Most variations in dental formulae of pinnipeds are probably due to the loss of teeth and the subsequent bony alveolar obliteration. These abnormalities make identification of the skulls somewhat difficult and may be the cause of systematic or taxonomic disagreements. For example Forbes (Trans. Zool. Soc. Lond., 11: 225–231, 1881) states, “As regards the genus Zalophus, it may be noted that Mr. O. Thomas has lately noticed a skull of Otaria jubata with the same number of molars as are supposed to characterize that genus (P.Z.S. 1881, p. 4).”