One of the most unique features that allies Aeolosaurus with other titanosaurs, specifically Gondwanatitan, is that the neural spines on the caudal vertebrae are angled forward in the direction of the head (anteriorly). That sort of trait is not common in the titanosaurs meaning that Gondwanatitan and Aeolosaurus are closely related. As some of the only material discovered with the type species, these caudal vertebrae were an important piece of the puzzle as to what this animal was exactly. They united Aeolosaurus with other titanosaurs as well because they were elongated medially from front to back and they possessed shallow fossae on the lateral sides of the centra; both are titanosaurid characters of caudal vertebrae. The initial puzzle pieces consisted of these few vertebrae, elements of the forelimbs, and the right hindlimb. These elements also aided in identification of the animal, of course.
The femur of Aeolosaurus was a rather large bone, as we expect from titanosaurs. The size, dimensions of proportion, and general shape of the femur all attributed to the diagnosis of belonging to a titanosaurid dinosaur. The relationships alluded to by the femur are hazy and basically educated guesses at this point as titanosaurid material is both rare and incompletely understood. However, the femur of Aeolosaurus is rather large and quite a nicely preserved bone all in all.