ECOLOGY AND BIOLOGY OF THE PACIFIG WALRUS 



117 



Fig. 81. Length of the cHnical 

 crown of the tusks of male (dots) 

 and female (circles) Pacific wal- 

 ruses, in relation to age. Each 

 point represents the longest tusk 

 in one specimen. Curves were 

 fitted visually. 



go « 

 o o o o 



8o° 



20 30 

 Age (years) 



40 



nearly in direct arithmetic relation to age (Fig. 81). This increase takes place 

 both in males and in females; its rate is slightly higher in the males. After about 

 15 years, the increase slows in males and virtually ceases in females. 



The tusks of males tend to be slightly longer than those of females of 

 comparable age. The mean difference usually is no more than about 3 or 4 cm, 

 up to about the 20th year; thereafter it may be as much as 10 cm. With few 

 exceptions, the length of the clinical crown of mature males 15 years old and 

 older ranges from about 35 to 65 cm and that of mature females from 25 to 

 55 cm. Maximum lengths in my series were 75 cm in a male and 68 cm in a 

 female. 



Length of clinical root. — The clinical root of the tusk is the portion proximal 

 to the gingival margin and enclosed within the socket. By this definition, the 

 entire unerupted tusk of fetal and newborn walruses is included, whereas only 

 the proximal part of the tusk is included in older animals. The length of the 

 clinical root is a function of the growth of the skull as well as of the tusk itself; as 

 the skull increases in size, the socket increases in depth. Increase in length of the 

 clinical root takes place for about 10 years in females and 15 years in males, after 

 which it reaches an asymptote of about 19 cm in males and 15 cm in females 

 (Fig. 82). 



