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Post by brobear on Oct 4, 2018 15:55:19 GMT -5
CONTINUED.... 4. Results 4.1. Systematic paleontology Bone specimens are five fragments of a cranium and one partial humerus assigned to the giant short-faced bear Arctodus simus (Fig. 2), and a partial femur, the distal portion of a humerus and the humerus of an immature individual assigned to the brown bear Ursus arctos (Fig. 3).
Class Mammalia Linnaeus, 1758
Order Carnivora Bowdich, 1821
Family Ursidae Gray, 1825
Subfamily Tremarctinae Merriam and Stock, 1925
Genus ArctodusLeidy, 1854
Arctodus simus (Cope, 1879)
Fig. 2
Synonymy: 1879. Arctotherium simum nov. sp. - Cope, p. 791; Cope, 1891, Plate XXI.
1911. Arctotherium californicum nov. sp. - Merriam, 1911, p. 164, figs. 1–3. 1911. Arctotherium yukonense nov. sp. - Lambe, 1911, p. 21, pt. 1–3.
1916. Dinarctotherium merriami nov. sp. - Barbour, 1916, p. 349, pt. 26, figs. 1–6.
Material: Partial cranium with most of the right maxilla in several fragments PC2-1a, b, c; palatine fragment PC2-1d; partial left humerus PC2-3.
Description: The PC2-1a (Fig. 2(2); Table 2) specimen is a right maxilla including the right upper fourth premolar to the right upper second molar (P4-M2). The teeth are well preserved. However, there is damage to the root of the M2, the posterior root of M1, the paracone and metacone, and to the enamel on the labial margin of P4. The P4 of the PC2-1a specimen shows evidence of dental caries, and is broken as to not retain a complete shearing attribute. We assign PC2-1a to A. simus based on the shape and size of the P4, M1, and M2, a partial sheering attribute in P4, as well as the high degree of crowding in the tooth row. The Pellucidar specimen is from a young adult according to degree of wear on the occlusal surfaces of the teeth, and is from a relatively small individual – possibly female – that compares well with A. simus from Potter Creek Cave, California (Kurtén, 1967). Arctodus simus, Pellucidar Cave Arctodus simus, Pleistocene Tooth Measurement RBCM PC2–1a Mean Range (N) SD I1 Greatest transverse diameter 8.26 9.0 8.8–9.2 (5) 0.1 Transverse diameter of alveolus 6.5 I2 Transverse diameter of alveolus 7.8 I3 Transverse diameter of alveolus 13.5 C1 Tranverse diameter of alveolus 30.2 P1 Transverse diameter of alveolus 7.6 P4–M2 Anterioposterior diameter 79.1 82.32 76.0–87.9 (11) a P4 Anteroposterior diameter 22.1 22.01 19.4–25.7 (33) a Greatest transverse diameter – 16.37 14.3–18.9 (32) a M1 Anteroposterior diameter 25.4 25.74 23.2–28.3 (44) Greatest transverse diameter (anterior width) 22.7 24.4 19.8–26.3 (44) a M2 Anteroposterior diameter 36.24 37.39 33.3–42.9 (42) a Greatest transverse diameter (anterior width) 23 23.68 20.8–26.6 (42)
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Post by brobear on Oct 4, 2018 15:56:16 GMT -5
CONTINUED... Cranial fragments PC2-1a-d (Fig. 2(1-4); Table 2) were found together in contact at the fossil locality and are from the same A. simus individual. Fragment PC2-1b (Fig. 2(1)) includes an anterior portion of the maxilla, part of the palatine process with anterior palatine foramen, and a portion of the premaxilla including alveoli for the relatively large upper third incisor and progressively smaller I2 and I1 that, other than damaged margins, are nearly complete. Posterior to the canine alveolus are three small premolar alveoli of which the first premolar is the largest. The maxillary-premaxillary suture is visible at the anterior margin of C1 and most of the right transverse palatine suture is preserved. According to the best-fit in the alveoli of the Pellucidar cranial fragments, specimen PC2-1d (Fig. 2(3)) is a lightly worn right I1. Specimen PC2-1c (Fig. 2(4)) is a partial palatine bone with a mid-palatine suture that runs posteriorly from the partially preserved incisive foramen.
Cranial fragment PC2-7 (Fig. 2(6)) is the partial left temporal bone with portions of the adjoining parietal and sphenoid bones of the A. simus individual. Skull shape distinguishes Arctodus from Ursus (Kurtén, 1967, Merriam and Stock, 1925). One aspect of this difference is the relative positioning of the numerous foramina on the ventral surface of the cranium, as these openings on the sphenoid are relatively more crowded in A. simus than in Ursus species. In specimen PC2-7 the position of the optic canal, superior orbital fissure, foramen rotundum, and foramen ovale are crowded as in A. simus, and based on this characteristic the specimen studied here is assignable to this species. The fragment has crushed bone surfaces and edges and shows an elongate tooth impression. PC2-3 (Fig. 2(5); Table 3) is a distal portion of a humerus that is assigned to A. simus based on the presence of an entepicondylar foramen and large size (Kurtén and Anderson, 1980). Measurements of the PC2-3 entepicondylar foramen and the piece of bone covering the foramen were found to differentiate the fossil specimen from those of modern black bears (Table 3). The break near midshaft, possibly made on fresh bone by a relatively strong impact, is a spiral fracture. The distal epiphysis of this bone specimen is absent and the articular surface is damaged and irregular, making it difficult to determine if the epiphysis was fused at the time of death of the animal.
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Post by brobear on Oct 4, 2018 15:57:40 GMT -5
Pellucidar Cave Arctodus simus, Potter Creek Cave Ursus americanus, Modern Measurement PC2-3 Mean Range (N) SD Mean Range (N) SD Transverse diameter of the diaphysis at midshaft 36.8 39.2 35.1–41.7 (4) 2.9 28.84 24.1–32.59 (3) 4.33 Maximum mediolateral diameter at superior margin of entepicondylar foramen 66.0 64.8 66.1–63.5 (2) 64.8 48.4 39.5–52.9 (3) 7.7 Minimum anterolateral diameter at superior margin of entepicondylar foramen 34.0 36.6 33.1–38.9 (4) 2.5 24.5 19.1–28 (3) 4.7 Anterior length of slip of bone covering the entepicondylar foramen 32.5 32.6 26.5–37.6 (4) 4.6 15.9 15.4–16.6 (3) 0.61 Width at middle of slip of bone covering the entepicondylar foramen 11.7 13.3 11–15 (4) 1.7 6.4 4.7–8.2 (3) 1.8 Thickness at middle of the slip of bone covering entepicondylar foramen 5.3 5.7 5.1–6.2 (4) 0.5 3.9 2.9–4.5 (3) 0.9 Remarks: Osteological characters that differentiate the fossil remains of Tremarctine and Ursinae bears – the two bear subfamilies indigenous to North America – include an extra lateral cusp between the trigonid and talonid on the m1, and a premasseteric fossa on the mandible in the former. Although not limited to Arctodus, an entepicondylar foramen on the humerus along with large size can be useful in differentiating these bears from Ursus (Merriam and Stock, 1925, Kurtén and Anderson, 1980). The maxillary teeth of Arctodus are distinguished from those of Ursus based on the protocone in P4 at a more anterior position than in Ursus, in the presence of an enamel ridge that extends between the apices of the paracone and metacone forming a shearing blade on P4, and by molars that are relatively short and broad in Arctodus (Merriam and Stock, 1925, Kurtén, 1967). Larger, wider, and more crowded teeth, as well as molar proportions differentiate A. simus from A. pristinus (Kurtén, 1967, Kurtén and Anderson, 1980, Emslie, 1995, Schubert et al., 2010). Because A. pristinus is restricted in time to no later than the middle Pleistocene (Emslie, 1995, Schubert et al., 2010), and to a geographic range in eastern North America (Kurtén, 1967) and Central Mexico (Dalquest and Mooser, 1980), we regard the Arctodus specimens described above as too young and too distant from the geographic range of A. pristinus to be assignable to that species.
Subfamily Ursinae G. Fisher, 1817
Genus UrsusLinnaeus, 1758 Ursus arctosLinnaeus, 1758
(Figs. 3.1–3.3)
Synonymy: Numerous species and subspecies have been assigned to this Holarctic bear (Pasitschniak-Arts, 1993); synonyms for this species are extensive and are not repeated here (Wilson and Reeder, 2005).
Material: The proximal half of a left humerus (PC2-11); a right humerus (PC2-13); a left femur (PC2-2).
Description: PC2-11 (Fig. 3(1); Table 4) is the proximal half of a left humerus. Features used to characterize this bone are the proximal portion of the deltoid ridge, a posterior portion of the intertuberal grove, and the teres eminence that appear prominently in this specimen as in Ursus (Merriam and Stock, 1925). Midshaft width and midshaft depth of the PC2-11 specimen are within the size range of adult brown bears, being both slightly larger than black bear and smaller than giant short-faced bear comparative material (Table 4). Ancient DNA analysis provides additional confirmation of the identification of this specimen as U. arctos. Carnivore tooth impressions are present on the shaft and humoral head.
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Post by brobear on Oct 4, 2018 15:58:32 GMT -5
Ursus arctos, Pellucidar Cave Ursus arctos, Modern Ursus americanus, Modern Arctodus simus, Pleistocene Measurement PC2-11 Mean Range (N) SD Mean Range (N) SD Mean Range (N) SD Greatest length of complete specimens – 352.4 287–450 (14) 45.9 286.8 247–324 (18) 24.4 484.4 436–633a (13) – Transverse diameter at the middle of the diaphysis 33.8 35.4 25.3–51.3 (17) 7.2 27.6 20–33.1 (22) 3.9 39.7 35.1–41.9 (4) 3.2 Anterioposterior diameter at the middle of the diaphysis 37.8 39 29.7–50.8 (17) 6.5 28.9 23.3–35.4 (22) 3.8 47.8 43.1–54 (4) 4.5 Measurement from Richards et al. (1996), (Appendix B); —: not available.
Specimen PC2-13 (Fig. 3(2); Table 5) is the right humerus of an immature bear. The proximal epiphysis of the humerus was not fused, as the proximal surface of the shaft shows signs of erosion. Suture lines are visible on the distal epiphysis. Prominent deltoid and supinator ridges and the absence of an entepicondylar foramen are features of this specimen consistent with Ursus (Merriam and Stock, 1925). The size of the PC2-13 specimen was compared with modern brown and black bears that have unfused proximal and fused distal epiphyses as in the Pellucidar specimen. Of four measurements, only the minimum distal depth at trochlea provided a clear indication of the species (Table 5). Ancient DNA analysis on the PC2-13 bone confirmed the identity of this specimen.
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Post by brobear on Oct 4, 2018 16:00:45 GMT -5
Ursus arctos, Pellucidar Cave Ursus arctos, Modern Ursus americanus, Modern Measurement PC2-13 Mean Range (N) SD Mean Range (N) SD Minimum length of shaft from base of proximal articular surface to the capitulum 235.0 229.0 176–255 (5) 26.0 241.0 222–257 (9) 13.0 Minimum transeverse diameter of the diaphysis 21.5 24.27 18.3–27.24 (5) 3.45 23.52 18.16–27.47 (9) 2.79 Minimum anterioposterior diameter of the diaphysis 21.5 28.28 17.5–35.75 (5) 6.9 24.23 21.63–28.96 (8) 2.16 Minimum distal depth at trochlea 22.0 22.7 19.4–26.6 (5) 2.5 19.1 16.75–21.3 (9) The left femur PC2-2 (Fig. 3(3); Table 6) is lacking the head and greater trochanter and shows damage at the distal end, particularly to the medial and lateral epicondyles. The specimen shows a strong medial ridge that extends proximally from above the medial condyle and does not appear rounded anteriorly, features consistent with Ursus (Merriam and Stock, 1925). In addition to these surface features, we assign this specimen to U. arctos based on three of four measurements on the PC2-2 femur that are consistent with adult brown bear. Only the minimum transverse diameter of the diaphysis overlaps with modern black bears in our sample (Table 6). The PC2-2 identification as U. arctos is additionally confirmed with genetic analysis.
Table 6. Comparative measurements (in mm) of bear femur PC2-2 from Pellucidar Cave with Modern Ursus arctos and U. americanus and Pleistocene Arctodus simus femora. Ursus arctos, Pellucidar Cave Ursus arctos, Modern Ursus americanus, Modern Arctodus simus, Pleistocene Measurement PC2-2 Mean Range (N) SD Mean Range (N) SD Mean Range (N) SD Greatest length of complete specimens – 418.0 352–534 (10) 61.0 324.0 282–381 (14) 27.0 558.1 490–723a (14) – Minimum length from trochanteric fossa to the intercondylar fossa 358.0 351.0 306–446 (14) 37.4 284.0 243–336 (15) 26.0 440.0 440 (aprox.) – Greatest breadth at proximal end – 107.73 83.6–124.4 (10) 19.7 76.4 73.5–88 (14) 7.0 126.5 122b–131b 6.4 Minimum transverse diameter of the diaphysis 32.2 37.4 27.7–52.2 (14) 6.4 27.5 23.4–32.7 (15) 3.2 43.2 42.2–44.1b (3) – Minimum anterioposterior diameter of the diaphysis 27.8 29.5 24.1–38.8 (14) 4.6 21.7 18.8–25 (15) 2.0 33.8 32.7–35 1.6 Greatest breadth of the distal end – 88.6 73.4–113 (10) 13.1 62.0 55.8–69 (14) 5.0 117.7 99–152a (14) – Minimum depth at centre of distal articular surface 45.7 47.4 39.9–62.1 (14) 6.2 36.9 33.3–42.9 (15) 3.1 52.3 47.4–55.6 (3) – 4.2. Radiocarbon results Six AMS radiocarbon age estimates and calibrated age ranges on the Pellucidar Cave bear specimens are shown in Table 1. Age estimates on brown bear (U. arctos) specimens are: • Left humerus PC2-11: 12,440 ± 35 BP = 14,888–14,239 cal. BP (UCIAMS 41051);
• Femur PC2-2: 12,425 ± 35 BP = 14,836–14,211 cal. BP (UCIAMS 41050);
• Right humerus PC2-13: 11,110 ± 30 BP = 13,082–12,845 cal. BP (UCIAMS 41052).
Age estimates on giant short-faced bear (A. simus) specimens are: • M2 PC2-1a: 11,720 ± 50 BP = 13,715–13,440 cal. BP (OxA 24005);
• Humerus PC2-3: 11,775 ± 30 BP = 13,725–13,477 cal. BP (UCIAMS 41048);
• Palatine PC2-1c: 11,615 ± 30 BP = 13,557–13,379 cal. BP (UCIAMS 41049). The giant short-faced bear M2 and Humerus age estimates are statistically the same at the 95% confidence level, as are age estimates for the palatine and M2. The palatine is statistically significantly younger than that of the humerus, although statistical similarity in the ages of the humerus and M2, and the palatine and M2, along with the lack of duplication of bone elements, similar ontogeny, color, condition of preservation, and proximity of these bone specimens at the fossil site suggest only one individual is present. Combined age estimates for the three giant short-faced bear specimens give a calibrated age range of 13,572–13,458 cal. BP with a median age of 13,517 cal. BP. We also report one AMS age estimate on an Ursus americanus partial cranium from northern Vancouver Island that gave an age estimate of 11,935 ± 40 BP = 13,964–13,575 cal. BP (SC-1; UCIAMS 56479).
4.3. Ancient DNA analysis Genetic analyses confirmed the assignment of specimens PC2-2, PC2-11 and PC2-13 as brown bear Ursus arctos. The DNA sequences for these specimens are 99% the same over the short region tested and match sequences from two different Canadian brown bear specimens available in GenBank: AF303110 (Delisle and Strobeck, 2002) and HE657204 (Hailer et al., 2012). For comparison, if the BLAST search was forced against the black bear Ursus americanusPallas, 1780, PC2-13 was only 84% similar. Phylogenetic analysis strongly supports the Pellucidar Cave brown bear as belonging to Clade 4 (Bayesian posterior probability = 0.90; Fig. 4), with all southern Canadian and continental U.S.A. brown bears. We recover a time to most common ancestor for this clade to be ∼56 ka BP (95% confidence interval: 36.0–88.6 ka BP). The common ancestor of the Pellucidar Cave individuals is estimated to be ∼25.4 ka BP (13.9–36.6 ka BP; Fig. 4).
No genetic identification could be made for the giant short-faced bear specimen PC2-3. Cloning of the only PCR amplification that could be achieved resulted in a variety of bacterial sequences, indicating that there is likely no surviving DNA in this fossil specimen.
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Post by brobear on Oct 4, 2018 16:02:16 GMT -5
NOTE: THIS is INTERESTING...
5. Discussion 5.1. Identification and genetic analysis Differentiating species of bears with bone specimens from North American contexts can be challenging. Although there are morphological characters that separate Ursus from Arctodus (Merriam and Stock, 1925, Kurtén, 1967, Kurtén and Anderson, 1980), measurements in this study and others (Christiansen, 1999) show that differentiating these bears is not always possible based on size alone. Similarly, modern brown bears are generally larger than black bears, though size does not separate these bears completely. Identifying fossils of these ursid species is additionally confounded by the larger body size of Pleistocene than modern black bears, as noted by Kurtén and Anderson (1980) and as further examined by others (Gordon, 1986, Nagorsen et al., 1995, Graham, 1991, Wolverton and Lyman, 1998).
When morphological characteristics and measurements of fossil specimens do not differentiate bears to the species level, the use of genetic techniques on bones can be beneficial. Genetic analyses may be particularly useful for identifying well-preserved specimens from late Pleistocene sites in the contiguous U.S.A., where the possibility of misattributed bear fossils appears to be more acute now that brown bears are known to have migrated south to the contiguous U.S.A. from Eastern Beringia (Matheus et al., 2004, Davison et al., 2011) before the LGM (Clark et al., 2009), where only giant short-faced and black bears were previously thought to occur (Kurtén and Anderson, 1980).
Genetic analyses on fossil specimens can also reveal biological and biogeographic relationships within a species. Our genetic results on brown bears from Vancouver Island place them in Clade 4 with the North American brown bears that last appear in Alaska around 36 ka BP, which is consistent with the migration of the species southward from Beringia prior to the LGM. All three Pellucidar specimens fall within the mitochondrial genetic diversity of extant brown bears from southern Canada and the contiguous U.S.A., differing from those Clade 3b individuals found to the north and in central B.C. The brown bear remains from Pellucidar Cave belonged to populations that entered the contiguous U.S.A. before the LGM and moved to Vancouver Island from the east or south and not from the north along the coast.
5.2. Co-occurrences of A. simus and U. arctos Radiocarbon results comparing brown and giant short-faced bears in Pellucidar Cave present an interesting perspective on the two species.
Based on an association of giant short-faced bears and brown bears at Little Box Elder Cave, Wyoming, Kurtén and Anderson (1974) proposed that giant short-faced bears may have been out-competed by brown bears as the latter expanded from eastern Beringia southward. Bones of both species have now also been reported from Alaska before ∼34 ka BP (Kurtén and Anderson, 1980, Matheus, 1995, Barnes et al., 2002, Harington, 2003, Matheus et al., 2004); in later Pleistocene deposits at Maricopa, California (Lundelius et al., 1983, Jefferson, 1991); and in Labor-of-Love Cave, Nevada (Emslie and Czaplewski, 1985). These data suggest that at times prior to the extinction of giant short-faced bears the two species occurred in overlapping geographic areas as brown bears spread throughout North America.
At Pellucidar Cave, age estimates on giant short-faced bear specimens indicate the species’ presence on Vancouver Island at ∼11.7 ka BP (∼13.5 cal. ka BP). Brown bear specimens from the same cave date to soon before (12,440 ± 35, 12,425 ± 30 BP; ∼14.5 cal. ka BP) and after this age (11,100 ± 30 BP; ∼13 cal. ka BP), but without temporal overlap with giant short-faced bears. An age estimate of 12,370 ± 35 BP (∼14.39 cal. ka BP; Steffen, 2016) on brown bear from the nearby Arch-2 Cave is consistent with the earliest brown bears from Pellucidar Cave. The individuals of the two species tested here did not live in the same cave at the same time. However, as few as 300–500 calendar years separate them, supporting that both species were present in the Vancouver Island area during the latest Pleistocene.
Although it is difficult to say for certain based on the available fossil record, the non-overlapping occurrences of brown and short-faced bears at Pellucidar Cave could be interpreted as niche partitioning to reduce territorial competition in these sympatric species.
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Post by brobear on Oct 4, 2018 16:10:15 GMT -5
5.3. Bone damage Several of the Pellucidar bone specimens show damage consistent with carnivore gnawing (Fig. 2, Fig. 3). G. Haynes (1983) differentiated gnawing damage to ungulate limb bones by extant large mammalian carnivores. He observed that tooth markings in trabecular bone, which often are most visible near long bone ends, typically are flat and square or rectangular when produced by bears, cone or truncated cone in canids and hyenas, and elongate V-shape in felids (G. Haynes, 1983: table 3). Although A. simus has carnassials with pointed cusps and sheering attributes so that tooth impressions from these bears can be expected to differ from those of extant ursine bears, no differences may be apparent in bears with worn or broken dentition. Based on these criteria, gnawing damage to the Pellucidar specimens is consistent with that of bears, the only confirmed large terrestrial carnivores on Vancouver Island during the late Pleistocene. A tooth impression on giant short-faced bear cranial fragment PC2-7 (Fig. 2(6)) is rectangular to oval in shape, and ∼19 mm long by ∼9 mm wide. The impression displays cusp marks consistent with the protoconid and the hypoconid on the trigonid and talonid of a bear m1, and could be from Ursus or Arctodus. Gnawing impressions on the head of the brown bear humerus (PC2-11; Fig. 3(1)) are flat-bottomed and up to 20 mm wide, indicating bears as a possible source of this damage. The condition of the epicondyles, greater trochanter and head of the brown bear femur (PC2-2; Fig. 3(3)) are also consistent with damage by bears. Irregular edges of the giant short-faced bear cranial fragments PC2-1 (Fig. 2(1, 2, 4)) and the distal end of humerus PC2-3 (Fig. 2(5)) may have resulted from carnivore gnawing, although there are no clear isolated tooth impressions on these specimens and breakage could have resulted from other sources such as crushing by roof fall. Spiral fracturing of distal humerus PC2-3 and the mid-shaft transverse/oblique break on PC2-11 occurred before substantial bone weathering (Behrensmeyer, 1978). The moist and cool environment in the cave may have delayed drying and cracking of bones such that these fractures could have occurred some time after the death of these animals.
Because giant short-faced bears have often been regarded as active agents in bone destruction (Kurtén, 1967, Guthrie, 1988, Voorhies and Corner, 1986, Gillette and Madsen, 1992) that break bones more readily than would typically be expected of extant bears (G. Haynes, 1983), it is conceivable that giant short-faced bears were a source of bone damage in this assemblage. Further, the non-contemporaneity of Ursus and Arctodus at the Pellucidar locality along with damage on the bones of both bears allows that this damage could have resulted from the same bear species as the specimen. With available information, however, it is impossible to determine which bear or bears might have been the source.
5.4. Fauna and vegetation Faunal and vegetation changes that occurred around the end of the Pleistocene are likely factors in the extirpation of giant short-faced bears from Vancouver Island. When these bears were on south Vancouver Island ∼27.1 cal. ka BP (22,750 ± 140 BP) they occupied a high trophic level in an open vegetation regime (Steffen and Harington, 2010) along with other large mammals (Harington, 1975) such as the mammoth Mammuthus columbi (including M. imperator) Falconer, 1857, mastodon Mammut americanumKerr, 1792, and helmeted muskox Bootherium bombifronsHarlan, 1825. During the final stages of glaciation along coastal B.C., ice sheets grew to their maximum extent across much of Vancouver Island at ∼17.4 cal. ka BP (14.5 ka BP), and then retreated rapidly (Porter and Swanson, 1998, Clague and James, 2002). Giant short-faced bears reinvaded Vancouver Island with a more modern fauna that included bison Bison antiquus (Leidy, 1852, Harington, 1975, Wilson et al., 2009) on southern Vancouver Island, as well as mountain goat Oreamnos americanusde Blainville, 1816 (Nagorsen and Keddie, 2000, Al-Suwaidi et al., 2006), brown bear (Steffen, 2016), and black bear (11,935 ± 40 BP, ∼13.76 cal. ka BP; UCIAMS 56479) on northern Vancouver Island. Of these large mammals, only the black bear remained on the island through the Holocene. Vegetation shifts at the end of the Pleistocene may have been unfavorable for giant short-faced bears. Coincident with the ∼13.5 cal. ka BP (∼11.7 ka BP) age of the giant short-faced bear remains, vegetation changed rapidly from open woodlands with abundant lodgepole pine Pinus contorta to increasingly closed forests with shade-tolerant spruce Picea, mountain hemlock Tsuga mertensiana, and red alder Alnus rubra. Increases in lodgepole pine, green alder A. crispa, and mountain hemlock ∼12.6 to ∼12.3 cal. ka BP (∼10.6 to ∼10.4 ka BP) point toward cool and moist conditions during the Younger Dryas stadial (Mathewes, 1993, Lacourse, 2005). Closed forests expanded into the early Holocene with western hemlock Tsuga heterophylla becoming dominant (Lacourse, 2005). The extirpation of many large mammals from Vancouver Island along with the vegetation shift to a closed forest regime at the end of the Pleistocene likely contributed to the local extirpation of giant short-faced bears by reducing the amount or quality of forage for its subsistence.
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Post by brobear on Oct 4, 2018 16:11:30 GMT -5
5.5. Diet and ecology The ecology of giant short-faced bears informs their occurrence at the fossil locality. Typically characterized as an open adapted species (Kurtén and Anderson, 1980, Harington, 1973, Matheus, 2003, Churcher et al., 1993, Richards et al., 1996), the distribution of giant short-faced bears indicates its occupation of diverse settings (Schubert et al., 2010). Even though these bears were not restricted to open areas and could occur in different environments, the timing of the regional shift from an open pine woodland habitat to a densely forested vegetation regime with the occurrence of the giant short-faced bear remains at Pellucidar Cave implies that these vegetation changes contributed to the local extirpation of this species.
Giant short-faced bears have been characterized on morphological grounds as carnivorous and possibly active predators (Kurtén, 1967, Harington, 1996, Kurtén and Anderson, 1980, Voorhies and Corner, 1986, Agenbroad, 1990, Guthrie, 1988, Gillette and Madsen, 1992, Churcher et al., 1993, Richards et al., 1996). These bears have also been described as strict scavengers with functional morphology suited to long-distance procurement of carcasses (Matheus, 2003), and as omnivorous (Baryshnikov et al., 1994, Sorkin, 2006) with flexible diets that varied according to resource availability similar to extant brown bears (Figueirido et al., 2010). The perspectives have also been offered by comparison with its closest living relative the South American spectacled bear Tremarctos ornatusGervais, 1855, that giant short-faced bears had omnivorous diets based on dental wear (Donohue et al., 2013), and mainly vegetation diets based on morphological similarities (Emslie and Czaplewiski, 1985; Meloro, 2011). Overall, recent literature provides little evidence that giant short-faced bears were primarily active carnivores or strictly vegetarian, and instead indicates that these bears were omnivores with scavenging tendencies.
Though giant short-faced bear diets may have varied regionally and through time, regular consumption of animal matter by these bears is supported by the presence of carnassial teeth with sheering attributes and a low jaw condyle relative to the tooth row (Kurtén, 1967, Voorhies and Corner, 1986). Meat consumption is confirmed by elevated δ13C and δ15N values in numerous late Pleistocene giant short-faced bear specimens from the northern part of their range, where these bears may have competed for food but usually occupied a higher trophic level compared with invading brown bears (Bocherens et al., 1995, Matheus, 1995, Barnes et al., 2002, Fox-Dobbs et al., 2008). That giant short-faced bears may have excluded brown bears from Eastern Beringia from ∼34 to ∼20 ka BP further suggests these large bears may typically have been dominant over brown bears.
Competition amongst bears may have increased as food resources shifted at the end of the Pleistocene, as our age estimates suggest giant short-faced bears temporarily displaced brown bears from the Pelludicar Cave area. As glaciers receded from this region at the end of the Pleistocene there may have been a relatively brief time when environmental conditions met the habitat and dietary requirements of giant short-faced bears. These requirements are likely to have included the existence of sufficient animal matter for subsistence as scavenged carcasses and possibly as prey. Giant short-faced bears could range widely for available forage (Kurtén, 1967, Matheus, 2001) and may have occupied and then left post-glacial Vancouver Island with the boom-and-bust availability of preferred habitat and foods as faunal turnover resulted in available carrion. When closed forests encroached and large meat packages dwindled, giant short-faced bears declined and brown bears recurred. Post-glacial shifts in available resources may also have promoted the eventual extirpation of brown bears from the island, though, unlike giant short-faced bears, brown bears persisted in adjacent areas (Mustoe et al., 2005). Greater dietary and habitat plasticity (Kurtén, 1967, Matheus, 1995) could have facilitated the persistence of brown bears and not of giant short-faced bears as environments changed abruptly toward the Holocene in this region.
On a continent-wide scale our perspective from Pellucidar Cave offers that brown and short-faced bears were sympatric at times as brown bears spread through North America. Our data and others support that giant short-faced bears may typically have dominated competitive interactions, particularly when their populations were robust, and displaced brown bears from specific localities. We suggest that at the end of the Pleistocene one reason brown bears persisted where giant short-faced bears died off is because giant short-faced bears may have been less flexible in adapting to new and rapidly changing environments that impacted the availability or quality of food and possibly habitat. Future studies of the trophic interactions of these bear species may show if competition is likely to have contributed to the changing availability of food resources for giant short-faced bears.
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Post by brobear on Oct 4, 2018 16:23:32 GMT -5
5.6. Implications for early people in the Americas Occurrences of brown and short-faced bears on Vancouver Island have implications for early human occupation. The timing and routes of early people in the Americas are enduring archaeological questions. Unequivocal archaeological evidence from Monte Verde in Chile dated to ∼15 cal. ka BP (∼12.5 ka BP; Dillehay, 1997) as well as from Swan Point in central Alaska, and a handful of other early archaeological sites indicate that people had colonized North and South America by ∼15–14 cal. ka BP (Yesner, 2001, Madsen, 2004, Madsen, 2015, Goebel et al., 2008, Meltzer, 2009). Recent radiocarbon age estimates on cut-marked bones from Bluefish Caves in the Yukon Territory show a human presence as early as 24,000 cal. BP (19,650 ± 130 14C BP; Bourgeon et al., 2017). An earlier find of a flaked mammoth bone radiocarbon dated to 24,000 BP has also been described from Bluefish Caves (Harington and Cinq-Mars, 2008). Together these data support a Beringian standstill hypothesis that suggests a small human population became isolated in Eastern Beringia and dispersed southward near the end of the LGM (Tamm et al., 2007, Mulligan et al., 2008, Raghavan et al., 2015, Llamas et al., 2016). Peak glacial conditions and a coalescence of the Cordilleran and Laurentide ice sheets east of the Rocky Mountain Range from approximately 24 to 14 cal. ka BP (∼20 and ∼12 ka BP) is likely to have provided no passageway for humans between eastern Beringia and the contiguous U.S.A. (Clague et al., 2004, Dyke, 2004, Pedersen et al., 2016). Coastlines west of the Cordilleran Ice Sheet in Southeast Alaska and B.C. were deglaciated before 15 cal. ka BP, included glacial refugia, and could have been a way that people dispersed southward (Heusser, 1960, Fladmark, 1979, Werner et al., 1982, Luternauer et al., 1989, Josenhans et al., 1995, Hebda et al., 1997, Barrie and Conway, 1999, Byun et al., 1999, Mandryk et al., 2001, Al-Suwaidi et al., 2006, Clague et al., 2004, Fedje and Mathewes, 2005, Carrara et al., 2007, Mackie et al., 2011, McLaren et al., 2014, Mathewes et al., 2015, Steffen, 2016). There has been much discussion about the timing and viability of the west coast refugium as a route for early people. The biological productivity of this region and the potential availability of food resources are part of these discussions.
The presence of large carnivores – brown and short-faced bears – indicates that the terrestrial environment of north Vancouver Island was a productive ecosystem between 14.7 and 12.95 cal. ka BP. Although people have abilities and technological capacities that can draw different affordances from environments than do bears, the presence of these carnivores indicates ecological conditions that could support people. Our data add to previous ages on large mammal fossils along the west coast, including mountain goat bones dated to 19.7 and 14.3 cal. ka BP (16,340 ± 60 BP and 12,340 ± 50 BP) that flank glacial sediments at Port Eliza Cave on the west coast of Vancouver Island (Al-Suwaidi et al., 2006), and brown bears dated to ∼17.5 and ∼13.1 cal. ka BP (14,390 ± 70 BP and 11,250 ± 70 BP) that indicate productive biological environments on Haida Gwaii (Mackie et al., 2011). Small mammals including deer mouse (Peromyscus; Gloger, 1841) and heather vole (Phenacomys; Merriam, 1889) were also present on post-glacial north Vancouver Island by ∼13.8 cal. ka BP (11,960 ± 45 BP; Steffen, 2016). The radiocarbon ages of the Vancouver Island bear specimens are additionally informative as they are older than the ages of large mammals documenting an ecologically productive corridor between the ice sheets after the LGM (Burns, 1996, Zazula et al., 2009), including age estimates on bison specimens dated to ∼13.4 cal. ka BP (∼11.5 ka BP) (Heintzman et al., 2016; see also Pedersen et al., 2016).
In addition to informing the availability of coastal landscapes for human occupation by nearly 15 ka BP, this study highlights the biogeographic passage of large terrestrial mammals south from Eastern Beringia before the LGM. Brown bears, woolly mammoths and steppe bison likely reached the southern refugium in the unglaciated U.S.A. during the mid-Wisconsin ice-free period. That route may have been feasible for humans as well (Harington, 2012), though the timing of these migrations may be too early to be directly relevant to human entry into the middle and southern latitude Americas (Goebel et al., 2008; but see Holen et al., 2017 for last interglacial age signs of people from southern California).
Humans moving into North America may have found large Pleistocene carnivores such as giant short-faced bears to be a barrier to gaining a foothold (Geist, 1989; but see Matheus, 2001). In addition to being the largest and most powerful carnivorous land mammals in North America, giant short-faced bears were capable of bursts of speed and had locomotor capabilities for obtaining distant subsistence resources (Harington, 1996, Matheus, 2003). Geist (1989) suggested that humans entering the Americas, though familiar with brown bears, would not have been able to effectively contend with the giant short-faced bear and other large Pleistocene carnivores, a situation that would have suppressed human population expansion. Geist's (1989) perspective, which explicitly refutes the notion of human supremacy in the ecology of Pleistocene North America and contrasts the hypothesis that large Pleistocene mammals were hunted to extinction as first peoples expanded through the continent (Martin, 1967), finds some support in the late Pleistocene record. Before the extinction of many Pleistocene mammals, people were thinly spread throughout the Americas with diverse archaeological lithic technologies including Clovis, Western Stemmed, and Fishtail traditions (Madsen, 2015). There is no strong evidence, however, that these people hunted large extinct Pleistocene carnivores, including no clear indication of direct human involvement in the extinction of giant short-faced bears (Faith and Surovell, 2009, Grayson and Meltzer, 2015: table 3). It is clear that people were at least occasionally involved in the death and/or butchery of several different large non-carnivorous Pleistocene mammals, particularly mammoths and mastodons (C.V. Haynes, 1964, Grayson and Meltzer, 2015), which may at times have put people in competition with giant short-faced bears for carcasses and possibly for prey. Defense against these large bears as well as abandonment of carcasses are plausible outcomes. Indeed, the relationship of people to giant short-faced bears is likely to have been uneasy at best.
Defining the causes of North American late Pleistocene extinctions has long been challenged by the need to separate the coincident occurrences of climate change and an expanding human presence, and of sorting out the consequences of these and other possible factors. Because the diversity of ecological responses to such factors in numerous extinct genera is potentially vast, we suggest seeking the effects that specific proximal causes may have had on such taxa in particular contexts leading up to extinction is a reasonable path toward understanding North American Quaternary extinctions as a whole. In this study, we examined the effects of competition with brown bears on giant short-faced bears in the context of vegetation and faunal change on Vancouver Island near the end of the Pleistocene. In doing so we hope to have contributed to this objective.
6. Conclusions We provided an account of the late Pleistocene distributions of brown bears and giant short-faced bears in western North America based on rare fossils of these bears from Vancouver Island, and we discussed these remains in terms of the competition hypothesis for the extinction of giant short-faced bears. A partial cranium and the distal portion of the shaft of a left humerus from the Pellucidar Cave fossil locality are referred to the giant short-faced bear Arctodus simus. Radiocarbon dates on these bones indicate that this species lived around the cave at ∼13.5 cal. ka BP. Part of a left humerus, a right humerus of an immature individual, and a left femur are referred to the brown bear Ursus arctos. Ancient DNA analysis indicates that brown bears residing on Vancouver Island near the end of the Pleistocene arrived from the east or south as they share ancestry with modern-day Clade 4 brown bears that are prominent in the contiguous U.S.A. but do not occur in B.C. north of the fossil site. Our radiocarbon ages indicate that brown bears lived at Pellucidar Cave at ∼14.5 cal. ka BP and ∼13 cal. ka BP. Together these radiocarbon ages suggest that competition was possible between brown and giant short-faced bears and may have resulted in niche partitioning for territory and cave use.
Post-glacial faunal and vegetation shifts changed the foraging options available to these large carnivores and are likely to have contributed to the arrival and the local extirpation of giant short-faced bears from Vancouver Island. A higher degree of dietary and habitat flexibility and possibly a comparatively smaller foraging radius than that of giant short-faced bears are likely to have facilitated brown bears persistence in the broader region into the Holocene. In terms of early human occupation in the Americas our study documents the existence of a robust ecosystem on north Vancouver Island that was available for human occupation, supporting the west coast as an option for early human occupation and migration.
Our paleontological and radiocarbon data on bear fossils from Pellucidar Cave together with the application of aDNA methods, as well as paleoecological and archaeological sources have provided some of the necessary details for defining how changes on the landscape, including competition with brown bears, may have affected giant short-faced bears leading up to their extinction. We show that changing species interactions can be considered in Pleistocene extinctions, and we highlight that rapid shifts in the availability or quality of food and habitat are likely to have been important in the extinction of giant short-faced bears.
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Post by brobear on Oct 4, 2018 16:34:23 GMT -5
KEY QUOTES from www.sciencedirect.com/science/article/pii/S0016699517300384 1 - Climate change and human impacts are often implicated in Quaternary megafaunal extinctions. The discovery of associated remains of extinct giant short-faced bears (Arctodus simus) and invading brown bears (Ursus arctos) raises the possibility of competition as another potential factor. 2 - Although it is difficult to say for certain based on the available fossil record, the non-overlapping occurrences of brown and short-faced bears at Pellucidar Cave could be interpreted as niche partitioning to reduce territorial competition in these sympatric species. 3 - Based on an association of giant short-faced bears and brown bears at Little Box Elder Cave, Wyoming, Kurtén and Anderson (1974) proposed that giant short-faced bears may have been out-competed by brown bears as the latter expanded from eastern Beringia southward. 4 - These data suggest that at times prior to the extinction of giant short-faced bears the two species occurred in overlapping geographic areas as brown bears spread throughout North America. 5 - Overall, recent literature provides little evidence that giant short-faced bears were primarily active carnivores or strictly vegetarian, and instead indicates that these bears were omnivores with scavenging tendencies. 6 - That giant short-faced bears may have excluded brown bears from Eastern Beringia from ∼34 to ∼20 ka BP further suggests these large bears may typically have been dominant over brown bears. 7 - Competition amongst bears may have increased as food resources shifted at the end of the Pleistocene, as our age estimates suggest giant short-faced bears temporarily displaced brown bears from the Pelludicar Cave area. 8 - When closed forests encroached and large meat packages dwindled, giant short-faced bears declined and brown bears recurred. Post-glacial shifts in available resources may also have promoted the eventual extirpation of brown bears from the island, though, unlike giant short-faced bears, brown bears persisted in adjacent areas (Mustoe et al., 2005). Greater dietary and habitat plasticity (Kurtén, 1967, Matheus, 1995) could have facilitated the persistence of brown bears and not of giant short-faced bears as environments changed abruptly toward the Holocene in this region. 9 - We suggest that at the end of the Pleistocene one reason brown bears persisted where giant short-faced bears died off is because giant short-faced bears may have been less flexible in adapting to new and rapidly changing environments that impacted the availability or quality of food and possibly habitat. Future studies of the trophic interactions of these bear species may show if competition is likely to have contributed to the changing availability of food resources for giant short-faced bears.
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Post by brobear on Oct 5, 2018 7:47:14 GMT -5
When I look at pictures of giant panda bears or Andean bears on nature documentaries in the wild, I never see them in water. This leads me to believe that the short-faced bear group were not fishers. Aquatic life were probably not on their menu. Another way of separating the two bear groups is "cat-skulled bears" ( short-faced bears ) and "dog-skulled bears" ( of the genus Ursus ). Both the panda bear and the Andean bear have extra-strong jaws... as did every cat-skulled bear I have researched.
Some information I read concerning the Andean bear's diet makes mention of the bear eating honey, some sites do not. I have read nothing of panda bear's eating honey. Could it be that those sites which mentions that Andean bears eat honey are merely making a generic statement based on the fact that they are bears? I have found no video's of either of these two cat-skulled bears eating honey. Both the panda bear and the Andea bear show sexual dimorphism; male larger than female. This is typical for both cat-skulled bears and dog-skulled bears.
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Post by brobear on Nov 30, 2018 6:02:27 GMT -5
www.sciencedirect.com/science/article/pii/S0016699517300384 6. Conclusions We provided an account of the late Pleistocene distributions of brown bears and giant short-faced bears in western North America based on rare fossils of these bears from Vancouver Island, and we discussed these remains in terms of the competition hypothesis for the extinction of giant short-faced bears. A partial cranium and the distal portion of the shaft of a left humerus from the Pellucidar Cave fossil locality are referred to the giant short-faced bear Arctodus simus. Radiocarbon dates on these bones indicate that this species lived around the cave at ∼13.5 cal. ka BP. Part of a left humerus, a right humerus of an immature individual, and a left femur are referred to the brown bear Ursus arctos. Ancient DNA analysis indicates that brown bears residing on Vancouver Island near the end of the Pleistocene arrived from the east or south as they share ancestry with modern-day Clade 4 brown bears that are prominent in the contiguous U.S.A. but do not occur in B.C. north of the fossil site. Our radiocarbon ages indicate that brown bears lived at Pellucidar Cave at ∼14.5 cal. ka BP and ∼13 cal. ka BP. Together these radiocarbon ages suggest that competition was possible between brown and giant short-faced bears and may have resulted in niche partitioning for territory and cave use. Post-glacial faunal and vegetation shifts changed the foraging options available to these large carnivores and are likely to have contributed to the arrival and the local extirpation of giant short-faced bears from Vancouver Island. A higher degree of dietary and habitat flexibility and possibly a comparatively smaller foraging radius than that of giant short-faced bears are likely to have facilitated brown bears persistence in the broader region into the Holocene. In terms of early human occupation in the Americas our study documents the existence of a robust ecosystem on north Vancouver Island that was available for human occupation, supporting the west coast as an option for early human occupation and migration. Our paleontological and radiocarbon data on bear fossils from Pellucidar Cave together with the application of aDNA methods, as well as paleoecological and archaeological sources have provided some of the necessary details for defining how changes on the landscape, including competition with brown bears, may have affected giant short-faced bears leading up to their extinction. We show that changing species interactions can be considered in Pleistocene extinctions, and we highlight that rapid shifts in the availability or quality of food and habitat are likely to have been important in the extinction of giant short-faced bears.
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Just the facts, man.
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Post by Just the facts, man. on Dec 4, 2018 0:46:47 GMT -5
Is it known whether grizzly bears still lived East of the Missouri, in Ameican native warrior history, prior to the introduction of Eurasian horses to the plains tribes, post-1492?
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Post by brobear on Jan 5, 2019 12:52:21 GMT -5
Is it known whether grizzly bears still lived East of the Missouri, in Ameican native warrior history, prior to the introduction of Eurasian horses to the plains tribes, post-1492? No. They were all West of the Mississippi River. It is a known fact that some big male grizzlies preyed upon mustangs.
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Post by brobear on Jan 5, 2019 12:58:30 GMT -5
The size of Pleistocene grizzlies in N. America is debatable, but we do know that they were smaller than those in Europe during the Ice Age. In a face-off between Arctodus simus and the European Steppe Bear, my nickel would be on the brown bear. While the giant short-faced bear might have a slight size advantage, the brown bear would be the better grappler. But this is meaningless as there was an ocean separating them.
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Post by King Kodiak on Jan 5, 2019 13:15:32 GMT -5
The size of Pleistocene grizzlies in N. America is debatable, but we do know that they were smaller than those in Europe during the Ice Age. In a face-off between Arctodus simus and the European Steppe Bear, my nickel would be on the brown bear. While the giant short-faced bear might have a slight size advantage, the brown bear would be the better grappler. But this is meaningless as there was an ocean separating them. Ok but for a Steppe brown bear to have a chance at beating a short faced bear you will need to have the largest possible specimen vs a close to an average short faced bear, (1800 lbs). the max weight of both is about 2200 lbs. would be an awesome battle.
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Post by brobear on Jan 5, 2019 14:01:37 GMT -5
The weights of both bears are greatly debated among the experts. Most actually place the giant short-faced bear at an average somewhere between 1200 and 1800 pounds. The European Steppe bear was of a similar weight - IMO.
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Post by brobear on Mar 7, 2019 2:01:35 GMT -5
shaggygod.proboards.com/ "Because no obvious climatic or environmental events appear to explain the extinction and recolonization of brown bears in eastern Beringia, alternative explanations need to be considered. There is a marked inverse correlation between the chronology of brown bears and the much larger, hypercarnivorous, shortfaced bears in eastern Beringia (Fig. 3A). Although the two species coexisted for at least 10,000 years (;45 to 35 ka B.P.) during the interstadial, short-faced bear fossil dates are concentrated between 35 to 21 ka B.P. when brown bears were absent. Furthermore, brown bear recolonization (;21 ka B.P.) is precisely coincident with the last record of short-faced bears in Beringia." "Stable-isotope data (Fig. 3B) suggest that the diets of the two bear species differed substantially while they were contemporaneous. Enriched levels of 15N show that short-faced bears were carnivorous, whereas brown bears were variably omnivorous and herbivorous, similar to most noncoastal bears today (Fig. 3B) (8, 19). In contrast, during the period 21 to 10 ka B.P. following the apparent extinction of short-faced bears in Beringia, brown bears also show an enriched mean 15 N signal relative to both the pre–35 ka B.P. and modern populations. However, competitive interaction is extremely difficult to infer from the paleo-record, and several environmental factors can affect isotopic ratios. In addition, much taxonomic turnover would be expected to occur around 21 ka B.P. during the environmental changes of the early LGM. If the enriched signal does indeed reflect a higher trophic level, then it may simply indicate an increased carcass biomass availability 21 to 10 ka B.P., which presumably disappeared following the extinction of many large-mammal taxa in the terminal Pleistocene."
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Post by brobear on Mar 7, 2019 2:02:22 GMT -5
Same author, earlier article:
"If short-faced bears were large, aggressive scavengers capable of stealing carcasses from other large carnivores, then it seems unlikely that brown bears could dominate them in direct interference competition. And while brown bears may have preferred to feed on animal carcasses, it seems more likely that they would have avoided direct confrontation with a dominant bear.
The ecological plasticity of brown bears and their ability to hibernate may have been the keys to their ultimate survival at the end of the Pleistocene, while Arctodus, the highly specialized forager, was not able to find a niche in Holocene ecosystems. Most likely, carcass densities on Holocene landscapes fell below levels necessary to sustain minimal viable populations of short-faced bears. Since many bears hibernate to survive poor food availability during winter, this may be an indirect indication that short-faced bears, and perhaps all New World bears, never evolved this strategy to survive seasonal dietary bottlenecks.”
Paul E. Matheus, 1995, Diet and co-ecology of Pleistocene short-faced bears and brown bears in eastern Beringia. Quaternary Research 44(3):447-453.
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Post by brobear on Mar 7, 2019 2:04:49 GMT -5
According to more recent data, the model of the GSFB as brown bear gate keeper to North America is challenged (see below article). Apparently, a small number of brown bears were able to migrate and penetrate as far south as southern Canada and the northern United States. Abstract Current biogeographic models hypothesize that brown bears migrated from Asia to the New World ~100 to 50 thousand years ago but did not reach areas south of Beringia until ~13 to 12 thousand years ago, after the opening of a mid-continental ice-free corridor. We report a 26-thousand-year-old brown bear fossil from central Alberta, well south of Beringia. Mitochondrial DNA recovered from the specimen shows that it belongs to the same clade of bears inhabiting southern Canada and the northern United States today and that modern brown bears in this region are probably descended from populations that persisted south of the southern glacial margin during the Last Glacial Maximum. Matheus P, Burns J, Weinstock J, Hofreiter M (2004) Pleistocene brown bears in the mid-continent of North America. Science 306: 1150. www.sciencemag.org/content/306/5699/1150.abstract
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