Age changes in some parts of skull of brown bear (Ursus arctos L.)
B.M. Zhitkov All-Russian Institute of Game and Fur Farming, Kirov, Russia
Significant morphological variability complicates the use of measurable traits to determine the sex and age of brown bears. In such a situation traits are particularly important that vary with age depending on the duration of exposure to physical activity. Natural cause of such a load is logical to consider the need for extraction and consumption of food. Priority attention should be given to the morphological changes of teeth and bones of the skull holding large chewing muscles. The material for the study were 32 skulls of brown bears of all ages from the collections of the Faculty of Biology of the Vyatka State Agricultural Academy, Kirov regional and Kirov city societies of hunters and fishermen. The place of bears' capture - Kirov, Arkhangelsk and Vologda regions, Perm area and Komi Republic. chewing surface of premolars and molars of the upper and lower jaw, angular and articular processes with the lateral side of the mandible, sagittal crests and selectively incisors were photographed to compare age-related changes. Chewing surface of molars are exposed to the greatest transformation with age. The clearly distinguishable hillocks on the surface of the teeth in young bears with time gradually erased disappear in adults, in old specimens formed through with a wide exposure of dentin. The process of erasure and disappearance of hillocks is less characteristic for the last premolars. Incisors significantly change with age. The incisors of young bears are long, wide at the top with a deepening in the center. The incisors of old bears are transformed into a solid row of uniformly raw of off and short teeth. The angular process in young animals is short and smooth. It is transformed with age into a long and wide, with distinct ridges. The edge of the ridges and surface roughness on the surface of the articular process also appear on with age. It becomes wider and more massive. The lateral surface of the jaw in young bears is smooth. In adults and older bears it is covered with numerous small ridges. The sagittal crest in young bears is absent or weakly expressed. The sagittal crest on the skulls of adult is long, tall, flattened at the back; the top line of the ridge is rough, sometimes with a dip in the middle. Natural explanation of this transformation is developing with age and duration of the functioning of the masticatory muscles. The maximum life of brown bear is some 40 years. To relate punctiliously observed morphological changes with time-specific steps that age is not possible.
Keywords: brown bear, skull, sagittal crest, jaw spines, teeth
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