Une comparaison des cranes et de la dentition des elephants de mer septentrional (Mirounga angustirostris) et mdridional (Mirounga leonina) a mis en ovidence les caracteres indicatifs de leur ovolution et de leur degre de parent^. Les postcanines postorieures soiit plus souvent bi-et tricuspides chez M. angustirostris, et il y a une tendance plus poussee ä la presence de racines doubles dans ces postcanines que chez M. leonina. II existe moins de dimorphisme sexuel chez M. angustirostris, et certaines dimensions craniennes son t proportionnellement plus petites que celles de M. leonina. Les differences principales sont en relation avec le raccourcissement du museau chez M. leonina. Ces caracteres, ainsi que la poriode de reproduction, le pelage et evidence des fossiles, sont ici trait£s dans leur contexte ovolutif. Une nouvelle interpretation de revolution du genre est presentee.The two species of elephant seals are among the best known marine mammals. Studies of the reproductive behavior, growth, longevity, and anatomy of elephant seals have provided information comparable in detail to those available for the northern fur seal (Callorhinus ursinus), perhaps the best known of all marine mammals. The phyletic relationships of elephant seals, however, are poorly known. Until recently even the subfamilial affinities of Mirounga were in doubt (King, 1966), and the most recent synthesis of evolutionary history within the genus is largely speculative (Hendey, 1972). There has been recent interest in such relatively sophisticated studies as dialect formation, comparative ethology, and protein polymorphisms among elephant seal populations (LeBceuf and Perterson, 1969 ;LeBceuf and Petrinovich, 1974;Bonnell and Selander, 1974). Accordingly, we have been prompted to investigate the differences between the two species of the genus in hopes of providing a more comprehensive understanding of elephant seal evolution.The genus is comprised of two allopatric species. Mirounga angustirostris, the northern elephant seal, has bred in historic times from Cabo San Lazaro, Baja California, Mexico at 24° N, to Point Reyes, California at 38° N (Scammon, 1874). Range limits of M. angustirostris out of the breeding season are reported as from the Gulf of Alaska in the north
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