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Fishery Bulletin 91(4), 1993 



CHARACTER 13(H) 



' FRONTAL 

 3 



Figure 1 



Non-metrical cranial characters utilized in this study following Perrin et al. (19821. Letters refer to 

 Table 1. 



Results 



Cranial maturity 



Relationships between the degree of fusion in cranial 

 sutures and sexual maturity for L. obscurus are shown 

 in Table 2. Less than 25% of the adults exhibited ad- 

 vanced rostral distal fusion (MXDIST=2) which, as in 

 L. obliquidens (see Walker et al., 1986), eliminates 

 MXDIST as a selection criterion for adult skulls in 

 this species (too many useful skulls would be rejected ). 

 However, three other sutures, frontale-supraoccipitale 

 (FROC), zygomatico-parietale/exoccipitale (ZYG), and 

 lacrimale-maxilla/frontale (LAC), had advanced fusion 

 (state=2) in 95%, 89 r /r, and 85%, respectively of the 

 sexually mature specimens. Equally important, only 

 two sexually immature specimens from New Zealand 

 showed full fusion in any of these sutures: one was a 

 pubescent female with large follicles (ZM39957) and 

 the other, an unusually large female without ovarian 

 corpora (ZM39561, 187 cm). Moreover, based on over- 



all size, those skulls fitted into the adult series. Skulls 

 with at least some fusion (state 1 or 2) in either 

 MXDIST, SYM, or PTPAL are very likely from sexu- 

 ally mature dolphins (see Table 2). 



Metrical characters 



Individual variation Summary statistics for cranial 

 characters in adult female and male dusky dolphins of 

 central Peru are presented in Table 3. Of 74 charac- 

 ters tested, only one (upper left tooth count, for fe- 

 males) departed significantly from normality 

 (Kolmogorov-Smirnov, P=0.017), which could be attrib- 

 uted to chance fluctuations. Homogeneity of variance 

 (95% confidence, TWOSAM, STSC Inc., 1989) was con- 

 firmed for all sex-paired characters. 



Statistics summarizing individual variation in cra- 

 nial characters are given also for mature dusky dol- 

 phins of northern Chile, southwestern Africa and New 

 Zealand (Table 3). No significant departures from nor- 



