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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