181 



Other obvious changes are required outside of the phocids (e.g., the pinnipeds should no 

 longer be a carnivoran suborder, but a tribe within the lutrines), but the wholesale 

 alterations to arctoid taxonomy that this would require, even ignoring the difficulties in 

 the application of the term "monophyly" to the pinnipeds (see above), are beyond the 

 scope of this study. 



Biogeography and fossil evidence 



As a group, the phocids possess one of the more interesting biogeographical distributions 

 among mammals. They are found in both hemispheres, but, excepting Monachus spp. 

 which are the only phocids to inhabit tropical climes, are largely limited to the polar and 

 sub-polar regions of each [see Scheffer (1958) and King (1983) for precise species ranges]. 

 This, coupled with a postulated North Atlantic origin for the family (McLaren 1975; Ray 

 1976a; Repenning et al. 1979), has led to many theories as to the development of the 

 current species distribution. It is not our intent here to develop a new biogeographic 

 hypothesis for the phocids based on the phylogeny advocated herein, but rather to compare 

 this phylogeny with some of the biogeographic hypotheses that have already been put 

 forth. 



The basic biogeographic theory for the phocids holds for a North Atlantic origin of the 

 family around the early middle Miocene [15 million years before present (MYBP)]. Fully- 

 fledged representatives of both the monachines and phocines are found in this initial fauna. 

 The remainder of the Miocene saw the isolation of a group of phocines (later to give rise 

 to Pusa spp.), and possibly isolated monachines, in the Paratethys Sea, a large ancient sea 

 covering much of what is now eastern Europe. Other phocines and monachines continued 

 to inhabit the North Atlantic at this time, with the monachines being the dominant form, 

 especially on the North American side (Hendey & Repenning 1972; Grigorescu 1976; Ray 

 1976a; Repenning et al. 1979). Climatic deterioration during the Pliocene evoked different 

 responses on the part of the North Atlantic phocids. The monachines largely retreated 

 southward, retaining their pagophobic habits, while the phocines, although also retreating 

 southward to some degree, responded more by adapting to the cooler climate (Hendey 

 1972; Ray 1976a). 



Within the monachines, Monachus spp. (or ancestors thereof) are posited to have remained 

 behind as the remainder of the subfamily continued moving southward. Two competing 

 hypotheses exist as to how the three species of monk seal arose: a progressive westward 

 waif dispersal from the northwest coast of Africa (Hendey 1972; de Muizon 1982a), or 

 the interruption of the gene flow of a wide-ranging North Atlantic population (giving rise 

 to Mediterranean and Caribbean populations), followed by waif dispersal to the Hawaiian 

 islands (Ray 1976a). In either case, M. schauinslandi and M. tropicalis are held to share 

 a common ancestor to the exclusion of M. monachus (in contrast to more recent opinion). 

 The remaining monachines continued their southward migration either on the Pacific side 

 of South America (Repenning et al. 1979), the Atlantic side (Hendey 1972), or on both 

 sides (Ray 1976a; de Muizon 1982a). 



