129 



Beyond this, independent reversals to state 0 occur within each subfamily (and twice 

 within the monachines), with Mirounga spp. again uniquely deriving state 9. 



107) mastoid lip in region of external cochlear foramen: 0 = absent; 1 = rudimentary or 

 present (Wyss 1988a). 



The presence of a mastoid lip that partially obscures the posterior wall of the auditory 

 bulla and the external cochlear foramen (see the following character) has been noted as 

 being diagnostic of the lobodontines (Repenning & Ray 1977; de Muizon & Hendey 1980; 

 de Muizon 1982a; Wyss 1988a). However, while the mastoid lip is a derived feature, it 

 is not unique to, or indeed universal among, the lobodontines. Instead, it appears conver- 

 gently in Leptonychotes, Lobodon, and the clade of Pusa sibirica plus Pusa hispida, with 

 polymorphic appearances in Enhydra, Lutra, Halichoerus, and Pusa caspica. 



108) external cochlear foramen: 0 = open: 1 = closed; 9 = absent (de Muizon 1982a). 

 The external cochlear foramen, first identified and named by Burns & Fay (1970). is 

 unique to phocids, linking the round window to the external surface of the skull to facilitate 

 underwater hearing (Repenning 1972; de Muizon 1982a). Although Repenning (1972) 

 states that the foramen is present in all phocids to various degrees, there is a tendency 

 towards the closure of the foramen in each subfamily to provide the resistance to increased 

 water pressure needed for deep diving (de Muizon 1982a). In the Monachinae, the external 

 cochlear foramen is covered by a mastoid lip in the lobodontines (de Muizon 1982a; Wyss 

 1988a; but see previous character). In the Phocinae, the closure is accomplished in 

 Halichoerus, Phoca spp., and Pusa spp. by an expansion of the auditory bulla (de Muizon 

 1982a). However, this closure is less absolute than that of the lobodontines (de Muizon 

 1982a), so that Burns & Fay (1970) merely note the presence of a reduced foramen in 

 these same phocines. 



The external cochlear foramen first arises as a synapomorphy of the phocids. (The 

 assessment of it being missing in the remaining caniforms is a posteriori, as there is no 

 objective way to distinguish between the states ''absent" and "closed" based on gross 

 examination of the skull.) The parallel trends towards the closure of the foramen in each 

 phocid subfamily were observed, although the distributions are modified somewhat. In the 

 monachines, it is generally closed in the lobodontines and Monachus tropicalis. This latter 

 observation requires either Monachus monachus and Monachus schauinslandi to 

 convergently re-open the foramen (DELTRAN optimization), or Monachus tropicalis to 

 reverse from a state 0 synapomorphy of Monachus spp. (ACCTRAN optimization). In the 

 phocines, parallel closure occurs in Erignathus and Pusa sibirica, the latter possibly as a 

 synapomorphy with Pusa hispida (ACCTRAN optimization). 



109) relationship between stylomastoid and auricular foramina: 0 = confluent / common; 

 1 = intermediate; 2 = separate; 9 = auricular foramen absent (de Muizon 1982a). 



In noting the "dumbbell-shaped" morphology of the stylomastoid foramen of most 

 phocines, Burns & Fay (1970) realized that this condition actually represents a confluence 

 between the anterior stylomastoid foramen and the posterior auricular foramen, the latter 

 of which is apparently unique to the phocids. These two foramina share a wide range of 

 morphologies, from completely separate to partially confluent, as in the phocines (Burns & 

 Fay 1970). to completely confluent as an auriculostylomastoid foramen in Mirounga spp. 



