1973 Volume 35 Issue 5 Pages 377-387_2
In the morphological changes of the skull of the Yezo brown bear (Ursus arctosyezoensis Lyd.) showing growth with postnatal development were observed the abrasionpatterns of teeth. And the relative growth between the abrasion patterns of teeth and the obliteration patterns of suurae to the basilar skull length (B-P) was analyzed statis-tically.The materials used in this study were 52 skulls (34 male and 18 female) which hadbeen described in the previous part of the present series (Table I).The abrasion degrees of teeth were determined by the method employed by MARTINand SALLER (Table 2).The local gradation of abrasion was recognized in both male and female upperincisors, but not in the lower incisors.Of the upper incisors, the first incisor was the first to show abrasion and followedby the second and the third incisor in this order with this regard.The relative advance in abrasion pattern of the upper incisor to the basilar skulllength (B-P) was showen by diphasic allometry with one critical point on the growtltcurve (Fig. 5). The position of the critical point on the growth curve was found atabout 285 mm in the male skull and at about 250 mm in the female skull by B-P. Inthe front of the point, the formula of growth curve was y:::0.12x -20.07 for the maleany y::: -0.0lx-[-13 for the female. In the backward of the point, it was y::0.63x -164.79for the male and y:O.87x -206.40 for the female.The relative advance in obliteration pattern of fifteen suturae and synchondroses tothe basilar skull length was also shown by diphasic allometry with one critical point onthe growtlx curve (Fig. 6).Tlte position of the critical point was found at about 290 mm in the male and atabout 260 rnm in the female.In the front of the point, the formula of the growth curve was y:O.O6x -4.87 for themale and y: -0.05x-[23 for the female. In the backward of the point, the formula wasy:J.24x -359.14 for the male and y:l.48x -375.70 for the female.An individual variation was noticed in the front of the critical point among thefemale skulls.The abrasion of teeth and the obliteration of suturae and synchondroses seemed tobe enhanced rapidly in the late stage when there was an increase in the basilar skulllength.It is reasonable to consider it an effective method for studying the indivi
