An Antarctic fur seal has been observed trying to have sex with a king penguin.
The South African-based scientists who witnessed the incident say it is the most unusual case of mammal mating behaviour yet known.
The incident, which lasted for 45 minutes and was caught on camera, is reported in the Journal of Ethology.
The bizarre event took place on a beach on Marion Island, a sub-Antarctic island that is home to both fur seals and king penguins.
Why the seal attempted to have sex with the penguin is unclear. But the scientists who photographed the event speculate that it was the behaviour of a frustrated, sexually inexperienced young male seal.
Equally, it might be been an aggressive, predatory act; or even a playful one that turned sexual.
"At first glimpse, we thought the seal was killing the penguin," says Nico de Bruyn, of the Mammal Research Institute at the University of Pretoria, South Africa.
The brazenness of the seal's behaviour left those who saw it in no doubt as to what was happening.
De Bruyn and a colleague were on Trypot beach at Marion Island to study elephant seals when they noticed a young, adult male Antarctic fur seal, in good condition, attempting to copulate with an adult king penguin of unknown sex.
Antarifornication doesn't roll that well off the tongue.