Van Waerebeek: Variation in skull morphology of Lagenorhynchus obscurus 



771 



Cyamid amphipods have never been found on L. 

 obscurus from Peru (Van Waerebeek, 1992b), whereas 

 in New Zealand they seem to be fairly common 

 (Cipriano, 1985). 



The actual distribution of L. obscurus populations is 

 generally comparable to that of the four species of 

 Cephalorhynchus, and the geographical dispersion may 

 have similarly evolved under the influence of the 

 eastflowing Westwind Drift, as proposed for 

 Cephalorhynchus spp. by van Bree ( 1986) and Robineau 

 (1989). The close affinity of the large-bodied Peruvian 

 dusky dolphin with the Pacific white-sided dolphin 

 (Webber, 1987; Van Waerebeek, 1992b) suggests that 

 the former probably represents the most ancestral 

 (plesiomorph) form of dusky dolphin from which the 



Argentinian, and small-bodied SW African and New 

 Zealand forms were derived. 



Acknowledgments 



I am especially grateful to Julio Reyes, Peter B. Best. 

 Carlos Guerra, and Walter Sielfeld for their kind per- 

 mission to examine skulls they themselves collected. 

 Special thanks are due also to Alan Baker, Peter van 

 Bree, J. Darby, Ewan Fordyce, James G. Mead, Mar- 

 tin Sheldrick, R. Thompson, and G. Tunnicliffe for free 

 access to collections under their care, and to J.C. Reyes, 

 Mark Chandler, Laura Chavez, Anne-Catherine 



