137 



are regained in Monachus monachus, and as a synapomorphy of Hydrurga and 

 Leptonychotes, before both the sagittal crests and temporal ridges are lost outright. 

 Halichoerus and Monachus tropicalis also possessed sagittal crests, albeit as a 

 polymorphism with other states. 



Teeth (23 characters) 



Despite the great importance attached to teeth by mammalian systematists, they are only 

 infrequently used as a systematic tool within the phocids. Much of this arises from the 

 trend toward homodonty in the pinnipeds, which largely eliminates many potential 

 morphological characters, combined with a high intraspecific variability in the phocids at 

 least (King 1966, 1983; Hillson 1986). Indeed, many studies tend to concentrate on 

 attributes of the dentition as a whole (e.g., tooth formulae), rather than on the morphology 

 of individual teeth (e.g., Burns & Fay 1970; de Muizon 1982a). Additionally, as Chapskii 

 (1955a) has noted for the phocines, the systematic value of phocid teeth may be limited 

 by the high functional demand placed upon them by food specialization within the group 

 and the resultant rapid evolution arising from this (also Davies 1958b). However, teeth 

 characteristics have played a major role in Chapskii's (1955a, 1967) attempts to sort out 

 phocine phylogeny. 



127) number of upper incisors in one-half of jaw: 0 = zero; 1 = one; 2 = two; 3 = three 

 (King 1966). 



Other than the possession of an inflatable nasal apparatus, the incisor formula was a key 

 character used to support the Cystophorinae, with both Cystophora and Mirounga 

 possessing a 2/1 pattern, as opposed to the 3/2 pattern of phocines or the 2/2 pattern of 

 monachines (Scheffer 1958; King 1964, 1966; Ridgway 1972). However, beyond the 

 convergent Cystophora and Mirounga (see King 1966), the incisor formula seems to 

 describe synapomorphies of both phocid subfamilies, although the phocines may retain 

 the ancestral phocid number (McLaren 1975). In an effort to generate synapomorphies 

 with some of the outgroup taxa (which are generally 3/3), we have split the incisor formula 

 into two characters, corresponding to the number of upper and lower incisors respectively. 

 Only Odobenus, Cystophora, and the monachines diverge from the plesiomorphic 

 condition of three upper incisors. Odobenus uniquely derives one upper incisor (Mivart 

 1885; Cobb 1933), although it is commonly misidentified as a postcanine due to its 

 position and the unusual pattern of dental succession in this animal (King 1983; see Cobb 

 1933). The condition of two upper incisors in Cystophora and the monachines represents 

 either a case of convergence (DELTRAN optimization), or a synapomorphy of the phocids, 

 with the remaining phocines reversing to re-obtain the primitive condition (ACCTRAN 

 optimization). 



128) number of lower incisors in one-half of jaw: 0 = zero; 1 = one; 2 = two; 3 = three 

 (King 1966). 



As with the upper incisors (see previous character), three lower incisors are plesiomorphic 

 for the caniforms. However, the reduction to two incisors now occurs either as a 

 synapomorphy of the lutrines plus the pinnipeds, with a reversal to the plesiomorphic 



