Researchers have discovered the world's smallest male reptile, sporting some proportionately huge genitals. 

Researchers have described one male and one female of the species Brookesia nana. The male measured just 13.5 millimeters from snout to cloaca (the multipurpose orifice used for both excretion and reproduction), making it the smallest adult reptile ever described.

The male was even smaller than its female counterpart, which had a length of 19.2 mm from snout to cloaca. 

“Given that the general body plan of reptiles is rather similar to that of mammals and humans, it is fascinating to see how miniaturized these organisms and their organs can get,” lead study author Frank Glaw, a herpetologist at the Bavarian State Collection of Zoology in Munich, told reporters.

But one of its organs could barely be described as miniature. The little B. nana’s reproductive organs (called hemipenes) measured about 18.5 per cent of his total body length.

The researchers say this is pretty average for the world’s tiniest lizards, whose genitals tend to range from 6.3 to 32.9 per cent of the male's total body length.

Such a prolific appendage is not unique in nature, the researchers note, with some ducks having a genital length equal to their body length, while the reproductive organs of barnacles are up to eight times longer than their bodies.

“[This] revealed an interesting pattern: The smallest species often have the proportionally largest genital sizes,” study co-author Mark Scherz, a herpetologist at the University of Potsdam in Germany, wrote in a blog post.

Dr Scherz suggests that because the female is considerably larger than the male of the species, the male retains genital size proportionate to his larger counterpart. 

But given that there are only two known specimens of B. nana, it is difficult to tell what their sexual dynamic might be.