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192 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY FIGURE 5.—Paratypes of Aquila bivia from Inglis IA, Citrus County, Florida: A, right tibiotarsus (UF 30012); B, left femur (UF 30019), in anterior (left) and posterior (right) views. For each specimen, scale= x 0.75, bar= 1 cm. fossil eagle did not differ significantly from those of the modern one (Howard, 1947). The ratio of carpometacarpus to femur length of recent Aquila chrysaetos shows considerable variation (range, 0.79-0.85; n=\l). The maximum lengths of these elements given by Howard (1932) for the Rancho La Brea eagle give a ratio of 0.83, or within the range of the modern species. If the carpometacarpus (UF 30015) and femur (UF 30019) of A. bivia are assumed to be from the same individual, they give a ratio of 0.85 and are thus within the range of modern A. chrysaetos. The tibiotarsus (UF 30012) of A. bivia, however, is longer and proportionally more gracile compared to A. chrysaetos (Table 2), suggesting that the fossil species had rela tively longer and more slender legs compared to other eagles of this genus. This large eagle is the first valid fossil species of Aquila to be described from North America. Two named species, A.ferox and A. lydekkeri, described from North America by Shufeldt (1915), are now recognized as synonyms of Minerva antiqua Shufeldt, an Eocene owl in the extinct family Protostrigidae (Olson, 1985). Aquila borrasi, described from the late Pleistocene of Cuba by Arredondo (1970, 1976), was discussed by Olson and Hilgartner (1982), who suggested that it may be related to the large, extinct hawk Titanohierax gloveralleni Wetmore (1937) of the Bahamas. They also suggested that none of the Cuban material was properly placed in the genus Aquila.
NUMBER 89 193 We compared the paratypical femur of A. borrasi (Arredondo, 1970, fig. 7) to femora of A. bivia and found it to differ in its relatively greater size, shaft more distinctly flared toward the ends, and the relatively large proximal pneumatic foramen. This femur does not appear to represent any living genus of hawk, eagle, or vulture, and we agree with Olson and Hilgartner (1982) that it probably is referable to Titanohierax. Bickart referred six specimens to Aquila sp. A and sp. B from the late Miocene/early Pliocene Big Sandy Formation, Arizona. These specimens are described as equal in size to or smaller than A. chrysaetos and probably do not represent A. bivia. Two other fossil species, Aquila delphinensis and A. pennato'ides, described by Gaillard (1938), are known from the late Miocene of France, each only by the proximal end of the tarsometatarsus These specimens were not available for comparison in this study, but their geographic location and age suggest that the Inglis fossils would not be referable to either of these species. Discussion The two new eagles described herein add to a growing list of living and extinct birds that indicate a former habitat corridor, extending from the Florida peninsula to western North America, that probably developed in the late Pliocene when climatic changes allowed xerophytes from the south to move northward and those from the north to move southward (Blair, 1958; Axelrod, 1979; Simpson and Neff, 1985). The resulting habitat apparently was a dry, thorn-scrub community and savannah as suggested by fossil and recent plant and animal distributions (Blair, 1958; Axelrod, 1979; Simpson and Neff, 1985) and was an important corridor for biotic dispersal during the Great American Biotic Interchange (Stehli and Webb, 1985). Based on topography, probable avenues of northward dispersal of Neotropical elements into the southwestern and southeastern United States were along the coastal lowland corridors on the eastern and western margins of mainland Mexico (i.e., below the Sierra Madre Oriental along the Gulf of Mexico and below the Sierra Madre Occidental along the Gulf of California; Figure 6). From these areas of entry, late Blancan and early Irvingtonian invaders from the tropics spread into savannah habitats on the Mexican Plateau and in the present-day southern United States. They moved especially into the southeastern United States (particularly the Florida peninsula, where the vertebrate fossil record is best known, but later as far north as South Carolina) but also into the southern Great Plains and to a lesser extent into present-day Sonora, Mexico, and southern California, probably via the western corridor. Some of these taxa dispersed as far north as present-day Idaho, although the greatest diversity extends no farther north than the Texas panhandle (Figure 6). Before now, the greatest evidence for the Gulf Coast corridor was shown primarily by mammalian faunas of the late Blancan and early Irvingtonian Land Mammal Ages in North America (Webb and Wilkins, 1984; Morgan, 1991; Figure 6, Table 3). Florida fossil faunas are characterized more by Neotropical influences during this period than by northern or western faunal elements (Webb and Wilkins, 1984; Morgan, 1991). The fossil herpetofauna from Inglis IA, however, indicates greater influence from xeric habitats in the western United States during the early phase of the Plio-Pleistocene (15 of 31 species identified; Meylan, 1982). Less has been documented in relation to fossil avifaunas in the Plio-Pleistocene, but evidence so far indicates similar disperal routes and timing as for the mammals. Vuilleumeir (1985) found that representatives of only three South American groups, the teratorns {Teratornis spp.), caracaras {Caracara plancus (J.F. Miller) and Milvago readei (Brodkorb)), and phorusrhacids {Titanis walleri), are known from the fossil record of Florida, and that there was a greater influence of North American taxa on South American avifaunas than the reverse. New fossil records indicate that additional extant Neotropical taxa, representing lowland forest and aquatic habitats, inhabited Florida during the Plio-Pleistocene. These taxa include the Least Grebe {Tachybaptus dominicus (Linnaeus)) and Great Black-hawk {Buteogallus urubitinga (Gmelin)) from Inglis 1 A, Ringed Kingfisher {Ceryle torquata (Linnaeus)) from Haile 7C, and Gray-breasted Crake (cf. Laterallus exilis (Temminck)) from Haile 16A (early Irvingtonian, 1.6-1.0 Ma; Carr, 1981; Emslie, 1998). Other extant species that first appear in the late Pliocene (Inglis IA) of Florida that have populations or closely related species in western North America are discussed by Emslie (1996, 1998). Extinct birds from the late Pliocene and early Pleistocene of Florida that reflect a common habitat between the peninsula and the western United States include the first record of an extinct cormorant {Phalacrocorax idahensis Marsh) from Florida (Emslie, 1998) and two species of pygmy-owls {Glaucidium spp.), which represent the first occurrence of this genus in eastern North America (Carr, 1981; Emslie, 1998; Table 3). In addition, teratorns {Teratornis spp.) first appear in Florida and the western United States in the late Blancan and represent a group that probably originated in South America (Campbell and Tonni, 1981; Emslie, 1988). Other taxa that arrived in the peninsula during this period include condors {Gymnogyps spp.), an extinct accipitrid vulture {Neophrontops slaughteri Feduccia), Aquila bivia and Amplibuteo concordatus, described herein, a tropical hawk-eagle {Spizaetus sp.), an undescribed chachalaca (Cracidae, indet.), and an extinct turkey {Meleagris leopoldi A.H. Miller and Bowman/M anza Howard) (Steadman, 1980; Carr, 1981; Emslie, 1988, 1992, 1998; Table 3). As with the mammals, these extant and extinct taxa provide strong evidence that xeric, thorn-scrub and savannah habitats once existed between the Florida peninsula and western North America. Other species of mammals and birds that appeared in North America during this time, however, reflect aquatic and lowland tropical forest environments (Table 3). The presence of
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192<br />
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY<br />
FIGURE 5.—Paratypes of Aquila bivia from Inglis IA, Citrus County, Florida: A, right tibiotarsus (UF 30012); B,<br />
left femur (UF 30019), in anterior (left) and posterior (right) views. For each specimen, scale= x 0.75, bar= 1 cm.<br />
fossil eagle did not differ significantly from those of the modern<br />
one (Howard, 1947).<br />
The ratio of carpometacarpus to femur length of recent Aquila<br />
chrysaetos shows considerable variation (range,<br />
0.79-0.85; n=\l). The maximum lengths of these elements<br />
given by Howard (1932) for the Rancho La Brea eagle give a<br />
ratio of 0.83, or within the range of the modern species. If the<br />
carpometacarpus (UF 30015) and femur (UF 30019) of A. bivia<br />
are assumed to be from the same individual, they give a ratio<br />
of 0.85 and are thus within the range of modern A. chrysaetos.<br />
The tibiotarsus (UF 30012) of A. bivia, however, is<br />
longer and proportionally more gracile compared to A. chrysaetos<br />
(Table 2), suggesting that the fossil species had rela<br />
tively longer and more slender legs compared to other eagles<br />
of this genus.<br />
This large eagle is the first valid fossil species of Aquila to be<br />
described from North America. Two named species, A.ferox<br />
and A. lydekkeri, described from North America by Shufeldt<br />
(1915), are now recognized as synonyms of Minerva antiqua<br />
Shufeldt, an Eocene owl in the extinct family Protostrigidae<br />
(Olson, 1985). Aquila borrasi, described from the late Pleistocene<br />
of Cuba by Arredondo (1970, 1976), was discussed by<br />
Olson and Hilgartner (1982), who suggested that it may be related<br />
to the large, extinct hawk Titanohierax gloveralleni Wetmore<br />
(1937) of the Bahamas. They also suggested that none of<br />
the Cuban material was properly placed in the genus Aquila.
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