A rubber version of which animal has become an iconic bath time toy?

For many decades, most duck figures have been made of vinyl, but we still call them rubber ducks. Rubber ducks naturally inspire water play that develops muscle strength and coordination. Rubber ducks have been recognized as the quintessential bathtub toy since 1970 when Ernie, the cheerful orange Muppet on Sesame Street, first sang the catchy song “Rubber Duckie You're The One” to his best bath time buddy.

Source: Ducks in the Window