Sanvito, S., F. Galimberti and E. H. Miller (2007). Having a big nose: structure, ontogeny and function of the elephant seal proboscis. Canadian Journal of Zoology 85: 207-220. The proboscis of male elephant seals (Mirounga) has been suggested as an example of a secondary sexual trait since Darwin. There has been much speculation about its social function (e.g. optical signal of breeding status, amplification of vocalizations, cue for female choice). However it has never been studied in detail, probably due to its fleshy nature that makes measurement difficult. In this paper, we employ photogrammetry to measure the proboscis and facial morphology of a large sample of wild, unrestrained southern elephant seals (Mirounga leonina). We describe ontogeny and allometry of the proboscis and analyze current phenotypic selection pressures on proboscis traits. We discuss the potential role of the proboscis in optical and acoustic signalling of male resource-holding potential and status. We demonstrate that proboscis size is positively correlated with both age and size independently, and that it is currently under a positive sexual selection pressure, even when the effect of selection on body size is removed. We suggest that selection on proboscis size is functionally related to the emission of agonistic vocalizations.