Southern elephant seal bulls commonly reach four to five metres in length and masses in the region of two to four tonnes, with exceptional animals recorded larger still. Females are much smaller, typically under a tonne and around two to three metres. No other member of the order Carnivora approaches this size.
The asymmetry is a consequence of the breeding system. Bulls hold beach territories and defend clusters of females against rivals in violent chest-to-chest contests, so the largest males father a disproportionate share of pups. Females gain nothing from that size and instead invest in an extraordinarily rich milk that weans a pup in roughly three weeks.
The headline figures deserve care. Historical mass estimates for the biggest bulls were often calculated from length rather than weighed, and very few multi-tonne animals have ever been placed on a scale. Length measurements taken on a beach are also sensitive to whether the animal is stretched or curled.