156 



Although reasonably common among the otarioids [especially the arctocephaline otariids 

 (the fur seals) and occasionally Odobenus], a distinct obturator nerve foramen separate 

 from the obturator foramen is present only in Monachus schauinslandi among phocids 

 (King & Harrison 1961: Ray 1976a: Repenning & Ray 1977: Wyss 1988a). Wyss (1988a) 

 has interpreted this feature as being primitive among the pinnipeds, and used the above 

 distribution to justify the sister taxon status of M. schauinslandi to the remaining phocids. 

 An identifiable obturator nerve foramen is periodically present in Cystophora and 

 Monachus tropicalis, but it is confluent with the obturator foramen (state 1). whereas it 

 is displaced towards the cotyloid notch of the acetabulum in Monachus schauinslandi 

 (state 0) (King & Harrison 1961: Repenning & Ray 1977: Wyss 1988a: pers. obs.). Any 

 appearance of the obturator nerve foramen (states 0 or 1 ) is apomorphic among the 

 caniforms. State 0 is only manifested in Monachus schauinslandi, while state 1 occurs 

 convergently in the otarioids and Monachus tropicalis. Cystophora was notably 

 polymorphic for states 1 and 2 for this character. 



174) ridges in anterior portion of obturator foramen: 0 = absent: 1 = present (pers. obs.) 

 (Fig.24). 



We noted this feature in the pelves of a diverse range of taxa. These ridges may be related 

 to the previous character, as their location closely approximated that of the incompletely 

 separated obturator nerve foramen in species such as Cystophora and Monachus tropicalis 

 (see previous character). In fact, these ridges may serve to segregate the obturator nerve 

 from various muscles of the hip. most notably the craniad insertions of the obturatorius 

 externus and internus muscles on the obturator membrane (Howell 1928; Miller 1962: 

 Pierard 1971). Admittedly, the term "■ridges" is inadequate as the ridges took on many 

 forms, ranging from actual longitudinally oriented ridges that in effect constricted the 

 anterior part of the obturator foramen, to small bony spurs. 



In general, the ridges tend to be absent in the fissipeds, although their appearance in Cards 

 renders the polarity of this character equivocal at the level of the Caniformia. The ridges 

 mark a synapomorphy of the pinnipeds, with the phocids showing a tendency towards 

 their loss. Ridges are consistently absent in Monachus spp. (possibly as a synapomorphy 

 with Lobodon: ACCTRAN optimization). Phoca vitulina. and the clade of Pusa hispida 

 plus Pusa sihirica. and polymorphically so in a number of other phocids. 



#177 



Fig.24: Lateral view of the 

 left pelvic girdle of Pusa 

 hispida illustrating selected 

 characters (indicated by their 

 number: see Character 

 Analysis) of this element. 

 Anterior is towards the left of 

 the page and dorsal to the top. 

 Adapted from de Muizon 

 (1982a). 



