The number of annuli and the time of annuli formation in different kinds of ursus arctos yesoensis teeth

Abstract

The age of Ursus arctos yesoensis was known to be determined by teeth annuli, but the number and clarity of annuli sometimes differed from bear to bear or between the different kinds of teeth obtained from the same individual. In order to examine the characteristics of teeth annuli, 2 bears of known age (No. 5 and 7) and 6 bears of unknown age were employed. The age of the bears of unknown was estimated by examining J1and P4teeth, which exhibited clear annuli. The teeth of J1, J2, J3, C, P1P4, M1, M2and M3of the lower jaw obtained from No. 7 bear and some others were analyzed for detecting morphological and numerical differences of annuli. The age estimated from the annuli of C was sometimes younger than the actual age by one year due probably to the delayed development of the canine. The annuli numbers observed in the other kind of teeth coincided with one another (Fig. 9-17). There were 2 assertions that in the first one, the annuli formed in the period before the hibernation, and that in another, it begun to form in the fall and completed in April or May of the next year. In No. 1 (11 years and 8 months) bear which was killed at the end of September, J1showed 11 annuli in the inner part of the ce-mentum, and the marginal cement layer was unstained. However, a little stained short line was found in it, indicating a new annulus formation (Fig. 1). P4of No. 2 (3y. & 9m.) bear which was killed in early October showed almost the same feature of new annulus formation as that of No. 1 (Fig. 2). J1of No. 3 (14y. & 10m.) bear which was killed at the end of November had 15 annuli, of which the outmost one was stained faintly (Fig. 3). J1of No. 4 (2y. & 10 m.) bear which was killed at the end of November showed about the same features as that of J1of No. 3 (Fig. 4). P4of No. 5 (5y. & 1m.) bear which was killed in the middle of Feburuary had 5 distinct annuli, and the outmost annulus was clear and perfect (Fig. 5). J1of No. 6 (11y. & 2m.) bear which was killed at the end of March had 11 clear annuli, and an unstained cementum layer was developing on the outer side of the outmost annulus (Fig. 6). P4of No. 7 (5y. & 3m.) bear which was killed in the middle of April showed 5 dark stained annuli, and an unstained cementum layer developed in some extent(Fig. 7). J1of No. 8 (10y. & 4m.) bear which was killed at the beginning of May showed 10 annuli with a well developed marginal unstained cementum layer (Fig. 8). It was clear that the formation of new annulus began in the middle of September and continued up to the end of April. The No. 5 bear was castrated male, so that it was suggested that the sex hormone had no relation to the annuli formation (Fig. 24). In this species the so-called accessory lines appeared, which closely resembled annuli and were also reported in grazzly bear. Therefore, in such a case, several kinds of teeth should be examined for an exact age determination. The mechanism of the accessory line formation and its significance are not known at present. © 1974, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.