142-606: Arctotherium ("bear beast") is an extinct genus of the Pleistocene short-faced bears endemic to Central and South America . Arctotherium migrated from North America to South America during the Great American Interchange , following the formation of the Isthmus of Panama during the late Pliocene . The genus consists of one early giant form, A. angustidens , and several succeeding smaller species, which were within
284-455: A baby tooth (dp4 molar) found in the Río Tomayate locality of Cuscatlán Formation of El Salvador , along with a partial Borophagus skull, dated to the latest Pliocene (2.588 Ma). The archaic form and size of the tooth is closest to A. angustidens , however as only one other baby tooth has been recovered from Arctotherium ( A . tarijense ), the tooth was only confidently assigned at
426-500: A scavenging lifestyle, and therefore retained in the Tremarctinae lineage in spite of size evolution. 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 , along with Arctotherium 's ability to exploit
568-613: A "gracile" appearance. Although longer, the proportions still overlap with Ursus , and the limb bones are stouter than in the large-bodied felids ( Panthera ). Rather than for running, these elongated limb bones may have evolved for increased locomotor efficiency during prolonged travel. This stiff-legged, swinging gait could have been similar to a polar bear's. Some researchers suggest that proportionally longer limbs may be an adaptation for increased vision over tall ground cover in an open habitat, or were used in tearing and pulling down vegetation. Researchers also disagree when interpreting
710-554: A 2009 study, the weight ranges for Arctotherium were calculated as follows- A. wingei at 51 kg-150 kg, A. vetustum at 102–300 kg (225–661 lb), A. tarijense at 135–400 kg (298–882 lb), A. bonariense between 171–500 kg (377–1,102 lb), and A. angustidens at 412–1,200 kg (908–2,646 lb). 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 (509 lb), and A. wingei specimens from
852-595: A 2021 study, the maximum prey for A. wingei would be around its own bodyweight (~83 kg (183 lb)). In the low-density savanna forests of the Brazilian intertropical region, A. wingei , pumas and jaguars played a supporting role to the (also likely solitary) Smilodon populator 's dominance of the regional predator guild, avoiding competition with Protocyon troglodytes in more open savanna. Being smaller and more herbivorous, A. wingei would have also likely competed with other smaller carnivorans present in
994-533: A black bear (Potter Cave). None of the specimens assigned to the larger morph ( A. s. yukonensis ) is from a cave passage, being usually isolated remains from open sites. Furthermore, over 70% of the smaller specimens (once assigned as the A. s. simus subspecies) are from cave deposits where bacula would likely be found if present, suggesting that mostly female individuals of A. simus were using caves. Therefore, in conjunction with ursid sexual dimorphism (e.g. male spectacled bears are 30% - 40% larger than females),
1136-418: A carnivorous diet). Below is a cladogram exploring the relationships between species of Arctotherium . Tremarctos [REDACTED] A. vetustum A. wingei A. angustidens A. bonariense A. tarijense Arctotherium was named by Hermann Burmeister in 1879. Tremarctinae (and therefore Arctotherium ) appeared to have disproportionately shorter snouts compared to most modern bears, hence
1278-585: A change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years. However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere . Glaciation in the Pleistocene
1420-559: A deeper but not a shorter face than most living bears. This characteristic is also shared by the only living tremarctine bear, the omni-herbivorous spectacled bear . Snout deepness could be variable, as specimens from Huntington Reservoir in Utah, and the Hill-Shuler locality , Texas, were noted as being distinctly "short-faced" in comparison with other Arctodus simus individuals. The orbits of Arctodus are proportionally small compared to
1562-574: A deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another isotope ratio versus time. Ratios are converted to a percentage difference from the ratio found in standard mean ocean water (SMOW). The graph in either form appears as a waveform with overtones . One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials. According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in
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#17328592811851704-462: 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. Notably, all three genera are first recorded from the Blancan (Late Pliocene) of North America , with
1846-421: A few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from
1988-546: A higher degree of forelimb dexterity. Originally evolved to facilitate arboreality , other researchers believe that the terrestrial Arctodus (along with Arctotherium and the giant panda ) retained this characteristic to assist in foraging for vegetation. The paws ( metapodials and phalanges ) of Arctodus were characteristically long, slender, and more elongated along the third and fourth digits compared to ursine bears . Arctodus ' paws were therefore more symmetrical than ursine bears, whose feet have axes aligned with
2130-450: A hypothesis for the colonization of Vancouver Island by Arctodus simus . Examinations on a mostly full sized young individual of Arctodus simus from an Ozark cave suggest that Arctodus , like other ursids, reached sexual maturity well before full maturity . Comparisons with black bears suggest the Arctodus specimen was either 4–6 years of age if female, or 6–8 years if the specimen
2272-485: A large home range and relatively small population size. However, this does not entirely preclude genetic diversity in Arctodus simus , with genetic samples from Chiquihuite Cave , Zacatecas indicating a deep divergence with previously studied specimens of A. simus . Additional specimens from the California Channel Islands and Wyoming have been sequenced, but are unassigned. Below is a cladogram exploring
2414-570: A major temperature drop and increased seasonality, and a faunal turnover which extinguished 70–80% of North American genera. Arctodus pristinus was mostly restricted to the more densely forested thermal enclave in eastern North America . A. pristinus has the greatest concentration of fossils in Florida, with the earliest finds being from the Late Blancan Kissimmee River 6 (2.7 - 2.2 Mya) and Santa Fe River 1 sites. During
2556-533: A member of various predator guilds across the species' range. A. wingei 's association with Protocyon in the terminal Pleistocene of the Yucatán , another animal previously thought to be endemic to South America , suggests a complex relationship of faunal interchange long after the Great American Interchange . Although mostly herbivorous, the modern spectacled bear is on occasion an active predator. The spectacled bear has several hunting techniques- principally,
2698-511: A more anterior protocone & extended enamel ridge forming a shearing blade on the maxillary P4 . The molars are also shorter & broader in Arctodus than brown bears. † Hemicyoninae † Ursavinae Ailuropodinae [REDACTED] Ursinae [REDACTED] † Plionarctos † Arctodus Tremarctos [REDACTED] † Arctotherium Arctodus belongs to the subfamily Tremarctinae, which appeared in North America during
2840-653: A more northern range. By the Late Pleistocene , A. tarijense held domain over the open and semi-arid Pampas and Patagonian habitats east of the Andes , inhabiting Argentina , Patagonian Chile , southern Bolivia , and Uruguay , 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
2982-440: 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, Pleistocene 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
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#17328592811853124-485: A pace at 8.5 km/h (5.3 mph), and would begin to gallop at 18.5 km/h (11.5 mph), a fairly high speed. Based on other mammals, the optimal pace speed of Arctodus would have been 13.7 km/h (8.5 mph). For comparison, hyenas cross country ~10 km/h (6.2 mph). This mobility would have facilitated travelling across a large home range, which Mattson suggests may have topped 1,000 square miles (2,600 km ). Swimming has also been presented as
3266-532: A pan-continental species in the Rancholabrean faunal stage (Late Pleistocene), sharing that distinction with the black bear . Despite Arctodus simus ' large temporal and geographic range, fossil remains are comparatively rare (109 finds as of 2010, in otherwise well-sampled localities). Around the size of grizzly bears , A. pristinus specimens closely overlap the size of Tremarctos floridanus , with some males of A. pristinus overlapping in size with
3408-523: A poor indicator of size in A. simus , as some medium-size individuals have teeth that surpass the size of those with the largest skeletons. Additionally, while A. simus evolved from the smaller A. pristinus , their teeth remained generally the same size. A specimen of A. simus from the Seale Pit of the Hill-Shuler locality, Texas, with only two premolars, crowding of the anterior premolar out of line, and
3550-567: A possible record of 9,000 BP in Muaco , Venezuela . Globally, in the Quaternary Extinction Event , extinction favoured 'conservative morphologies' in ursid body plans, such as those found in the T. ornatus . Pleistocene The Pleistocene ( / ˈ p l aɪ s t ə ˌ s iː n , - s t oʊ -/ PLY -stə-seen, -stoh- ; referred to colloquially as the Ice Age )
3692-479: A predatory lifestyle- in particular the large canines , the high-crowned lower first molar , and the possible carnassial shear with the upper fourth premolar . However, the wearing of the molars to a relatively flat & blunt loph (suitable as a crushing platform as per modern omnivorous bears), small shear facet, and the flattened cusps across age ranges (unlike carnivores, which instead have carnassial shears) disagrees with this hypothesis. Dentition can be
3834-542: A reduced or no sagittal crest. Although there are limited samples, the middle ear bones of A. simus are proportionally larger than modern ursine bears, suggesting the species was particularly attuned to low-frequency sounds. Morphologically, Arctodus simus exhibits masticular characteristics common to herbivorous bears. This includes cheek teeth with large, blunt surface areas, a deep mandible, and large mandibular muscle attachments (which are rare in carnivorous mammals). As herbivorous carnivorans such as Arctodus lack
3976-436: A reduced slicing dentition length when compared to A. pristinus . Instead, Arctodus simus was most similar to Arctotherium angustidens- however, both species of Arctodus and Arctotherium angustidens were still comfortably in the "omnivorous" bear cranio-morphotype. The premolars and first molars of Arctodus pristinus are relatively smaller and more widely spaced than those of Arctodus simus . In A. pristinus ,
4118-568: A team of Russian scientists in collaboration with Princeton University announced that they had brought two female nematodes frozen in permafrost , from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet. The evolution of anatomically modern humans took place during the Pleistocene. At the beginning of the Pleistocene Paranthropus species were still present, as well as early human ancestors, but during
4260-500: A typical prey weight of 100 kg (220 lb), with a maximum of 300 kg (661 lb). A. tarijense competed against Smilodon populator , giant jaguars ( Panthera onca mesembrina ), pumas , Lycalopex , Cerdocyon , Conepatus , Didelphis , and Dusicyon avus in Late Pleistocene Argentina , occasionally hunting camelids and horses as a supplement to scavenging, smaller prey and herbivory. A. tarijense
4402-530: 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 (243 lb) (hypothetical typical weight range = 106–122 kg (234–269 lb)), and A. tarijense at ~139 kg (306 lb) (102–189 kg (225–417 lb)). According to
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4544-452: A wide and shortened rostrum , potentially giving Arctodus a more felid -like appearance. Matheus suggested that a broad snout could have housed a highly developed olfactory apparatus , or accommodated a larger throat passage to bolt down large food items, akin to spotted hyenas. However, this apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with ursine bears; Arctodus has
4686-418: A wider and shorter muzzle, was suggested to be an undescribed form of Arctodus . Researchers have differing interpretations on the limb morphology of Arctodus . A comprehensive 2010 study concluded that the legs of Arctodus weren't proportionally longer than modern bears would be expected to have, and that bears in general are long-limbed animals, obscured in life by their girth and fur. The study concluded
4828-499: Is between 3.4 and 4.3 m (11 and 14 ft). It would still make the species the largest bear ever found, and contender for the largest carnivorous land mammal known. Legend: [REDACTED] Arctotherium sp. [REDACTED] A. angustidens. [REDACTED] A. bonariense [REDACTED] A. tarijense Almost all Arctotherium species appear to be largely restricted to the Southern Cone , particularly Argentina , with
4970-765: Is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America , and several hundred in Eurasia . The mean annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F). Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over
5112-444: Is much variation in adult size among specimens- the lack of finds, sexual dimorphism , individual variation and potentially ecomorphs could be augmenting the average size of both species of Arctodus . Size differences between specimens of Arctodus simus (such as skull and long bone dimensions) led Kurtén to suggest a larger northern/central subspecies ( A. s. yukonensis ) and a southern subspecies ( A. s. simus ). evolving in
5254-454: Is no systematic correspondence between pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined. The sum of transient factors acting at
5396-513: Is the geological epoch that lasted from c. 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations . Before a change was finally confirmed in 2009 by the International Union of Geological Sciences , the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of
5538-611: Is thought to have reoccupied caves excavated by Xenarthra , such as the mylodonts Glossotherium and Scelidotherium , and the pampatheriid Pampatherium . As suitable paleoburrows are rare before the Great American Interchange , it has been suggested that predation and competition for dens by the newly arrived eutherian carnivores , especially by A. angustidens , increased the rate of xenarthran cave excavations . The evolution of highly-modified spiny osteoderms in Pleistocene-era Glyptodon has been attributed to
5680-530: Is unclear. A. angustidens remains have been dated to between 1Ma to 0.7 Ma of the Pleistocene, which corresponds with the Ensenadan period (although the younger dates are uncertain). A. angustidens went extinct at the start of the Lujanian (~700,000 years ago), replaced by medium-sized Arctotherium species. The first recorded successor species was A. vetustum ( Middle Pleistocene ), then shortly thereafter by
5822-470: 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. The shape of
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5964-638: The Alpine ice sheet on the Alps . Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were ice-covered. South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide Ice Sheet retreated, north-central North America was completely covered by Lake Agassiz . Over a hundred basins, now dry or nearly so, were overflowing in
6106-503: The Americas . Of these short-faced bears, Arctodus was the most widespread in North America. However, the genus was restricted to the Pleistocene. A. pristinus went extinct around 300,000 years ago, with A. simus disappearing ~12,800 years ago in the Late Pleistocene extinctions . The cause behind these extinctions is unclear, but in the case of A. pristinus , this was likely due to climate change and competition with other ursids, such as
6248-521: The ICS timescale, the Pleistocene is divided into four stages or ages , the Gelasian , Calabrian , Chibanian (previously the unofficial "Middle Pleistocene"), and Upper Pleistocene (unofficially the "Tarantian"). In addition to these international subdivisions, various regional subdivisions are often used. In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for
6390-582: The Isthmus of Panama , causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia . The end of the Early Pleistocene is marked by
6532-482: The La Brea Tar Pits at ~372 kilograms (820 lb), smaller than recovered brown bear remains (~455 kilograms (1,003 lb), although these remains postdate Arctodus ). A 1999 study by Per Christiansen calculated a mean weight of ~770 kilograms (1,700 lb) from seven male A. simus limb bones, suggesting large males weighed between 700 kilograms (1,500 lb) and 800 kilograms (1,800 lb). There
6674-660: The Laurentide Ice Sheet . Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch , which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ('most new' or 'newest') from the Greek πλεῖστος ( pleīstos ) 'most' and καινός ( kainós ( Latinized as cænus ) 'new'). This contrasts with
6816-511: The Lujanian . 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. Along with clues from various teeth of A. wingei , carbon isotope studies suggest that A. wingei , at least in
6958-593: The Mid-Pleistocene Transition , with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans also spread to the Australian continent and the Americas for the first time, co-incident with
7100-545: The Middle Hemphillian (earliest Late Miocene , ~10 Ma) of North America; Plionarctos is last recorded in the early Blancan (Early Pliocene, ~3.3 Ma). Around the Miocene - Pliocene boundary (~5 Ma) Tremarctines , along with other ursids , experienced an explosive radiation in diversity, as C4 vegetation ( grasses ) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and
7242-497: The Middle Pleistocene . 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
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#17328592811857384-635: The Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and to the west in the Atlas Mountains . In the northern hemisphere, many glaciers fused into one. The Cordilleran Ice Sheet covered the North American northwest; the east was covered by the Laurentide . The Fenno-Scandian ice sheet rested on northern Europe , including much of Great Britain;
7526-501: The black bear and Tremarctos floridanus . A. simus likely went extinct due to ecological collapse disrupting the vegetation and prey it relied on. Arctodus was first described by Joseph Leidy in 1854, with finds of A. pristinus from the Ashley Phosphate Beds , South Carolina. The scientific name of the genus, Arctodus , derives from Greek, and means "bear tooth". The first fossils of Arctodus simus were found in
7668-551: The elbow joint suggests the possibility of semi-arboreal locomotion for Arctodus sp ., Arctotherium bonariense , and A. wingei , but 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 fossil Arctodus and Arctotherium retained this feature in relation to their higher degree of forelimb dexterity. As these genera convergently evolved towards an increased body size, this high degree of proximal dexterity may have been advantageous for
7810-518: The gut microbiota to efficiently break down plant matter, these features created a high mechanical advantage of the jaw to break down plant matter via extensive chewing or grinding. Although the low mandibular condyle relative to the tooth row (and therefore potential wide gape) of Arctodus simus has been inferred as an adaptation for carnivory, it is also present in the omni-herbivorous spectacled bear. However, both Arctodus pristinus and Tremarctos floridanus have condyles raised well above
7952-522: The humerus of Arctodus simus . Sorkin argued that the pronation of the forearm and the flexion of the wrist and digits, and more lightly muscled forelimbs, all of which are crucial to grasping a large prey animal with the forepaws, were probably less powerful in Arctodus than in either the brown bear or in Panthera . This is due to a weak medial epicondyle and reduced development of the pronator teres muscle. The forelimb of Arctodus could have been in
8094-477: The last glacial period ended about 10,000 years ago. Over 11 major glacial events have been identified, as well as many minor glacial events. A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials". These events are defined differently in different regions of
8236-598: The spectacled bear is capable of climbing trees , Arctotherium is thought to be non-arboreal. The last known records of Arctotherium are an ambiguous find of A. bonariense from Uruguay ( cf. / aff , either ~36,900 or ~14,485 BP of the Sopas Formation , A. tarijense at 10,345 BP in the Cueva Del Puma , Patagonia , Chile , and A. wingei at 12,850 BP in the Sistema Sac Actun ( Yucatán ), Mexico , with
8378-588: The woolly rhinoceros , various giraffids , such as the Sivatherium ; ground sloths , Irish elk , cave lions , cave bears , Gomphotheres , American lions , dire wolves , and short-faced bears , began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice , migratory birds, and swifter animals like whitetail deer had replaced
8520-578: The Americas . The modern spectacled bear may have hybridised with Arctotherium as they migrated southwards into South America. However, the ranges of the spectacled bear, a specialist of highland Andean forests, and the more open adapted Arctotherium , could have co-existed in South America. The remains of A. wingei in the Hoyo Negro of the Yucatán appear to be in association with human remains. The oldest known specimen of Arctotherium consists of
8662-524: The BIR, such as jaguarundi , Lycalopex , Chrysocyon , Cerdocyon , Theriodictis , Speothos , Nasua , Procyon , Eira , Conepatus , Galictis , and Leopardus . Additionally, as dire wolves ( Aenocyon dirus ) and Smilodon fatalis inhabited north-western South America , and were joined by American lions , grey wolves and coyotes in Central America , A. wingei would have been
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#17328592811858804-478: The Brazilian intertropical region at ~83 kg (183 lb). An extraordinarily large specimen of A. angustidens recovered in 2011 from Buenos Aires shows an individual estimated, using the humerus, to weigh between 983 and 2,042 kg (2,167 and 4,502 lb). However, the authors consider the upper limit as improbable, and say that 1,588 to 1,749 kg (3,501 to 3,856 lb) is more likely. An estimated standing height for this A. angustidens individual
8946-639: 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 bears and polar bears . According to
9088-558: The Early Pleistocene Gelasian . Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced. By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number and interglacials receive an odd number. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16. The warmest interglacials were 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under
9230-409: The Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors. The Mid-Pleistocene Transition , approximately one million years ago, saw
9372-854: The Eurasian cave bear last shared a common ancestor with the tremarctine Arctodus circa 13.4 million years ago. Fossils of Arctodus pristinus can be confused with the similarly sized, partially contemporaneous short-faced bear , Tremarctos floridanus . Arctodus has higher crowned and considerably larger teeth than its relative Tremarctos . A. pristinus can be distinguished by broader and taller molars on average, but as they are often worn, differentiation can be difficult. Moreover, diagnosing isolated A. simus remains (such as femora, scapulae, certain vertebrae, ribs, podials) from brown bears can be challenging, as some large brown bears overlap in dimensions with small Arctodus simus . Beyond standard differences between tremarctine and ursine bears , A. simus has
9514-688: The Irvingtonian and Rancholabrean respectively. However, the discovery of a very large southern Arctodus simus in Florida and New Mexico (deep within the supposed range of A. s. simus ), & possibly Rancho La Brea, and notably small specimens from the Yukon and Vancouver Island , put doubt on this designation. Perceived ecomorphologies are possibly due to the low number of specimens, and sex-biased sampling. For example, only one baculum (penis bone) has been recovered from over 100 giant short-faced bear sites in North America, although it may belong to
9656-802: The Middle Pleistocene of Kansas, with A. simus migrating east in the Late Pleistocene (around the extinction of A. pristinus ). Although both Arctodus species co-inhabited North America for at least half a million years during the Middle Pleistocene ( A. pristinus went extinct ~300,000 BP ), there is no direct evidence of overlap or competition in the fossil record as of yet, as both species established largely separate ranges . Irvingtonian age (1,900,000 BP - 250,000 BP) specimens of Arctodus simus are particularly sparse. Finds are mostly from California, with additional remains from Texas, Kansas, Nebraska, and Montana. However, A. simus became
9798-554: The Middle Pleistocene. Both species are relatively rare in the fossil record. Today considered to be an enormous omnivore, Arctodus simus is believed to be one of the largest known terrestrial carnivorans that has ever existed. However, Arctodus , like other bears, was highly sexually dimorphic. Adult A. simus ranged between 300 and 950 kilograms (660 and 2,090 lb), with females clustering at ≤500 kilograms (1,100 lb), and males around 800 kilograms (1,800 lb). The largest males stood at 1.67 metres (5 ft 6 in) at
9940-479: The North American west. Lake Bonneville , for example, stood where Great Salt Lake now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided . African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation. It has been estimated that during
10082-434: The Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. Radiocarbon dating is considered to be inaccurate beyond around 50,000 years ago. Marine isotope stages (MIS) derived from Oxygen isotopes are often used for giving approximate dates. Pleistocene non-marine sediments are found primarily in fluvial deposits , lakebeds, slope and loess deposits as well as in
10224-490: The Pleistocene's overall climate could be characterised as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru , warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It
10366-494: The Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP . The start date has now been rounded down to 2.580 million years BP. The IUGS has yet to approve a type section , Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary ( i.e.
10508-782: The Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka. During the 2.5 million years of the Pleistocene, numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of
10650-411: The Pleistocene, the plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period. In glacial periods, the sea level would drop by up to 120 m (390 ft) lower than today during peak glaciation, exposing large areas of the present continental shelf as dry land. According to Mark Lynas (through collected data),
10792-550: The Potter Creek Cave, Shasta County , California, by J. A. Richardson in 1878, and were initially described as Arctotherium simum by Edward Drinker Cope in 1879. Historically, all specimens were grouped together under A. pristinus , until a revision by Björn Kurtén in 1967. In the 19th and early 20th centuries, specimens of Arctodus were occasionally referred to Arctotherium , and vice versa. However, today neither genera are considered to have overlapped, with
10934-472: The Yukon suggest an extremely low level of genetic diversity among the 23 individuals studied (≤ 44,000 C BP), with only seven haplotypes recovered. Genetic diversity was comparable to modern endangered fauna, such as the brown kiwi and African cheetah. Explanations include a genetic bottleneck before 44,000 C BP, or a low level of genetic diversity being a feature of a species which was primarily solitary, with
11076-687: The appearance of Homo sapiens about 300,000 years ago. Artifacts associated with modern human behavior are unambiguously attested starting 40,000–50,000 years ago. According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciation in the Middle Palaeolithic during the Eemian Stage , spreading all over the ice-free world during the late Pleistocene. A 2005 study posits that humans in this migration interbred with archaic human forms already outside of Africa by
11218-490: The arrival of large carnivorans such as A. angustidens in South America. It has been suggested that as a diverse carnivore guild became established in South America , the Arctotherium genus began to revert to more classic ursid diets as the ecosystem matured in the Middle Pleistocene. After A. angustidens became extinct, two forms begin to appear in the fossil record. The A. bonariense / A. tarijense species complex
11360-515: The articles for those names. Both marine and continental faunas were essentially modern but with many more large land mammals such as Mammoths , Mastodons , Diprotodons , Smilodons , tigers , lions , Aurochs , short-faced bears , giant sloths , species within Gigantopithecus and others. Isolated landmasses such as Australia , Madagascar , New Zealand and islands in the Pacific saw
11502-555: The axis of the foot on either side). The trackways suggest that Arctodus had an oval-shaped, undivided pad on its sole, front paws that were slightly larger than its back paws, possessed long claws, and had its hind foot overstep the forefoot when walking, like modern bears. An additional A. simus paw print measuring 15 cm (5.9 in) long and 19 cm (7.5 in) wide has been recovered from White Sands National Park , New Mexico. Some claw marks attributed to Arctodus simus at Riverbluff Cave (as they were four meters above
11644-541: 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
11786-604: The closest point of contact being México, with the giant Arctodus simus in Valsequillo , Puebla , and the smaller Arctotherium wingei in the Yucatán Peninsula . Other early researchers believed Arctodus to be a sister lineage of the agriotheriin Indarctos . Sometimes described as the "American cave bear", Arctodus should not be mistaken for the similarly large Eurasian cave bear ( Ursus spelaeus ). As an ursine ,
11928-529: The earliest parts of the late Miocene epoch in the form of Plionarctos . The medium-sized Arctodus pristinus, Tremarctos floridanus and Arctotherium sp. evolved from Plionarctos in the Blancan age of North America. The genetic divergence date for Arctodus is ~5 million years ago, around the Miocene - Pliocene boundary, when tremarctine bears, along with other ursids, experienced an explosive radiation in diversity, as C 4 vegetation ( grasses ) and open habitats dominated. The world experienced
12070-516: The early Irvingtonian faunal stage , a western population of A. pristinus evolved into the enormous A. simus, with the earliest confirmed records being at least 780,000 years old from the Irvington type locality in California. Correspondingly, A. simus is most plentiful from western North America, albeit preferring mixed habitat such as temperate open woodlands. Their ranges may have met in
12212-586: The early stages of cursorial evolution, being capable of more efficient and high-speed straight-line locomotion (relative to extant bears), and was possibly more adept at pursuing large prey than polar and brown bears . On the other hand, some researchers argue that the epicondyles were still well developed, with this wide range of ulna rotation suggests that forearms of Arctodus were powerful and could subdue large prey. A 2013 examination of Rancho La Brean specimens found that they did not possess distally elongated limbs, which discredited cursoriality. Furthermore,
12354-606: The entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania . The current decaying glaciers of Mount Kenya , Mount Kilimanjaro , and
12496-772: The evolution of large birds and even reptiles such as the Elephant bird , moa , Haast's eagle , Quinkana , Megalania and Meiolania . The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major extinction event of large mammals ( megafauna ), which included mammoths , mastodons , saber-toothed cats , glyptodons ,
12638-444: The extinction of most large-bodied animals in these regions. The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by
12780-506: The features of the dentition can be quite variable, particularly the M2 molar. An analysis of the Hunter-Schreger bands from the teeth of A. pristinus and A. simus demonstrated an evolutionary trend towards partially reinforced tooth enamel . This has been convergently evolved with giant pandas, agriotheriin bears, and Hemicyon . The dentition of A. simus has been used as evidence of
12922-412: The females of A. simus. Floridan A. pristinus individuals were calculated to an average of ~140 kilograms (310 lb). However, the dimensions of some individuals from Port Kennedy Bone Cave and Aguascalientes suggest that northern and western A. pristinus may have been larger than Floridan A. pristinus , being up to 400 kilograms (880 lb). Some A. simus individuals might have been
13064-485: The first possible record of Arctotherium sp. being a tooth found in the Cuscatlán Formation of El Salvador , dated to the latest Pliocene (2.588 Ma). The oldest dated confirmed remains of Arctotherium in South America are those of the gigantic A. angustidens from Buenos Aires , Argentina . What the evolutionary history of Arctotherium was beforehand, particularly regarding its sudden significant size,
13206-568: The floor of the cave) were nearly 20 cm in width. The presence of a partial false thumb in Arctodus simus is a characteristic shared with Tremarctos floridanus and the spectacled bear, and is possibly an ancestral trait. Absent in ursine bears , the false thumb of the spectacled bear has been suggested to assist in herbivorous food manipulation (such as bromeliads , leaves, berries, tree bark & fruits, cactus fruits & pulp, palm hearts & fronds), or arboreality . Beyond carbohydrate-associated dental pathologies present in
13348-430: The frequency of fossil finds. A separate Andean form of Arctotherium is also suggested to have existed at the end of the Pleistocene, consisting of the type A. wingei specimen from Tarija and an Argentine Andean individual, in contrast with the larger and more robust Brazilian A. wingei specimens. Curiously, while Arctotherium 's known species dramatically shrank in size after A. angustidens , Arctodus underwent
13490-475: The genus level as Arctotherium sp. Arctotherium only reappears in the fossil record 1 million years ago as A. angustidens , from the Buenos Aires province of Argentina. A. angustidens is the only known species of Arctotherium from the Early Pleistocene. The first recorded Arctotherium specimens in South America occur alongside the earliest known South American records of several other carnivorans :
13632-471: The genus, extensive pathologies have been preserved on the most nearly complete skeleton of Arctodus . The leading hypothesis suggests the Fulton County Arctodus specimen suffered from a syphilis -like ( treponemal ) disease, or yaws , based on the various lesions present. The same individual records a pathological growth distorting the right humerus , with abscesses are noted between
13774-414: The glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another. For most of the 20th century, only
13916-450: The historical terminology was established. Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: pluvia , rain). A pluvial is a warmer period of increased rainfall; an interpluvial is of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread. There
14058-445: The immediately preceding Pliocene ("newer", from πλείων ( pleíōn , "more") and kainós ) and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος ( hólos , "whole") and kainós ) epoch , which extends to the present time. The Pleistocene has been dated from 2.580 million (±0.005) to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of
14200-613: The large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometres of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred metres. The modern continents were essentially at their present positions during
14342-516: The large body size, taller front legs, high shoulders, short and sloping back, and long legs of Arctodus also compounded locomotive efficiency, as these traits swelled the amount of usable elastic strain energy in the tendons, and increased stride length, making Arctodus built more for endurance than for great speed. His calculations suggested that Arctodus likely had a top speed of 40–45 kilometres per hour (25–28 mph), and based on hyaenid proportions, would shift from singlefoot locomotion to
14484-474: The larger, massive Arctodus individuals are often considered male, particularly older males, with the smaller, more lightly built individuals being females. Sexual dimorphism may also explain A. simus teeth (from multiple individuals at the same site) generally clustering into two sizes. The two species of Arctodus are differentiated not only by size, but also by the shorter snout, greater prognathism , more robust teeth and longer limbs of A. simus, and
14626-436: The largest land-dwelling specimens of Carnivora that ever lived in North America. Standing up on its hind legs, A. simus stood 2.4–3.4 m (8–11 ft), with a maximum vertical arm reach of 4.3 metres (14 ft). When walking on all fours, A. simus stood 1–1.67 m (3.3–5.5 ft) high at the shoulder, with the largest males being tall enough to look an adult human in the eye. The average weight of A. simus
14768-457: The late Pleistocene, incorporating archaic human genetic material into the modern human gene pool. Arctodus Arctodus is an extinct genus of short-faced bear that inhabited North America during the Pleistocene (~2.5 Mya until 12,800 years ago). There are two recognized species : the lesser short-faced bear ( Arctodus pristinus ) and the giant short-faced bear ( Arctodus simus ). Of these species, A. simus
14910-526: The latest period of repeated glaciation , up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9700 BCE (11,700 calendar years BP). The end of the Younger Dryas is the official start of the current Holocene Epoch . Although it is considered an epoch, the Holocene is not significantly different from previous interglacial intervals within the Pleistocene. In
15052-466: The lower Palaeolithic they disappeared, and the only hominin species found in fossilic records is Homo erectus for much of the Pleistocene. Acheulean lithics appear along with Homo erectus , some 1.8 million years ago, replacing the more primitive Oldowan industry used by A. garhi and by the earliest species of Homo . The Middle Paleolithic saw more varied speciation within Homo , including
15194-431: The mandible, and possible carnassial shears. Additionally, the diet of A. wingei was not necessarily orthodox, with carnivory likely peaking in times of resource instability. For example, several bite marks on recovered fossils of herbivores, such as Glossotherium and Equus , are suggested to have been inflicted by scavenging short-faced bears across Lujanian South America . A. bonariense and A. tarijense had
15336-478: The megafauna and migrated north. Late Pleistocene bighorn sheep were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed. The extinctions hardly affected Africa but were especially severe in North America where native horses and camels were wiped out. In July 2018,
15478-505: The molars and on both ulna . Hypotheses include syphilis, osteoarthritis , a fungal infection in addition to long term syphilis, or an infected wound. Several specimens from Fairbanks , Alaska, also exhibit either pathological growths or periodontal disease , along with a healed toe bone from Big Bear Cave, Missouri. Paul Matheus proposed that Arctodus simus may have moved in a highly efficient, moderate-speed pacing gait, more specialized than modern bears. His research concluded that
15620-511: The more robustly built A. bonariense ( Middle / Late Pleistocene ), along with A. tarijense ( Middle Pleistocene to the Early Holocene ) . While the smallest but most widespread species, A. wingei , is only confirmed from the Late Pleistocene and Early Holocene , the species' more tropical disposition is thought to greatly limit fossilisation. That, along with A. wingei' s more ancestral position in Arctotherium , suggests an origin in
15762-455: The most lateral (fifth) digit. Also, the first digit of Arctodus was positioned more closely and parallel to the other four digits (i.e. with straight toes, Arctodus had less lateral splaying). However this is potentially contradicted by possible Arctodus simus trackways from near Lakeview , Oregon, with strong toe splaying, three centrally aligned & evenly spaced toes at the front, and two almost perpendicular lateral toes (80° from
15904-419: The name "short-faced" was given to them. This apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with ursine bears; Arctotherium had a deeper but not a shorter face than most living bears. To differentiate between the species size can sometimes help, but cranial and dental features need to be examined for a definite identification. The upper canine
16046-426: The opposite transformation, transitioning from the medium-sized A. pristinus to the gigantic A. simus by the end of the Pleistocene. Except for an extraordinarily large specimen of A. angustidens , the largest specimens of A. simus and A. angustidens are said to be comparable to one another, and match the absolute upper size limit (~1000kg) of a terrestrial carnivore (based on the more restrictive energy base for
16188-656: The other hand, A. wingei spanned across the northern, more mixed/forested and tropical parts of the continent, throughout the tropical savanna forests of Brazil to Bolivia , Venezuela , and into North America ( Belize and the Yucatán Peninsula , Mexico ). Tremarctos does not appear in the South American fossil record until the Holocene , 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
16330-472: The period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology . The name is a combination of Ancient Greek πλεῖστος ( pleîstos ) 'most' and καινός ( kainós ; Latinized as cænus ) 'new'. At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by
16472-418: The plane of the teeth. The purpose of the highly vaulted calvarium and straight cheek bones of Arctodus simus have been similarly disputed. A 2009 analysis of the mandibular morphology of tremarctine bears found notable differences between Arctodus pristinus and Arctodus simus , with A. simus specimens possessing a concave jaw, large masseter and temporalis muscles, deeper horizontal ramus and
16614-493: The predator guild in the Early Pleistocene Argentina . The extinction of the scavenger-niche specialist procyonid Chapalmalania 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,
16756-412: The predatory niches formerly occupied by the native typical South American groups such as metatherian sparassodonts and phorusracids that had largely gone extinct shortly prior to their arrival. In the Ensenadan , A. angustidens was only rivalled in size by Smilodon populator , with Theriodictis platensis , Canis gezi , Protocyon scagliorum , Panthera onca and pumas rounding out
16898-417: The ratio of O to O (two isotopes of oxygen ) by mass (measured by a mass spectrometer ) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in O , which is included in the tests of the microorganisms ( foraminifera ) contributing the calcite. A more recent version of
17040-455: The recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy. However, the revised definition of the Quaternary , by pushing back the start date of
17182-530: The relative proportions of each species' molars and premolars. Arctodus pristinus is distinguished from A. simus smaller, narrower, and less crowded teeth. However, the morphologies of both species are otherwise very similar. As a result, differentiating Arctodus simus from Arctodus pristinus can be difficult, as male individuals of Arctodus pristinus can overlap in size with female individuals of Arctodus simus . Arctodus simus superficially resembled living hyaenids in skull shape and relative lengths of
17324-444: The relatively broad humeral & femoral epicondyles were characteristic of diggers and polar bears, and suggested Arctodus simus could have foraged for roots, tubers and ground squirrels and/or had developed forelimb muscles to immobilze moving prey. The shape of the elbow joint , along with an well-developed medial epicondyle which forms an angle with the condyle , and shallower olecranon fossa , would have given Arctodus
17466-565: The richest records being in the Buenos Aires Province . The exceptions are the Tarija formation in southern Bolivia where three species have been recovered, a possible record of A. vetustum in Brazil , unassigned Arctotherium sp. postcranial remains from Rio Grande do Sul , a Blancan -age unassigned Arctotherium tooth from El Salvador , and A. wingei, which almost exclusively inhabited
17608-407: The sabre-toothed cats Smilodon and Homotherium , the puma ( Puma concolor ), the jaguar ( Panthera onca ), some large 25–35 kg (55–77 lb) canids , and several smaller (<15 kg (33 lb)) mustelids , canids , felids and mephitids . The North American carnivorans that invaded South America, including short-faced bears and Smilodon , probably quickly adopted
17750-415: 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 together (postulated to have been
17892-407: The sampling process makes use of modern glacial ice cores. Although less rich in O than seawater, the snow that fell on the glacier year by year nevertheless contained O and O in a ratio that depended on the mean annual temperature. Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of
18034-490: The shoulder, and up to 3.4 metres (11 ft) tall on their rear legs. Studies suggest that Arctodus simus browsed on C 3 vegetation and consumed browsing herbivores such as deer , camelids , and tapir . A. simus preferred temperate open woodlands but was an adaptable species, taking advantage of many habitats and feeding opportunities. Arctodus belongs to the Tremarctinae subfamily of bears, which are endemic to
18176-488: The size of the skull, and somewhat laterally orientated (a characteristic of tremarctine bears), more so than actively predatory carnivorans or even the brown bear , suggesting that stereoscopic vision was not a priority. The optic canal and other sphenoidal openings crowd together more in A. simus than in Ursus . As with Tremarctos ornatus , specimens with a large sagittal crest were likely male, whereas females had
18318-647: The size range of modern bears . Arctotherium was adapted to open and mixed habitat. They are genetically closer to the spectacled bear ( Tremarctos ornatus ), than to Arctodus of North America, implying the two extinct forms evolved large size in a convergent manner. Arctotherium is part of the Tremarctinae subfamily of bears, otherwise known as the short faced bears , which also includes Arctodus (North American short faced bears) and Tremarctos (the Floridian and modern spectacled bear ). Tremarctinae originate with their common ancestor, Plionarctos , in
18460-632: The sole factor responsible for the variations in climate since they explain neither the long-term cooling trend over the Plio-Pleistocene nor the millennial variations in the Greenland Ice Cores known as Dansgaard-Oeschger events and Heinrich events. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores. In oxygen isotope ratio analysis, variations in
18602-421: The study of cyclical climate changes. The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since
18744-418: The supposed "long-legged" appearance of the bear is largely an illusion created by the animal's relatively shorter back and torso. In fact, Arctodus probably had an even shorter back than other bears, due the necessary ratio between body length and body mass of the huge bear. However, other researchers argue that the limb bones of Arctodus simus are proportionally longer than those of other bears, leading to
18886-597: The trunk, back and limbs. The most nearly complete skeleton of A. simus found in the United States was unearthed in Fulton County , Indiana; the original bones are in the Field Museum of Natural History , Chicago. Members of the Tremarctinae subfamily of bears appear to have a disproportionately short snout compared with most modern bears, giving them the name "short-faced". Arctodus has also been argued to exhibit
19028-487: 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, including but not limited to horses , tapirs , camelids , macraucheniids , glyptodonts , giant ground sloths , toxodontids , and gomphotheres by A. angustidens . Of the dentition known from later Arctotherium species, only one specimen of A. bonariense exhibits
19170-622: The upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W. The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone , isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils : Discoaster pentaradiatus and Discoaster surculus . The Pleistocene covers
19312-543: Was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes. The main factor at work in climate cycling is now believed to be Milankovitch cycles . These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion. The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's albedo. Milankovitch cycles cannot be
19454-425: Was between 957 kg and 317 kg (699 lb). Hypothetically, the largest individuals of A. simus may have approached 1,000 kilograms (2,200 lb), or even 1,200 kg (2,600 lb). However, a 2006 study argued that the maximum size of Arctodus was ~555 kilograms (1,224 lb), based on the largest known skull. Additionally, a 1998 study calculated the average weight of Arctodus specimens from
19596-620: Was composed of adaptable, cosmopolitan omnivores, whereas A. vetustum & A. wingei were largely herbivorous. However, as A. vetustum and A. wingei are the most archaic species of Arctotherium , their lineage must have existed before the emergence of A. angustidens in the Enseadan period of the Early Pleistocene. A. bonariense is believed to have convergently evolved several adaptations with Arctodus simus and Agriotherium / Huracan , such as proportionally longer limbs, very large body size, short broad rostrums, premasseteric fossa on
19738-570: Was highly carnivorous, with scavenging likely making up a considerable portion of its diet. 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, giant ground sloths, and toxodontids, to Smilodon populator and giant jaguars . Smilodon fatalis , Arctotherium bonariense , Canis nehringi , maned wolves , and humans would have also joined this predator guild at various stages of
19880-446: Was larger, is known from more complete remains, and is considered one of the best known members of North America's extinct Ice Age megafauna . A. pristinus was largely restricted to the Early Pleistocene of the eastern United States , whereas A. simus had a broader range, with most finds being from the Late Pleistocene of the United States, Mexico and Canada. A. simus evolved from A. pristinus , but both species likely overlapped in
20022-519: Was male. Additionally, wear patterns on the individual's teeth are similar to a 4-6 year old Ursus americanus . Fused sutures , epiphyses , and epiphyseal plates , along with tooth eruption , have been used to determine adulthood in Arctodus. Legend: [REDACTED] Main mitochondrial haplogroup of A. simus (haplotypes A, B, C, D, E, F, G) [REDACTED] Chiquihuite Cave A.simus An examination of mitochondrial DNA sequenced from specimens of Arctodus simus from Alaska, Alberta, Ohio and
20164-528: Was ~625 kilograms (1,378 lb), with the maximum recorded at 957 kilograms (2,110 lb). In a 2010 study, the mass of six A. simus specimens was estimated; half of the specimens weighed between 740 kg (1,631 lb) and 957 kg (2,110 lb), with a mean weight of ~850 kg, suggesting larger specimens were probably more common than previously thought. However, the other specimens were calculated to be less than 500 kg (1,100 lb). The weight range calculated from all examined specimens
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