Scientists have reported the discovery of a chameleon species that could be the world's smallest reptile.
The chameleon, dubbed Brookesia nana, was discovered living in the rainforests of the Sorata Massif in northern Madagascar, according to a study published in the journal Scientific Reports.
The authors of the study found two specimens of the species: one adult male and one female. The male is smaller than the female, measuring just 13.5 millimeters (0.53 inches) long from the snout to the cloaca—an orifice seen in many vertebrates into which the intestinal, urinary and genital tracts open.
This makes it the smallest adult reptile of any sex, according to the authors of the study. In fact, the males are even smaller than another tiny reptile from the same genus (group of species) known as Brookesia micra, which has a body size of around 16 millimeters, as well as another diminutive gecko species from the Caribbean, called Sphaerodactylus ariasae, which has similar measurements.
The female Brookesia nana, however, measured 19.2 millimeters (0.75 inches) from snout to cloaca, which would make it larger than the females of the Sphaerodactylus ariasae species. The females of this species hold the record of being the smallest female reptiles.
So while adult males of Brookesia nana may be the smallest known reptiles, the same cannot be said for the adult females, co-author of the study Mark D. Scherz from the University of Potsdam in Germany wrote in a blog post.
Significant differences in body size and shape—known as sexual dimorphism—are common among male and female chameleons. As such, whether or not the new species can be considered the smallest reptile on Earth depends on how scientists compare species.
For example, they could be compared based on the male or female body size, or the midpoint of the two, according to Scherz.
"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 author of the study Frank Glaw from the Bavarian State Collection of Zoology in Munich told Live Science.
Intriguingly, the researchers found that the males of Brookesia nana have large genitalia relative to their tiny size. In fact, the hemipenis—a reproductive organ seen in lizards and snakes—of the male measured nearly a fifth of the animal's total body length when fully turned outwards.
"In spite of its small size, the male holotype of B. nana has quite large genitalia," Scherz wrote. "This prompted us to look at the relationship between genital and body size in chameleons, which revealed an interesting pattern: the smallest species often have the proportionally largest genital sizes.
"We think that this might also be related to size dimorphism: if the female remains larger than the male, a constraint is placed on the reduction of the male genital size."
