Vampyravus orientalis, from the Oligocene of Fayum, Egypt was the first fossil bat described from Africa. It is represented by a single, relatively large humerus from an unknown horizon in the Jebel Qatrani Formation. Based on regression analyses of skeletal proportions of modern bats, we developed a set of equations to estimate body mass of fossil bats from known skeletal elements in order to test the hypothesis that Vampyravus could have been within the body size range of other Fayum bats, including several recently described taxa from the Jebel Qatrani and underlying Birket Qarun Formations. Our findings indicate that only Witwatia could have had a body mass similar to Vampyravus. Witwatia is known only from Quarry BQ-2 (Late Eocene, Priabonian) in the Birket Qarun Formation. Therefore Vampyravus is between 2 and 7 million years younger, depending on where within the Jebel Qatrani Formation it was found. Also, a recently discovered distal humerus of Witwatia from BQ-2 demonstrates that this taxon differs substantially from Vampyravus in comparable morphology. Vampyravus is distinct from all other Fayum fossil bats. Vampyravus shares characteristics of the proximal and distal humerus with several extant bat groups including phyllostomids, some rhinolophoids, natalids, emballonurids, and rhinopomatids. The latter two families are represented by fossil forms in the Fayum. Although Vampyravus is much larger than either the Fayum emballonurid or rhinopomatid, relatively large size typifies many taxa representing modern bat groups in the Fayum, making it all the more conceivable that Vampyravus could belong to one of these families.