131 



condition), with only Pusa sibirica obtaining an intermediate separation. Reversals to the 

 plesiomorphic condition occur in both subfamilies: Pagophilus and Phoca vitulina among 

 phocines, and Hydrurga and Lobodon among monachines. For the two monachines, this 

 occurs either due to convergence (DELTRAN optimization), or as a synapomorphy 

 followed by a reversal for the remaining, more terminal taxa (ACCTRAN optimization). 

 Thus, with the addition of the phocids, the distribution of our coding largely matches that 

 of Wozencraft (1989). This is due to either the two codings being synonymous (i.e., our 

 coding matches the intent of his original definition) or correlated in some manner. 



113) relative size of dorsal region of petrosal: 0 = unexpanded; 1 = intermediate; 2 = 

 expanded (Wyss 1988a). 



Several mechanisms allow for the pinnipeds to improve their underwater hearing: creating 

 an external cochlear foramen (see characters #107 and 108), exposing the petrosal 

 externally (see character #84), increasing the size of the Promontorium, and/or generally 

 increasing the size of the petrosal (Repenning 1972; Repenning & Ray 1977; de Muizon 

 1982a). This character and the following one each deal with mechanisms employed by 

 the phocids to increase the size of the petrosal. As defined by Repenning & Ray (1977), 

 the dorsal part of the petrosal is that region above the line extending from the vestibular 

 aqueduct across the top of the cochlear aqueduct to the anterodorsal surface of the petrosal 

 apex. This region is clearly expanded in virtually all known phocids (fossil and Recent), 

 except Monachus schauinslandi. The largely unexpanded dorsal region in this phocid (to 

 the exclusion of the other members of Monachus) has been used as evidence to support 

 its status as the most primitive of all phocids (Repenning & Ray 1977; Wyss 1988a). 

 An unexpanded dorsal region of the petrosal is indeed plesiomorphic among the 

 Caniformia. However, our observations reveal that the apomorphic, expanded 

 morphologies (states 1 and 2) have a wider distribution than previously stated, 

 characterizing such non-phocids as Martes, Ursus, and Odobenus [for Odobenus, at least, 

 this morphology may be associated with a greatly expanded petrosal apex (Repenning 

 1975; see following character)]. All three represent convergent evolution (together with 

 the phocids), although ACCTRAN optimization indicates that the expanded condition may 

 be a synapomorphy of the pinnipeds, with Zalophus reversing to re-obtain the primitive 

 condition. Among the phocids, an expanded dorsal petrosal is universal except for several 

 monachines: Ommatophoca, Monachus schauinslandi, Monachus tropicalis (all state 0), 

 and Monachus monachus (state 1). This may represent a synapomorphy of the group, with 

 a reversal in Lobodon and further derivation in Monachus monachus (ACCTRAN 

 optimization), or independent evolution in the various clades (DELTRAN optimization). 



114) relative size and shape of petrosal apex: 0 = absent / unexpanded and pointed; 1 = 

 intermediate; 2 = dorsoventrally thickened and bulbous (Wyss 1988a). 



Overlapping the previous character somewhat, this character specifically examines the very 

 apex of the dorsal region of the petrosal. Wyss (1988a) notes that the phocids exclusive 

 of Monachus spp. are united by a massive expansion of the apex, causing it to present a 

 dorsoventrally thickened, bulbous morphology. This morphology has been held to provide 

 a greater sensitivity to sound underwater (Hendey & Repenning 1972), and is in contrast 

 to the condition in most other carnivores and the otarioids, where the apex is unexpanded 



