Determination of age in representatives of the genus Sylvaemus by the degree of molar wear

Abstract

Various methods are used to identify representatives of the genus Sylvaemus, most of which are metric. In order to exclude anomalies in further calculations and to minimize allometric variations associated with the growth of animals, it is necessary to take into account age as an important factor of variability. Usually, a number of criteria are used to determine the age and describe the growth of mice: measurements of body and skull parameters, body weight, the degree molar wear, and the weight of the lens of the eye. Length is a more consistent guide for determining the age of mice than body weight, which usually ceases to be directly related to age after reaching adult size. Age can also be determined by the fusion of the epiphysis with the diaphysis in the bones of the limbs and by the degree of development of the thymus. Most often, teeth are used to determine age. Among such age criteria, we distinguish eruption and replacement of teeth sets, tooth growth in length, overgrowth of the tooth pulp cavity, tooth wear, and annual layers in the tooth tissues. Usually, the age of mice is determined by the degree of molar wear. Some authors do not consider this method universal due to individual feeding habits of animals and other environmental factors. The order of wear of tooth rows can sometimes change, and the degree of wear of the right and left tooth rows can also differ. The craniological collection of small mammals of O. V. Zorya, collected in the territory of Kharkiv Oblast, Ukraine, was studied. In total, 198 specimens of three species of the genus Sylvaemus were analysed: Sylvaemus uralensis, Sylvaemus sylvaticus, and Sylvaemus tauricus. Analysed were 14 odontometric and 23 craniological characters. Among the metric characters, four odontometric (LM2, WM1, LM2, LM123) and nine craniological characters (LIOC, LD, LFI, LPP, WCH, GLS, DI, LLM, LM) made the greatest contribution to the age group differentiation of mice of the genus Sylvaemus. Among the features that contributed the most to the differentiation, length measurements prevailed. LLM, LM123, LPP, LIOC, and GLS are the least variable metric characters. It is not possible to divide the sample of mice of the genus Sylvaemus into age groups based on odontometric and craniological character since the ranges of values of metric characters overlap.