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Post by grrraaahhh on Apr 4, 2011 16:58:46 GMT -9
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Post by grrraaahhh on Apr 4, 2011 16:59:20 GMT -9
Polar Bear
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Post by grrraaahhh on Apr 4, 2011 17:00:37 GMT -9
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Post by grrraaahhh on Apr 4, 2011 17:00:46 GMT -9
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Post by grrraaahhh on Apr 11, 2011 7:15:14 GMT -9
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Post by grrraaahhh on May 4, 2011 7:14:53 GMT -9
Anecdotal evidence of a bear's bite force strength: Text Extract:"The ground cover was beaten down and the ground surface disturbed in many places with footprints pushed 10-15 cm or more into wet soil. We suggest that the grizzly bear surprised the muskox bull while it was grazing on sedge (indicated by rumen contents). The bear most likely grabbed the bull above the muzzle. In response, the bull must have braced its front legs and tried to dislodge the bear, suggested by front-foot hoof prints driven deep (15 cm) into the churned-up ground. Either the bull collapsed or the bear swung him off balance. At that point, the bear probably transferred its bite to just below the back of the bull’s horn boss. After making the kill, the bear dragged the carcass to where we found it, and had begun feeding when we interrupted. We returned about 48 hours later and found a light grey wolf (Canis lupus) and a grizzly bear whose colouring suggested it was not the bear that had made the kill. The carcass was dismembered and had settled into the wet ground. Most of the muscle masses and the internal organs had been consumed and the limb bones were scattered around the hide. The rumen had been pulled from the carcass but had not been fed on." "The destruction of the facial area was also the mode of attack of a barren-ground grizzly bear killing a caribou cow whose carcass we found on the Beverly caribou herd’s calving ground, northeast of the Thelon Game Sanctuary, in June 1981. Griffel and Basile (1981) described puncture wounds in the frontal or jugal bones of 109 of 332 bear- killed sheep (Ovis aires) in Idaho. The facial area is richly innervated, and Mystervd (1975) in Griffel and Basile (1981) suggested that unconsciousness and hypoxic asphyxiation would follow severe and sudden injury to that area. Also, the seizing of the muskox bull’s muzzle would reduce chances of the muskox using its horns to gore the bear and increase the bear’s chances of throwing the muskox off its feet." "Tener (1965) summarized predation on muskoxen and noted that Pederson’s report of a possible kill by a polar bear (Ursus rnaritimus) may be the only reported instance of bear predation."Source: Muskox Bull Killed by a Barren-Ground Grizzly Bear, Thelon Game Sanctuary, N.W.T. ARCTIC, Vol 35, No 4 (1982). PDF LINK: arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/2364/2341
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Post by grrraaahhh on May 5, 2011 6:35:09 GMT -9
The Use of the Skull in Age Determination of the Brown Bearby B. P. ZAVATSKY Borogov State Agricultural Enterprise, Krasnoyarsk Kray, U.S.S.R.Bears: Their Biology and ManagementVol. 3, A Selection of Papers from the Third International Conference on Bear Research and Management, Binghamton, New York, USA, and Moscow, U.S.S.R., June 1974. IUCN Publications New Series no. 40 (1976), pp. 275-279 To understand many aspects of the biology of bears, it is necessary to establish age of animals. Without this ability, it is impossible to determine the age structure of the population, rate of growth, onset of sexual maturity, lifespan, etc. Accurate age of bears after one year may be determined by the number of layers in dental root cement. The first work on this technique was reported by Smirnov (1960) ... 'in the bear, the layer of cement is most exact and one can consider that each layer signifies one year of life.' Rausch (1961) studied American bears of known age and established that there is an annual layer of dentine and cement and also a yearly outgrowth on the root of the tooth; according to the number of annual layers in the length of the tooth, one can distinguish ten age classes. Mundy and Fuller (1964) determined the age of grizzlies (Ursus arctos) by the cement layers of the third molar. Because the third molar of the lower jaw cuts through in the bear in the second year of life, its age can be determined by the number of cement layers plus one year. Manning (1964) took as significant the degree of concretion of skull sutures, the thickness of enamel on teeth, and the form of the skull outgrowths as a technique in the determination of the age of the polar bear. By these criteria he identified four age classes and determined the ages of the bears to the sixth year. Sauer, Fry and Brown (1966) determined the ages of black bears (Ursus americanus) according to the lengths of the incisors to a thickness of 250 microns in sequential sections of 25 microns. They discovered that wild bears did not differ from bears living in captivity. They showed that sequential layers of cement did not always correlate with age or were sometimes completely absent, and in wild bears of known age each cement layer corresponded to one year in the life of the bear. Ushivtsev (1972) used the same criteria for determining the age of the brown bear (Ursus arctos) of Sakhalin Oblast and came to the same conclusion. Inukai Masaaki (1972) discovered that the age of the brown bears of Hokkaido, according to sections of the incisors, up to a year old cannot be determined by this method because there were no definite layers of dental cement, but in older bears they are in annual layers. Thus all researchers attempting to determine the ages of bears came to the same conclusion: that the number of layers of tooth cement corresponds to a year in the life of the bear. This position was taken for the basis of our studies and thus accurate growth of bears of the Turykhan population was determined according to the number of cement layers at the root of the tooth. As the basis of our research on the skulls of brown bears in the Borogov State Agricultural Enterprise, located in the middle Yenesey region (33, 040 sq. km.), forty-three skulls were collected between 1967 and 1973 from bears in a comparatively small region. Therefore, errors connected with geographical variability of the species can be excluded. The analysis of the collected material was conducted according to the method of Klevezal and Kleynenberg (1967) on microtome sections of roots of bear teeth. To select the most suitable tooth from several skulls of the collection, we sliced all teeth, sections of jaws, and different parts of each tooth. PDF LINK: www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_3/Zavatsky_Vol_3.pdf
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Post by grrraaahhh on May 5, 2011 6:44:07 GMT -9
Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae)Abstract Patterns of morphological variation in the skulls of extant bears were studied as they relate to diet and feeding behaviour. Measurements of craniodental features were used to compute indices that reflect dietary adaptations of the dentition and biomechanical properties of the skull, jaw and related musculature. Species were classified as either carnivores, omnivores, herbivores or insectivores. Differences among dietary groups were assessed with analysis of variance and discriminant factor analysis. Results demonstrated significant morphological separation among all four groups. Carnivores were distinguished by, among other features, molar size reduction, flexible mandibles and, most surprisingly, relatively small carnassial blades. In contrast, herbivores displayed, among other features, large molar grinding areas, rigid mandibles and large carnassial blades. The insectivorous sloth bear was characterized by extreme reduction of the post-canine teeth. As expected, omnivores tended to have morphology intermediate between that of carnivorous and herbivorous ursids. Comparison with previous studies revealed that bears exhibit a different set of morphological specializations for diet than other carnivoran groups. Carnivorous ursids, for example, were found to share aspects of craniodental morphology with omnivorous canids. The relatively weak adaptations for carnivory observed in bears may be the result of selection for the ability to cope with temporal fluctuations in dietary components. The giant panda Ailuropoda melanoleuca was found to have a relatively stiff jaw and great mechanical advantage of the jaw-closing muscles, features previously observed in carnivorous canids and unexpected in this herbivorous bear. Comparison of patterns of morphological variation and patterns of phylogenetic relationships among species revealed surprisingly strong congruence between morphology and phylogenetics. Subscription Link: journals.cambridge.org/action/displayAbstract?fromPage=online&aid=216609Evolutionary implications of bite mechanics and feeding ecology in bearsAbstractBite forces (BFs) based on a dry skull static model were computed for 122 specimens of all eight species of extant ursids. It was found that the giant panda has high BFs for its body size, and large moment arms about the temporomandibular joint, both muscle inlever moment arms and outlever moment arms to the carnassial and canine. The insectivorous sloth bear and to some extent the omnivorous black bears were the opposite. The small sun bear has very large canines and high BFs, which are not well understood, but could potentially be related to its frequent opening of tropical hardwood trees in pursuit of insects. Force profiles along the lower jaw revealed significant differences among the various species, both related to diet and inferred applied BFs. The panda is the only specialized ursid with respect to craniodental morphology and BFs, but is still unspecialized for herbivory compared with other large, herbivorous mammals, probably owing to a rather short evolutionary history, but possibly its morphology is constrained by genealogy. The low BFs in the sloth bear and its mandibular force profiles are derived for a diet of insects and fruit, requiring only low BFs and largely dorsoventral bite moments. In contrast, the unspecialized morphology and moderate BFs relative to body size of the polar bear and spectacled bear are probably also a result of a short evolutionary history. Subscription Link: onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2006.00286.x/abstractBite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxaAbstract We provide the first predictions of bite force (BS) in a wide sample of living and fossil mammalian predators. To compare between taxa, we calculated an estimated bite force quotient (BFQ) as the residual of BS regressed on body mass. Estimated BS adjusted for body mass was higher for marsupials than placentals and the Tasmanian devil (Sarcophilus harrisii) had the highest relative BS among extant taxa. The highest overall BS was in two extinct marsupial lions. BFQ in hyaenas were similar to those of related, non-osteophagous taxa challenging the common assumption that osteophagy necessitates extreme jaw muscle forces. High BFQ in living carnivores was associated with greater maximal prey size and hypercarnivory. For fossil taxa anatomically similar to living relatives, BFQ can be directly compared, and high values in the dire wolf (Canis dirus) and thylacine (Thylacinus cynocephalus) suggest that they took relatively large prey. Direct inference may not be appropriate where morphologies depart widely from biomechanical models evident in living predators and must be considered together with evidence from other morphological indicators. Relatively low BFQ values in two extinct carnivores with morphologies not represented among extant species, the sabrecat, Smilodon fatalis, and marsupial sabretooth, Thylacosmilus atrox, support arguments that their killing techniques also differed from extant species and are consistent with ‘canine-shear bite’ and ‘stabbing’ models, respectively. Extremely high BFQ in the marsupial lion, Thylacoleo carnifex, indicates that it filled a large-prey hunting niche. FREE PDF LINK: rspb.royalsocietypublishing.org/content/272/1563/619.full.pdf+html
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Post by grrraaahhh on May 5, 2011 6:47:51 GMT -9
Adaptation of the muscles of mastication to the flat skull feature in the polar bear (Ursus maritimus).Abstract The muscles of mastication of the polar bear (Ursus maritimus) and those of the brown bear (U. arctos) were examined by anatomical approach. In addition, the examination of the skull was carried out in the polar bear, brown bear and giant panda (Ailuropoda melanoleuca). In the polar bear, the rostro-ventral part of the superficial layer of the M. masseter possessed the abundant fleshy portion folded in the rostral and lateral directions like an accordion. Moreover, the rostro-medial area of the superficial layer became hollow in the nuchal direction when the mouth was closed. The M. temporalis of the polar bear covered up the anterior border of the coronoid process of the mandible and occupied the almost entire area of the cranial surface. The M. pterygoideus medialis of the polar bear was inserted on the ventral border of the mandible and on the ventral part of the temporal bone more widely than that of the brown bear. As results of our measurements of the mandible, an effect of the leverage in the polar bear was the smallest in three species. In the polar bear, the skull was flat, and the space between zygomatic arch and ventral border of the mandible, occupied by the M. masseter was the narrowest. It is suggested that the muscles of mastication of the polar bear is adapted to the flat skull feature for supplementing the functions. FREE PDF LINK: www.jstage.jst.go.jp/article/jvms/62/1/7/_pdf
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Post by grrraaahhh on Jun 29, 2011 11:55:04 GMT -9
Text extract from Naturalist Terry Domico:
"The brown bear is stout and rather chunky in shape, with a large hump of fat and muscle over the shoulders and very long claws. It has a wide, massive head that some people describe as being somewhat "dish faced" in appearance. That big head is equipped with extremely powerful jaws. I once saw a big male, trapped in a leg snare set by researchers, take out its frustration on some neighboring trees. In one bite he bit completely through a 4-inch (10-cm) -diameter pine, snapping it off. It also chewed through several 6- and 8-inch (15- and 20-cm) -diameter trees. One stump looked as though it had been dynamited. When we slammed the sharp end of a geologist's pick into the trunk of one of those trees, it only penetrated about 1.5 inches (3.8 cm) into the wood."
Domico, T. and M. Newman. 1988. Bears of the world. Facts on File.
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Post by grrraaahhh on Jun 29, 2011 23:01:58 GMT -9
Text extract from Naturalist Terry Domico: "The brown bear is stout and rather chunky in shape, with a large hump of fat and muscle over the shoulders and very long claws. It has a wide, massive head that some people describe as being somewhat "dish faced" in appearance. That big head is equipped with extremely powerful jaws. I once saw a big male, trapped in a leg snare set by researchers, take out its frustration on some neighboring trees. In one bite he bit completely through a 4-inch (10-cm) -diameter pine, snapping it off. It also chewed through several 6- and 8-inch (15- and 20-cm) -diameter trees. One stump looked as though it had been dynamited. When we slammed the sharp end of a geologist's pick into the trunk of one of those trees, it only penetrated about 1.5 inches (3.8 cm) into the wood." Domico, T. and M. Newman. 1988. Bears of the world. Facts on File. Photo credit: Terry Domico.
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Post by grrraaahhh on Jul 16, 2011 7:59:32 GMT -9
Grizzly Bear: How did the brown bear develop strong & powerful jaw muscles on a heavy diet of vegetation materials? Beyond the simple plant item diet for example berries; brown bears developed their powerful jaw muscles by eating difficult roots and tubers.
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Post by grrraaahhh on Jul 24, 2011 8:00:53 GMT -9
INTRODUCTION Various attempts at understanding geographic variation in Polar bears have been made since Knotterus-Meyer (1908) began to confuse the issue by recognizing seven forms of what had previously been considered a monotypic circum-polar species. The most recent and noteworthy contribution was by Manning (1971), who outlined the earlier work. Briefly summarized, Manning demonstrated a cline of increasing size from East Greenland across Canada to the Bering Strait. He suggested that the population of largest bears, from the Bering Strait area and southward, could be considered subspecifically distinct, but left it unnamed pending further investigation. The present study was initiated in order to examine more closely the extent and kind of geographic variation in Alaskan polar bears. A variety of multivariate analyses were conducted on Manning's data, and on additional specimens obtained since the completion of Manning's work. MATERIALS AND METHODS A total of 295 skulls of Alaskan polar bears was examined. The seventeen skull measurements used and described by Manning (1971) were taken with calipers. The measurements were: (1) Condylobasal length (CBL); (2) Molar-premaxilla length (MPL); (3) Mastoid breadth (MB); (4) Zygomatic breadth (ZB); (5) Supra-orbital breadth (SB); (6) Cranial length (CL); (7) Facial length (FL); (8) Maxilla-supraorbital height (MSH); (9) Least cranial breadth (LCB); (10) Interorbital breadth (IB); (11) Breadth at canines (BC); (12) Palatal breadth (PB); (13) Length P4 to M2 (LP4-M2); (14) Crown length of M2 (LM2); (15) Crown length of Ml (LM1); (16) Coronoid height (CH); (17) Condylopalatal length (CPL). Wilson, E. Don. Cranial Variation in Polar Bears Bears: Their Biology and Management Vol. 3, A Selection of Papers from the Third International Conference on Bear Research and Management, Binghamton, New York, USA, and Moscow, U.S.S.R., June 1974. IUCN Publications New Series no. 40 (1976), pp. 447-453.
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Post by grrraaahhh on Nov 8, 2011 15:23:24 GMT -9
Measurement of a bear's bite force (depending on which specie of bear) is not an easy task. Some variables are difficult to quantify. There is anecdotal evidence of a bear's bite force strength as explained from the literature (see relating posts/threads) and similarly there are data provided in the form of popular media by bear specialists/biologist: "Grizzly bears have a bite-force of over 8,000,000 pascals, enough to crush a bowling ball."1 Pascal = 1 N/m2. natgeotv.com/uk/casey-and-brutus-grizzly-encounters/factsMoving onto additional literature sources: "The disparity in body size between carnivorous bears and their preferred prey suggests that bears are able to rely on muscular strength to process kills, rather than depending on well-developed craniodental adaptations that enhance muscle leverage and dental function that are typical of canids that hunt large prey (Van Valkenburgh & Koepfli, 1993). Instead, carnivorous ursids are more similar to omnivorous canids, which also outweigh their typical prey, though to a less dramatic degree. Whereas carnivorous bears may be as much as 100 times heavier than their prey, coyotes and red foxes typically take prey as large as a third of their own body mass (Van Valkenburgh & Koepfli, 1993)."
Sacco, T. and Van Valkenburgh, B. (2004), Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae). Journal of Zoology, 263: 41–54. There are different models to examine as well: "Therefore, researchers have turned to models to estimate bite forces based on approximations of the structure of the skull and the physiology of the muscles that adduct the jaws. Bite force estimates are often used in comparative studies, where they are correlated with ecological tasks (Christiansen, 2007; Kiltie, 1982), stress distribution in the skull (Christiansen and Adolfssen, 2005; Thomason, 1991), and morphological variables such as bite point, gape, skull size or muscle mass (Dumont and Herrel, 2003; Herrel et al., 2008; Williams et al., 2009)."
"Thomason's method of predicting bite force is the model that is most commonly applied to mammals (Christiansen and Adolfssen, 2005; Christiansen and Wroe, 2007; Ellis et al., 2008; Thomason, 1991; Thomason et al., 1990; Wroe et al., 2005). The values of bite force predicted by this method are based on a static 2-D lever mechanics model in which muscle forces are determined from an assumed muscle stress and an estimated muscle area. These predicted values are consistently lower than in vivo measurements (Christiansen and Wroe, 2007; Ellis et al., 2008). It is not clear why this is the case, although one possibility is that the method by which muscle areas are determined is a source of error (Christiansen and Wroe, 2007)." Davis JL, Santana SE, Dumont ER, Grosse I (2010) Predicting bite force in mammals: two-dimensional versus three-dimensional lever models. Journal of Experimental Biology 213: 1844–1851. PDF LINK: jeb.biologists.org/content/213/11/1844.full.pdf+html
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Post by grrraaahhh on Nov 16, 2011 3:57:46 GMT -9
Greece: Brown bear activity in the form of bite marks on a rural power pole. Photo credit: Alexadros Karamandlidos/Arcturos (BBC).
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