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Tremarctinae

Tremarctinae is a subfamily of the bear family Ursidae, endemic to the Americas and characterized by its short-faced morphology, which includes the only extant species, the spectacled bear (Tremarctos ornatus), and various extinct genera such as Arctodus, Arctotherium, Plionarctos, and additional Tremarctos species.^[1]^[2] This subfamily originated from Asian Ursavus ancestors around the Miocene-Pliocene boundary and dispersed to North America by the late Miocene, eventually reaching as far south as Patagonia.^[3]^[2] The spectacled bear, also known as the Andean bear, is the sole living member of Tremarctinae and inhabits montane forests and páramos along the Andes from Colombia to Bolivia, including Ecuador and Peru, at elevations of 200–4,750 meters.^[4] Primarily herbivorous, it consumes over 90% vegetation such as bromeliads, fruits, and bamboo, supplemented by occasional animal matter, and possesses specialized cranial features like a massive skull and short snout adapted for processing fibrous plants.^[4]^[3] Classified as Vulnerable by the IUCN Red List, its population is estimated at approximately 18,000 individuals as of 2017 but faces threats from habitat loss and human-wildlife conflict.^[4]^[5] Extinct tremarctines, often called short-faced bears, dominated Pleistocene ecosystems across both North and South America, with some species like Arctodus simus and Arctotherium angustidens ranking among the largest terrestrial mammalian carnivores ever, exceeding 1,000 kg in body mass.^[1] These giants exhibited convergent evolution in their massive size and morphology, likely as an adaptation to scavenge megafaunal carcasses amid intense competition, though most went extinct by the end of the Pleistocene.^[1] Fossils of species such as Tremarctos floridanus, a herbivorous North American form twice the size of the modern spectacled bear, reveal a biochron spanning from the late Miocene to the Holocene, highlighting the subfamilies' diverse adaptive radiation across continents.^[3]^[2]

Taxonomy and Systematics

Classification History

The subfamily Tremarctinae was initially conceptualized through the description of its type genus, Tremarctos, by French paleontologist Paul Gervais in 1855, who distinguished it as a unique lineage within the family Ursidae based on cranial and dental features of South American fossils, marking the recognition of short-faced bears as a separate group from Old World ursines.^[6] In the early 20th century, classifications increasingly grouped extinct short-faced bears such as Arctodus from North America and Arctotherium from South America under Tremarctinae, with key contributions from John C. Merriam and Chester Stock in 1925, who formally erected the subfamily name while debating its status as either a tribe or full subfamily due to morphological overlaps with other ursids. Mid-20th-century taxonomy saw significant shifts, particularly through George Gaylord Simpson's comprehensive 1945 classification of mammals, which solidified Tremarctinae as a distinct, New World endemic subfamily within Ursidae, emphasizing its isolation from Eurasian bear lineages and incorporating early fossil evidence to support its monophyly.^[7] Key revisions occurred in the 1980s and 1990s, notably in Björn Kurtén and Elaine Anderson's 1980 monograph on Pleistocene mammals of North America, which integrated extensive fossil data to refine genera such as Plionarctos (an early tremarctine) and Tremarctos, clarifying synonymies and stratigraphic ranges while affirming the subfamilial boundaries.^[8] A key revision in the 1990s, including the description by Eleonora Trajano and Horacio Ferrarezzi of a new fossil tremarctine skull and mandible from Ubajara in northeastern Brazil, expanded the known geographic distribution and spurred phylogenetic reassessments of extinct forms like Arctotherium.^[9]

Phylogenetic Relationships

Tremarctinae forms a monophyletic clade within the family Ursidae, positioned as the sister group to Ursinae (the true bears), with their divergence estimated at approximately 10–12 million years ago during the Miocene epoch.^[10] This separation is supported by both morphological and molecular evidence, highlighting Tremarctinae's distinct evolutionary trajectory in the Americas relative to the Old World ursine bears.^[11] Within Tremarctinae, the internal phylogeny places Plionarctos as the basal genus, originating in North America during the Miocene, followed by the radiation of more derived forms including the North American giant short-faced bear Arctodus and the South American Arctotherium, culminating in the crown-group genus Tremarctos, which includes the extant spectacled bear.^[12] This sequential branching is inferred from cladistic analyses of cranial and dental morphology, as well as postcranial adaptations, indicating a progressive adaptation to New World environments.^[13] Molecular evidence from mitochondrial DNA sequences has revealed convergent evolution of gigantism in the Pleistocene species Arctodus simus from North America and various Arctotherium species from South America, despite their geographic separation, with body masses exceeding 1,000 kg in both lineages driven by similar ecological pressures.^[14] These findings underscore parallel evolutionary responses to open habitats and prey availability across continents. Cladistic analyses incorporating new fossil specimens from South America have suggested that Arctotherium may be paraphyletic, potentially requiring subdivision into multiple genera based on variations in mandibular robusticity and dental morphology observed in Brazilian and Argentinean material.^[9] This challenges earlier monophyletic interpretations and emphasizes the need for revised taxonomy informed by ongoing discoveries. Molecular clock estimates, calibrated with fossil constraints, position the major radiation of Tremarctinae in the New World after the Great American Biotic Interchange, around 2.5–3 million years ago, coinciding with intensified faunal exchanges and habitat diversification in South America.^[15]

Morphology

Cranial Features

Tremarctinae exhibit distinctive cranial morphology adapted for powerful mastication, particularly evident in their shortened rostrum compared to the more elongated snouts of Ursinae bears. This relative shortening, often resulting from reduced nasal bones and deeper facial profiles, creates the characteristic "short-faced" appearance and allows for a broader attachment area for jaw muscles. The zygomatic arches are notably robust and expanded laterally, facilitating greater bite forces at the molars, which may have supported processing of tough vegetation or bone-crushing activities in both extinct and extant species.^[16]^[3] In extinct giant forms such as Arctodus simus, the cranium features an enlarged sagittal crest that rises prominently above the braincase, providing enhanced anchorage for temporalis muscles, alongside hypertrophied mastoid processes that bolster the origin of the sternomastoideus and other neck musculature for powerful jaw adduction. These adaptations correlate with facial proportions similar to those of modern bears of comparable body size when scaled appropriately, though the reduced nasal bones and deeper profile give the appearance of a shortened face; this morphology supports high-force biting suited to omnivorous habits. Fossils of Arctodus display these traits prominently, with sagittal crests reaching heights of 50 mm in large specimens, underscoring the subfamily's evolutionary emphasis on cranial strength.^[17]^[18] The dental formula across Tremarctinae genera is uniformly I 3/3, C 1/1, P 4/4, M 2/3, reflecting a conserved ursid pattern but with modifications for omnivory or herbivory. Carnassial teeth (P4/m1) are reduced in shearing capability compared to more carnivorous carnivorans, while premolars are enlarged and robust, often with blunt cusps suited for crushing plant material or small bones. Hypertrophied canines in short-faced bears suggest potential for scavenging or occasional hypercarnivory, though fossil tooth wear patterns—characterized by heavy attrition on molars and premolars consistent with abrasive, fibrous diets—indicate predominantly omnivorous habits akin to modern brown bears.^[19]^[16] Among extant representatives, Tremarctos ornatus possesses a vaulted forehead and further reduced nasal bones, contributing to a more domed cranial profile that contrasts with the flatter, broader skulls of extinct Arctotherium species, which emphasize lateral expansion for muscle attachment over vertical height. These variations highlight intra-subfamily diversity, with the spectacled bear's configuration supporting its primarily folivorous diet through efficient processing of epiphytic bromeliads and fruits. Tooth wear in Arctotherium fossils similarly shows patterns of heavy occlusal flattening, reinforcing interpretations of versatile feeding strategies across the lineage.^[3]^[20]^[21]

Postcranial Features

The postcranial skeleton of Tremarctinae exhibits significant variation across genera, reflecting adaptations to diverse locomotor strategies in extinct and extant species. In Arctodus simus, the limbs are elongated relative to body size, with an intermembral index (IMI) of 95-96 calculated as [(humerus length + radius length) / (femur length + tibia length)] × 100, indicating relatively long forelimbs that support cursorial capabilities for sustained travel rather than explosive acceleration.^[22] Specific measurements from fossil specimens show humerus lengths averaging 594 mm and femur lengths 651 mm, yielding a humerus-femur ratio of approximately 0.91, which contributes to a high-shouldered posture.^[22] Largest individuals reached estimated bipedal shoulder heights of up to 3.4 m, enhancing reach and visibility in open habitats.^[22] In contrast, Arctotherium species display more robust postcranial elements, including thick-walled long bones that suggest a graviportal posture suited to supporting immense body mass.^[23] Fossil humeri in Arctotherium angustidens measure up to 620 mm in length with substantial mid-shaft circumferences, while pelvic fragments show circular acetabula around 62 mm in diameter, indicating strong weight-bearing articulations.^[23]^[24] Scapular remains are robust with pronounced spines and acromia, further evidencing structural reinforcement for graviportal locomotion.^[24] Short-faced bears (Arctodus and Arctotherium) share forelimb hyper-specializations, including shortened metacarpals that are gracile relative to proximal elements, with third metacarpal mediolateral width-to-length ratios averaging 0.16 in Arctodus simus.^[25] These features, combined with reduced olecranon processes on the ulna (olecranon-to-shaft length ratio of 0.2), are evidenced by fossil metrics from multiple specimens and suggest capabilities for grappling or manipulating large items, though optimized more for locomotor efficiency than intensive digging.^[25] Claw morphology is inferred from phalangeal robustness, with distal widths supporting strong, curved unguals suited to securing footing or prey.^[25] Like other ursids, Tremarctinae possess reduced tails and plantigrade feet, facilitating stable weight distribution during quadrupedal movement.^[22] In the extant Tremarctos ornatus, paws are broader with bare, padded soles that enhance grip on bark and rock, adaptations evident in trackway fossils and modern observations supporting frequent arboreal climbing.^[26] Body mass estimates for Tremarctinae derive from regression formulas applied to femoral circumference, among other metrics. For Arctodus simus, values reach up to 900 kg using such regressions on proximal limb bones.^[22] Arctotherium species exceed 1,600 kg, with A. angustidens averaging 1,588 kg (range 983-2,042 kg) based on femoral and humeral circumferences via allometric equations like those of Anyonge (1993).^[23]^[24] These estimates align with cranial robusticity indicators, underscoring overall skeletal scaling in the subfamily.^[23]

Evolutionary History

Origins and Divergence

The subfamily Tremarctinae originated in North America during the late Miocene, approximately 10 million years ago, evolving from an Ursavus-like ancestor that had migrated from Eurasia across the Bering land bridge.^[27] This dispersal event marked the initial establishment of early bear lineages in the New World, with Tremarctinae diverging from the Ursinae subfamily around 12-14 million years ago.^[27] Following this split, Tremarctinae adapted to the forested environments of proto-North America, developing traits suited to arboreal and omnivorous lifestyles in dense woodland habitats.^[27] The initial radiation of Tremarctinae occurred during the Pliocene, between 5 and 3 million years ago, exemplified by the genus Plionarctos, which represents an early shift toward the characteristic short-faced morphology seen in later members of the subfamily.^[28] This evolutionary development coincided with environmental changes that favored more specialized cranial structures for processing diverse plant and animal matter.^[28] A pivotal event in Tremarctinae history was the Great American Biotic Interchange around 2.7 million years ago, which facilitated the southward migration of these bears into South America via the newly formed Isthmus of Panama.^[13] This interchange led to the isolation and diversification of Tremarctinae lineages in the southern continent, where they became endemic.^[13] Tremarctinae did not survive into the post-Pleistocene in North America, with the extinction of North American species, including giant short-faced bears, occurring around 11,000 years ago.^[29] This terminal event is attributed to synergistic effects of rapid climate warming at the end of the Last Glacial Maximum and the arrival of humans, which disrupted habitats and prey availability.^[30]

Fossil Record

The fossil record of Tremarctinae commences in the late Miocene to early Pliocene of western North America with the genus Plionarctos, representing the earliest known members of the subfamily.^[28] Fossils of Plionarctos have been documented from multiple sites in this region, including the Ringold Formation in eastern Washington, where specimens date to the Blancan North American Land Mammal Age.^[31] These remains, including cranial and postcranial elements, indicate an anagenetic lineage that persisted through the Pliocene.^[31] During the Pleistocene, tremarctines achieved widespread distribution and prominence, particularly with the genus Arctodus in North America. Arctodus simus, the giant short-faced bear, is recorded from over 100 localities spanning from the Yukon Territory in Canada to Mexico, encompassing diverse environments across the continent.^[32] Notable sites include the Rancho La Brea Tar Pits in California, where more than 30 individuals have been recovered from Rancholabrean-age deposits (approximately 40,000 to 10,000 years ago), providing abundant skeletal material for study.^[33] This extensive fossil assemblage highlights A. simus as one of the most ubiquitous large carnivorans of the Pleistocene in North America.^[29] In South America, the tremarctine record begins later, with the genus Arctotherium appearing in the late Pliocene and persisting through the Pleistocene. The earliest confirmed remains of Arctotherium angustidens, the largest known species, come from the Buenos Aires Formation in Argentina, dated to around 2 million years ago during the Ensenadan South American Land Mammal Age.^[34] Subsequent fossils document the diversification and gigantism of Arctotherium species, including massive forms from the Tarija Formation in Bolivia, which spans the middle Pleistocene (approximately 1.0 to 0.7 million years ago) and yields complete skeletons exceeding 1,600 kg in estimated body mass.^[35] These South American sites, such as those near Tarija, reveal a radiation tied to the Great American Biotic Interchange, with Arctotherium occupying diverse habitats from Andean foothills to coastal plains.^[13] The extinction of most tremarctine lineages occurred at the end of the Pleistocene. In North America, Arctodus simus and related taxa disappeared around 11,000 years before present (BP), coinciding with the terminal Pleistocene faunal turnover.^[36] South American Arctotherium species persisted slightly longer, with the latest unequivocal records dating to approximately 10,000 BP, though sparse Holocene evidence from sites in Argentina and Bolivia remains debated and may represent reworking or misdating rather than survival.^[13] Only the smaller Tremarctos ornatus endured into the present as the sole extant tremarctine.^[37]

Paleobiology

Diet and Ecology

Ancestral Tremarctinae likely maintained an omnivorous diet, incorporating both plant and animal matter, as evidenced by their generalized dental morphology and broad isotopic signatures in early fossil representatives. This dietary flexibility is characteristic of the subfamily's origins, allowing adaptation to diverse Pleistocene environments across the Americas. Cranial adaptations, such as robust jaws and varied tooth morphologies, facilitated this omnivory by enabling processing of tough vegetation alongside softer animal tissues.^[38] In the genus Arctodus, particularly A. simus, dietary reconstruction reveals a shift toward greater carnivory compared to ancestral forms. Stable isotope analysis of bone collagen yields δ¹³C values ranging from -21.0‰ to -18.1‰ and δ¹⁵N values from 7.5‰ to 9.9‰, consistent with a diet heavily reliant on terrestrial herbivores and indicating a higher trophic position than co-occurring black bears (Ursus americanus). These signatures suggest meat comprised a substantial portion of the diet, supporting interpretations of Arctodus as a hypercarnivorous scavenger or occasional predator in open habitats.^[39]^[40] Species of Arctotherium, such as A. angustidens, exhibited an omnivorous diet incorporating both vegetable matter and substantial animal matter from large vertebrates, as evidenced by morphology, dental pathology, stable isotopes, and biomechanics. This mixed diet positioned Arctotherium as a versatile feeder in South American ecosystems, similar to its North American relatives.^[41]^[42] The scavenging hypothesis is prominent for short-faced bears (Arctodus and Arctotherium), bolstered by biomechanical models of their crania. Finite element analysis estimates bite forces up to approximately 1,800 N at posterior tooth positions, enabling efficient bone-crushing and access to marrow in large carcasses—adaptations suited to kleptoparasitism or opportunistic feeding on megafaunal remains rather than active hunting. Dental microwear textures align with this, showing patterns of hard-object feeding comparable to modern bone-consuming carnivores like spotted hyenas.^[42]^[43]^[44] Niche partitioning is evident within Tremarctinae, exemplified by the extant spectacled bear (Tremarctos ornatus), which is predominantly frugivorous and arboreal, relying on fruits, bromeliads, and foliage accessed via climbing in Andean forests. This contrasts sharply with the more terrestrial, ground-foraging habits of extinct relatives like Arctodus and Arctotherium, which exploited open plains for scavenging or foraging; isotopic and morphological data suggest such differentiation reduced competition and allowed coexistence in overlapping ranges.^[43]^[45]^[46] As apex scavengers or predators, short-faced bears exerted significant ecological influence on Pleistocene megafauna communities, potentially shaping assemblage dynamics through carcass utilization. Fossil sites reveal bone modifications attributable to ursid gnawing, such as tooth marks on ungulate and proboscidean remains, indicating these bears competed with or displaced other carnivores and accelerated nutrient recycling in tundra and grassland ecosystems. Their extinction around 11,000 years ago contributed to shifts in scavenger guilds, altering energy flow in post-glacial food webs.^[47]^[48]^[49]

Locomotion and Habitat Use

The giant short-faced bear Arctodus simus displayed cursorial adaptations in its postcranial skeleton, particularly in the forelimb, where elongated and gracile proportions—such as a straighter humeral shaft (bow angle approximately 180°) and a reduced olecranon process on the ulna (olecranon-to-shaft length ratio of 0.2)—facilitated extended stride lengths and efficient, sustained locomotion at moderate speeds of up to 40–45 km/h.^[25] These features, including balanced interelemental ratios (e.g., radius length to humerus length of 0.78–1.01), supported a pacing gait optimized for endurance rather than rapid acceleration, aligning with its role in covering vast distances across open steppe-tundra and grassland habitats during Pleistocene glacial maxima.^[50] Such locomotor efficiency likely enabled scavenging in expansive, non-forested environments spanning over 2,000,000 km² in Eastern Beringia, where home ranges exceeded 1,000 km² to track dispersed megafaunal carcasses.^[50] In the extant spectacled bear Tremarctos ornatus, semi-arboreal locomotion predominates, with strong, curved claws enabling proficient climbing of trees and vines up to diameters matching the bear's paw size, as indicated by scratch and rub marks on trunks and branches exceeding 3 m in height.^[51] This vertical mobility allows access to fruit and epiphytes in the canopy of Andean cloud forests, where bears construct leafy platforms for resting and foraging, reflecting specialized adaptations for a subtropical, montane habitat.^[52] Unlike more terrestrial ursids, T. ornatus spends significant time elevated, using its arboreal prowess to navigate dense vegetation and avoid ground-level competitors.^[53] The massive South American short-faced bears of the genus Arctotherium, particularly A. angustidens, exhibited a graviportal stance inferred from robust postcranial elements, including thicker limb shafts and broader joint surfaces relative to length, which supported body masses exceeding 1,000 kg in mixed woodland-steppe settings of the Pleistocene Pampas.^[54] This posture emphasized weight-bearing stability over speed, suited to semi-open habitats where trackway evidence from regional formations suggests deliberate, quadrupedal progression rather than agile maneuvers.^[55] Tremarctinae as a whole experienced habitat shifts from closed-canopy forests in the Miocene to expansive open landscapes by the Pleistocene, with stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) from North American Arctodus fossils indicating transitions to C₃-dominated grasslands and tundra, alongside evidence of latitudinal or altitudinal migrations to track megafaunal resources during glacial cycles.^[50] No anatomical or fossil evidence supports hibernation in the subfamily; instead, nomadic foraging is inferred from large estimated home ranges and continuous dental wear patterns in Arctodus specimens, suggesting year-round activity without seasonal dormancy.^[50] In the extant Tremarctos ornatus, the absence of hibernation aligns with its subtropical range, where stable climates permit perpetual foraging across altitudinal gradients.^[53]

Extant Representatives

Spectacled Bear Biology

The spectacled bear (Tremarctos ornatus), the only extant member of the subfamily Tremarctinae, is a medium-sized ursid with adults weighing 80–200 kg and exhibiting marked sexual dimorphism, where males are approximately 40% larger than females. Its pelage is typically black to dark red-brown, featuring dense, long, coarse fur and distinctive creamy white markings on the face, chin, neck, chest, and around the eyes that form spectacle-like patterns, though these vary individually and may be absent in some specimens. Adaptations for an arboreal lifestyle include strong, curved, nonretractable claws on all feet for gripping bark and flexible ankles with a specialized tarsus, comprising five ligaments and a well-developed meniscus, enabling agile climbing in rugged Andean terrain.^[56]^[57]^[58] This species is endemic to the Andes Mountains, ranging from Venezuela in the north to northern Argentina in the south, across diverse habitats including cloud forests, páramo grasslands, and dry forests at elevations from 200 to 4,750 m. Populations are highly fragmented due to habitat loss, with an estimated total of 13,000–18,000 individuals distributed unevenly: approximately 1,100–1,600 in Venezuela, 3,000–6,000 in Colombia, 1,200–2,000 in Ecuador, around 5,000 in Peru, and 3,000 in Bolivia. These bears maintain home ranges of 5–23 km² in forested areas, reflecting their adaptability to steep, vegetated slopes.^[57]^[59]^[60]^[4]^[61] Spectacled bears are solitary outside of mating and maternal periods, with breeding occurring year-round and no fixed season, though peaks may align with food availability. Females reach sexual maturity at 4–5 years, followed by a gestation period of 215–240 days, often involving delayed implantation; litters typically consist of 1–3 cubs (average 2), born weighing 300–500 g in dens or tree nests, with cubs dependent on the mother for 1–2 years of lactation and care. Males do not participate in rearing, and interbirth intervals span 2–3 years.^[57]^[59]^[62] Behaviorally, spectacled bears are primarily diurnal, exhibiting bimodal activity patterns with peaks in mid-morning and mid-afternoon, and they are proficient climbers, spending significant time in trees to forage, rest, and evade threats. They construct nests or platforms in trees, often utilizing epiphyte-laden branches such as those supporting bromeliads, and in arid regions, they may seek shelter amid cacti stands or rock outcrops for protection. Communication relies heavily on olfaction via scent-marking, supplemented by vocalizations including bellows and roars for territory defense, shrill screeches for alarm, and soft purrs between mothers and cubs.^[57]^[63]^[59] Recent genetic studies from 2024–2025 indicate low phylogeographic structure across the species' range, with minimal spatial differentiation in populations such as those in Ecuador, suggesting recent colonization from southern refugia and gene flow despite habitat fragmentation; mitochondrial haplotype diversity is moderate (H_d ≈ 0.86), but overall heterozygosity (H_e ≈ 0.59–0.60) is lower than in other ursids like black bears. This contrasts with pronounced sexual dimorphism, reinforcing the species' evolutionary adaptations to varied ecological pressures in the Andes.^[64]^[65]^[4]

Conservation and Threats

The spectacled bear (Tremarctos ornatus), the sole surviving member of the Tremarctinae subfamily, is classified as Vulnerable on the IUCN Red List due to ongoing population declines driven by multiple anthropogenic pressures.^[57] The species' global population is estimated at fewer than 18,000 individuals, with a continuing decline inferred from habitat degradation across its Andean range.^[66] Habitat loss represents the primary threat, primarily through deforestation for agriculture, livestock grazing, and logging in the tropical Andes, where rates of forest cover loss remain among the highest globally.^[67] This fragmentation isolates bear populations, reducing access to critical feeding areas in cloud forests and páramos, and exacerbating vulnerability to local extinctions.^[66] Human-bear conflicts further compound risks, as bears occasionally prey on livestock or raid crops like maize, prompting retaliatory killings by farmers; in Peru alone, approximately 200 bears are killed annually due to such conflicts.^[68] Poaching for body parts, including claws, teeth, fat, and meat—often for traditional medicine or trophies—adds to mortality, though it is less prevalent than habitat-related threats.^[69] Conservation measures include legal protections under CITES Appendix I since 1975, prohibiting international trade and enforced across the bear's range in six countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, and Argentina.^[70] The Andean Bear SAFE Program, launched in 2023, coordinates multi-country efforts to safeguard populations through habitat restoration, camera trap monitoring for population assessments, and the development of wildlife corridors to reconnect fragmented landscapes.^[71] Climate change poses an emerging threat, with species distribution models projecting significant range contraction—potentially up to 40-50% in suitable habitats—by 2050 due to upward shifts in cloud forest zones and altered vegetation patterns.^[72] Positive outcomes have been observed in protected areas, such as Venezuela's national parks, where anti-poaching patrols and ecotourism initiatives have stabilized local populations by reducing illegal killings and fostering community support for bear conservation.^[73] These efforts highlight the potential for targeted interventions to mitigate threats and support the long-term persistence of this iconic species.

References

[1]
Ancient mitochondrial DNA reveals convergent evolution of giant ...
The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ever lived: the ...Missing: taxonomy | Show results with:taxonomy
[2]
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6422017/
[3]
Tremarctos floridanus – Florida Vertebrate Fossils
Apr 10, 2015 · Tremarctos floridanus, or the Florida spectacled bear, is an extinct member of the ursid subfamily Tremarctinae. Tremarctine bears are a ...Missing: taxonomy | Show results with:taxonomy
[4]
Tremarctos ornatus (Andean bear)
The Andean bear has been listed since 1973 as Vulnerable by Red List of Threatened Species (IUCN) and included in Appendix I of CITES since 1977. Hunting bans ...
[5]
Tremarctos Gervais 1855 - Zenodo
Jul 15, 2021 · GERVAIS, P. M. 1855. Histoire naturelle de mammiferes avec l'indication de leurs moeurs, et de leurs rapports avec les arts, le commerce et l' ...
[6]
Classification of mammals : Simpson, George Gaylord
May 9, 2020 · Classification of mammals. by: Simpson, George Gaylord. Publication date: 1945. Collection: taxonomyarchive; additional_collections. Language ...Missing: Tremarctinae | Show results with:Tremarctinae
[7]
https://archive.org/details/bulletin-american-museum-natural-history-85-001-350
[8]
A fossil bear from northeastern Brazil, with a phylogenetic analysis ...
The skull with mandible of a fossil tremarctine bear from Ubajara county, northeastern Brazil, is described and compared to other specimens belonging to the ...
[9]
[PDF] Ancient genomes reveal hybridisation between extinct short-faced ...
Mar 10, 2021 · The divergence of Tremarctinae and Ursinae was constrained to between 7 and 13. 379 mya based on the presence of putative early tremarctine ...
[10]
Phylogenetic signal analysis in the basicranium of Ursidae ... - PeerJ
Mar 15, 2019 · Ursidae is a monophyletic group comprised of three subfamilies: Tremarctinae, Ursinae and Ailuropodinae, all of which have a rich ...
[11]
Phylogenetic signal analysis in the basicranium of Ursidae ...
Mar 15, 2019 · Ursidae is a monophyletic group comprised of three subfamilies: Tremarctinae, Ursinae and Ailuropodinae, all of which have a rich geographical ...<|control11|><|separator|>
[12]
The fossil record of South American short-faced bears (Ursidae ...
The Tremarctinae subfamily is distributed exclusively in America, from Alaska to southern Patagonia. Its biochron comprises the temporal lapse between Late ...Missing: classification | Show results with:classification
[13]
Ancient mitochondrial DNA reveals convergent evolution of giant ...
Apr 1, 2016 · The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ...Missing: 20th | Show results with:20th
[14]
Ancient mitochondrial DNA reveals convergent evolution of giant ...
Our mean estimate for the time of divergence between Tremarctos and Arctotherium was. 4.1 Ma (95% highest posterior density, HPD ¼ 3.0–5.3 Ma), and 4.8 Ma for ...
[15]
Demythologizing Arctodus simus, the 'short-faced' long-legged and ...
In this study, we review the previous evidence on the paleobiology of the giant, 'short-faced' bear Arctodus simus (Mammalia: Carnivora: Ursidae)
[16]
[PDF] What size were Arctodus simus and Ursus spelaeus (Carnivora
The skull is also shorter and broader than those of extant ursids; it has a wide and short- ened rostrum, giving it a more felid-like appear- ance (Kurtén 1967 ...
[17]
[PDF] Giant short-faced bear (Arctodus simus yukonensis) remains from ...
Apr 28, 1995 · The sagittal crest rises to a maximum of 50 mm above the braincase. Features typical of the species include the short, wide snout (including.
[18]
Andean Bear (Tremarctos ornatus) (Chapter 7) - Bears of the World
As characteristic of the subfamily Tremarctinae, the Andean bear's skull is massive, deep, and convex (Mondolfi Reference Mondolfi1989), and it is the shortest ...
[19]
Inferring palaeoecology in extinct tremarctine bears (Carnivora ...
In this study we explore the ecomorphological patterns of extinct tremarctine bears in South America during the Great American Biotic Interchange (GABI).Missing: classification | Show results with:classification
[20]
GIANT SHORT-FACED BEARS (ARCTODUS SIMUS) IN ...
Jan 1, 2010 · The lesser short-faced bear, Arctodus pristinusLeidy, 1854 is well represented from this region, particularly Florida, but all known occurrences ...
[21]
[PDF] INFORMATION TO USERS Reproduced with permission of the ...
I reconstructed aspects of Arctodus' trophic position and paleodiet by analyzing stable isotope ratios (5 nC and 6 15N) in bone collagen extracted from east.
[22]
The Largest Known Bear, Arctotherium angustidens, from the Early ...
Aug 6, 2025 · TABLE 3—Body mass estimations (kg) of Arctotherium angustidens from ... With an average body mass estimated at 700-800 kg (Christiansen ...
[23]
[PDF] Ursidae (Mammalia, Carnivora) from the Quaternary of western Rio ...
This work describes the first postcranial material from Rio Grande do Sul referred to Arctotherium and estimates the in- dividual's body mass through allometric ...
[24]
[PDF] Cursorial Adaptations in the Forelimb of the Giant Short-Faced Bear ...
... metacarpal cross-sectional shape (though on average, that of the sun bear is equivalent to that of the wolf and hyena, the wider metacarpals perhaps.
[25]
Bears can 'bear' a variety of environments! Andean bears live in ...
Feb 21, 2023 · Both bear species are arboreal, meaning you may find them climbing trees. ... paws have bare soles, which aid in gripping and climbing trees.<|control11|><|separator|>
[26]
Mitochondrial genomes reveal an explosive radiation of extinct and ...
Jul 28, 2008 · The posterior mean of the divergence time between bears and the harbor seal was estimated at 36 million years ago (Ma), which agrees with ...
[27]
Plionarctos, a tremarctine bear (Ursidae: Carnivora) from Western ...
Aug 10, 2025 · Plionarctos forms a paraphyletic stem-group for the Tremarctinae. Species of this genus can be traced successively into the Pliocene where they ...<|separator|>
[28]
Biogeographic problem-solving reveals the Late Pleistocene ...
Sep 16, 2020 · Mitchell, K. J. Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America.
[29]
Synergistic roles of climate warming and human occupation in ...
Jun 17, 2016 · The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, ...
[30]
[PDF] A RECORD FROM HAGERMAN FOSSIL BEDS NATIONAL ...
The Hagerman Fossil Beds National Monument (HAFO) in southcentral Idaho includes hundreds of fossil localities from the Blancan Land Mammal Age, and the ...
[31]
Plionarctos | 2 Publications | 44 Citations | Top Authors | Related ...
Abstract: The Pliocene Ringold Formation of eastern Washington has yielded important new materials of tremarctine bears of the anagenetic Plionarctos lineage.
[32]
"Giant Short-Faced Bears (Arctodus Simus) in Pleistocene Florida ...
Jan 1, 2010 · Fossils of the giant short-faced bear, Arctodus simus (Cope, 1879), have been recovered from over 100 localities in North America, extending from Mexico to ...<|separator|>
[33]
[PDF] Arctodus simus (Cope, 1879) from Riverside County, California
In California, A. simus is known from several Rancholabrean localities, including Potter Creek Cave and Rancho La. Brea, and early Irvingtonian sites at ...
[34]
[PDF] South American giant short-faced bear (Arctotherium angustidens) diet
In the present study, a similar approach is used for. Arctotherium fossil teeth compared to those of coeval herbivores, and the difference between the carbon ...
[35]
Middle Pleistocene age of the fossiliferous sedimentary sequence ...
The highly fossiliferous sediments of the Tolomosa Formation from Tarija, southern Bolivia, represent one of the most important localities in South America ...
[36]
Ancient mitochondrial DNA reveals convergent evolution of giant ...
The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ever lived: the ...
[37]
Ancient mitochondrial DNA reveals convergent evolution of giant ...
Apr 1, 2016 · The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ...Missing: Merriam | Show results with:Merriam
[38]
Inferring palaeoecology in extinct tremarctine bears (Carnivora ...
Aug 6, 2025 · ... (Simpson 1945). The majority of students, however, have separated these 2 families but frequently disagree on where the line between canids ...
[39]
Stable isotopes (13C, 15N) and paleodiet of the giant short-faced ...
The carbon isotopic values for Arctodus simus ranged from -21.0 to -18.1‰, while nitrogen values ranged from 7.5 to 9.9‰, indicating carnivorous dietary habits, ...Missing: hypercarnivory consumption percentage
[40]
Dietary niche separation of three Late Pleistocene bear species from ...
Jun 27, 2022 · In these Pleistocene Vancouver Island samples, δ13C values appear to increase stepwise with δ15N values, indicating a trophic level diet–tissue ...
[41]
Giants beasts updated: A review of new knowledge about the South ...
Nov 10, 2024 · ... diet rich in grasses, while the hypsodonty index indicates adaptation to the wear effect of both diet and environment. They applied their ...
[42]
South American giant short-faced bear (Arctotherium angustidens) diet
Aug 6, 2025 · ornatus we further estimated the body mass of Arctotherium in order to know if our estimations, bias published equations, were feasible.
[43]
Was the Giant Short-Faced Bear a Hyper-Scavenger? A New ...
Oct 30, 2013 · We use the resulting baseline data to evaluate the hypothesis that the Pleistocene giant short-faced bear, Arctodus simus, was a bone consumer and hyper- ...Missing: 1800 | Show results with:1800
[44]
(PDF) Was the Giant Short-Faced Bear a Hyper-Scavenger? A New ...
Aug 6, 2025 · Here, we assess correspondence of dental microwear textures of first and second lower molars with diet in extant ursids. We use the resulting ...Missing: Arctotherium | Show results with:Arctotherium
[45]
Tremarctos ornatus - an overview | ScienceDirect Topics
The Andean bear (Tremarctos ornatus), also known as the spectacled bear, is the only living species of the subfamily Tremarctinae within the family Ursidae.<|control11|><|separator|>
[46]
Andean bear Tremarctos ornatus natural history and conservation
Aug 5, 2025 · They are omnivorous with a frugivorous/folivorous emphasis that is ... 1986, Goldstein & Kattan 2001). DIET. Diet is one of the most ...
[47]
Late Pleistocene giant short‐faced bears, mammoths, and large ...
Jul 20, 2009 · Based on comparisons with the feeding behavior and bone alteration patterns of extant hyenas, cats, wolves, and bears, we conclude that at least ...Missing: impact | Show results with:impact
[48]
On the Association of Giant Short-Faced Bear (Arctodus simus) and ...
Aug 6, 2025 · Climate change and human impacts are often implicated in Quaternary megafaunal extinctions. The discovery of associated remains of extinct ...
[49]
Late Pleistocene megafauna extinction leads to missing pieces of ...
Sep 19, 2022 · We hypothesized that loss of large-bodied mammals at the terminal Pleistocene profoundly altered the ecology of surviving mammals, disrupting ...
[50]
[PDF] Locomotor Adaptations and Ecomorphology of Short-Faced Bears in ...
Arctodus and other bears using the width:length ratio. (W/L) of the ... 1 IMI = humerus length + radius length / femur length + tibia length x 100. 2 ...
[51]
[PDF] Selection of Trees Marked by Rubbing by Andean Bears in the ...
Several of the trees had scratch marks on branches over 3 m from the ground, suggesting that the bears might climb trees to leave marks. (Figure 8). The broken ...Missing: semi- | Show results with:semi-
[52]
[PDF] Spectacled Bear Conservation Action Plan - El Bosque Protector
Spectacled bears are able to climb vines and understory trees with diameters equal to that of their front paws in order to reach fruit in trees with diameters ...
[53]
[PDF] Andean-Bear-Rehabilitation-Guidelines-1.pdf
arboreal in nature. They are agile climbers, and are able to climb not only trees but also vertical rock walls. (Fig. 5). They are very good swimmers, and ...
[54]
Ecomorphology of the giant short-faced bears Agriotherium and ...
Aug 6, 2025 · The hypothesis that giant short-faced bears of the genera Agriotherium and Arctodus were primarily carnivorous and preyed on large terrestrial mammals is ...
[55]
[PDF] LIBRO DE RESÚMENES - Asociación Paleontológica Argentina
Nov 27, 2024 · cranio-mandibular features of Mylodontinae, postcranial features of Lestodontinae, and distinctive ... femoral length of ~1300 cm and a body mass ...
[56]
(PDF) Tremarctos ornatus (Carnivora: Ursidae) - ResearchGate
Aug 9, 2025 · Tremarctos ornatus (FG Cuvier, 1825) is a tremarctine bear commonly known as the Andean bear. It is a medium-sized bear with black to dark red-brown pelage.Missing: vaulted | Show results with:vaulted
[57]
IUCN Red List of Threatened Species
Current population trend · Number of mature individuals · Population severely fragmented · Continuing decline of mature individuals.
[58]
Spectacled Bear - The Animal Files
Males are usually 30 - 40% larger than females. They have thick, brown/black fur and cream coloured markings on their muzzle, throat, chest and around their ...<|separator|>
[59]
(PDF) Andean Bear ( Tremarctos ornatus ) - ResearchGate
Andean bears, Tremarctos ornatus (Cuvier, 1825), are medium-sized ursids with rounded heads and ears, and short necks and snouts. Their head-body length is ...Missing: broader | Show results with:broader
[60]
Meet the Spectacled Bear: South America's Only Bear
Jun 5, 2025 · This figure illustrates the historical and current distribution of three representative genera within the subfamily Tremarctinae: Plionarctos, ...Missing: taxonomy | Show results with:taxonomy
[61]
Tremarctos ornatus (spectacled bear) - Animal Diversity Web
Tremarctos ornatus is the only species of bear native to South America. It can be found throughout mountainous regions of the Andes in Ecuador, Colombia, ...Missing: vaulted bones
[62]
Andean (Spectacled) Bear | San Diego Zoo Animals & Plants
Andean bears are true arboreal bears, using their long, sharp front claws to climb and forage for food. They sometimes build leafy platforms in trees where ...
[63]
Effects of the Ecuadorian Andes on genetic structure of the ... - Nature
Sep 24, 2025 · Spectacled bears are short-faced, with an adult weight ranging from 30 to 200 kg and body length from 0.88 to 2.22 m with adult females, being a ...Missing: dimorphism | Show results with:dimorphism
[64]
Evidence of population genetic structure in Ecuadorian Andean bears
Feb 3, 2024 · We found a moderate genetic diversity in the analyzed populations (Table 3) with an overall expected heterozygosity (He) of 0.60 and an average ...Missing: phylogeographic dimorphism
[65]
The IUCN Red List of Threatened Species
**Summary:**
[66]
Andean Bears - WCS.org
In recent decades, deforestation has caused a dramatic decline in Andean bear populations, and estimates suggest fewer than 18,000 bears now survive in the wild ...
[67]
Andean Bear Research and Action: Home
Research and Action in the Andean Bear Corridor. Deforestation rates in the Andes, where Andean (Spectacled) Bears live, are among the highest on the planet ...
[68]
Making Andean Bears a Priority in Peru - Conservation Nation
Threatened by habitat destruction, human conflict, and poaching for the illegal wildlife trade, it is estimated that around 200 Andean bears are killed by ...Missing: annually | Show results with:annually
[69]
Poaching threatens South America's only bear species
May 31, 2019 · Poaching threatens South America's only bear species. Shamans peddle the teeth, fat, and penis bones of this protected species. ByEduardo ...``i Got Everything'' · The Miraculous Cream · Enforcing The Law, Reducing...<|control11|><|separator|>
[70]
Spectacled Bear - CITES
Common name: Spectacled bear, Andean bear. Scientific name: Tremarctos ornatus. Distribution: South America CITES listing: Appendix I (01/07/1975)
[71]
[PDF] Andean Bear SAFE - Assets Service
The primary goal of the Andean Bear SAFE Program and this program plan is to support conservation of Andean bears by executing and directly supporting strategic.
[72]
Predictive Modelling of Current and Future Potential Distribution of ...
The spectacled, or Andean, bear (Tremarctos ornatus) is classified as vulnerable by the IUCN due to climate change and human-induced habitat fragmentation.
[73]
Spectacled bear conservation and dispersal corridors in Venezuela.
Aug 8, 2025 · Cordillera de Mérida, with 13,348 km2 of total forest area, is fragmented into 4 blocks where bear populations are threatened and likely to lose ...