The family of marsupials with arguably the most extraordinary sex-lives of any mammals has been expanded. A new species of antechinus has been discovered in the high altitude forests south of Brisbane, Australia. The discovery of a new mammal is a rare event, and always excites scientists, but antechinuses' matings means this one has attracted particular interest.

Male antechinuses, and relatives such as the brush-tailed phascogale, are almost all semelparous, meaning they only experience one mating season in their lives. While this practice is familiar from Pacific salmon, and common amongst insects, it is very rare amongst mammals. Antechinuses however, do it in style.

Born in November, the males reach sexual maturity around August, at which point they simply lose interest in anything else. They don't sleep or eat but spend their entire time looking for someone to have sex with. When they find a willing female the deed itself can last for 12 hours – an impressive length of time for an animal the size of a mouse and a lifespan of a year.

To keep up such a frenetic sexual pace the males strip their body of vital proteins and suppress their immune systems, with inevitable consequences. Within a few weeks all the males are dead. The process is pretty exhausting for the female as well, particularly since they often mate with several males and store the sperm until they ovulate at the end of the breeding season, producing a litter with multiple fathers. Some females survive to do this three times, but most die after weaning their first litter.

The new species, dubbed the black-tailed antechinus, was previously thought to be a subtype of the only member of the genus that manages to break this pattern. Some male, and an unusually large number of female, dusky antechinuses (Antechinus swainsonnii) make it through the mating season to do it all again the following year.

It is as yet unknown if any black-tailed antechinuses, (A. arktos) as the new species has been named in the journal Zootaxa , manage to do the same thing, hopefully earning them respect among whippersnappers who've never seen a spring. A arktos and A swainsonii turn out to be as genetically distinct as species biologists never had problems distinguishing, so the dusky version's survival powers may not carry through to its look-alike. Dead males have been found in spring, indicating many, if not all, don't survive mating.

When the wrongly identified population were first found back in the 1960s Dr Steve Van Dyck of the Queensland Museum says, “I just went up there on a motorbike and stuck out three traps and caught some with no difficulty at all.” Since the late 1990s, however, 3500 similar traps have been set, and Van Dyck says, “The only caught some near Springbrook with great difficulty.” Consequently A artkos is thought to be locally extinct across much of its former range. The paper's authors are applying for an endangered species listing. However, being isolated to the tops of mountains the black-tailed antechinus is particularly threatened by Global Warming, raising fears it may become extinct within years of discovery.

Despite the past confusion the black-tailed antechinus looks different from its relatives. "The tail emerges from a body that is very shaggy, very hairy, with really long guard hairs," said Dr Andrew Baker of the Queensland University of Technology. "On the rump of the animal it becomes almost an orangey-brown colour, but where the tail emerges from the rump there is quite a distinct change from orange rump to black tail. It's a very short-furred tail and they have black feet as well." The black-tailed antechinus also has a larger skull than its relatives.

The antechinus mating season occurs during the southern hemisphere winter when food is in short supply, leading to the theory that their behaviour was a sort of self-sacrifice. However, last year Dr Diana Fisher of the University of Queensland published a paper demonstrating that the death was a consequence of the energy put into mating to make sure an individuals' genes are carried on. Any male not willing to devote themselves to all day shagathons risks having his sperm displaced by competitors.