141 



of one or both of the accessory cusps, the formation of additional accessory cusps 

 (typically posteriorly), or both (Doutt 1942; Ridgway 1972; de Muizon & Hendey 1972; 

 see characters #138 and 139). In Erignathus, the diagnostic tooth wear is so extreme as 

 to frequently obliterate the triconodont morphology of the postcanines (Chapskii 1955a; 

 Burns 1981; King 1983). All these variations on the triconodont theme were still classified 

 as triconodont, so long as such an origin could be reasonably established. 

 The plesiomorphic condition of multicuspate postcanines was found in all fissiped 

 outgroups. This is reduced in the pinnipeds, but the ancestral form is equivocal between 

 states 0 and i. The otarioids largely obtain peg-like or unicuspate postcanines, although 

 Zalophus is polymorphic between states 0 and 1 . This latter observation accords with the 

 assessment that accessory cusps represent a derived feature in the otariids (Repenning & 

 Tedford 1977). Most phocids display triconodont postcanines, which develop either 

 ancestrally for the family as a whole (ACCTRAN optimization), or convergently in each 

 subfamily, with the phocids primitively retaining the equivocal pinniped ancestral state 

 (DELTRAN optimization). Only Lobodon (state 2) and Mirounga leonina (state 0, possibly 

 as a synapomorphy of Mirounga spp.; ACCTRAN optimization) fail to exhibit triconodont 

 postcanines. The unicuspate teeth of M. leonina appear to develop from the fusion of the 

 individual cusps of a triconodont precursor (pers. obs.). 



138) tendency to form additional cusps in triconodont postcanines: 0 = absent; 1 = present; 

 9 = n/a - postcanines not triconodont (Chapskii 1955a). 



As mentioned above, the triconodont morphology tends to show a high degree of variation 

 from the basic (idealized) pattern. In most cases, the exact morphology of the postcanines 

 is associated with prey type (Chapskii 1955a; Davies 1958b). This and the following two 

 characters attempt to diagnose any systematic trends in this variation. The tendency to 

 form additional accessory cusps in triconodont teeth is primarily manifested in the addition 

 of small fourth cusp (and, occasionally, a very small fifth cusp) posteriorly, although an 

 additional anterior cusp is possible. This multicuspate condition has been implicated in 

 the retention of actively moving prey items (Chapskii 1955a). Additional accessory cusps 

 have been variously noted for most of Histriophoca, Pagophilus, Phoca spp., and Pusa 

 spp. (Doutt 1942; Chapskii 1955a). Chapskii (1955a) indicates that an additional cusp may 

 also be formed, albeit very rarely, in Erignathus. 



This character applies only to three distantly related clades within the phocids: the phocines 

 (with and without the polymorphic Cystophora), Hydrurga, and Monachus spp. [Together 

 with similar distributions in the following two characters, this could be interpreted to 

 support independent origins of the triconodont morphology in each phocid subfamily (see 

 previous character). As well, the indication that the plesiomorphic state 9 is ancestral for 

 the polymorphic Zalophus hints at a convergent origin for triconodont postcanines in 

 otariids (also Repenning & Tedford 1977).] The distribution of this character is 

 complicated and shows no clear pattern under either optimization criterion. However, the 

 tendency to gain additional accessory cusps was consistently present in two main groups: 

 Monachus schauinslandi (possibly together with Monachus tropicalis; ACCTRAN 

 optimization), and Phoca spp. plus Pusa spp. Likewise, the lack of the tendency was found 

 in three clades: Monachus monachus, Halichoerus, and Erignathus plus Histriophoca plus 

 Pagophilus. 



