''Arctotherium'' ("''bear beast''") is an extinct genus of the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

short-faced bears endemic to

Central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

. ''Arctotherium'' migrated from

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

during the

Great American Interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which lan ...

, following the formation of the

Isthmus of Panama The Isthmus of Panama ( es, Istmo de Panamá), also historically known as the Isthmus of Darien (), is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country ...

during the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58bear Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Nor ...

s. ''Arctotherium'' was adapted to open and mixed habitat. They are genetically closer to the spectacled bear (''Tremarctos ornatus''), than to ''

Arctodus ''Arctodus'' is an extinct genus of short-faced bear that inhabited North America during the Pleistocene (~2.5 Mya until 12,000 years ago). There are two recognized species: the lesser short-faced bear (''Arctodus pristinus'') and the giant short- ...

'' of North America, implying the two extinct forms evolved large size in a convergent manner, perhaps to facilitate dominating other carnivores in the competition for the biggest carcasses.

Evolution

Tremarctinae

''Arctotherium'' is part of the

Tremarctinae The Tremarctinae or short-faced bears is a subfamily of Ursidae that contains one living representative, the spectacled bear (''Tremarctos ornatus'') of South America, and several extinct species from four genera: the Tremarctos floridanus, Florid ...

subfamily of bears, otherwise known as the short faced bears, which also includes ''

'' (North American short faced bears) and '' Tremartcos'' (the Floridian and modern spectacled bear). Tremarctinae originate with their common ancestor, ''

Plionarctos ''Plionarctos'' is an extinct genus of bear endemic to North America from the Miocene to the Pliocene, ~10.3—3.3 Mya (unit), Mya, existing for about 7 million years. ''Indarctos'' (10.7—9.2 Mya) preceded ''Plionarctos'' by only a few thousan ...

,'' in the Middle Hemphillian (earliest

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

, ~10 Ma) of North America; ''Plionarctos'' is last recorded in the early Blancan (Early Pliocene, ~3.3 Ma). Around the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Tremarctines, along with other

ursids The Ursid (URS) meteor activity begins annually around December 17 and runs for over a week, until the 25th or 26th. This meteor shower is named for its radiant point, which is located near the star Beta Ursae Minoris (Kochab) in the constellat ...

, experienced an explosive radiation in diversity, as C4 vegetation (

grasses Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...

) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and a faunal turnover which extinguished 60–70% of all Eurasian faunal genera, and 70–80% of North American genera. Correspondingly, recent genetic studies suggest that the mean divergence dates for ''Arctotherium'', ''Arctodus'' and ''Tremarctos'' was 4.8 Ma, and between ''Arctotherium'' and ''Tremarctos'' at 4.1 Ma. Interestingly, all three genera are first recorded from the

Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years Before Present, BP, a period of .

(Late Pliocene) of

, with the first possible record of ''Arctotherium sp.'' being a tooth found in the

Cuscatlán Formation The Cuscatlán Formation is a geologic formation in El Salvador. It preserves fossils dating back to the Pliocene to Middle Pleistocene (Blancan to Irvingtonian) period. Fossil content * ''Borophagus hilli'' * '' Meizonyx salvadorensis'' * '' M ...

El Salvador El Salvador (; , meaning " The Saviour"), officially the Republic of El Salvador ( es, República de El Salvador), is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south b ...

, along with a partial ''

Borophagus ''Borophagus'' ("gluttonous eater") is an extinct genus of the subfamily Borophaginae, a group of canids endemic to North America from the Middle Miocene epoch through the Early Pleistocene epoch 12—1.8 Mya. Evolution ''Borophagus'', like ot ...

'' skull, dated to the latest

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

South America

The oldest dated confirmed remains of ''Arctotherium'' in

are those of the gigantic ''A. angustidens'' from

Buenos Aires Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata, on South ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. What the evolutionary history of ''Arctotherium'' was beforehand, particularly regarding its sudden significant size, is unclear. ''A. angustidens'' remains have been dated to between 1Ma to 0.7 Ma of the Pleistocene, which corresponds with the

Ensenadan The Ensenadan age is a period of geologic time (1.2–0.8 Ma) within the Early Pleistocene epoch of the Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the ...

period (although the younger dates are uncertain). ''A. angustidens'' was eventually replaced at the start of the

Lujanian The Lujanian age is a South American land mammal age within the Pleistocene and Holocene epochs of the Neogene, from 0.8–0.011 Ma or 800–11 tya. It follows the Ensenadan. The age is usually divided into the middle Pleistocene Bonaerian stage ...

(~700,000 years ago) by medium-sized ''Arctotherium'' species- first by ''A. vetustum'' (

Middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. The ...

), then shortly thereafter by the more robustly built ''A. bonariense'' ( Middle /

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division of ...

), along with ''A. tarijense'' (

to the

Early Holocene In the geologic time scale, the Greenlandian is the earliest age or lowest stage of the Holocene Epoch or Series, part of the Quaternary. Beginning in 11,650 BP (9701 BCE or 300 HE) and ending 8,276 BP (6237 BCE or 3764 HE), it is the earlies ...

)''.'' While the smallest but most widespread species, ''A. wingei'', is only confirmed from the

and

, the species' more tropical disposition is thought to greatly limit fossilisation. That, along with ''A. wingeis more ancestral position in ''Arctotherium'', suggests an origin in the

. Within ''Arctotherium'', two clades are thought to exist- ''A. bonariense'' and ''A. tarijense'' have been described as the most derived species of the genus, whilst ''A. vetustum'' and ''A. wingei'' are regarded the most archaic, even more so than ''A. angustidens''. Of these successor species, ''A. tarijense'' and ''A. wingei'' are by far the most successful when taking into account temporal & geographic range, and the frequency of fossil finds. A separate Andean form of ''Arctotherium'' is also suggested to have existed at the end of the Pleistocene, if those finds aren't representative of the currently

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

-restricted '' T.ornatus''. Curiously, while ''Arctotherium'''s known species dramatically shrank in size after ''A. angustidens'', ''

'' underwent the opposite transformation, transitioning from the medium-sized ''A. pristinus'' to the gigantic ''A. simus''. by the end of the Pleistocene.

Description

Taxonomy

Rare Spectacled or Andean Bear (31645919165)

''Arctotherium'' was named by

Hermann Burmeister Karl Hermann Konrad Burmeister (also known as Carlos Germán Conrado Burmeister) (15 January 1807 – 2 May 1892) was a German Argentine zoologist, entomologist, herpetologist, botany, botanist, and coleopterologist. He served as a professor at ...

in 1879.

(and therefore ''Arctotherium'') appear to have a disproportionately shorter snouts compared with most modern bears, giving them the name "short-faced." This apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with

ursine Ursine may refer to: Zoology * Loosely, Ursidae, members of the bear family (conventionally designated ursids) ** Following the taxonomic convention, Ursinae, the subfamily Places * Ursine, Nevada Ursine is an unincorporated community and cens ...

bears; ''Arctotherium'' had a deeper but not a shorter face than most living bears. Although size can help differentiate the species, only cranial and dental identifiers can be used to differentiate between species. The upper canine is very similar between species of ''Arctotherium'', differing mainly in size. The canine of ''A. wingei'' is the smallest among the species. The lower canine of ''A. wingei'' presents two enamel ridges as in ''A. angustidens'' and ''A. tarijense'', while in ''A. vetustum'' and ''A. bonariense'' there are three ridges. In ''A. vetustum'', the distal ridge is very small and the mesial ridge is small, while in ''A. angustidens'' and ''A. tarijense'' both ridges are large. With regard to locomotion, although the shape of the

elbow joint The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the media ...

suggests '' Arctodus sp''., ''Arctotherium bonariense'', and ''A. wingei'' the possibility of retaining semi-arboreal adaptations, the size of the elbow joint does not. As the medial epicondyle is particularly expanded in these species, it is likely that (as for the

giant panda The giant panda (''Ailuropoda melanoleuca''), also known as the panda bear (or simply the panda), is a bear species endemic to China. It is characterised by its bold black-and-white coat and rotund body. The name "giant panda" is sometimes us ...

) the fossil ''Arctodus'' and ''Arctotherium'' retained this character in relation to their higher degree of forelimb dexterity. As these genera's convergent evolution towards large body size that could have been favoured by scavenging adaptations, then high degree of proximal dexterity could have been advantageous for these species and retained in the Tremarctinae lineage in spite of size evolution.

Size

''Arctotherium'' species ranged between a variety of sizes, both between species and individuals of the same species. The sole remaining Tremarctine bear, the spectacled bear, exhibits strong sexual dimorphism, with adult males being 30%–50% larger than females.

Phylogenetic bracketing Phylogenetic bracketing is a method of inference used in biological sciences. It is used to infer the likelihood of unknown traits in organisms based on their position in a phylogenetic tree. One of the main applications of phylogenetic bracketing ...

, along with ''Arctotherium'''s ability to exploit a variety of resource rich/poor environments and niches, can help explain ''Arctotherium'''s morphological diversity. Various attempts to calculate each species' body mass have been made; for example, a 2006 study calculated the mean weight of two species, ''A. bonariense'' at ~110 kg (hypothetical typical weight range = 106 kg-122 kg), and ''A. tarijense'' at ~139 kg (102 kg-189 kg). According to a 2009 study, the weight ranges for ''Arctotherium'' were calculated as follows- ''A. wingei'' at 51 kg-150 kg, ''A. vetustum'' at 102 kg-300 kg, ''A. tarijense'' at 135 kg-400 kg, ''A. bonariense'' between 171 kg-500 kg, and ''A. angustidens'' at 412 kg-1,200 kg. The study considered each end figure as the maximum hypothetical weight. Further studies calculated an ''A. tarijense'' specimen's weight (MACN 971) at 231 kg, and ''A. wingei'' specimens from the Brazilian intertropical region at ~83 kg. An extraordinarily large specimen of ''A. angustidens'' recovered in 2011 from

shows an individual estimated, using the humerus, to weigh between . However, the authors consider the upper limit as improbable, and say that is more likely. An estimated standing height for this ''A. angustidens'' individual is between . It would still make the species the largest bear ever found, and contender for the largest carnivorous land mammal known.

Paleobiology

Early Pleistocene

The first recorded ''Arctotherium'' specimens in

occur alongside the earliest known South American records of several other

carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

ns: the sabre-toothed cats ''

Smilodon ''Smilodon'' is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related ...

'' and ''

Homotherium ''Homotherium'', also known as the scimitar-toothed cat or scimitar cat, is an extinct genus of machairodontine saber-toothed predator, often termed scimitar-toothed cats, that inhabited North America, South America, Eurasia, and Africa during th ...

'', the

puma Puma or PUMA may refer to: Animals * ''Puma'' (genus), a genus in the family Felidae ** Puma (species) or cougar, a large cat Businesses and organisations * Puma (brand), a multinational shoe and sportswear company * Puma Energy, a mid- and d ...

(''Puma concolor''), the

jaguar The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus '' Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the th ...

(''Panthera onca''), some large 25 kg–35 kg

canids Canidae (; from Latin, ''canis'', "dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found within th ...

, and several smaller (<15 kg)

mustelids The Mustelidae (; from Latin ''mustela'', weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks and wolverines, among others. Mustelids () are a diverse group and form the largest family in the ...

felids Felidae () is the family of mammals in the order Carnivora colloquially referred to as cats, and constitutes a clade. A member of this family is also called a felid (). The term "cat" refers both to felids in general and specifically to the do ...

and mephitids. The

North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

carnivorans Carnivora is a monophyletic order of placental mammals consisting of the most recent common ancestor of all cat-like and dog-like animals, and all descendants of that ancestor. Members of this group are formally referred to as carnivorans, ...

that invaded South America, including short-faced bears and ''

'', probably quickly adopted the predatory niches formerly occupied by the native typical South American groups such as

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...

sparassodont Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thoug ...

carnivores that had largely gone extinct shortly prior to their arrival.

''A. angustidens''

In the

, ''A. angustidens'' was only rivalled in size by ''

Smilodon populator ''Smilodon'' is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related ...

'', with '' Theriodictis platensis'', '' Canis gezi,'' '' Protocyon scagliorum,'' ''

Panthera onca The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus ''Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the thi ...

'' and pumas rounding out the predator guild in the

Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...

. The extinction of the scavenger-niche specialist

procyonid Procyonidae is a New World family of the order Carnivora. It comprises the raccoons, ringtails, cacomistles, coatis, kinkajous, olingos, and olinguitos. Procyonids inhabit a wide range of environments and are generally omnivorous. Character ...

Chapalmalania ''Chapalmalania'' is an extinct genus of procyonid from the Pliocene (Chapadmalalan to Uquian) of Argentina and Colombia (Ware Formation, Cocinetas Basin, La Guajira). Description Though related to raccoons and coatis, ''Chapalmalania'' was a ...

'' during this faunal turnover event is hypothesized as being the gateway for ''A. angustidens''' gigantism. Using carbon isotopes, ''A. angustidens diet has been posited to be omnivorous with a preference towards large quantities of meat. Beyond the scavenging of mega-herbivore carcasses, the type of tooth wear present amongst ''A. angustidens'' specimens, in addition to the frequency of broken teeth from most specimens (especially at older ages), suggests the active predation of large vertebrates by ''A. angustidens''. Of the dentition known from later ''Arctotherium'' species, only one specimen of ''A. bonariense'' exhibits the same cracked teeth which ''A. angustidens'' had, although extreme wear of the occlusal molar surface is common throughout the genus. Moreover, pathologies found on a huge specimen of ''A. angustidens'', being multiple deep injuries which had long healed despite infection, demonstrate a lifestyle of conflict. Three ''A. angustidens'' individuals were discovered in a

paleoburrow A paleoburrow is an underground shelter (tunnel, burrow, lair, etc.) excavated by extinct paleo-vertebrate megafauna (i.e., giant mammals, such as ground sloths) that lived in the prehistory, prehistoric era. A crotovina is a paleoburrow filled wit ...

together (postulated to have been a mother with adolescent cubs), which opens the possibility that ''A. angustidens'' lived in family groups. ''A. tarijense'' and ''A. wingei'' are also hypothesized to have utilised dens. In contrast with the spectacled bear's tropical and temperate habitat,

Argentina's seasonal and often harsh climate suggests quasi-hibernation would have been an effective strategy for survival, as ursine bears do today. ''A. angustidens'' is thought to have reoccupied caves excavated by

Xenarthra Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Ex ...

, such as the mylodonts ''

Glossotherium ''Glossotherium'' is an extinct genus of mylodontid ground sloths of the subfamily Mylodontinae, which includes large ground-dwelling sloths. It represents one of the best known members of the family, along with ''Mylodon'' and ''Paramylodon''. ...

'' and ''

Scelidotherium ''Scelidotherium'' is an extinct genus of ground sloth of the family Scelidotheriidae, endemic to South America during the Late Pleistocene epoch. It lived from 780,000 to 11,000 years ago, existing for approximately . Description It is chara ...

'', and the pampatheriid ''

Pampatherium ''Pampatherium'' is an extinct genus of xenarthran that lived in the Americas during the Pleistocene. Some species went extinct right at the Pleistocene-Holocene border. Distribution ''Pampatherium humboldtii'' and ''P. typum'' lived in South Ame ...

''. As suitable

s are rare before the

, it has been suggested that predation and competition for dens by the newly arrived eutherian carnivores increased the rate of

xenarthran Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extin ...

cave excavations.

Middle Pleistocene onwards

It has been suggested that as a diverse carnivore guild became established in

, ''Arctotherium'' began to revert to a more classically ursid omnivorous diet as the ecosystem matured, with ''A. tarijense'' being an adaptable, cosmopolitan omnivore, and ''A. wingei'' being largely herbivorous. However, the diet of ''A. wingei'' was not necessarily orthodox, as several bite marks on recovered fossils of herbivores, such as ''

'' and '' Equus'', are suggested to have been inflicted by scavenging short-faced bears across

. Carnivory would have likely peaked in times of resource instability.

''A. bonariense'' & ''A. tarijense''

Guanaco (Lama guanicoe) en el Parque Nacional Patagonia

''A. bonariense'' and ''A. tarijense'' had a typical prey weight of 100 kg, with a maximum of 300 kg. ''A. tarijense'' competed against ''

'', giant jaguars (''

Panthera onca mesembrina ''Panthera onca mesembrina'' is an extinct subspecies of the jaguar that was endemic to southern South America during the Pleistocene epoch (1.8 mya–11,000 years ago). Its fossils have been excavated primarily in Argentina and Chile, though fe ...

''), pumas, ''

Lycalopex The South American foxes (''Lycalopex''), commonly called ''raposa'' in Portuguese, or ''zorro'' in Spanish, are a genus from South America of the subfamily Caninae. Despite their name, they are not true foxes, but are a unique canid genus more ...

Cerdocyon The crab-eating fox (''Cerdocyon thous''), also known as the forest fox, wood fox, bushdog (not to be confused with the bush dog) or maikong, is an extant species of medium-sized canid endemic to the central part of South America since at least ...

Conepatus The hog-nosed skunks belong to the genus ''Conepatus'' and are members of the family Mephitidae (skunks). They are native to the Americas. They have white backs and tails and black underparts. Species Extinct species †''Conepatus robustus'' ...

Didelphis ''Didelphis'' is a genus of New World marsupials. The six species in the genus ''Didelphis'', commonly known as Large American opossums, are members of the ''opossum'' order, Didelphimorphia. The genus ''Didelphis'' is composed of cat-sized ...

,'' and ''

Dusicyon avus ''Dusicyon avus'' is an extinct species of cerdocyonine canid in the genus ''Dusicyon,'' native to South America during the Pleistocene and Holocene epochs. It was medium to large, about the size of a German shepherd. It was closely related to t ...

'' in

, occasionally hunting

camelids Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, ...

and

horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

as a supplement to scavenging, smaller prey and herbivory. Although carnivory increased the further south ''Arctotherium'' lived, carbon isotopes suggest that ''A. tarijense'''s prey weight limit peaked at 300 kg, leaving the (subadult and younger) mega-mammals, such as the

gomphotheres Gomphotheres are any members of the diverse, extinct taxonomic family Gomphotheriidae. Gomphotheres were elephant-like proboscideans, but do not belong to the family Elephantidae. They were widespread across Afro-Eurasia and North America during ...

, macraucheniids,

giant ground sloths ''Megatherium'' ( ; from Greek () 'great' + () 'beast') is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene through the end of the Pleistocene. It is best known for the elephant-sized type species ' ...

glyptodont Glyptodonts are an extinct subfamily of large, heavily armoured armadillos. They arose in South America around 48 million years ago and spread to southern North America after the continents became connected several million years ago. The best-kn ...

s, and toxodontids, to ''Smilodon populator'' and giant jaguars. ''

Smilodon fatalis ''Smilodon'' is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related ...

'', ''Arctotherium bonariense'', ''

Canis nehringi ''Canis nehringi'' is an extinct species of canid. ''Canis gezi'', a poorly known small wolf from the Ensenadan of South America, appears to have given rise to ''Canis nehringi'', a Lujanian species from Argentina. Betra's analysis in 1988, place ...

,''

maned wolves The maned wolf (''Chrysocyon brachyurus'') is a large canine of South America. It is found in Argentina, Brazil, Bolivia, Peru, and Paraguay, and is almost extinct in Uruguay. Its markings resemble those of foxes, but it is neither a fox nor a w ...

, and

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s would have also joined this predator guild at various stages of the

. However, a fragmented ''Arctotherium'' c.f. ''tarijense'' tooth from Baño Nuevo-1 cave in southern Chile preserves cavities, which could be interpreted as a consequence of consuming carbohydrate-rich foods such as fruit or honey. A further microwear analysis attempt of the tooth in 2015 was complicated by hard plant and bone consumption causing similar damage to teeth in omnivores.

''A. vetustum'' & ''A. wingei''

Parque Estadual do Lajeado - TO (vista ampla do cerrado)

Along with clues from various teeth of ''A. wingei'', carbon isotope studies suggest that ''A. wingei'', at least in the Brazilian intertropical region, were highly herbivorous, specialising in C3 vegetative matter such as fruits and leaves. This is not to diminish potential carnivory in ''A. wingei'', as the same study pointed to isotope spikes indicating the consumption of the ground sloth ''Nothrotherium'' ''maquinense'' (hypothesized as a preference for younger individuals and opportunistic scavenging), and ''A. wingei'' itself, which could represent cannibalism for juveniles or cubs, as observed in

American black bear The American black bear (''Ursus americanus''), also called simply a black bear or sometimes a baribal, is a medium-sized bear endemic to North America. It is the continent's smallest and most widely distributed bear species. American black bear ...

s and

polar bear The polar bear (''Ursus maritimus'') is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear specie ...

s. According to a 2021 study, the maximum prey for ''A. wingei'' would be around its own bodyweight (~83 kg). In the low-density savanna forests of the Brazilian intertropical region, ''A. wingei'', pumas and

s played a supporting role to the (also likely solitary) ''

'''s dominance of the regional predator guild, avoiding competition with ''

Protocyon troglodytes ''Protocyon'' is an extinct genus of large canid endemic to South and North America during the Late Pleistocene living from 781 to 12thousand years ago. Description ''Protocyon'' was a hypercarnivore, suggested by its dental adaptations. Like man ...

'' in more open savanna. Being smaller and more herbivorous, ''A. wingei'' would have also likely competed with other smaller

ns present in the BIR, such as

jaguarundi The jaguarundi (''Herpailurus yagouaroundi'') is a wild cat native to the Americas. Its range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes. The jaguarundi is a medium-sized ...

, ''

'', ''

Chrysocyon The maned wolf (''Chrysocyon brachyurus'') is a large canine of South America. It is found in Argentina, Brazil, Bolivia, Peru, and Paraguay, and is almost extinct in Uruguay. Its markings resemble those of foxes, but it is neither a fox nor a w ...

'', ''

Theriodictis ''Theriodictis'' is an extinct genus of hypercarnivorous wolf-like canid endemic to South America during the Pleistocene, living from 1.2 Ma- 500,000 years ago and existing for approximately . Fossil distribution The fossil remains are confi ...

'', ''

Speothos ''Speothos'' is a genus of canid found in Central and South America. The genus includes the living bush dog, '' Speothos venaticus'', and an extinct Pleistocene species, '' Speothos pacivorus''. Unusually, the fossil species was identified and ...

'', ''

Nasua ''Nasua'' is a genus of coatis of the family Procyonidae. Two additional species of coatis, commonly known as mountain coatis, are placed in the genus ''Nasuella''. Characteristics ''Nasua'' differs from ''Nasuella'' in being larger and hav ...

'', ''

Procyon Procyon () is the brightest star in the constellation of Canis Minor and usually the eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Minoris, which is Latinize ...

'', ''

Eira Eira is a neighborhood in Helsinki, the capital of Finland. History The district dates back to the early 20th century and received its name after Eira Hospital in the neighboring district of Ullanlinna, which in turn took its name from Eira ...

'', ''

Galictis A grison , , also known as a South American wolverine, is any mustelid in the genus ''Galictis''. Native to Central and South America, the genus contains two extant species: the greater grison (''Galictis vittata''), which is found widely in Sou ...

'', and ''

Leopardus ''Leopardus'' is a genus comprising eight species of small cats native to the Americas. This genus is considered the oldest branch of a genetic lineage of small cats in the Americas whose common ancestor crossed the Bering land bridge from Asia ...

.'' Additionally, as

dire wolves The dire wolf (''Aenocyon dirus'' ) is an extinct canine. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor ''Smilodon''. The dire wolf lived in the Americas and eastern Asia during the L ...

(''Aenocyon dirus'') and ''

'' inhabited north-western

, and were joined by American lions,

grey wolves The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly u ...

and

coyotes The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

, ''A. wingei'' would have been a member of various predator guilds across the species' range.

Paleo-ecological reconstructions

Although mostly herbivorous, the modern spectacled bear is on occasion an active predator. The spectacled bear has several hunting techniques- principally, the bear surprises or overpowers its prey, mounts its back, and consumes the immobilised animal while still alive, pinning the prey with its weight, large paws and long claws. Alternatively, the bear pursues the prey into rough terrain, hillsides, or precipices, provoking its fall and/or death. After death, the prey is dragged to a safe place (usually a nest over a tree, or a forested area) and consumed, leaving only skeletal remains. These behaviours have been suggested as ''Arctotherium'''s hunting strategies as well. However, although the spectacled bear is capable of

climbing trees Climbing Trees are a Welsh four-piece "Cymrucana" band based in Pontypridd, South Wales. The group currently features Matthew Frederick (piano/guitar/vocals), Colenso Jones (guitar/bass/vocals), Martin Webb (guitar/bass/vocals) and James Benn ...

, ''Arctotherium'' is thought to be non-arboreal.

Distribution and habitat

Other than ''A. wingei,'' the

''Arctotherium'' sp. tooth from

, and a possible record of ''A. vetustum'' in

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, all ''Arctotherium'' species appear to be largely restricted to the

Southern Cone The Southern Cone ( es, Cono Sur, pt, Cone Sul) is a geographical and cultural subregion composed of the southernmost areas of South America, mostly south of the Tropic of Capricorn. Traditionally, it covers Argentina, Chile, and Uruguay, bou ...

, particularly

, with the richest records being in the

Buenos Aires Province Buenos Aires (), officially the Buenos Aires Province (''Provincia de Buenos Aires'' ), is the largest and most populous Argentine province. It takes its name from the city of Buenos Aires, the capital of the country, which used to be part of th ...

. By the

, ''A. tarijense'' held domain over the open and semi-arid

Pampas The Pampas (from the qu, pampa, meaning "plain") are fertile South American low grasslands that cover more than and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos, and Córdoba; all of Uruguay; and Brazil ...

and

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

n habitats east of the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, inhabiting

, Patagonian Chile, southern Bolivia, and

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

, although ''A. bonariense'' may have also been contemporary in Late Pleistocene Uruguay. ''A. tarijense'' has been described as having a very low density of fossil material in Patagonia. On the other hand, ''A. wingei'' spanned across the northern, more mixed/forested and tropical parts of the continent, throughout the tropical savanna forests of

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

, and into

(

Belize Belize (; bzj, Bileez) is a Caribbean and Central American country on the northeastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a wate ...

and the

Yucatán Peninsula The Yucatán Peninsula (, also , ; es, Península de Yucatán ) is a large peninsula in southeastern Mexico and adjacent portions of Belize and Guatemala. The peninsula extends towards the northeast, separating the Gulf of Mexico to the north ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

). ''A. wingei'''s association with ''

Protocyon ''Protocyon'' is an extinct genus of large canid endemic to South and North America during the Late Pleistocene living from 781 to 12thousand years ago. Description ''Protocyon'' was a hypercarnivore, suggested by its dental adaptations. Like man ...

'' in the terminal Pleistocene of the

Yucatán Yucatán (, also , , ; yua, Yúukatan ), officially the Free and Sovereign State of Yucatán,; yua, link=no, Xóot' Noj Lu'umil Yúukatan. is one of the 31 states which comprise the political divisions of Mexico, federal entities of Mexico. I ...

, another animal previously thought to be endemic to

, suggests a complex relationship of faunal interchange long after the

Extinction

The last known records of ''Arctotherium'' are an ambiguous find of ''A. bonariense'' from

(

cf. The abbreviation ''cf.'' (short for the la, confer/conferatur, both meaning "compare") is used in writing to refer the reader to other material to make a comparison with the topic being discussed. Style guides recommend that ''cf.'' be used onl ...

aff #REDIRECT AFF Aff comes from Brazil and comes from the great general Barbaros Kee. it comes from that he often used to say Aff when he did something. {{R from other capitalisation ...

, either ~36,900 or ~14,485 BP of the

Sopas Formation ''Sopas'' is a Filipino macaroni soup made with elbow macaroni, various vegetables, and meat (usually chicken), in a creamy broth with evaporated milk. It is regarded as a comfort food in the Philippines and is typically eaten during breakfast, ...

, ''A. tarijense'' at 10,345 BP in the Cueva Del Puma,

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, and ''A. wingei'' at 12,850 BP in the

Sistema Sac Actun Sistema Sac Actun (from Spanish and Yucatec Maya meaning "White Cave System") is an underwater cave system situated along the Caribbean coast of the Yucatán Peninsula with passages to the north and west of the city of Tulum. Discovery of a connec ...

(

, with a possible record of 9,000 BP in Muaco,

. Interestingly, the remains of ''A. wingei'' in the Hoyo Negro of the

appear to be in association with human remains. ''

Tremarctos ''Tremarctos'' is a genus of the bear subfamily Tremarctinae, endemic to Americas from the Pliocene to recent. The northern species, the Florida short-faced bear, became extinct 11,000 years ago.B. Kurten & E. Anderson (1980): Pleistocene mam ...

'' does not appear in the South American fossil record until the

, suggesting that the extant spectacled bear descends from an independent, later dispersal event from North America to that of ''Arctotherium'', possibly after ''A. wingei'' became extinct in

the Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...

. The modern spectacled bear may have hybridised with ''Arctotherium'' as they migrated southwards into South America. Globally, in the

Quaternary Extinction Event The Quaternary period (from 2.588 ± 0.005 million years ago to the present) has seen the extinctions of numerous predominantly megafaunal species, which have resulted in a collapse in faunal density and diversity and the extinction of key ecolog ...

, extinction favoured 'conservative morphologies' in ursid body plans, such as those found in the '' T. ornatus''.

References

{{Taxonbar, from=Q2076664 Pleistocene bears Pleistocene carnivorans Prehistoric carnivoran genera Pleistocene mammals of North America Blancan Pleistocene El Salvador Fossils of El Salvador Pleistocene mammals of South America Uquian Ensenadan Lujanian Pleistocene Argentina Pleistocene Bolivia Pleistocene Brazil Pleistocene Chile Pleistocene Venezuela Fossils of Argentina Fossils of Bolivia Fossils of Brazil Fossils of Chile Fossils of Venezuela Fossil taxa described in 1857