"That we know of" is carrying a lot of weight. I would also challenge your implicit assumption here. We can absolutely observe that other animals have quite clear social roles, tied to their sex. Lionesses do the majority of the hunting, lions guard the pride against threat and encroaching males. Sexual dimorphism in the animal kingdom isn't limited to physical appearance, it's incorporated into behaviors as well. We can observe that other animals do actually have gender roles - and we can also observe rare occasions where one of those animals defies those gender roles. For example, there was a case of a male tiger adopting and raising a weaned cub that had lost its mother. Male tigers don't do childcare, they're pretty much a hit-it-and-quit-it species.
You're assuming that humans are exceptional in that we have behavioral and presentational differences by sex, and we also have some rare instances where individuals step outside of those norms. I don't think it's exceptional at all. I do, however, think that some humans have reified gender roles to a prescriptive level... and most of those who do so are trans rights activists.