116 



shows a lower degree of intergeneric and intraspecific variation than other regions of the 

 skull (King 1966). However, despite its apparent stability, there is still the potential for 

 some homoplasy within this region (see Hunt & Barnes 1994). Important basicranial 

 characters involve such landmarks as the carotid canal [the distinguishing feature of arctoid 

 carnivores (Wyss 1988a)], the auditory bulla, and various other processes and foramina 

 of the region. 



75) visibility of the mastoid process in dorsal view: 0 = not visible; 1 = visible (Wyss 

 1988a). 



The condition whereby the mastoid process is visible in dorsal view is unusual among 

 mammals, being restricted primarily to the phocines, with some convergent appearances 

 in the monachines (King 1966; Burns & Fay 1970; Ray 1976b; de Muizon 1982a, Wyss 

 1988a). Typically, Monachus spp. and/or Ommatophoca are implicated (King 1966; Ray 

 1976b; de Muizon 1982a), although Burns & Fay (1970) indicated that it occurred in about 

 half of all the monachine specimens they examined. These convergent appearances can 

 apparently be eliminated if the character is recoded to examine for the presence or absence 

 of a medially curving mastoid crest (de Muizon 1982a), or, equivalently, of a distinct 

 oblique ridge formed by the mastoid process (Burns & Fay 1970). The presence of either 

 of these synonymous features is apparently exclusive to the phocines (Burns & Fay 1970: 

 de Muizon 1982a). We retained the less precise coding in an effort to determine the exact 

 distribution of this character among the Monachinae. 



As indicated above, the apomorphic morphology (state 1) is primarily restricted to, and 

 universal among, the phocines. Pusa caspica and Pusa sibihca appear to be independently 

 losing this trait, primarily due to a reduction in the size of the mastoid process. Convergent 

 appearances of this trait were consistently observed in only two monachines, Monachus 

 monachus and Ommatophoca, as well as in the fissiped Procyon. 



76) relative shape of basioccipital-basisphenoid region: 0 = concave; 1 = flat; 2 = convex 

 (Wyss 1988a). 



Burns & Fay (1970) noted that all phocines share a relatively flat to convex basioccipital- 

 basisphenoid region, as opposed to the strongly concave form in monachines. Wyss 

 (1988a) extended this last observation to include the otarioids, adding that he believed the 

 concave morphology to be primitive (presumably for the pinnipeds), and therefore not 

 synapomorphic for the monachines. We have modified the coding of this character 

 somewhat by dividing the state "flat to convex" into its two constituent morphologies. 

 In contrast to Wyss (1988a), our analysis indicates that a flat morphology is primitive for 

 the arctoids (the plesiomorphic state for the caniforms is equivocal), as well as for the 

 pinnipeds. Instead, a concave basioccipital-basisphenoid region is a derived trait, possibly 

 characterizing the monachines ancestrally (ACCTRAN optimization). However, it is only 

 manifested in Mirounga spp. among extant species; the remaining monachines largely 

 emulate the supposed phocine condition, displaying either the flat (Ommatophoca) or 

 convex morphologies (Hydrurga, Lobodon, Monachus spp.), or both (Leptonychotes). The 

 phocines tend towards retention of the flat morphology, with only Halichoerus and Phoca 

 vitulina developing the convex condition. This latter state also appears convergently in 

 Canis and Enhydra. 



