92 



14) relative lengths of anterior prongs of nasal bones with a trident-shaped (= tri-lobular) 

 morphology: 0 = lateral prongs greater than medial prong; 1 = lateral prongs subequal 

 with medial prong; 2 = lateral prongs less than medial prong; 9 = n/a - nasal bones not 

 trident-shaped (pers. obs.). 



One mechanism to account for the numerous derivations of the hypothesized 

 plesiomorphic trident-shaped nasal bones is through the differential expression of the 

 lateral versus medial prongs. In particular, an extreme reduction of the medial prongs could 

 lead to a bi-lobular morphology, that of the lateral prongs to a uni-lobular morphology, 

 and that of both sets of prongs to the flattened morphology of the otarioids (see previous 

 character). 



Most of the Caniformia retain the plesiomorphic condition, whereby the lateral prongs are 

 longer than the medial one. The remaining apomorphic states display limited distributions, 

 primarily among the pinnipeds. The condition in which the nasal bones do not possess a 

 trident-shaped morphology occurs only among the otarioids, Mirounga spp., and possibly 

 Cystophora and Monachus monachus (both of which are polymorphic with other states), 

 and may diagnose the pinnipeds ancestrally (ACCTRAN optimization). State 2 occurs 

 unequivocally only in Ursus and Lobodon, while state 1 is found in Halichoerus, 

 Pagophilus, and polymorphically with state 0 in Histriophoca. 



15) visibility of nasal septum in dorsal view: 0 = does not extend beyond nasals (not 

 visible); 1 = extends beyond nasals (visible) (King 1956; pers. obs.) (Fig. 18). 



Our observations for the previous nasal characters revealed that the nasal septum, which 

 typically lies beneath and is covered by the nasals, was occasionally visible in dorsal view. 

 Typically, when this situation occurred, the septum extended anteriorly to be visible 

 between the prongs of the trident-shaped nasals, although it did extend completely beyond 

 the nasals on some occasions. King (1956) lists these morphologies as a general tendency 

 of Monachus spp., occurring to the greatest extent in M. tropicalis and the least in M. 

 schauinslandi. Its appearance in M. monachus seems to be limited to old individuals (King 

 1956). This condition has also been noted in the fossil lobodontine Homiphoca capensis 

 (de Muizon & Hendey 1980). Although we observed this derived condition (state 1) in 

 numerous isolated phocid specimens, it was only consistently present in Monachus 

 tropicalis, suggesting that its absence may be an artifact of preparation in some taxa. In 

 any case, the systematic value of this apparently autapomorphic character is limited here. 



16) shape of posterior edge of nasals, I: 0 = v-shaped (convergent); 1 = w-shaped (diver- 

 gent) (Wozencraft 1989). 



This character essentially amounts to the relationship between the nasals and the frontals. 

 The divergent morphology is obtained when the frontal bones project between the nasals, 

 while the convergent morphology is obtained by the reverse situation (King 1983). Despite 

 noting the differences between the two taxa for this feature, Wozencraft (1989) proposed 

 the divergent morphology as a synapomorphy of the otarioids. However, this has been 

 criticized by Wyss & Flynn (1993), who note that Odobenus really possesses more of a 

 flat termination to the nasals. Under the definition employed above, this would appear to 

 be a modification of the convergent condition. However, despite recognizing the flattened 

 termination, King (1983) still scored Odobenus as possessing the divergent morphology. 



