Within the possible bird families that the holotype may belong, it is distinguished from the old-world buzzards (Aegypiinae) and eagle-vultures (Gypaetinae) by its shallow fossa m. brachialis, a more bulbous processus flexorius and a broader condylus dorsalis.[1] These features also distinguish the bone from Ospreys. Within the family Accipitridae the bone is similar to the genera Hieraaetus and Aquila. The two genera are very similar in morphology, and separation of the two is very difficult; they may be merged in the future. However the bone is closer in appearance to the modern species Aquila audax, Aquila chrysaetos and Aquila fasciata though is distinct enough to be considered a separate species. On the fossil the tuberculum supracondylare ventrale is flat unlike that of the modern species.[1]
The humerus is 27.7 millimetres (1.09 in) wide on the distal end, while the shaft is broken off and missing above the fossa m. brachialis but enough bone is present to show that the shaft is curved. A. bullockensis was smaller in size then A. audax, A. chrysaetos and larger than A. fasciata. Though many members of Aquila display sexual dimorphism, the size of humerus is not a distinct feature.[1]
Aquila bullockensis is one of the oldest members of the genus. The two species A. delphinensis and A. pennatoides which are from deposits in Grive-Saint-Alban, France, were described by Claude Gaillard in 1938 and also date to the Middle to Late Miocene. Of the other known Accipitridae bones from the Bullock Creek deposits several may belong to A. bullockensis, but none have been studied in depth to date.[1]
