Jefferson: Sexual dimorphism and development in Phocoenoides dalli 



125 



Figure 9 



Shape of Dall's porpoise tail 

 flukes: (a) calf (TAJ 171). (b) 

 mature female (TAJ 121). (c) 

 mature male (TAJ 090). 



subjective observations suggested that there may be 

 significant sexual dimorphism in the shape of the tlukes 

 (Fig. 9). 



Newborn porpoises have flukes in which the trailing 

 edge is more or less concave, and the tips are fairly 

 rounded. As age increases, the trailing edge approaches 

 a straight line, and the tips become more pointed and 

 recurved. Some animals have flukes with a convex trail- 

 ing edge, and these are almost always adult males 

 (animals with extremely convex flukes are always 



males). There seems to be much individual variability 

 in this feature, however, as some mature males do not 

 have convex flukes. Quantitative data are needed to 

 further explore the relationship between fluke shape 

 and age/sex class. 



Coloration 



Urogenital color pattern The coloration of the uro- 

 genital area of Dall's porpoise has been previously 

 reported to be sexually-dimorphic (Morejohn et al. 



