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Ice free corridor, full article on pre-Clovis settlement, Mexican Transition Zone, Leptobison/Bison hanaizumiensis, List of extinct Pleistocene megafauna split from QEE, Miocene aridification of Australia, "Vanishing Indian" paradigm, Arroyo del Vizcaíno site, ?execution by dog?
Arctodus simus inhabited Californian savannas for over a million years.
With over 50% (22/38) of specimens found in the contiguous United States from the terminal Pleistocene (<40,000 BP), the Western USA was highly productive habitat for Arctodus simus.[5] In particular, the Pacific Mountain System seems to represent a cradle of evolution for Arctodus simus. The earliest finds of Arctodus simus are from California, from early and middle Irvingtonian age sites such as Vallecito Creek, Irvington, Riverside, and Fairmead.[13][14][15][16]
Evidence from Inland California suggests that despite the shift to aridified environments from the Early to Late Pleistocene of California (1.1Ma to ~15,000 BP), Arctodus simus remained consistent with the consumption of C3 resources. This period saw the evolution from wetter mixed woodland-grassland and marsh/prairie C3 dominated environs at Irvington and Fairmead, to the more arid, mixed C3-C4 savannas of the McKittrick Tar Pits. Whereas jaguars, Homotherium, Miracinonyx and Smilodon ultimately transitioned to Panthera atrox and coyotes in the local predator guild, only dire wolves and Arctodus simus remained ever present. Foraging opportunities would have been plentiful for Arctodus, with grasses, chenopods, Xanthium, cattails, sedges, willow, oak, spruce, juniper, and sagebrush at Fairmead, and pines, juniper, saltbush, manzanita, and wild cucumber at McKittrick.[17] To what extent Arctodus fed on this vegetation, versus consuming generalists and specialized browsers such as deer (Cervus & Odocoileus), camelids (Hemiauchenia & Camelops), Paramylodon, and peccaries can be clued from the La Brea Tar Pits. Microwear and general wear patterns on the teeth of recovered from Arctodus specimens are most similar to the herbivorous spectacled bear, and suggest that they avoided hard/brittle foods, and had a more specialized diet than black bears recovered from the same site. Should Arctodus have also been a predator, competition with closed habitat, browser specialists would have included Smilodon and Panthera atrox in Late Pleistocene inland California.[17][18][19] Many more finds come from across California, and Oregon,[20][21][22] where the semi-arid woodland/scrub transitioned to forest-steppe.[7]
A reconstruction of Rancholabrean New Mexico (White Sands).
The Intermontane Plateau, which largely hosted subalpine parkland,[7] had the highest number of Arctodus simus specimens south of the ice sheets. The region has yielded some of the largest specimens of A. simus, including, what was once the largest specimen on record, from Salt Lake Valley, Utah.[23] In contrast with other parts of North America, the plateau received more rainfall during the Late Pleistocene, because glacially cooled air collided with hot desert air, resulting in increased precipitation and cool cloudy conditions. As a result, this greatly expanded the range of woodlands where desert exists today, with pluvial lakes being abundant in the south-west. The mid-Wisconsian U-Bar cave (New Mexico) was populated by fauna typically found in cooler and more mesic habitats, particularly habitats characterized by a notable pulse of cool-season precipitation, relatively warm winters, and limited warm-season moisture. Sagebrush, grasses, and woodland vegetation suggests cooler summers and a more pronounced emphasis on cool-season precipitation than in lowland New Mexico (Dry Cave). This more xeric and warmer climate contrasts with the sagebrush steppe-woodland of the Last Glacial Maximum. Notable fauna which lived alongside Arctodus simus included Shasta ground sloth, shrub-ox, pronghorns (Stockoceros,Capromeryx), Camelops, Odocoileus, horses, Lynx, puma, black bear, mountain goats, prairie dogs, and Stock's vampire bat.[24][25] Dire wolves were also found in association with Arctodus simus at U-Bar cave, along with Conkling Cavern- both species are the most common carnivorans of Rancholabrean New Mexico.[26] Beyond New Mexico,[27][28][29][30][31] other important specimens have also been found in Arizona, Idaho, Montana,[32] Nevada,[33] and Utah. The Intermontane Plateau extended deep into Mexico, where it demarked the southernmost habitat of Arctodus simus.
Dire wolves are often found at the same localities as Arctodus simus, and were the most common predator of western North America.
Comparatively, the Rocky Mountain System had the fewest number of specimens of Arctodus simus in western North America. However, one of the youngest dated Arctodus simus is from a cave near Huntington Reservoir, Utah, which sits at an elevation of 2,740m (~9,000 ft),. The central and southern Rocky Mountains may have acted as refugia for Arctodus simus, in addition to other contemporary high-elevation alpine fauna such as Colombian mammoths, mastodon, horses, and giant bison ≤11,400 BP (10,000 14C BP).[34][35][36] Other remains have been found from Natural Trap Cave and Little Box Elder Cave in Wyoming,[37] and Montana.[38]
Interior USA
The Interior Plains were composed of temperate steppe grassland,[7] and among the specimens yielded from this region is one the largest Arctodus simus currently on record, from the banks of the Kansas river. The Irvingtonian age Doeden gravel pits in Montana preserves an open grassland habitat, with riparian woodlands, and likely some shrublands.[39]Arctodus simus co-existed with ground sloths (Megalonyx, Paramylodon), Pacific mastodon, camels, and oxen (Bootherium).[40][41][42] As bison were yet to migrate into North America, Colombian mammoths and horses dominated these Sangamonian grasslands.[43] Additional Irvingtonian remains have been recovered from Arkalon in Kansas, Hay Springs in Nebraska, and Rock Creek in Texas.
Arctodus also roamed the southern mixed grasslands of Texas.
Whereas the northern plains aridified into cold steppe in the Rancholabrean age (e.g. Mammoth site, South Dakota),[44] the southern plains were a parkland with riparian deciduous forests (e.g. hackberry), and large expanses of mixed grass prairie grasslands grading into wet meadows. At Lubbock Lake on the Llano Estacado, Texas, above freezing/mild winters and cool summers highlighted a regional climate of reduced seasonality and stable humidity in the latest Pleistocene.[45] Overall, Arctodus simus, grey wolves and coyotes were part of a predator guild throughout the Rancholabrean great plains, and were joined by Colombian mammoths, camels, Hemiauchenia, and American pronghorns. In the northern plains, woolly mammoths also ranged across the steppe, whereas in the south, Smilodon, dire wolves, grey fox and red fox in the south preyed upon horses prairie dogs, horses (Equus & Haringtonhippus), peccaries, Odocoileus, Capromeryx, Bison antiquus and Holmesina.[44][45] Beyond Texas,[46]Arctodus has also been found from the Kaw River and Jinglebob in Kansas.[47]
In the lowlands in the eastern Interior plains, the plains transitioned to closed habitat. At the terminal Pleistocene Sheriden Cave, Ohio, a mosaic habitat consisting of marsh, open woodland, and patchy grassland was home to Arctodus simus, Cervalces scotti, caribou, peccaries (Platygonus, Mylohyus), giant beaver, porcupine, and American pine marten.[48][49] Similar remains have been found in Indiana and Iowa.[50]
To the south, the Interior Highlands had a very high density of Arctodus simus specimens (second only to the black bear),[5] due to the high rate of preservation in the cave-rich region. Sympatry between the two species is most apparent in Missouri- Arctodus simus has been found in association with black bears at Riverbluff, Bat and Big Bear caves.[51] At Riverbluff Cave, the most abundant claw marks are from Arctodus simus. Some being up to 4 meters high on the cave walls, they are most abundant at the bear beds and their associated passageways, indicating a close relationship with denning. Other impressions found include claw marks from a large cat (either Panthera atrox or Smilodon fatalis) and Platygonus trackways.[52] Big Bear Cave preserves fossilized hair associated with Arctodus.[53] During the Last Glacial Maximum, both bears were joined by dire wolves, coyotes, jaguars, snowshoe hare, groundhogs and beavers at Bat Cave, which also records thousands of Platygonus remains. These fauna inhabited well-watered forest-grassland ecotone with a strong taiga influence. These open woodlands were dominated by pines and spruce, and to a lesser extent by oaks.[54][55][56][57] However, evidence from Riverbluff Cave suggests that the region occasionally cycled through drier, grassier periods in the last 55,000 years.[58]
Open boreal woodlands provided adequate resources for Arctodus simus.
Eastern USA
Compared to other regions, Arctodus simus was relatively rare in eastern North America.[5] To the north, the Appalachian Highlands were dominated by taiga.[7] Post-LGM Saltville, Virginia, was a mosaic of grassy/herb laden open areas intermixed with open canopy boreal woodlands (oaks, pines, spruce, birch, firs) and marshes. Inhabiting in this C3 resource dominated environment were Arctodus simus, mastodon, (southernmost) woolly mammoths, oxen (Bootherium), horses, caribou, ground sloths (Megalonyx), dire wolves, beavers, Cervalces, and a variety of warm-adapted reptiles, suggesting that a more mesic and less seasonal climate allowed for the mixing of more typically northern and southern fauna. Heavy bone damage on a mammoth carcass by both dire wolves and Arctodus suggests a potentially competitive scavenging relationship [59][60] Additional remains have been found at Island Ford Cave in Virginia, and Frankstown in Pennsylvania.
Lake Rousseau, Florida, is the south-easternmost locality which Arctodus simus is known to have inhabited.
To the south, the Atlantic Plains covered a great expanse of lowland, from the open deciduous woodlands of the Atlantic coast, to the semi-arid woodland/scrub of Florida, to the spruce-fir conifer forests and open habitat of the Gulf Coastal Plain. Although scarce, this contrast of habitats highlights the adaptability of Arctodus simus. At the Rainbow River and Lake Rousseau localities in Rancholabrean Florida, three Arctodus simus specimens have been recovered, alongside Smilodon, dire wolves, jaguars, ground sloths (Paramylodon, Megalonyx), llamas (Palaeolama, Hemiauchenia), Vero's tapir, giant beaver, capybara, Holmesina, horses, Bison antiquus, mastodon, Colombian mammoths and Tremarctos floridanus, in a climate similar to today's. That one of the three individuals was a very large, older specimen establishes extreme sexual dimorphism as the explanation behind size differences in Arctodus simus. Furthermore, the abundance of black bears, and particularly Florida short faced bears in Florida, has led to a theorized niche partitioning of ursids in Florida, with Tremarctos floridanus being herbivorous, and black bears and Arctodus simus being omnivorous, with Arctodus being possibly more inclined towards carnivory.[4]
In the Black Belt of Late Pleistocene Mississippi, a terrestrial floodplain at Cedar Creek hosted a mixture of grassland and mixed woodlands adapted species (including Arctodus simus). Horses, then bison, are the most numerous of the fauna, but were also joined by Colombian mammoths, coyotes, Dasypus bellus and Holmesina on the plains. Mastodon, ground sloths (Eremotherium, Megalonyx), peccaries (Platygonus, Mylohylus), deer (Cervus, Odocoileus), lynx, black bear, Florida short-faced bear, margays, gray fox, Hemiauchenia, turkeys and racoons in the open woodlands, with giant beavers, lesser beavers, and capybara inhabiting the marshes. Coyotes and black bears from this locality are unusually small for the Late Pleistocene. Further west, in the Mississippi Alluvial Plain, the fauna Arctodus simus encountered at the Bar, Arkansas was similar to Saltville, Virginia, with the addition of Paleolama, Bison, Mylohyus, black bears, tapirs, manatees and alligator snapping turtles. During the Last Glacial Maximum, in part due to glacial meltwaters producing a cold microclimate, boreal forests extended from 40° N to coastal regions near 23° N. Mississippi's boreal forests were dominated by pine, spruce, ash, aspen, oak and hickory, with more deciduous trees and herbs/grasses in the lowlands. However, the presence of the giant tortoise, Hesperotestudo crassiscutata, in both localities is indicative of mild winters, and limited seasonality.[61][62][63][64]Arctodus, along with Colombian mammoths, seems to have avoided the coastal savannas of the south east, where Mixotoxodon was present. Additional finds of south-eastern Arctodus simus are from Alabama,[65] South Carolina.[66] and Texas.[67][68]
Canada
On the boundary of the northern glacier
The vast majority of Canada was glaciated during the Late Pleistocene. However, southern Alberta may have been spared, providing a tundra ecosystem (at least until the Last Glacial Maximum).[69]Arctodus simus remains have been recovered from the mid-Wisconsian (~22,000 BP) near Edmonton, forming a predator guild with the gray wolf and American lion. Also present were Megalonyx, horses (E. conversidens & E. niobrarensis), caribou, camels, mammoths (Colombian and woolly), mastodon, bison (B. priscus & B. latifrons), and oxen (Ovibos & Bootherium). The higher diversity of grazers to browsers suggested a more open environment- that the American lion individual was noticeably smaller than its southern contemporaries contrasts with the huge Arctodus and large wolf specimens.[70]
The entry to the ice-free corridor to Beringia may have also been near Edmonton, providing a migration pathway to Beringia. Arctodus remains from similar habitat has also been recovered from Saskatchewan,[71] and from the forest-steppe of Late Pleistocene Vancouver Island.[72][73]Arctodus was a scarce member of the Pleistocene fauna of southern Canada- extant herbivorous bears are browsers, not grazers, so the scarcity of Arctodus in mid-latitude North America may be due to a lack of suitable vegetation on the steppe. On the other hand, should Arctodus simus have been a large and strict carnivore, perhaps Arctodus simus would never have been very numerous in an open ecosystem.[70]
Mostly isolated by the Cordilleran and Laurentide ice sheets, Beringia is considered ecologically separate to the rest of North America, being largely an extension of the Eurasian mammoth steppe.[74] However, due to the occasional opening of an ice-free corridor, and the migration barrier of the Beringian gap, meant that Eastern Beringia (Alaska and the Yukon) supported a unique assemblage of fauna, with many endemic North American fauna flourishing (such as Arctodus simus) within a mostly Beringian ecosystem.[75] This mostly open and treeless steppe-tundra, dominated by grasses, sedges, Artemisia spp., and a range of other forbs had a cold, dry climate, which prevented glaciation. Currently, all specimens of A. simus in Beringia have been dated to a 27,000 year window (50,000 BP~23,000 BP) from Eastern Beringia.[76][72] However, additional undated remains may be of Sangamonian age.[77] The largest skull of A. simus known was recovered from the Yukon, and may represent the largest specimen known.[78][79]
The North Slope of Alaska <40,000 BP (Ikpikpuk and Titaluk rivers) preserves an upland and floodplain environment, with horses, bison then caribou being the most populous herbivores, and woolly mammoths, muskoxen, elk and saiga antelope more scarce. Cave lions, bears (Ursus arctos and Arctodus simus), and Beringian wolves made up the megafaunal predator guild.[80][81] That caribou and muskox utilized the warmer, wetter portions of the regional vegetation mosaic (similar to the moist acidic tundra vegetation which dominates today), while horse, bison, and mammoth were dryland specialists,[80] may reflect the preferred habitat of Arctodus, as isotope data suggests caribou and muskox were principal components of the carnivorous portion of Beringian Arctodus simus' diet.[82]
Additionally, upon the flooding of the Bering Strait and expansion of peatlands in Eastern Beringia during MIS-3, lions, brown bears and Homotherium went regionally extinct ~35,000 BP, whereas Arctodus persisted. Simultaneously, muskox, bison, non-caballine horses (Haringtonhippus) and other megafaunal herbivores in Beringia experienced population bottlenecks in MIS-3, whilst mammoth populations steadily declined. This restriction of prey and habitat could explain the extinctions. However, genetically distinct Panthera spelaea and brown bears appear in MIS-2 circa the extinction of Arctodus in a re-emerged Beringia ~23,000 BP (possibly due to sharp climatic cooling associated with Heinrich Event-2), opening up the possibility that some level of competition was at play.[76][82][83][84] The idea that Arctodus had a kleptoparasitic relationship with wolves and Homotherium in Beringia has been explored,[82] and with the additional possibility that Arctodus restricted brown bears and Homotherium access to caribou pre-LGM.[85]
Not only did Arctodus likely compete at a higher trophic level than the majority of brown bears in Beringia, Arctodus' nitrogen-15 levels are higher in the Yukon, suggesting that Arctodus possibly occupied an even higher trophic level there relative to other Arctodus in Beringia. However, isotope differences more likely reflect subtle differences in the isotopic composition of primary producers in the region.[86][87]
It would be reasonable to assume that meat and bone marrow were likely to be the primary food resources for some northern populations of A. simus, in which the survival during the cold season could have depended on the regular scavenging of ungulate carcasses, as is the case with Alaskan brown bears.[88] Ultimately, an opportunistic foraging strategy including up to 50% vegetation, and the meat of reindeer, muskox, carrion, and possibly some predators, is consistent with the isotopic data and the conclusions of the ecomorphological studies.[82]
Data
Below is a table comparing the dimensions of several adult Arctodus simusfemora,[89][90][70] including one of the largest on record from Bonner Springs, Kansas,[citation needed] and some associated weight estimates.[88] Also included is the mean from 9 specimens in Björn Kurtén's seminal 1967 study.[91]
^"However, only a few of the BPA species have been demonstrated in recent years to be strictly Rancholabrean markers in the Eastern U.S. These include Meleagris gallopavo (see Barkalow 1972, Steadman 1980) and Megalonyx jeffersonii (see review of Morgan & Hulbert 1995), both reported by Kaye (1974); and Arctodus simus (see Pinsof 1992, 1998, Richards et al. 1996), Tremarctos floridanus (see Cassiliano 1999, Morgan & Hulbert 1995), and Leopardus wiedii amnicola (see Kurtén & Anderson 1980, Werdelin 1985), all reported by Kurtén & Kaye (1982). This writer will soon be reporting two other mammalian species (Canis dirus and Leopardus pardalis) from the BPA that may also prove to be useful Rancholabrean index fossils in the Southeast." Downloaded.
^ abCite error: The named reference :5 was invoked but never defined (see the help page).
^Dundas, Robert G.; Chatters, James C. (2013-01-01). "The mid-Irvingtonian Fairmead Landfill fossil site, Madera County Paleontology Collection, and Fossil Discovery Center of Madera County, California". In Keith Putirka (ed.). Geologic Excursions from Fresno, California, and the Central Valley. Geological Society of America. pp. 63–78. doi:10.1130/2013.0032(04). ISBN978-0-8137-0032-8.
^ abCite error: The named reference :232 was invoked but never defined (see the help page).
^Harris, Arthur H. (1993). "Quaternary Vertebrates of New Mexico"(PDF). Vertebrate Paleontology in New Mexico, New Mexico Museum of Natural History and Science. Bulletin 2: 179–197.
^Morgan, Gary S.; Lucas, Spencer G.; Love, David (2009). "Cenozoic vertebrates from Socorro County, central New Mexico"(PDF). In Virgil Lueth; Spencer G. Lucas; Richard M. Chamberlin (eds.). New Mexico Geological Society Fall Field Conference Guidebook: 60 Geology of the Chupadera Mesa. pp. 321–336.
^Young, Robert R.; Burns, James A.; Smith, Derald G.; Arnold, L. David; Rains, R. Bruce (1994-08-01). "A single, late Wisconsin, Laurentide glaciation, Edmonton area and southwestern Alberta 2.3.CO;2". Geology. 22 (8): 683–686. doi:10.1130/0091-7613(1994)022<0683:ASLWLG>2.3.CO;2. ISSN0091-7613.
^David Webb, S.; Graham, Russell W.; Barnosky, Anthony D.; Bell, Christopher J.; Franz, Richard; Hadly, Elizabeth A.; Lundelius, Ernest L.; Gregory McDonald, H.; Martin, Robert A. (2003), "Vertebrate paleontology", Developments in Quaternary Sciences, vol. 1, Elsevier, pp. 519–538, doi:10.1016/s1571-0866(03)01025-x, ISBN978-0-444-51470-7, retrieved 2022-06-28
^Storer, J. (2003). Froese, D.G.; Zazula, G. D. (eds.). "Vertebrate Palaeontology of the Klondike Area"(PDF). 3rd International Mammoth Conference Field Guide to Quaternary Research in the Klondike Goldfields. Occasional Papers in Earth Sciences No. 6: 24–29 – via Palaeontology Program, Government of the Yukon.
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