The relationship between the four principal pinniped karyotypes

The karyotypes of 5 pinnipeds, Arctocephalus pusillus 2n = 36, Callorhinus ursinus 2n = 36, Odobenus rosmarus 2n = 32, Monachus schauinslandi 2n= 34 and Phoca fasciata 2n = 32, were studied. Based on the present and previously studied material a comparison based on G-band patterns was made between the four principal pinniped karyotypes. The otariid and odobenid karyotypes are closely related, the otariid kakyotype being the more ancestral. The 2n = 32 phocid karyotype has evolved from the 2n = 34 karyotype by a two pair fusion. The similarity between the 2n = 36 otariid and the 2n = 34 phocid karyotypes is greater than the similarity between either of these karyotypes and any carnivore karyotype. The karyological analysis thus support the theory of a monophyletic origin of the Pinnipedia even if it cannot be completely excluded that the recent pinnipeds evolved from different ancestors that shared the same karyotype.