160 



to aid in swimming. This condition is obtained in virtually all Recent pinnipeds, the only 

 exceptions being Odobenus, where they are rarely fused, and Monachus schauinslandi, 

 where they are almost never fused (Ray 1976a; Repenning & Ray 1977; de Muizon & 

 Hendey 1980; de Muizon 1982a; King 1983; Wyss 1988a). Complete fusion is typically 

 observed in later fossil pinnipeds, but not in the earlier basal forms (Repenning & Ray 

 1977; de Muizon & Hendey 1980; Wyss 1988a), leading to suggestions that the unfused 

 morphology is primitive for phocids (Ray 1976a; de Muizon 1982a). In addition to the 

 two extreme morphologies, we noted that in some specimens, preliminary fusion had 

 occurred between the epiphysial heads (typically in the anterodorsal region), but was 

 incomplete in other regions. In accordance with King's (1956) suggestion that the fusion 

 between the tibia and the fibula may be among the last to occur during ontogeny, this 

 latter condition (state 1) may represent a developmental artifact. 



Any fusion of the tibia and fibula is apomorphic within the Caniformia. Martes is unique 

 among fissipeds in displaying the rudimentary fusion of these two elements (state 1). At 

 the earliest, complete fusion occurs as a synapomorphy of the pinnipeds (with a reversal 

 in Odobenus; ACCTRAN optimization), but for the phocids in any case (with a convergent 

 appearance in Zalophus; DELTRAN optimization). Full or partial reversals within the 

 phocids are reasonably limited. Partial reversals occur independently in the phocines Phoca 

 largha and Pusa sibihca (possibly as a synapomorphy with Pusa hispida; ACCTRAN 

 optimization). A full reversal unites the monachines Lobodon plus Monachus spp., 

 although all species except Monachus schauinslandi are polymorphic for states 0 and 1. 

 184) relative degree of development of the post-tibial (= intercondyloid) fossa of tibia: 0 

 = weak; 1 = strong (King 1966; Wyss 1988a). 



King (1966) distinguished between the phocines and monachines by noting a greater 

 tendency for a more pronounced post-tibial fossa in the former (also de Muizon & Hendey 

 1980). Other than for a curious tendency towards the phocine condition in the fossil 

 lobodontine Homiphoca (Hendey & Repenning 1972; de Muizon & Hendey 1980), this 

 appears to be a unique feature for the phocines, with the fossa being shallow in the 

 otarioids and most fissiped carnivores (Wyss 1988a). However, among the outgroups 

 examined here, only Canis demonstrated a weak post-tibial fossa, rendering the polarity 

 of this character equivocal at the level of the Caniformia. The strong fossa typical of 

 fissipeds is largely retained in the pinnipeds, with only Monachus schauinslandi plus 

 Monachus tropicalis, Phoca largha, and Pusa sibihca independently deriving a weak 

 fossa. This outcome (plus the high incidence of polymorphism in this character) seriously 

 detracts from the ability of this character to distinguish between the two phocid 

 subfamilies, and may stem from the lack of any substantial difference between the two 

 character states. This, in turn, might relate to the lack of any substantial differences among 

 caniform astragalar trochleae, the structure that articulates with the post-tibial fossa. 

 *185) robustness of calcaneum: 0 = smaller than or subequal to astragalus; 1 = larger than 

 astragalus (de Muizon 1982a). 



The comparative robustness of the calcaneum, when the astragalus is used as a reference, 

 merely reflects the presence or absence of the posterior process on the plantar aspect of 

 the astragalus. As this duplicates character #186, this character was excluded. 



