144 



The tendency to single-rootedness of the upper postcanines is an apomorphic condition 

 uniting the pinnipeds ancestrally, with a parallel appearance in Ursus. This contrasts with 

 the opinion that the otariids possess double-rooted postcanines (except for the first) 

 ancestrally (Repenning & Tedford 1977). However, the single-rooted morphology is only 

 retained in the otarioids. Cystophora, Halichoerus. and Mirounga spp.. before reversals to 

 the plesiomorphic morphology occur in each phocid subfamily. The case in which all the 

 upper postcanines were single-rooted was slightly rarer, occurring only among Zalophus 

 [although M 1 is double-rooted in a number of other otariids (Repenning & Tedford 1977: 

 King 1983)] and Mirounga spp. 



144) tendency to single-rooting of lower postcanines: 0 = absent: 1 = present (de Muizon 

 1982a). 



Under ACCTRAN optimization, the distribution of the tendency to single-rooting of the 

 lower postcanines is identical to that of the upper postcanines. However, the polymorphic 

 nature of Cystophora leads to another possibility, that of convergent evolution in the 

 otarioids [thereby possibly rescuing Repenning & Tedford"s (1977) hypothesis of double- 

 rooted postcanines ancestrally in the otariids]. Halichoerus. and Mirounga spp. 

 (DELTRAN optimization). Again, single-rooting of all lower postcanines was limited to 

 Zalophus and Mirounga spp. 



145) relative size of gap between upper postcanines 4 and 5: 0 = smaller than other gaps: 

 1 = subequal to other gaps; 2 = larger than other gaps: 9 = n/a - postcanine homolog}' 

 uncertain (Ridgway 1972: pers. obs.). 



Ridgway ( 1972) used the relative size of the gaps between the postcanines (less than versus 

 equal to a tooth width) as a means of distinguishing between the genera Erignathus and 

 Halichoerus. However, during our observations, we noted that the gaps between the 

 postcanines of a given individual were not of a consistent size. Typically, it was the gap 

 between the last two postcanines that was the discrepant one. and the character was 

 recoded to reflect this observation. A relatively large such gap was noted for Histriophoca 

 by Scheffer (1960). and for Homiphoca and Leptonychotes by de Muizon & Hendey 

 (1980). 



Again, this character was only applied to the phocids due to the difficulties of establishing 

 postcanine homologies between the phocids and the putative outgroups. Primitively, the 

 phocids possess subequal gaps among all the postcanines (state 1). The phocines internal 

 to Cystophora largely derive a relatively enlarged gap. with only Pagophilus and Pusa 

 hispida re-obtaining subequal gaps. Virtually all monachines retain the primitive phocid 

 morphology, with only Leptonychotes paralleling the phocine condition. 



146) crowding of postcanines (upper and/or lower): 0 = not touching / overlapping: 1 = 

 touching or overlapping (Ridgway 1972). 



This character is to some degree an age-dependent one. In phocids. the deciduous dentition 

 is shed or resorbed around the time of birth (Allen 1887: Bertram 1940: Ling & Bryden 

 1981: King 1983; Stewart & Stewart 1987). causing the adult teeth to initially be crowded 

 and overlapping in the smaller juvenile skull (Doutt 1942: Chapskii 1967). [In most other 

 mammals, such crowding is avoided by having a reduced deciduous dentition associated 

 with the shorter rostrum of immature individuals (Hillson 1986).] As the animal reaches 



