147 



Mandible (3 characters) 

 Although it is frequently mentioned in species descriptions, the mandible exclusive of the 

 teeth has not been a common source of characters in recent systematic studies of the 

 phocids. This has not always been the case. Chapskii (1955a) asserts that the general form 

 of the mandible (and especially of its posterior margins) contains important taxonomic 

 information, a source of information previously exploited primarily by Russian 

 systematists. Another possible character, which was not examined here, deals with the 

 mandibular symphysis which appears to be generally more robust in the monachines than 

 in the phocines (pers. obs.). 



150) shape of lingual face of mandible at middle postcanines: 0 = concave; 1 = flat; 2 = 

 convex (Ridgway 1972). 



This character has been employed to distinguish between the genera Phoca spp. (state 2) 

 and Pusa spp. (state 0) (Ridgway 1972). A flat morphology is plesiomorphic among 

 caniforms, with the remaining apomorphic states possessing limited distributions, and 

 among the pinnipeds only. A concave morphology appears independently on a number of 

 occasions: Odobenus, Lobodon, Mirounga spp., and Monachus tropicalis. The convex 

 morphology was only noted for Cystophora and Halichoerus. This arises either as a 

 synapomorphy of the phocines as a whole, with the remaining taxa reversing to the 

 plesiomorphic condition (ACCTRAN optimizations), or independently in the two taxa 

 (DELTRAN optimization). Phoca spp. and Pusa spp. were not distinguished by this 

 character, as both genera were characterized by a flat morphology. 



151) shape of posteroventral edge of mandible: 0 = rounded; 1 = jagged (Ridgway 1972). 

 In effect, this character deals with the size of the angular process. A rounded posteroventral 

 edge of the mandible (small angular process) has been noted independently for Hydrurga 

 (Ridgway 1972) and Ommatophoca (Mivart 1885). However, this apomorphic condition 

 generally seems to be a synapomorphy of the monachines minus the elephant seals 

 {Mirounga spp.) as a whole. Although a reduction of the angular process seems to 

 characterize all phocids to some degree, a substantial reduction (to the apomorphic 

 condition) occurs only in Cystophora and Erignathus among phocines. 



Taylor (1914) holds the reduction of the angular process to be an aquatic adaptation, with 

 the support provided by the aquatic medium allowing for reduced muscle masses, and 

 therefore reduced muscle attachment points. However, why this would affect the angular 

 process is unclear. The angular process is the posteromost extent of the insertion of the 

 pterygoideus internus (= lateralis) (Davis 1964), but neither a relative reduction, nor a 

 shift in the insertion of this muscle has been described in the phocids (see Howell 1928; 

 Bryden 1971; Pierard 1971). This character may, in fact, be homoplastic as a true reduction 

 of the process (e.g., as in Leptonychotes), or an expansion of the angle of the jaw 

 subsuming the process (e.g., as in Monachus monachus) will both give the appearance of 

 a reduced angular process. 



152) distinct medially directed flange along ventral edge of jaw located posterior to 

 mandibular symphysis and ventral to posterior postcanines: 0 = absent; 1 = present (King 

 1972). 



