122 



condition of this character and they were coded as "unknown".] Although this distribution 

 appears to support Wyss's (1987) contention of an Odobenus-phocid clade (also Wyss & 

 Flynn 1993). the interpretation of this distribution here is for either parallel origins in each 

 of the two taxa (DELTRAN optimization), or for a synapomorphy of the pinnipeds as a 

 whole, with Zalophus reversing to re-obtain the primitive condition (ACCTRAN 

 optimization). 



*87) hypomastoid fossa (found along posteroventral edge of the auditory bulla and 

 containing the stylomastoid groove): 0 = absent: 1 = present (Wozencraft 1989). 

 With recoding. this character was included in character #88. 



88) depth of hypomastoid fossa: 0 = shallow: 1 = medium: 2 = deep: 9 = absent 

 (Wozencraft 1989). 



The presence of a hypomastoid fossa was employed by Wozencraft (1989) to unite the 

 otarioids with the ursids. Perhaps the key to this outcome is the defining of the fossa so 

 as to be dependent on the presence of a petromastoid ridge running between the 

 paroccipital and mastoid processes (see character #89). However, our observations 

 revealed that these two features are not always coincidental, with many phocids possessing 

 an apparent hypomastoid fossa while lacking the petromastoid ridge. Thus, we modified 

 Wozencraft' s (1989) coding of the character so that the two features now appear as separate 

 characters here (see character #89). 



The presence of a hypomastoid fossa is primitive among the Caniformia: however, it is 

 difficult to be more specific due to the high incidence of polymorphism in the basal 

 arctoids. Canis is characterized by a shallow fossa, while Procyon and Ursus may share 

 a deep fossa (ACCTRAN optimization only). The apomorphic loss of the fossa unites 

 Mattes, the lutrines, and the pinnipeds. Several reversals towards a redevelopment of the 

 fossa occur in the pinnipeds, primarily among the otarioids (states 0 or 2) and the 

 monachines. For the monachines. a shallow fossa is regained internal to Mirounga spp.. 

 and is increased to a deep fossa in Monachus spp. Only scattered phocines regain the 

 hypomastoid fossa: Cystophora (states 1 and 2). Erignathus (states 0 and 1 ). and possibly 

 Pagophilus and Phoca vitulina (both states 0 and 9) 



89) distinct petromastoid ridge connecting paroccipital and mastoid processes: 0 = absent: 

 1 = present (Wozencraft 1989). 



As mentioned above, this feature rather than the hypomastoid fossa (see character #88) 

 was perhaps the key to Wozencraft (1989) uniting the otarioids (also Mivart 1885; Howell 

 1928) with the ursids (also Davis 1964). In contrast, de Muizon ( 1982b) (as cited in Wyss 

 1987) has used the reduction or outright loss of the petromastoid ridge as an apomorphic 

 trait uniting the mustelids (exclusive of leptarctines and melines. but including lutrines) 

 with the phocids. Wyss (1987) discounts this assessment, noting that the mastoid region 

 in phocids is highly modified, thus rendering the comparison w ith the mustelid region 

 somewhat dubious. As well, apparent petromastoid ridges have been described for 

 Leptonychotes, Monachus spp.. and Ommatophoca (Mivart 1885: Wyss 1987). 

 Complicating all this is the often highly variable form of the petromastoid ridge. We 

 observed that it rarely takes the form of a distinct ridge, but is instead usually fairly low 

 and rounded. As well, in taxa such as Canis and Procyon. what might be called the 



