the species Elephas falconeri for many of the smallest molars selected from the material originally ascribed by Hugh Falconer to Elephas melitensis.This...
) and many other islands
- Giant swan (Cygnus falconeri) of Malta
- Giant dormice: Minorcan Giant Dormouse
The Minorcan Giant Dormouse, scientifically known as Hypnomys mahonensis is an animal extinct from Europe....
, Majorcan Giant DormouseThe Majorcan Giant Dormouse, scientifically known as Hypnomys morphaeus or Eliomys morpheus , is an animal extinct from Europe. It is considered an example of Island gigantism....
.
North America
During the last 50,000 years, including the end of the last glacial period, approximately 33 genera of large mammals have become extinct in North America. Of these, 15 genera extinctions can be reliably attributed to a brief interval of 11,500 to 10,000 radiocarbon years
before presentBefore Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use 1 January 1950 as the arbitrary origin of the age scale...
, shortly following the arrival of the Clovis people in North America. Most other extinctions are poorly constrained in time, though some definitely occurred outside of this narrow interval. Contrary to this, only about half a dozen small mammals disappeared during this time. Previous North American extinction pulses had occurred at the end of glaciations, but not with such an imbalance between large mammals and small ones. (Moreover, previous extinction pulses were not comparable to the Quaternary extinction event; they involved primarily species replacements within ecological niches, while the latter event resulted in many ecological niches being left unoccupied.) The megafaunal extinctions include twelve genera of edible herbivores (
H), and five large, dangerous carnivores (
C). North American extinctions included:
- American horse
The horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, five species (Asian horses survived) (H)
- Western camels Camelops
Camelops is an extinct genus of camels that once roamed western North America, where it disappeared at the end of the pleistocene about 10,000 years ago. Its name is derived from the Greek κάμελος + , thus "camel-face."...
(H)
- North American llama
The llama is a South American camelid, widely used as a pack animal by the Incas and other natives of the Andes mountains. In South America llamas are still used as beasts of burden, as well as for the production of fiber and meat....
s (H)
- Deer
Deer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Animals from related families within the order Artiodactyla are often also considered to be deer – these include muntjac and water deer...
, two genera (H)
- Pronghorn
The Pronghorn , is a species of ungulate mammal native to interior western and central North America. Though not a true antelope, it is often known colloquially as the Prong Buck, Pronghorn Antelope or simply Antelope , as it closely resembles the true antelopes of the Old World and fills a similar...
, two genera (one survived) (H)
- Stag-moose
The Stag-moose or Stag moose was a large moose-like deer of North America of the Pleistocene epoch. It was slightly larger than the moose, with an elk-like head, long legs, and complex palmate antlers...
(H)
- Shrub-ox
The shrub-ox is an extinct genus and species of Bovidae native to North America. It is a close relative of the musk-ox....
and Harlan's muskox (the Arctic Muskox survived) (H)
- Giant Beaver
The Giant Beaver was a huge species of the family Castoridae , endemic to North America during the Pleistocene epoch , existing for approximately .-Morphology:...
(H)
- Saiga (H)
- Teratorns (C)
- Capybara
Neochoerus pinckneyi was a North American species of capybara. While capybaras originated in South America, formation of the Isthmus of Panama three million years ago allowed some of them to migrate north as part of the Great American Interchange...
(H)
- Eremotherium
Eremotherium is an extinct genus of actively mobile ground sloth of the family Megatheriidae, endemic to North America and South America during the Pleistocene epoch...
and NothrotheriopsNothrotheriops is a genus of Pleistocene ground sloth found in North and South America. This genus of bear-sized xenarthran was related to the much larger, and far more famous Megatherium, although it has recently been placed in a different family, Nothrotheriidae.Fossils of the best-known...
, megatheriid ground slothGround sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may survived until 1550 AD; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP for...
s (H)
- Megalonyx
Megalonyx is an extinct genus of giant ground sloths living from the Hemphillian of the Late Miocene through to the Rancholabrean of the Late Pleistocene . Their closest living relatives are the two-toed sloths .Endemic to North America, these animals are the most widespread fossils of the family...
, a megalonychid ground sloth (H)
- Paramylodon
Paramylodon is an extinct genus of ground sloth known from North America deposits in Mexico and the United States. Currently there is just one recognized species, P. harlani, that is commonly referred to as Harlan's ground sloth in honor of American paleontologist Dr. Richard Harlan who first...
, a mylodontid ground sloth (H)
- Glyptodont
Glyptodonts were large, more heavily-armored relatives of extinct pampatheres and modern armadillos. They first evolved during the Miocene in South America, which remained their center of species diversity...
s (H)
- Pampatheres
Pampatheridae is an ancient family, now extinct, of large armadillo-like plantigrade armored xenarthrans. They are related to Glyptodontidae, an extinct family of much larger and more heavily armored xenarthrans, as well as to extant armadillos . Pampatheres evolved in South America during its...
(H)
- Short-faced bears (larger than the present Grizzly Bear
The grizzly bear , also known as the silvertip bear, is a subspecies of brown bear that generally lives in the uplands of western North America....
) (C)
- Florida Cave Bear
Tremarctos flordianus known commonly as the Florida cave bear is an extinct genus of the family Ursidae, subfamily Tremarctinae endemic to North America during the Pleistocene epoch , existing for approximately ....
(C)
- The saber-toothed cat
Saber-toothed cat refers to extinct subfamilies of Machairodontinae , Barbourofelidae , and Nimravidae as well as two marsupial families that were found worldwide from the Eocene-Pleistocene epochs , existing for approximately .The Nimravidae are the oldest entering the landscape around 42 mya and...
Smilodon fatalisSmilodon , often called saber-toothed cat or saber-toothed tiger, is an extinct genus of the subfamily machairodontine saber-toothed cats endemic to North America and South America living from the Early Pleistocene through Lujanian stage of the Pleistocene epoch , existing for approximately 1.790...
(C)
- The 'scimitar cat' Homotherium
Homotherium is a genus of machairodontine saber-toothed cats, often termed scimitar cats, endemic to North America, Europe, Asia, and Africa during the Miocene epochs , existing for approximately ....
(C)
- American lion
The American lion also known as the North American lion or American cave lion, is an extinct feline of the family Felidae, endemic to North America during the Pleistocene epoch , existing for approximately .It was one of the largest subspecies of cat ever to have existed, and the largest lion in...
(larger than the current African LionThe Lion is one of four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
but probably a fairly recent immigrant through Beringia) (C)
- American cheetah (not a true cheetah) (C)
- Dire wolf
The Dire Wolf is an extinct carnivorous mammal of the genus Canis, and was most common in North America and South America from the Irvingtonian stage to the Rancholabrean stage of the Pleistocene epoch living 1.80 Ma—11,000 years ago, existing for approximately .-Relationships:Although it...
(C)
- Mammoth
A mammoth is any species of the extinct genus Mammuthus. These proboscideans are members of Elephantidae, the family of elephants and mammoths, and close relatives of modern elephants. They were often equipped with long curved tusks and, in northern species, a covering of long hair. They lived from...
, several species (H)
- American mastodon
Mastodons or mastodonts were large tusked mammal species of the extinct genus Mammut found in Asia, Africa, Europe, North America and Central America from the Oligocene through Pleistocene, 33.9 mya to 11,000 years ago. The American mastodon is the most recent and best known species of the group...
, Mammut americanum (H)
- Ancient bison (H)
- Flat-headed & Long-nosed peccaries Mylohyus
Mylohyus is an extinct genus of peccary found in North and Central America. It evolved in the Pliocene and its extinction is probably as recent as 9,000 years ago. It would have been familiar with early humans....
, PlatygonusPlatygonus is an extinct genus of herbivorous peccary of the family Tayassuidae, endemic to North America from the Miocene through Pleistocene epochs , existing for approximately ....
(H)
- California & Vero tapirs (H)
The survivors are as significant as the losses:
bisonMembers of the genus Bison are large even-toed ungulates within the subfamily Bovinae. Two extant species and four extinct species are recognized...
,
mooseThe moose or common elk , , is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a "twig-like" configuration....
(recent immigrants through Beringia),
elk-Various species of deer:** European Elk , also known as Moose** North American Elk , also known as Wapiti** Indian Elk , also known as Sambar...
, caribou,
deerDeer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Animals from related families within the order Artiodactyla are often also considered to be deer – these include muntjac and water deer...
,
pronghornThe Pronghorn , is a species of ungulate mammal native to interior western and central North America. Though not a true antelope, it is often known colloquially as the Prong Buck, Pronghorn Antelope or simply Antelope , as it closely resembles the true antelopes of the Old World and fills a similar...
, muskox,
bighorn sheepBighorn sheep is a species of sheep in North America with large horns. The horns can weigh up to , while the sheep themselves weigh up to...
, and
mountain goatThe Mountain Goat , also known as the Rocky Mountain Goat, is a large-hoofed mammal found only in North America. Despite its vernacular name, it is not a member of Capra, the genus of true goats...
s. All save the pronghorns descended from Asian ancestors that had evolved with human predators. Pronghorns are the second fastest land mammal (after the
cheetahThe cheetah is an atypical member of the cat family that is unique in its speed, while lacking climbing abilities. The species is the only living member of the genus Acinonyx...
), which may have helped them elude hunters.
The culture that has been connected with the wave of extinctions in North America is the paleo-Indian culture associated with the
Clovis peopleThe Clovis culture is a prehistoric Paleoindian culture that first appears in the archaeological record of North America around 11,500 rcbp radiocarbon years ago, at the end of the last glacial period, characterized by a particular tool kit adapted to the hunting of large mammals...
(
q.v.), who were thought to use
spear throwerAn atlatl or spear-thrower is a tool that uses leverage to achieve greater velocity in dart-throwing, and includes a bearing surface which allows the user to temporarily store energy during the throw...
s to kill large animals. The chief opposition to the "prehistoric overkill hypothesis" has been that population of humans such as the Clovis culture were too small to be ecologically significant. Other generalized evocations of climate change fail under detailed scrutiny.
Lack of
tameableDomestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. A defining characteristic of domestication is artificial selection by humans...
megafauna was perhaps one of the reasons why Amerindian civilizations evolved differently than
Old WorldThe Old World consists of those parts of Earth known to Europeans, Asians, and Africans in the 15th century.-Regions:The Old World includes Europe, Asia, and Africa , plus surrounding islands...
ones. Critics have disputed this by arguing that
llamaThe llama is a South American camelid, widely used as a pack animal by the Incas and other natives of the Andes mountains. In South America llamas are still used as beasts of burden, as well as for the production of fiber and meat....
s,
alpacaAlpaca is a domesticated species of South American camelid. It resembles a small llama in superficial appearance.Alpacas are kept in herds that graze on the level heights of the Andes of Ecuador, southern Peru, northern Bolivia, and northern Chile at an altitude of to above sea-level, throughout...
s, and
bisonMembers of the genus Bison are large even-toed ungulates within the subfamily Bovinae. Two extant species and four extinct species are recognized...
were domesticated.
South America
At the Pleistocene-Holocene transition South America, which had remained largely unglaciated except for increased mountain glaciation in the
AndesThe Andes are the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America...
, saw an extinction wave, which carried off many large species. Today there is no wild land mammal left on this continent weighing more than a modern tapir.
- Smilodon
Smilodon , often called saber-toothed cat or saber-toothed tiger, is an extinct genus of the subfamily machairodontine saber-toothed cats endemic to North America and South America living from the Early Pleistocene through Lujanian stage of the Pleistocene epoch , existing for approximately 1.790...
fatalis and populator
- Arctodus
Arctodus simus, also known as the giant short-faced bear, is an extinct species of bear. The genus Arctodus is known as the short-faced or bulldog bears. A. simus is the largest bear, and more generally, the largest mammalian land carnivore within the last 800,000 years...
- Ground sloth
Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may survived until 1550 AD; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP for...
s of three families
- Glyptodonts
- Pampathere
Pampatheridae is an ancient family, now extinct, of large armadillo-like plantigrade armored xenarthrans. They are related to Glyptodontidae, an extinct family of much larger and more heavily armored xenarthrans, as well as to extant armadillos . Pampatheres evolved in South America during its...
s
- Hippidion
Hippidion was a Welsh pony-sized horse that lived in South America during the Pleistocene epoch, between two million and 10,000 years ago....
- Horse (Equus
Equus may refer to:* Equus , a genus of animals including horses, donkeys, zebras and onagers* Equus , a play by Peter Shaffer* Equus , a film adaptation of the Peter Shaffer play...
)
- Toxodon
Toxodon is an extinct mammal of the late Pliocene and Pleistocene epochs about 2.6 million to 16,500 years ago. It was indigenous to South America, and was probably the most common large-hoofed mammal in South America at the time of its existence....
- Macrauchenia
Macrauchenia was a long-necked and long-limbed, three-toed South American ungulate mammal, typifying the order Litopterna. The oldest fossils date back to around 7 million years ago, and M...
- Cuvieronius
Cuvieronius is an extinct New World genus of gomphothere. It is named after the French naturalist Georges Cuvier, stood 2.7m tall and looked like a modern elephant except for its spiral-shaped tusks....
- Stegomastodon
Stegomastodon is an extinct genus of gomphothere, a family of proboscideans. It is not to be confused with the genus Mammut from a different proboscidean family, whose members are commonly called "mastodons", nor with the genus Stegodon, from yet another proboscidean sub-family, whose members are...
Australia
The sudden spate of extinctions occurred earlier than in the Americas. Most evidence points to the period immediately after the first arrival of humans — thought to be a little under 50,000 years ago — but scientific argument continues as to the exact date range. The Australian extinctions included:
- Diprotodon
__FORCETOC__Diprotodon was the largest known marsupial that ever lived. It, along with many other members of a group of unusual species collectively called the Australian megafauna, existed from 1.6 million years ago until about 40,000 years ago . Diprotodon spp...
s (giant relatives of the wombatWombats are Australian marsupials; they are short-legged, muscular quadrupeds, approximately in length with a very short tail. They are found in forested, mountainous, and heathland areas of south-eastern Australia and Tasmania...
s)
- Zygomaturus
Zygomaturus is an extinct giant marsupial from Australia during the Pleistocene. It had a heavy body and thick legs and is believed to be similar to the modern Pygmy Hippopotamus in both size and build. The genus moved on all fours. It lived in the wet coastal margins of Australia and became...
trilobus (a large marsupialMarsupials are an infraclass of mammals, characterized by a distinctive pouch , in which females carry their young through early infancy.- History :...
herbivore)
- Palorchestes
Palorchestes azael is an extinct herbivorous terrestrial mammal genus of the family Palorchestidae endemic to Australia living from the Late Miocene subepoch through Pleistocene and in existence for approximately .-Description:Palorchestes azael was marsupial that was almost as large as a horse,...
azael (a marsupial "tapirA tapir is a large browsing mammal, roughly pig-like in shape, with a short, prehensile snout. Tapirs inhabit jungle and forest regions of South America, Central America, and Southeast Asia. There are four species of Tapirs, being the Brazilian tapir, the Malayan tapir, Baird's tapir and the...
")
- Macropus titan (a giant kangaroo
A kangaroo is a marsupial from the family Macropodidae . In common use the term is used to describe the largest species from this family, especially those of genus Macropus, Red Kangaroo, Antilopine Kangaroo, Eastern and Western Grey Kangaroo...
)
- Procoptodon
Procoptodon was a genus of giant short-faced kangaroo living in Australia during the Pleistocene epoch. P. goliah, the largest kangaroo that ever existed, stood approximately 3 metres tall and weighed about ....
goliah (a hoof-toed giant short-faced kangaroo)
- Wonambi naracoortensis (a five-to-six-metre-long Australian constrictor snake
Snakes are elongate legless carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic amniote vertebrates covered in overlapping scales...
)
- Thylacoleo carnifex (a lioness-sized marsupial carnivore)
- Megalania prisca (a giant monitor lizard)
Some extinct megafauna, such as the
bunyipThe bunyip is a mythical creature from Australian folklore. Various accounts and explanations of bunyips have been given across Australia since the early days of the colonies. It has also been identified as an animal recorded in Aboriginal mythology, similar to known extinct animals.-...
-like diprotodon, may be the sources of ancient
cryptozoological legendsCryptozoology refers to the search for animals which are considered to be legendary or otherwise nonexistent by mainstream biology...
.
New Zealand
c. AD 1500, several species became extinct after
PolynesiaPolynesia is a subregion of Oceania, comprising a large grouping of over 1,000 islands scattered over the central and southern Pacific Ocean.-Definition:...
n settlers arrived, including:
- Ten species of Moa
The moa were ten species of flightless birds endemic to New Zealand. The two largest species, Dinornis robustus and Dinornis novaezelandiae, reached about in height with neck outstretched, and weighed about ....
, giant flightless ratiteA ratite is any of a diverse group of large, flightless birds of Gondwanan origin, most of them now extinct. Unlike other flightless birds, the ratites have no keel on their sternum - hence their name, which comes from the Latin for raft...
birds.
- The giant Haast's Eagle, Harpagornis
- The flightless predatory Adzebill
The adzebills were two closely related bird species, the North Island Adzebill, Aptornis otidiformis, and the South Island Adzebill, Aptornis defossor, of the extinct family Aptornithidae. The family was endemic to New Zealand.They have been placed in the Gruiformes but this is not entirely certain...
s.
Pacific, including Hawaii
Recent research, based on archaeological and
paleontologicalPaleontology
[from Greek: παλαιός "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought"] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments...
digs on 70 different islands, has shown that numerous species went extinct as people moved across the Pacific, starting 30,000 years ago in the
Bismarck ArchipelagoThe Bismarck Archipelago is a group of islands off the northeastern coast of New Guinea in the western Pacific Ocean and is part of the Islands Region of Papua New Guinea.-History:...
and
Solomon IslandsThe Solomon Islands is a country in Melanesia, east of Papua New Guinea, consisting of nearly one thousand islands. Together they cover a land mass of 28,400 square kilometres . The capital is Honiara, located on the island of Guadalcanal.The Solomon Islands are believed to have been...
(Steadman & Martin 2003). It is currently estimated that among the bird species of the Pacific some 2000 species have gone extinct since the arrival of humans (Steadman 1995). Among the extinctions were:
- The Moa-nalo
Moa-nalo are a group of extinct aberrant, goose-like ducks that formerly lived on the Hawaiian Islands in the Pacific. They were the major herbivores on most of these islands for the last 3 million years or so, until they became extinct after human settlement.-Description:The moa-nalo were unknown...
s, giant grazing HawaiiHawaii is the newest of the 50 U.S. states, and is the only state made up entirely of islands. It is located on an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia. The state was admitted to the Union on August...
an ducks.
- The Nēnē-nui
The Nēnē-nui or Woodwalking Goose is an extinct species of goose that once inhabited Maui and possibly Kauai, Oahu and perhaps Molokai in the Hawaiian Islands...
, or Woodwalking Goose, a large species of goose that once inhabited island of Maui
- Sylviornis
Sylviornis is an extinct genus of galliform bird containing a single species, S. neocaledoniae, or erroneously, "New Caledonian Giant Megapode". Technically, the latter is incorrect because it has recently been found not to be a megapode, but the sole known member of its own family, the...
, a giant galliformGalliformes are an order of birds containing turkeys, grouse, chickens, quails, and pheasants. More than 250 living species are found worldwide. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
bird on New CaledoniaThe Biodiversity of New Caledonia, a large Pacific island group, is considered to be one of the most important in the world. The island supports high levels of endemism, with many unique plants, insects, reptiles and birds. The island has no native mammals except for bats, and no native amphibians...
.
- Mekosuchine crocodiles on New Caledonia, Fiji
Fiji , officially the Republic of the Fiji Islands , is an island nation in the South Pacific Ocean east of Vanuatu, west of Tonga and south of Tuvalu. The country comprises an archipelago of about 322 islands, of which 106 are permanently inhabited, and 522 islets...
and SamoaSamoa , officially the Independent State of Samoa , is a country governing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and Savai'i...
.
- Meiolaniid turtles
Meiolania is an extinct genus of cryptodire turtle from the Oligocene to Holocene, with the last relic populations at New Caledonia which survived until 2,000 years ago....
on Lord Howe IslandLord Howe Island is a small island in the Tasman Sea east of the Australian mainland. The Lord Howe Island Group, including nearby Ball's Pyramid, is administered by the Lord Howe Island Board,, and is part of the Mid-North Coast Statistical Division of New South Wales, Australia...
and New Caledonia.
Madagascar
Starting with the arrival of humans c. 2000 years ago, nearly all of the island's megafauna became extinct, including:
- Eight or more species of elephant birds
Elephant birds are an extinct family of flightless birds comprising the genera Aepyornis and Mullerornis.-Description:The elephant birds, which were giant ratites native to Madagascar, have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar in the...
, giant flightless ratiteA ratite is any of a diverse group of large, flightless birds of Gondwanan origin, most of them now extinct. Unlike other flightless birds, the ratites have no keel on their sternum - hence their name, which comes from the Latin for raft...
s in the genera Aepyornis and Mullerornis.
- 17 of 50 species of lemur, including:
- Giant aye-aye
The Giant Aye-aye is an extinct relative of the Aye-aye. It lived in Madagascar. It appears to have disappeared less than 1,000 years ago, but is entirely unknown in life, and only known from subfossil remains....
(Daubentonia robusta)
- sloth lemurs, including chimpanzee-sized Palaeopropithecus and gorilla-sized Archaeoindris
Archaeoindris fontoynonti is an extinct species of Malagasy lemur that was the largest primate to evolve on Madagascar. It weighed about 200kg and measured around 1.5m in height, more than a silverback gorilla. Archaeoindris is one of five known members of the Palaeopropithecinae subfamily...
- Megaladapis
Koala lemurs, also known as Megaladapis, belong to the family Megaladapidae and the genus Megaladapis, consisting of three extinct species of lemurs that once inhabited the island of Madagascar...
, an orangutan-sized arboreal lemur
- Giant tortoise
Giant tortoises are characteristic reptiles of certain tropical islands. They occur in such places as Madagascar, the Seychelles, Mauritius, Réunion, the Galápagos Islands, Sulawesi, Timor, Flores and Java, often reaching enormous size—they can weigh as much as 300 kg and can grow to be 1.3...
- Three species of Malagasy Hippopotamus
Several species of Malagasy Hippopotamus lived on the island of Madagascar but are now believed to be extinct. The animals were very similar to the extant Hippopotamus and Pygmy Hippopotamus...
Africa
Though the effect wasn't devastating, certain large African mammals died from the continent.
- Several genera of giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all land-living animal species, and the largest ruminant. It is covered in large, irregular patches of yellow to black fur separated by white, off-white, or dark yellowish brown background. The average mass for an adult male...
have gone extinct, including SivatheriumSivatherium ' is an extinct genus of giraffe that ranged throughout Africa to Southern Asia . The African species, S...
.
- Wolves
Xenocyon lycaonoides or African Wolf is an extinct canid endemic to Europe, Eurasia, and Asia, during the Pleistocene living from 1.8 Ma—126,000 years ago and existed for approximately ....
(with the exception of the Ethiopian WolfThe Ethiopian wolf , also known as the Abyssinian wolf, Abyssinian fox, red jackal, Simien fox, or Simien jackal is a canid native to Africa...
) and BearsThe Atlas Bear was a subspecies of the Brown Bear, but is sometimes considered a distinct species. It was Africa's only native bear. Once inhabiting the Atlas Mountains and neighboring areas, from Morocco to Libya, the animal is now thought to be extinct...
died out from Africa
- A few species of warthog
The Warthog or Common Warthog is a wild member of the pig family that lives in Africa....
went extinct; MetridiochoerusMetridiochoerus is an extinct genus of pig indigenous to the Pliocene and Pleistocene of Africa.-Description:Metridiochoerus was a large animal, in length, resembling a giant warthog. It had two large pairs of tusks which were pointed sideways and curved upwards...
and the Cape WarthogThe Cape Warthog is an extinct animal that had originally resided in South Africa.The Cape Warthog is quite distinguishable from other hogs, yet it has similar properties to that of a Somali Warthog...
- Deinotherium
Deinotherium , also called the Hoe tusker, was a gigantic prehistoric relative of modern-day elephants that appeared in the Middle Miocene and continued until the Early Pleistocene. During that time it changed very little...
, Elephas reckiElephas recki is an extinct species of African elephant. At up to 15 feet in shoulder height, it was one of the largest elephant species to have ever lived. It is believed that E. recki ranged throughout Africa between 3.5 and 1 million years ago. The Asian Elephant is the only extant member of...
, Loxodonta adaurora (a species of African Elephant), AnancusAnancus is an extinct genus of gomphothere that lived in the late Miocene and early Pleistocene, from 3 to 1.5 million years ago. Their fossils have been found in Africa, Europe, and Asia....
and Mammuthus subplanifronsA mammoth species that inhabited all of South Africa during the Pliocene. It's known as the South African Mammoth. It was a subspecies of the African Mammoth....
, relatives to the elephantElephants are large land mammals in two genera of the family Elephantidae: Elephas and Loxodonta. Three species of elephant are living today: the African Bush Elephant, the African Forest Elephant and the Asian Elephant...
died out.
- Hippopotamus gorgops
Hippopotamus gorgops is an extinct species of hippopotamus. It first appeared in Africa during the late Miocene, and eventually migrated into Europe during the early Pliocene . It became extinct prior to the Ice Age.With a length of and a shoulder height of H...
- False Saber-toothed Cats like Dinofelis
Dinofelis is a genus of saber-toothed cats belonging to the tribe Metailurini. They were widespread in Europe, Asia, Africa and North America at least 5 million to about 1.2 million years ago...
die out.
- The Giant Long-horned Buffalo Pelorovis
Pelorovis was an extinct genus of African wild cattle, which first appeared in the Pliocene, 2.5 million years ago, and became extinct during the Holocene, some 4,000 years ago.-Description:...
went extinct, along with the quaggaThe quagga is an extinct subspecies of the Plains zebra, which was once found in great numbers in South Africa's Cape Province and the southern part of the Orange Free State. It was distinguished from other zebras by having the usual vivid marks on the front part of the body only...
.
- Megalotragus
Megalotragus is a genus of very large extinct African alcelaphines from the Pliocene and Pleistocene. It resembled modern hartebeests, but differed in larger body size, it includes the largest bovids in the tribe Alcelaphini, reaching a shoulder height of 1,4 m. Megalotragus disappeared at the end...
, a large hartebeest
Indian Ocean Islands
Starting c. 500 years ago, a number of species became extinct upon human settlement of the islands, including:
- Several species of giant tortoise on the Seychelles
Seychelles , officially the Republic of Seychelles , is an archipelago nation of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar...
and Mascarene IslandsThe Mascarene Islands is a group of islands in the Indian Ocean east of Madagascar comprising Mauritius, Réunion, Rodrigues, Cargados Carajos shoals, plus the former islands of the Saya de Malha, Nazareth and Soudan banks. The collective title is derived from the Portuguese navigator Pedro...
- Many species of birds
Since 1500, over 190 species of birds have become extinct, and this rate of extinction seems to be increasing. The situation is exemplified by Hawaii, where 30% of all known recently extinct bird taxa originally lived...
on the Mascarene Islands, including the DodoThe dodo was a flightless bird endemic to the Indian Ocean island of Mauritius. Related to pigeons and doves, it stood about a meter tall, weighing about , living on fruit and nesting on the ground....
, the Rodrigues SolitaireThe Rodrigues Solitaire was a flightless member of the pigeon order endemic to Rodrigues, Mauritius. It was a close relative of the Dodo....
, and the unrelated Réunion SolitaireThe Réunion Sacred Ibis or Réunion Flightless Ibis , is an extinct bird species that was native to the island of Réunion...
.
Hunting hypothesis
The Hunting hypothesis suggests that humans hunted megaherbivores to extinction. As a result, carnivores and scavengers that depended upon those animals became extinct from lack of prey.
Therefore this theory holds Pleistocene humans responsible for the megafaunal extinction. One variant, often referred to as
overkill, portrays humans as hunting the megafauna to extinction within a relatively short period of time. Some of the direct evidence for this includes: fossils of megafauna found in conjunction with human remains, embedded arrows and tool cut marks found in megafaunal bones, and cave paintings that depict such hunting.
BiogeographicalBiogeography is the study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, and at what abundance....
evidence is also suggestive; the areas of the world where humans evolved currently have more of their Pleistocene megafaunal diversity (the
elephantElephants are large land mammals in two genera of the family Elephantidae: Elephas and Loxodonta. Three species of elephant are living today: the African Bush Elephant, the African Forest Elephant and the Asian Elephant...
s and
rhinoRhinoceros , often colloquially abbreviated rhino, is a name used to group five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia. Three of the five species—the Javan, Sumatran and Black Rhinoceros—are...
s of
AsiaAsia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population.Asia is traditionally defined as part of the...
and
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
) compared to other areas such as
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
, the
AmericasThe Americas, or America, are lands in the Western hemisphere or New World, comprising the continents of North America and South America with their associated islands and regions. America may be ambiguous in English, as it is more commonly used to refer to the United States of America...
,
MadagascarMadagascar, or Republic of Madagascar , is an island nation in the Indian Ocean off the southeastern coast of Africa. The main island, also called Madagascar, is the fourth-largest island in the world, and is home to 5% of the world's plant and animal species, of which more than 80% are endemic to...
and
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
, areas where early humans were non-existent. Based on this evidence, a picture arises of the megafauna of Asia and Africa evolving
with humans, learning to be wary of them, and in other parts of the world the wildlife appearing ecologically naive and easier to hunt. This is particularly true of island fauna, which display a dangerous lack of fear of humans.
Circumstantially, the close correlation in time between the appearance of humans in an area and extinction there provides weight to this theory. This is perhaps the strongest evidence, as it is almost impossible that it could be coincidental when science has so many data points. For example, the woolly mammoth survived on
islandsWrangel Island is an island in the Arctic Ocean, between the Chukchi Sea and East Siberian Sea. Wrangel Island lies astride the 180° meridian. The International Date Line is displaced eastwards at this latitude to avoid the island as well as the Chukchi Peninsula on the Russian mainland...
despite
worsening climatic conditionsThe neoglaciation describes the documented cooling trend in the Earth's climate during the Holocene, following the retreat of the Wisconsin glaciation, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate...
for thousands of years after the end of the last glaciation, but they died out when humans arrived around 1700 BC. The megafaunal extinctions covered a vast period of time and highly variable climatic situations. The earliest extinctions in Australia were complete approximately 30,000 BP, well before the last glacial maximum and before rises in temperature. The most recent extinction in New Zealand was complete no earlier than 500 BP and during a period of cooling. In between these extremes megafaunal extinctions have occurred progressively in such places as North America, South America and Madagascar with no climatic commonality. The only common factor that can be ascertained is the arrival of humans.
World wide extinctions seem to follow the migration of humans and to be most severe where humans arrived most recently and least severe where humans were originally – Africa (see figure at left). This suggests that in Africa, where humans evolved, prey animals and human hunting ability evolved together, so the animals evolved avoidance techniques. As humans migrated throughout the world and became more and more proficient at hunting, they encountered animals that had evolved without the presence of humans. Lacking the fear of humans that African animals had developed, animals outside of Africa were easy prey for human hunting techniques. It also suggests that this is independent of climate change (see figure at left).
Extinction through human hunting has been supported by archaeological finds of mammoths with projectile points embedded in their skeletons, by observations of modern naïve animals allowing hunters to approach easily and by computer models by Mosimann and Martin, and Whittington and Dyke, and most recently by Alroy.
Eugene S. Hunn, President of the Society of Ethnobiology, offers a dissenting view. He points out that the birthrate in hunter-gatherer societies is generally too low, that too much effort is involved in the bringing down of a large animal by a hunting party, and that in order for hunter-gatherers to have brought about the extinction of megafauna simply by hunting them to death, an extraordinary amount of meat would have had to have been wasted. It is possible that those who advocate the overkill hypothesis simply have not considered the differences in outlook between typical forager (hunter-gatherer) cultures and the present-day industrial cultures which exist in modernized human societies; waste may be tolerated and even encouraged in the latter, but is not so much in the former. It may be noted that in relatively recent human history, for instance, the Lakota of North America were known to take only as much bison as they could use, and they used virtually the whole animal—this despite having access to herds numbering in the millions. Conversely, "buffalo jumps" featured indiscriminate killing of a herd. However, Hunn's comments are in reference to a hunter-prey equilibrium state reached after thousands of years of coexistence, and are not relevant to hunters newly arrived on a virgin land mass full of easily taken big game. The well-established practice of industrial-scale moa butchering by the early Maori, involving enormous wastage of less choice portions of the meat, indicates that these arguments are incorrect.
Overkill Hypothesis
The overkill hypothesis, a variant of the hunting hypothesis, was proposed 40 years ago by Paul S. Martin, now Professor of Geosciences Emeritus at the Desert Laboratory of the
University of ArizonaThe University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...
. It sparked debate which continues today. In contrast to other hunting hypothesis it explains the megafaunal extinctions within a relatively short period of time. The most convincing evidence of his theory is that 80% of the North American large mammal species disappeared within 1000 years of the arrival of humans on the Western Hemisphere continents.
Shortcomings of the Hunting Hypothesis
The major objections to the theory are as follows:
- In predator-prey models it is unlikely that predators could over-hunt their prey since predators need their prey as food to sustain life and reproduce.. This criticism has been rejected by many ecologists because humans have the widest dietary choice of any predator and are perfectly capable of switching to alternative prey or even plant foods when any prey species becomes rare. Humans have indisputably hunted numerous species to extinction, which renders any argument that human predators can never hunt prey to extinction immediately invalid.
- There is no archeological evidence that megafauna other than mammoths, mastodons, gomphothere
Gomphotheriidae is a diverse taxonomic family of extinct elephant-like animals , called gomphotheres. They were widespread in North America during the Miocene and Pliocene epochs, 12-1.6 million years ago. Some lived in parts of Eurasia, Beringia and, following the Great American Interchange,...
s and bison were hunted. (Meltzer) Overkill proponents, however, say this is due to chance and the low probability of animals with low populations to be preserved. (Martin) Additionally, biochemical analyses have shown that Clovis tools were used in butchering horses and camels.
- A small number of animals that were hunted, such as a single species of bison
Members of the genus Bison are large even-toed ungulates within the subfamily Bovinae. Two extant species and four extinct species are recognized...
, did not go extinct. However the surviving bison species in North America was a recent Eurasian immigrant that arrived in the Americas at approximately the same time as humans and was thus well-adapted to human hunting pressure. In contrast at least three endemic American bison species did become extinct. Bison also are r type herbivores and reproduce rapidly compared to other species that did go extinct such as proboscideans and horses.
- The dwarfing of animals is not explained by overkill. Numerous authors, however, have pointed out that dwarfing of animals is perfectly well explained by humans selectively harvesting the largest animals, and have provided proof that even within the 20th century numerous animal populations have reduced in average size due to human hunting.
- Eurasian Pleistocene megafauna went extinct in roughly same time period despite having a much longer time to adapt to hunting pressure by humans. However, the extinction of the Eurasian megafauna can be viewed as a result of a different process than that of the American megafauna. The latter case occurred after the sudden appearance of modern human hunters on a land mass they had never previously inhabited, while the former case was the culmination of the gradual northward movement of human hunters over thousands of years as their technology for enduring extreme cold and bringing down big game improved. Thus, while the hunting hypothesis does not necessarily predict the rough simultaneity of the north Eurasian and American megafaunal extinctions, this simultaneity cannot be regarded as evidence against it.
- The hypothesis that the Clovis culture
The Clovis culture is a prehistoric Paleoindian culture that first appears in the archaeological record of North America around 11,500 rcbp radiocarbon years ago, at the end of the last glacial period, characterized by a particular tool kit adapted to the hunting of large mammals...
represented the first humans to arrive in the New World has been disputed recently. (See Models of migration to the New WorldThere have been several models of migration to the New World proposed by various academic communities. The question of how, when and why humans first entered the Americas is of intense interest to archaeologists and anthropologists and has been a subject of heated debate for centuries...
)
Climate change hypothesis
At the end of the 19th and beginning of the 20th centuries, when scientists first realized that there had been glacial and
interglacialAn interglacial is a geological interval of warmer global average temperature that separates glacial periods within an ice age. The current Holocene interglacial has persisted since the end of the Pleistocene, about 11,400 years ago....
ages, and that they were somehow associated with the prevalence or disappearance of certain animals, they surmised that the termination of the Pleistocene
ice ageThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
might be an explanation for the extinctions.
Critics object that since there were multiple glacial advances and withdrawals in the evolutionary history of many of the megafauna, it is rather implausible that only after the last glacial would there be such extinctions.
Some evidence weighs against this theory as applied to Australia. It has been shown that the prevailing climate at the time of extinction (40,000–50,000 BP) was similar to that of today, and that the extinct animals were strongly adapted to an arid climate. The evidence indicates that all of the extinctions took place in the same short time period, which was the time when humans entered the landscape. The main mechanism for extinction was likely fire (started by humans) in a then much less fire-adapted landscape. Isotopic evidence shows sudden changes in the diet of surviving species, which could correspond to the stress they experienced before extinction.
Increased temperature
The most obvious change associated with the termination of an ice age is the increase in temperature. Between 15,000
BPBefore Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use 1 January 1950 as the arbitrary origin of the age scale...
and 10,000 BP, a 6
°CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
increase in global mean annual temperatures occurred. This was generally thought to be the cause of the extinctions.
According to this hypothesis, a temperature increase sufficient to melt the
Wisconsin ice sheetThe last glacial period was the most recent glacial period within the current ice age, occurring in the Pleistocene epoch. It began about 110,000 years ago and ended about 9,600 - 9,700 BC. During this period there were several changes between glacier advance and retreat. The maximum extent of...
could have placed enough thermal stress on cold-adapted mammals to cause them to die. Their heavy fur, which helps conserve body heat in the glacial cold, might have prevented the dumping of excess heat, causing the mammals to die of heat exhaustion. Large mammals, with their reduced
surface area-to-volume ratioThe surface-area-to-volume ratio also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area per unit volume of an object or collection of objects. The surface area to volume ratio is measured in units of inverse distance...
, would have fared worse than small mammals.
Shortcomings of the Temperature Hypothesis
More recent research has demonstrated that the annual mean temperature of the current interglacial that we have seen for the last 10,000 years is no higher than that of previous interglacials, so the same large mammals survived similar temperature increases. Therefore warmer temperature alone is not a sufficient explanation.
In addition, numerous species such as mammoths on
Wrangel IslandWrangel Island is an island in the Arctic Ocean, between the Chukchi Sea and East Siberian Sea. Wrangel Island lies astride the 180° meridian. The International Date Line is displaced eastwards at this latitude to avoid the island as well as the Chukchi Peninsula on the Russian mainland...
and St. Paul Island survived in human-free refugia despite changes in climate. This is precisely the opposite of what would be expected if climate change were responsible. Under normal ecological assumptions island populations should be more vulnerable to extinction due to climate change because of small populations and an inability to migrate to more favorable climes.
Increased continentality affects vegetation in time or space
Other scientists have proposed that increasingly extreme weather — hotter summers and colder winters — referred to as "
continentalityContinentality is the tendency of land to experience more thermal variation than water, due to the land's lower specific heat capacity. Continental climate also tends to be dryer than oceanic climate as there is less moisture input to the atmosphere from evaporation...
", or related changes in rainfall caused the extinctions. The various hypotheses are outlined below.
Vegetation changes: geographic
It has been shown that vegetation changed from mixed
woodlandEcologically, a woodland is an area covered in trees, usually at low density, forming an open habitat, allowing sunlight to penetrate between the trees, and limiting shade. Woodland may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to...
-
parklandParkland or Parklands may refer to:* A park* Aspen parkland, a biome transitional between prairie and boreal forest * Landscaped parkland, a managed rural area associated with European country houses such as Longleat-Place names:United States...
to separate
prairiePrairies are considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type...
and woodland. This may have affected the kinds of food available. If so,
herbivoreA herbivore is an animal that is adapted to eat plants and not meat.Herbivory is a form of predation in which an organism consumes principally autotrophs such as plants, algae and photosynthesizing bacteria....
s might not have found the plants with which they had evolved and thus would have fallen prey to the anti-herbivory toxins in the plants that remained available. Shorter growing seasons may have caused the extinction of large herbivores and the dwarfing of many others. In this case, as observed, bison and other large
ruminantPhysiologically, a ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach, known as the rumen, then regurgitating the semi-digested mass, now known as cud, and chewing it again. The process of rechewing the cud to...
s would have fared better than horses, elephants and other
monogastricA monogastric organism has a simple single-chambered stomach, whereas ruminants have a four-chambered complex stomach. Examples of monogastric animals include humans, pigs, dogs, and cats....
s, because ruminants are able to extract more nutrition from limited quantities of high-
fiberDietary fiber , sometimes called roughage, is the indigestible portion of plant foods that pushes food through the digestive system, absorbing water and easing defecation...
food and better able to deal with anti-herbivory toxins. So, in general, when vegetation becomes more specialized, herbivores with less diet flexibility may be less able to find the mix of vegetation they need to sustain life and reproduce within a given area.
Rainfall changes: time
Increased continentality resulted in reduced and less predictable rainfall limiting the availability of plants necessary for energy and nutrition. Axelrod and Slaughter have suggested that this change in rainfall restricted the amount of time favorable for reproduction. This could disproportionately harm large animals, since they have longer, more inflexible mating periods, and so may have produced young at unfavorable seasons (i.e., when sufficient food, water, or shelter was unavailable because of shifts in the growing season. In contrast, small mammals, with their shorter
life cycleA life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
s, shorter reproductive cycles, and shorter
gestationGestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals duringpregnancy can have one or more gestations at the same time ....
periods, could have adjusted to the increased unpredictability of the climate, both as individuals and as species which allowed them to synchronize their reproductive efforts with conditions favorable for offspring survival. If so, smaller mammals would have lost fewer offspring and would have been better able to repeat the reproductive effort when circumstances once more favored offspring survival.
Shortcomings of the continentality hypotheses
Critics have identified a number of problems with the continentality hypotheses.
- Megaherbivores have prospered at other times of continental climate. For example, megaherbivores thrived in Pleistocene Siberia
Siberia , is the vast region constituting almost all of Northern Asia and for the most part currently serving as the massive central and eastern portion of the Russian Federation, having served in the same capacity previously for the USSR from its beginning, and the Russian Empire beginning in the...
, which had and has a more continental climate than Pleistocene or modern (post-Pleistocene, interglacial) North America.
- The animals that went extinct actually should have prospered during the shift from mixed woodland-parkland to prairie, because their primary food source, grass, was increasing rather than decreasing. Although the vegetation did become more spatially specialized, the amount of prairie and grass available increased, which would have been good for horses and for mammoths, and yet they went extinct.
- Although horses went extinct in the New World, they were successfully reintroduced by the Spanish in the 16th century – into a modern post-Pleistocene, interglacial climate. Today there are feral
A feral organism is one that has escaped from domestication and returned, partly or wholly, to a wild state. The introduction of feral animals or plants to their non-native regions, like any introduced species, can disrupt ecosystems and may, in some cases, contribute to extinction of indigenous...
horses still living in those same environments. They find a sufficient mix of food to avoid toxins, they extract enough nutrition from forage to reproduce effectively and the timing of their gestation is not an issue. Similarly, mammoths survived the Pleistocene Holocene transition on isolated, uninhabited islands in the Mediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by Africa, and on the east by the Levant. The sea is technically a part of the Atlantic Ocean, although it...
and on Wrangel Island in the Siberian Arctic until 4,000 to 7,000 years ago.
- Large mammals should have been able to migrate, permanently or seasonally, if they found the temperature too extreme, the breeding season too short, or the rainfall too sparse or unpredictable. Seasons vary geographically. By migrating away from the equator
The equator is the intersection of the Earth's surface with the plane perpendicular to the Earth's axis of rotation and containing the Earth's center of mass. In simpler language, it is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole that divides the Earth...
, herbivores could have found areas with growing seasons more favorable for finding food and breeding successfully. Modern-day African elephants migrate during periods of droughtA drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
to places where there is apt to be water.
- Large animals store more fat in their bodies than do medium-sized animals and this should have allowed them to compensate for extreme seasonal fluctuations in food availability.
The extinction of the megafauna could have caused the disappearance of the mammoth steppe. Alaska now has low nutrient soil unable to support bison, mammoths, and horses. R. Dale Guthrie has claimed this as a cause of the extinction of the megafauna there; however, he may be interpeting it backwards. Chapin (Chapin 1980) showed that simply adding fertilizer to the soil in Alaska could make grasses grow again like they did in the era of the mammoth steppe. Possibly, the extinction of the megafauna and the correspoding loss of dung is what led to low nutrient levels in modern day soil and therefore is why the landscape can no longer support megafauna.
Shortcomings of both Climate Change and Overkill
Neither the Overkill
sensu stricto nor Climate Change hypotheses explain several observations.
- Browsers, mixed feeders and non-ruminant grazer species suffered most, while ruminant grazers generally survived. However a broader scope of overkill predicts this perfectly because changes in vegetation wrought by anthropogenic
Anthropogenic effects, processes or materials are those that are derived from human activities, as opposed to those occurring in biophysical environments without human influence....
fire preferentially selects against browse species.
- Many surviving mammal species were sharply diminished in size, a fact which many authors have pointed out perfectly fits the Overkill Hypothesis and is reflected in the dwarfing of many hunted species even within the 20th century.
Because of perceived shortcomings of the Overkill or Climate Change hypotheses alone, some scientists support a combination of Climate Change and Overkill.
Theory
The Hyperdisease Hypothesis attributes the extinction of large mammals during the late Pleistocene to indirect effects of the newly arrived
aboriginal humansThe term indigenous peoples can be used to describe any ethnic group of people who inhabit a geographic region with which they have the earliest known historical connection, alongside more recent immigrants who have populated the region and may be greater in number...
.
The Hyperdisease Hypothesis proposes that humans or animals traveling with them (e.g., chickens or domestic dogs) introduced one or more highly virulent diseases into vulnerable populations of native mammals, eventually causing extinctions. The extinction was biased toward larger-sized species because smaller species have greater resilience because of their life history traits (e.g., shorter gestation time, greater population sizes, etc). Humans are thought to be the cause because other earlier immigrations of mammals into North America from Eurasia did not cause extinctions.
Diseases imported by people have been responsible for extinctions in the recent past; for example, bringing avian
malariaMalaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria, killing between one and...
to Hawaii has had a major impact on the isolated birds of the island. MacPhee is searching
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
in mammoth remains from
Wrangel IslandWrangel Island is an island in the Arctic Ocean, between the Chukchi Sea and East Siberian Sea. Wrangel Island lies astride the 180° meridian. The International Date Line is displaced eastwards at this latitude to avoid the island as well as the Chukchi Peninsula on the Russian mainland...
in
SiberiaSiberia , is the vast region constituting almost all of Northern Asia and for the most part currently serving as the massive central and eastern portion of the Russian Federation, having served in the same capacity previously for the USSR from its beginning, and the Russian Empire beginning in the...
; he hopes to find evidence of
infectionAn infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply, usually at the expense of the host. The infecting organism, or pathogen, interferes with the normal functioning of the...
.
If a disease was indeed responsible for the end-Pleistocene extinctions, then there are several criteria it must satisfy (see Table 7.3 in MacPhee & Marx 1997). First, the
pathogenA pathogen , infectious agent, or germ, is a biological agent that causes disease or illness to its host....
must have a stable
carrierAn asymptomatic carrier is a person or other organism that has contracted an infectious disease, but who displays no symptoms. Although unaffected by the disease themselves, carriers can transmit it to others...
state in a reservoir species. That is, it must be able to sustain itself in the environment when there are no susceptible
hostIn biology, a host is an organism that harbors a parasite , or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
s available to infect. Second, the pathogen must have a high infection rate, such that it is able to infect virtually all individuals of all ages and sexes encountered. Third, it must be extremely lethal, with a mortality rate of c. 50–75%. Finally, it must have the ability to infect multiple host species without posing a serious threat to humans. Humans may be infected, but the disease must not be highly lethal or able to cause an
epidemicDefining an epidemic can be subjective, depending in part on what is "expected". An epidemic may be restricted to one locale , more general or even global...
.
One suggestion is that pathogens were transmitted by the expanding
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s via the domesticated
dogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
s they brought with them. Unfortunately for such a theory it can not account for several major extinction events, notably Australia and North America. Dogs did not arrive in Australia until approximately 35,000 years after the first humans arrived and approximately 30,000 years after the megafaunal extinction was complete and as such can not be implicated. In contrast numerous species including wolves, mammoths, camelids and horses had emigrated continually between Asia and North America over the past 100,000 years. For the disease hypothesis to be applicable in the case of the Americas it would require that the population remain immunologically naive despite this constant transmission of genetic and pathogenic material.
Shortcomings of the Hyperdisease Hypothesis
- No evidence of disease has been found.
- Generally speaking, disease has to be very virulent to kill off all the individuals in a genus
In biology, a genus is a taxonomic unit used in the classification of living and fossil organisms. The term comes from Latin genus "descent, family, type, gender" , cognate with – genos, "race, stock, kin" ..In addition, genus is a taxonomic rank in the hierarchy In biology, a genus (plural:...
or speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
. Even such a virulent disease as West Nile VirusWest Nile virus is a virus of the family Flaviviridae. Part of the koji Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, and...
is unlikely to have caused extinction.
- The disease would need to be implausibly selective while being simultaneously implausibly broad. Such a disease needs to be capable of killing of three species of bison while leaving a third very closely related species unaffected. It would need to be capable of killing off flightless birds while leaving closely related flighted species unaffected. Yet while remaining sufficiently selective to afflict only individual species within genera it must be capable of fatally infecting across such clades as birds, marsupial
Marsupials are an infraclass of mammals, characterized by a distinctive pouch , in which females carry their young through early infancy.- History :...
s, placentals, testudines, and crocodilians. No disease with such a broad scope of fatal infectivity is known, much less one that remains simultaneously incapable of infecting numerous closely related species within those disparate clades.
Second-Order Predation
Scenario
The Second-Order Predation Hypothesis says that as humans entered the New World they continued their policy of killing predators, which upset the ecological balance of the continent causing
overpopulationOverpopulation is a condition where an organism's numbers exceed the carrying capacity of its habitat. In common parlance, the term usually refers to the relationship between the human population and its environment, the Earth....
, environmental exhaustion, and environmental collapse. The hypothesis accounts for changes in animal, plant, and, human populations.
The scenario is as follows:
- After the arrival of H. sapiens in the New World, existing predators must share the prey populations with this new predator. Because of this competition, populations of original, or first-order, predators cannot find enough food they are in direct competition with humans.
- Second-order predation begins as humans begin to kill predators.
- Prey populations are no longer well controlled by predation. Killing of nonhuman predators by H. sapiens reduces their numbers to a point where these predators no longer regulate the size of the prey populations.
- Lack of regulation by first-order predators triggers boom-and-bust
The term boom and bust refers to a great buildup in the price of a particular commodity or, alternately, the localized rise in an economy, often based upon the value of a single commodity, followed by a downturn as the commodity price falls due to a change in economic circumstances or the collapse...
cycles in prey populations. Prey populations expand and consequently overgraze and over-browse the land. Soon the environment is no longer able to support them. As a result, many herbivores starve. Species that rely on the slowest recruiting food become extinct, followed by species that cannot extract the maximum benefit from every bit of their food.
- Boom-bust cycles in herbivore populations change the nature of the vegetative environment, with consequent climatic impacts on relative humidity and continentality. Through overgrazing and overbrowsing, mixed parkland becomes grassland, and climatic continentality increases.
Support
This has been supported by a computer model, the Pleistocene Extinction Model (PEM), which, using the same assumptions and values, compares hypotheses with Second-Order Predation. The findings are that Second Order-Predation is more consistent with extinction than is Overkill (results graph at left). The PEM was run to test combination hypotheses by artificially introducing sufficient climate change to cause extinction. When Overkill and Climate Change are combined they balance each other out. Climate Change reduces the number of plants, Overkill removes animals, therefore fewer plants are eaten. Second-Order Predation combined with Climate Change exacerbates the extinction (results graph at right).
Second-Order Predation and other theories
- Climate Change: Second-Order Predation accounts for the changes in vegetation, which in turn may account for the increase in continentality. Since the extinction is due to destruction of habitat it accounts for the loss of animals not hunted by humans. Second-Order Predation accounts for the dwarfing of animals as well as extinctions since animals that could survive and reproduce on less food would be selectively favored.
- Hyperdisease: The reduction of carnivores could have been from distemper or other carnivore disease carried by domestic dogs.
- Overkill: The observation that extinctions follow the introduction of humans is supported by the Second-Order Predation hypothesis.
Shortcomings of the Second-Order Predation Hypothesis
- No evidence of humans hunting predators has been found in the New World though it has been found in Siberia.
- Like all climate-based theories, the model predicts large extinctions in response to climate change and without human hunting, so it is unable to explain why these extinctions did not occur during numerous deglaciations of equal intensity, or why they did not occur at high latitudes in Eurasia.
- It assumes decreases in vegetation due to climate change, but deglaciation doubled the habitable area of North America.
- Climate change had little effect on vegetation or the distribution of small mammals, reptiles, and amphibians throughout the southern half of the United States, not to mention tropical regions throughout the Americas that also suffered catastrophic extinctions.
- Any vegetational changes that did occur failed to cause almost any extinctions of small vertebrates, and they are more narrowly distributed on average.
- The model specifically assumes high extinction rates in grasslands, but most extinct species ranged across numerous vegetation zones, historical population densities of ungulates were very high in the Great Plains, these environments support high ungulate diversity throughout Africa, and extinction intensity was equally severe in forested environments.
- It is unable to explain why large herbivore populations were not regulated by surviving carnivores such as grizzly bears, wolves, pumas, and jaguars whose populations would have increased rapidly in response to the loss of competitors.
- It does not explain why almost all extinct carnivores were large herbivore specialists such as sabre toothed cats and short faced bears, but most hypocarnivores and generalized carnivores survived.
- There is no historical evidence of boom and bust cycles causing even local extinctions in regions where large mammal predators have been driven extinct by hunting. The recent hunting out of remaining predators throughout most of the United States has not caused massive vegetational change or dramatic boom and bust cycles in ungulates.
- It is not spatially explicit and does not track predator and prey species separately, whereas the multispecies overkill model does both.
- The multispecies model produces a mass extinction through indirect competition between herbivore species: small species with high reproductive rates subsidize predation on large species with low reproductive rates. The fact that all prey species are lumped in the Pleistocene Extinction Model explains why it performs poorly without adding extra assumptions about climate change and cascade effects.
- Everything explained by this model also is explained by the multispecies model, but with less assumptions, so this one is not parsimonious.
Comet Hypothesis
First publicly presented at the Spring 2007 joint assembly of the
American Geophysical UnionThe American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
in Acapulco, Mexico, the comet hypothesis suggests that the mass extinction was caused by a swarm of comets 12,900 years ago. Debate around this hypothesis has included, among other things, the lack of an impact crater, relatively small increased level of
IridiumIridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
in the soil, and the highly improbable nature of such an event. Using photomicrograph analysis, research published in January 2009 has found evidence of nanodiamonds in the soil from six sites across North America including Arizona, Minnesota, Oklahoma, South Carolina and two Canadian sites. Similar research found nanodiamonds in the
Greenland ice sheetThe Greenland ice sheet is a vast body of ice covering 1.71 million km², roughly 80% of the surface of Greenland. It is the second largest ice body in the World, after the Antarctic Ice Sheet. The ice sheet is almost 2,400 kilometers long in a north-south direction, and its greatest width is 1,100...
.
Hyperdisease Hypothesis
Second-Order Predation