145 



maturity, the skull grows, allowing the postcanines more room (Doutt 1942), as was clearly 

 demonstrated in an age series of Phoca largha (Chapskii 1967). 



This character may also be susceptible to the potential case of paedomorphosis in the 

 phocids, and especially in the phocines (see King 1972; Wyss 1994). As it applies to this 

 character, two main skull types have been observed to exist. The skulls of the smaller 

 phocids have been described as possessing a more "juvenile'* appearance due to their 

 relatively large crania and relatively small rostra (King 1972). With their smaller rostra, 

 these "juvenile" skulls may demonstrate a higher incidence of postcanine crowding. 

 Conversely, the skulls of the larger phocids present a more "adult" appearance, with 

 relatively smaller crania and longer rostra (King 1972). This skull type might therefore 

 be expected to lack crowding of the postcanines. 



Finally, this character has been noted to be sexually dimorphic in Phoca vitulina (Allen 

 1902), but not Phoca largha (Chapskii 1967), two otherwise closely related species. 

 Despite these problems, the crowding of the postcanines has been used by Ridgway (1972) 

 to distinguish between the genera Phoca (state 1) and Pusa (state 0). 

 As evidenced by the fissipeds observed in this study, the Caniformia are primitively 

 characterized by having the postcanines in contact with one another (but typically merely 

 touching and not overlapping). The converse condition is proposed as a synapomorphy of 

 the Pinnipedia, with reversals in Monachus monachus, M. schauinslandi (a possible 

 synapomorphy of Monachus spp.; ACCTRAN optimization), and Phoca vitulina, all of 

 which possess the juvenile skull type. However, numerous other phocines (most notably 

 Pusa spp.) with the same skull type do not demonstrate this trait, placing the correlation 

 between skull type and postcanine crowding in some doubt. Bearing this in mind, the 

 observation that the postcanines are not in contact in the phocids primitively may 

 contradict King's (1972) hypothesis that the ancestral phocids possessed a juvenile skull 

 type, while supporting Wyss's (1994) interpretation of it being a secondary derivation. 

 147) obliqueness of postcanine implantation relative to long axis of tooth row (upper and 

 lower): 0 = straight; 1 = anterior / posterior end of postcanine directed laterally (de Muizon 

 1982a). 



This character is related in many ways to the previous one. In young animals, or those 

 with a juvenile skull type, the relatively short tooth row will crowd the postcanines and 

 push them out of line. With an increase in age (or a change to the adult skull type), the 

 postcanines should fall back into line in the relatively longer tooth row (Doutt 1942; de 

 Muizon 1982a). Apart from those species listed under the previous character, de Muizon 

 (1982a) claimed a tendency towards oblique implantation of the postcanines as a 

 synapomorphy of Monachus spp. (but relatively greater in M. monachus than in either M. 

 schauinslandi or M. tropicalis) due to the relative shortness of their tooth rows. King 

 (1972) noted an oblique orientation of the lower teeth of M. monachus in particular. This 

 condition may also characterize other phocids with a juvenile skull type. In particular, 

 Chapskii (1955a) comments that Phoca spp. is often noted for the obliqueness of its 

 postcanines. 



The apomorphic condition, in which the postcanines are obliquely implanted, displays a 

 virtually identical distribution as the previous character: Monachus spp. (but including M. 



