''Pengana'', also referred to as ''flexiraptor'', is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

bird of prey Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorous bird species that actively predation, hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed ...

that lived during the

late Oligocene The Chattian is, in the geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the pro ...

in what is now

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. It is known only from a fragment of the tibiotarsus that was collected from the

Riversleigh World Heritage Area Riversleigh World Heritage Area is Australia's most famous fossil location, recognised for the series of well preserved fossils deposited from the Late Oligocene to more recent geological periods. The fossiliferous limestone system is located n ...

. The tibiotarsus is unusual in that it allowed for the leg to be swivelled backwards and sideways, making it well adapted to reaching into holes and crevices and extracting prey. The genus is only known from a single species, ''Pengana robertbolesi''.

History and naming

The first known fossils of ''Pengana'' were collected from the Sticky Beak site at the

, northwestern

. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, catalogued as QM F16865, is the distal end of the left

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These ...

. A fragment of a femur from the White Hunter site might be referable to the genus on the grounds of its size, age and uniqueness compared to other Australian accipitrids. The Sticky Beak and White Hunter sites are both interpreted as being

in age, which would make ''Pengana'' one of the oldest known accipitrid from Australia. In 1993, Walter E. Boles described ''Pengana robertbolesi'' as a new genus and species of accipitrid on the basis of the tibiotarsus. The generic name, ''Pengana'', is stated to have been derived from an Aboriginal word for 'hawk', although no particular language was specified. The specific name, ''robertbolesi'', is in honour of the author's father, Richard Boles.

Description

The only remains that can be confidently assigned to ''Pengana'' is the distal end of a tibiotarsus. The piece of bone is roughly rectangular in appearance and is overall flat. It shares a lot of similarities with the extant Harrier-hawks and Crane hawk. The supratendinal bridge, which is positioned just above the

condyles A condyle (;Entry "condyle"
in

, is almost horizontal, angled at 30°. Both the internal and external condyles are flattened mediolaterally (side-to-side) and run parallel to the proximodistal midline of the shaft. The shaft of the tibiotarsus is compressed from the front to the back. It, however, differs from the Harrier-hawks and Crane hawk in a number of ways. For instance, both the supratendinal canal and anterior intercondylar fossa have a greater proportional width. The distal opening to the supratendinal canal is situated above the internal condyle rather than at the lateral edge of it. In addition, tibiotarsus itself is twice as large as those of the modern taxa. Boles (1993) stated ''Pengana'' to be larger than any living species of Australian bird of prey, with the notable exception of

Wedge-tailed eagle The wedge-tailed eagle (''Aquila audax'') also known as the eaglehawk, is the largest bird of prey in the continent of Australia. It is also found in southern New Guinea to the north and is distributed as far south as the state of Tasmania. A ...

and

White-bellied sea eagle The white-bellied sea eagle (''Icthyophaga leucogaster''), also known as the white-breasted sea eagle, is a large diurnal bird of prey in the family Accipitridae. Originally described by Johann Friedrich Gmelin in 1788, it is closely related ...

Classification

Due to the lack of material, the exact position of ''Pengana'' within Acciptiridae is currently unknown. Boles (1993) dismissed the idea of a close relationship with Harrier-hawks and Crane hawks, noting that similarities between the three taxa were limited only to the intertarsal joint. This would suggest that a double-jointed ankle had at

evolved independently Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

at least three times within Acciptridae. Regardless, ''Pengana'', and the similarly aged '' Archaehierax'', demonstrate that there was at least two different clades of accipitrids present in Australia close to the Oligocene-Miocene boundary.

Paleobiology

Features of the intertarsal joint (i.e a more horizontal supratendinal bridge and flattened distal condyles) suggests a greater degree of flexion backwards and sideways than in most acciptirids. A comparable leg-structure can be found in Crane hawks and Harrier-hawks, which allows them to easily reach into holes and crevices in search of prey. Based on the leg proportions of the two aforementioned hawks, ''Pengana'' might have had a total hindlimb length of 585-630 mm (23-25 in). With its long legs, it may have been able to probe into hollows that were at least 400 mm (15.7 in) deep. Its larger size compared to the two hawks meant that it could have hunted larger prey, specifically in the 250-300 g (0.6-0.7 lbs) range. During the late Oligocene, the Riversleigh World Heritage Area would have been predominantly covered in temperate open forest or

woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...

. Plant fossils from the late Oligocene or early Miocene-aged Dunsinane site indicate the presence of

deciduous In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...

vine thickets and

sclerophyllous Sclerophyll is a type of vegetation that is adapted to long periods of dryness and heat. The plants feature hard leaves, short internodes (the distance between leaves along the stem) and leaf orientation which is parallel or oblique to direct ...

vegetation. However, undoubted

rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...

plant taxa, such as '' Pleiogynium wannanii'', are known from the same site, which suggests that patches of rainforest would have also been present, specifically around pools or along watercourses. Australia's climate at the time was cool and dry, before shifting to a more warm and wet climate during the early Miocene.

References

{{Taxonbar, from=Q1094535 Birds of prey Accipitridae Fossil taxa described in 1993 Miocene birds of Australia Riversleigh fauna