Age changes in some parts of skull of brown bear (Ursus arctos L.)
Chashchukhin V.А., DSc, professor, leading researcher
B.M. Zhitkov All-Russian Institute of Game and Fur Farming, Kirov, Russia
E-mail: vniioz@mail.ru
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.
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Skull-Based Method of Age Determination for the Brown Bear Ursus arctos Linnaeus, 1758
V.Yu. Guskov
Open Access funded by Far Eastern Federal University
Under a Creative Commons license
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doi:10.1016/j.als.2015.04.002
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Abstract
Due to the lack of a proper technique for determining the ages of brown bears, a simple and straightforward method that is based on published data and our own observations is proposed. This method is based on the simultaneous use of the following different skull parameters to more accurately determine the ages of brown bears: size and weight parameters, degree of obliteration of the joints, degree of wear of the teeth, and development of the flanges. The proposed method contributes to non-destructive age determination, allows for the discrimination of immature and adult bears and also classifies the skulls of adult animals into one of the five selected age groups.
Determining the Age of the Skull: Challenges and Approaches
The determination of the exact age of an animal presents certain difficulties when working with morphological material. The inclusion
of the animal in a particular analysis and the interpretation of the results depend on the accuracy of the determination. Incorrect
definitions lead to errors in the analysis of the data and potentially to the presentation of incorrect hypotheses, particularly when
working with large animals (for example, brown bears) that live long lives, during which their morphological characteristics change.
To solve this problem, it is necessary to create a methodology for determining the age of the studied species. Accounting for a
greater number of parameters that change with age (such as size, weight and craniometrical indicators) increases the probability
of at least identifying the age within a range of 2 to 3 years if not the specific age.
The parameters available for reviews also vary depending on the material that is being examined. For example, when working with
live animals, craniometrical indicators are not available. The well-proven methods of age determination based on teeth cuts require
destructive interference with the integrity of the skull, which is not always possible for work with museum specimens because it
can lead to an inability to measure some of the parameter
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