"When we tried to collect semen by [electrically-stimulated ejaculation] before, not only did we not get a single drop, but the whole penis swelled up to a four-headed monster that wouldn't fit the female reproductive tract, which has only two branches"The bizarre sex life of the spiny anteater has been exposed by researchers – the male ejaculates using only one half of its penis. New findings about the creature’s sex life may seem salacious but they could help shed light on an evolutionary mystery.
It seems that the way the mammal ejaculates is similar to the way reptiles do – by shutting down one side of its penis before secreting semen from the other side. Reptiles have a pair of male members called hemipenes for sex, and they use only one of the two during each act of copulation.
The spiny anteater (Tachyglossus aculeatus), also known as the short-beaked echidna, is a primitive mammal found in Australia and New Guinea. Like the platypus, it is a monotreme, laying eggs instead of bearing live young.
Monotremes have many features in common with reptiles, and the hope is that by studying them, scientists may find clues as to how mammals evolved.
The spiny anteater, however, is notoriously difficult to observe in the wild and shows little enthusiasm for breeding in captivity, so nobody had managed to observe them ejaculate before.(more from newscientist)