Post by brobear on Mar 26, 2017 23:51:27 GMT -5
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Evolutionary implications of bite mechanics and feeding ecology in bears
Bite 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.
Adaptation of the muscles of mastication to the flat skull feature in the polar bear (Ursus maritimus).
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.
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.
Evolutionary implications of bite mechanics and feeding ecology in bears
Bite 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.
Adaptation of the muscles of mastication to the flat skull feature in the polar bear (Ursus maritimus).
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.
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.
