Accipitridae (Vigors, 1824)

Gaff, Priscilla & Boles, Walter E., 2010, A New Eagle (Aves: Accipitridae) from the Mid Miocene Bullock Creek Fauna of Northern Australia, Records of the Australian Museum 62 (1), pp. 71-76 : 72

Family Accipitridae (Vigors, 1824)

The Bullock Creek humerus can be distinguished from that of both groups of Old World vultures because it possesses a shallower fossa m. brachialis, more bulbous processus flexorius and a relatively broader condylus dorsalis. Pandion differs by its reduced epicondylus dorsalis, more excavated fossa m. brachialis, narrower fossa olecrani and narrower condyles. The two species of Hieraaetus examined show almost no differences from species of Aquila . Other than a somewhat more pronounced gap between the processus flexorius and condylus ventralis (in distal view), the only significant character is one of size (see also Louchart et al., 2005).

Species of Aquila (based on A. audax , A. chrysaetos and A. fasciata ) and Hieraaetus ( H. morphnoides and H. pennatus ) can be distinguished from those of Haliaeetus ( H. leucogaster , H. leucocephalus ) by the same suite of distal humeral characters ( Fig. 2 ): (1) the ventral side of the distal end, including the epicondylus ventralis, projects further ventrally, in cranial view, (2) the fossa olecrani is shallower (deeper, more defined in Haliaeetus ); (3) the scar for M. pronator superficialis (proximal to the tuberculum supracondylare ventrale) is deeper and more circular (slightly shallower, less defined circle); (4) the incisura intercondylaris is excavated distally, in cranial view (not visible in specimen of A. fasciata ) (not excavated); (5) the processus flexorius is round and protruding distally in cranial view and caudally in medial view (base less rounded, not projecting as far distally or medially); (6) the tuberculum supracondylare ventrale is attenuated proximodorsally (rounded dorsally); and (7) the ratio of shaft width to distal width is less (greater) ( Table 1; Fig. 3 ).

The Bullock Creek humerus agrees with those of extant species of Aquila in all these character states. It more closely resembles these species than those of Hieraaetus morphnoides and H. pennatus by having a reduced gap between the processus flexorius and condylus ventralis. Accordingly, the fossil is assigned to Aquila .

Figures

Figure 2. Distal humeri of extant Australian eagles; upper, caudal view; lower, cranial view. (A), Haliaeetus leucogaster. (B), Aquila audax. (C), Hieraaetus morphnoides. Bar equals 10 mm. Numbers refer to characters used to separate Haliaeetus from Aquila-Hieraaetus (see text). Character 7 show the points at which the shaft width measurement was taken proximal of the epicondylus dorsalis.

Figure 3. Shaft and distal widths (mm) of Bullock Creek humerus compared to those of extant eagles. Squares,Aquila: crossed, A.bullockensis; black,A.audax; grey, A.chrysaetos; open, A.fasciata. Diamonds, Hieraaetus: black, H. morphnoides; open, H. pennatus. Circles, Haliaeetus: black, H. albicilla; grey, H.