Miller, EH & DJ Boness. 1979. Remarks on display functions of the snout of the grey seal, Halichoerus grypus (Fab.), with comparative notes. Canadian J of Zoology, 57: 140-148.

Abstract: “Adult males of the grey seal, Halichoerus grypus (Fab.) (Phocidae), display the large snout conspicuously in threats. The male’s snout has probably evolved through sexual selection as a visual display organ, as in some other extant phocids: the hooded seal, Cystophora cristata (Nilsson) and the two species of elephant seals, Mirounga (Gray). This may also be true of the extinct desmatophocid Allodesmus Kellogg. Cephalic display organs in the form of long tusks have also evolved twice in the Odobenidae (walruses). Comparable display structures do not occur in the Otariidae (fur seals and sea lions). However, the massive neck of adult male otariids is important in undirected static-optical threat displays, especially at long range, and in some kinds of short-range threats. Also, adult otariids show sexual dimorphism in facial appearance, which varies interspecifically.

Pinniped species in which large mature males have prominent, constant-growing cephalic display structures show fluid spacing among rutting males, and much agonistic communication at the water surface and on land or ice. This correlation may reflect selective pressures on males to affirm social status repeatedly, through displays which communicate their age (hence strength and experience), and their resource-accruing abilities.”