Juvenile female fossas pass through a phase researchers call transient masculinization. Their clitoris enlarges into a structure resembling the male's spined baculum-supported penis, and their coat shifts from grey to the orange colouring typical of adult males. This masking persists for roughly the first one to two years of life, both in wild populations and in zoo-managed breeding colonies where it has been closely observed.
The leading explanation is that looking male shields young females from aggression and unwanted mating attempts by adult males while their bodies are still developing. Once true sexual maturity approaches, at around two years old, the masculinized features regress and the coat lightens to the female's normal colour. Fossas are otherwise solitary and elusive, so much of this pattern has been documented through captive breeding programmes that allow repeated observation of the same individuals over time.
What remains less settled is how universal the trait is across the wild population and whether its function is purely social deterrence or also tied to hormonal timing of growth. Because fossas are difficult to study in dense Madagascan forest, most detailed anatomical descriptions come from a limited number of captive and museum specimens rather than large wild samples.