The Ross sisters peaked their career during 1940s. The stage names of American singers and dancers were Maggie, Aggie and Elmira. Not just the dance was their feature: the sisters became particularly noted for their acrobatics and contortionism. Their skills sometimes seem to be unreal.
Their performances were first reviewed in Billboard in September 1942. Especially prominent was their appearance in Broadway Rhythm film, 1944. More than 70 years have passed, but nobody managed to repeat this trick yet!