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| Archaehierax sylvestris Mather, Lee, Camens & Worthy, 2021 |
ABSTRACT
The Australian pre-Pleistocene fossil record of Accipitridae (eagles, hawks, old-world vultures) comprises one latest Oligocene or early Miocene and one middle Miocene species, each represented by partial bones. Globally, most fossil accipitrids are based on single bones. The recent discovery of an older and considerably more complete accipitrid from late Oligocene sediments in Australia is therefore significant. It is derived from the Pinpa Local Fauna from the Namba Formation at Lake Pinpa, South Australia (~26–24 Ma). The fossil, described as Archaehierax sylvestris gen. et sp. nov., represents a raptor that was larger than the black-breasted buzzard Hamirostra melanosternon but smaller and more gracile than the wedge-tailed eagle Aquila audax. Comprehensive morphological and molecular phylogenetic analyses resolved Archaehierax as a basal accipitrid, not closely related to any living subfamily and perhaps the sister taxon to all other accipitrids exclusive of elanines. Relatively short wings similar to species of Spizaetus and Spilornis suggest it was adapted for flight within enclosed forests. Additional accipitrid fossils from the Namba Formation, a distal femur and a distal humerus, are incomparable with the holotype of A. sylvestris; they may represent distinct species or smaller individuals of the new taxon.
KEYWORDS: Lake Pinpa, Accipitriformes, Cenozoic fossil birds, accipitrid evolution, Australia
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| Skeleton of an osprey by Eyton (1867) with shaded sections indicating which bones are preserved in the fossil of Archaehierax sylvestris. |
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| A comparison of the prepared fossil tarsometatarsus (foot bone) and a hypothesised silhouette of Archaehierax sylvestris (left) compared to the wedge-tailed eagle Aquila audax (right). The scale bar is 10 mm long. |
Systematic palaeontology
Class Aves Linnaeus, 1758
Order Accipitriformes Vieillot 1816 Family Accipitridae Vigors, 1824
Subfamily: Archaehieraxinae subfam. nov.
Type genus: Archaehierax gen. nov.
Remarks:
The fossil is identified as an accipitrid due to the following combination of characters: Skull – Rostrum deep and narrow, with hooked tip and a large, broad nasal aperture; Tibiotarsus – Pons supratendineus ossified, aligned steeply transversely, medially placed, with unbranched canalis tendinosus, and distal condyles much wider than craniocaudally deep; Tarsometatarsus – Robust, with monosulcate hypotarsus, the lateral and medial hypotarsal crests widely separated and trochleae metatarsorum splayed both medially and laterally, and dorsally arched in distal view; Foot – Four digits with raptorial unguals, those of digits 1 and 2 relatively large; Digit IV – phalanges 2 and 3 are very short compared to phalanx 4.
The fossil can be excluded from Falconiformes (Falconidae) and the other families of Accipitriformes (Cathartidae, Sagittariidae, Pandionidae) by the morphology of the tarsometatarsal hypotarsus cristae and sulcus. The cristae are fused or partially fused together to enclose the sulcus in Cathartidae, Sagittariidae, and Pandionidae, while in Falconidae the medial crista is connected to the shaft by a ridge that extends two-thirds of its length, features that are absent in the fossil.
Diagnosis:
Accipitrids in which the following autapomorphic features are found: the pila medialis of the sternum dorsally separates two deep pneumatic fossae, the humerus has the caput humeri only slightly elevated proximally past the tuberculum ventralis, the tip of the processus procoracoideus of the coracoid sharply curves inwards ventrally towards the medial face of the bone, the tibiotarsus has the lateral/distal retinaculum scar in a deep fossa, the tarsometatarsus is relatively elongate with narrow trochleae metatarsorum that are separated by wide incisurae, and the incisura for the m. flexor hallucis brevis tendon is large, distinct, and extends distal to the fossa metatarsi I. In addition to this, the following features occur: the rostral tip of the rostrum is hooked below the tomial margin at a relatively shallow 30–40° angle, the quadrate has a deep, distinct foramen pneumaticum caudomediale, and the sternum has the apex carinae displaced caudally from the base of the spina externa.,
Genus Archaehierax Mather, Lee, Camens and Worthy gen. nov.
Etymology: Archaehierax is derived from the Greek words ‘archaios’, meaning ancient, and ‘hierax’, meaning hawk. Gender masculine.
Archaehierax sylvestris Mather, Lee, Camens and Worthy gen. et sp. nov.
Etymology: The species name ‘sylvestris’ is derived from the Greek world ‘sylvas’, meaning forest, and the Latin suffix ‘-estris’, meaning ‘belonging to’.
Ellen K. Mather, Michael S. Y. Lee, Aaron B. Camens and Trevor H. Worthy. 2021. An Exceptional Partial Skeleton of A New Basal Raptor (Aves: Accipitridae) from the late Oligocene Namba Formation, South Australia. Historical Biology: An International Journal of Paleobiology. DOI: 10.1080/08912963.2021.1966777
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