Amplibuteo: an oversized hawk with a revised name

Amplibuteo is the historical genus name for a large New World hawk from the late Pleistocene of Peru. The type species Amplibuteo hibbardi is now generally combined as Buteogallus hibbardi: a 2021 review found that the proposed genus-level traits fell within variation of Buteogallus. Fossils from the Talara asphalt deposits include 52 elements assigned to at least seven individuals, but they are disarticulated and do not form seven complete skeletons. The extinct bird catalogue records both the historical name and revised placement so that literature under either remains findable.

Quick facts

Bird bones from the Talara asphalt

Kenneth Campbell named the type species in 1979 from fossil birds recovered at Talara in Peru’s Piura region. The Royal Ontario Museum had collected thousands of bird bones there in 1958. Campbell studied a diverse avifauna and erected several new taxa from bones preserved in asphalt. The name Amplibuteo hibbardi honours palaeontologist Claude Hibbard.

The holotype, ROM 16905, is a nearly complete left tarsometatarsus. It measures 134.1 millimetres in length; the proximal and distal ends are about 25.0 and 27.1 millimetres wide in the original description. These numbers describe the fossil element, not the bird’s mass or wingspan.

The referred sample contains 52 elements attributed to at least seven individuals. It includes lower-leg and foot bones, parts of the beak and lower jaw, shoulder bones, upper and lower wing elements, a femur and other fragments. This makes the bird better known than a species represented by one bone, but the remains were not seven articulated skeletons. The assignment relies on anatomical similarity and compatible size among separate pieces.

What made the hawk unusually large?

The robust tarsometatarsus and other limb bones indicate an accipitrid larger than the living Great Black Hawk, one of the largest modern hawks in the Americas. Campbell noted differences in limb proportions and ridges and described cranial and wing fragments as well. But “large” should not become a precise height or mass unless the assumptions and specimen basis are given: no complete bird was weighed or preserved.

Hawks use the tarsometatarsus and toes to support the body and grasp prey. The bone’s size and joint surfaces help describe how the foot was built, but do not yield an exact grip force. That would depend on soft tissues, muscle dimensions and biomechanics not preserved in the fossils. Comparisons with living hawks suggest function; the fossil anatomy sets the limits.

Parts of the skull and jaws were also described, including narrow external nostrils. Isolated cranial bones do not make a complete head. The recovered bones provide useful details of shoulder, wing and hind limb, while much of the body and its proportions remain uncertain.

Why the genus name changed

Campbell distinguished Amplibuteo from other hawks using a combination of anatomical features and its large dimensions. Later authors questioned whether these characters justified a separate genus. In a 2021 review of the giant hawk Amplibuteo woodwardi from Florida, David Steadman and David Carr compared the fossil species and concluded that Amplibuteo should be treated as a junior synonym of Buteogallus. The Peruvian bird is consequently called Buteogallus hibbardi.

A synonym is a name considered to refer to the same taxonomic group under the selected classification. The fossil has not become smaller or less distinctive: the question is whether its preserved traits warrant a genus separate from Buteogallus. The combination changes while the species epithet hibbardi remains, so both names matter when following older and newer literature.

The asphalt deposits and bird community

Talara is an asphalt deposit that preserved a large sample of vertebrates. Bone accumulations form through complex processes and over time; many taxa at one locality do not prove that they interacted. The deposit discussed in the Russian account is estimated at about 13,900 years old. That is an age estimate for the deposit, not a date directly measured from the holotype.

A large hawk could have hunted prey, scavenged, or done both. No associated prey skeleton, stomach contents or kill site identifies what Buteogallus hibbardi regularly ate. Fossils establish a large bird of prey and its regional presence, not a preserved hunting scene.

How to read a reconstruction

An illustration can show a large hawk with a powerful foot and flight-capable wings, using the preserved limb and shoulder material and comparisons with living accipitrids. Exact plumage, colours, soft parts and behaviour are not directly known. It should not be confused with the giant teratorn Argentavis, a different bird in a different family, with a vastly larger wingspan.

The most secure account combines the type ankle bone, the broader disarticulated sample and the modern taxonomic revision. Amplibuteo remains an important historical name for the Talara hawk; Buteogallus hibbardi reflects its current generic placement.