I don't think anyone should really need a study to show that elephants are intelligent and can work cooperatively to achieve a goal (see, for example, this video of elephants rescuing a baby elephant from a water hole). Still, this is an interesting video, which I found at Arbroath.
"Smelling isn't everything" said the Elephant. "Why," said the Bulldog, "if a fellow can't trust his nose, what is he to trust?" "Well, his brains perhaps," she replied mildly.” (C.S. Lewis)