Friday, March 17, 2023

[PaleoOrnithology • 2023] Dynatoaetus gaffae • A Giant Raptor (Aves: Accipitridae) from the Pleistocene of southern Australia


Dynatoaetus gaffae
Mather, Lee, Camens & Worthy, 2023

The giant accipitrid Dynatoaetus gaffae gen. et sp. nov. is described from existing and newly collected material. Initial fossil remains were collected from Mairs Cave (Flinders Ranges, South Australia) in 1956 and 1969, and comprised a sternum, distal humerus and two ungual phalanges. A further 28 bones from this individual—including the neurocranium, vertebrae, furculum, and additional wing and leg bones, most of which were incomplete—were discovered at the site in 2021. This allowed identification of additional fossils from the same species in collections from Cooper Creek (Lake Eyre Basin, SA), Victoria Fossil Cave (Naracoorte, SA) and Wellington Caves (Wellington, NSW). Dynatoaetus has variable similarity across elements to those of living species in the Perninae, Gypaetinae, Circaetinae and Aegypiinae. Parsimony and Bayesian phylogenetic analyses of combined morphological and DNA data resolved it as the immediate sister-group to the Aegypiinae within the Circaetinae + Aegypiinae clade. The robust and eagle-like morphology of the lower hindlimbs suggest that the species was a predator, rather than a scavenger, and thus functionally similar to large circaetines such as the Philippine Eagle Pithecophaga jefferyi. Furthermore, this new species is the largest known bird of prey from Australia, much larger than the modern Wedge-Tailed Eagle Aquila audax. It is outsized in Australasia only by female Hieraaetus moorei (the extinct Haast’s Eagle from New Zealand). It is inferred to have been Australia’s top terrestrial avian predator during the Pleistocene, ranging from arid inland Australia to the more temperate coast, and likely became extinct around the time of the megafaunal mass extinction which peaked around 50 Ka. Its extinction in the late Pleistocene, along with the recently described scavenging vulture Cryptogyps lacertosus, marked a distinct decline in the diversity and function of Australia’s raptor guild.

Keywords: Aegypiinae, Accipitriformes, Circaetinae, Taxonomy, Extinction, Pleistocene predatory birds

Visual representation of the parts of the skeleton known from Dynatoaetus gaffae (coloured grey). Image based on Meyer (1897), plate 121

Systematic palaeontology
Accipitriformes Vieillot 1816
Accipitridae Vigors 1824

Dynatoaetus gen. nov.
Diagnosis: A large accipitrid distinguishable from other genera by the following combination of characters: a neurocranium that is (1) relatively short and wide compared to Aquila audax; (2) has the line linking the tip of the processus zygomaticus to the ventral tip of the processus paroccipitalis aligned about 45 degrees to the plane of basioccipital-parasphenoidal plane and ventrally encloses a tympanic recess that is longer than high; (3) the condylus occipitalis is relatively large; (4) the mamillar tuberosities (tubercula basilaria) are robust, and prominent caudally; (5) the foramen magnum is near-perpendicular to the basioccipital plane (~ 10 degrees off perpendicular); (6) has prominent tubercula for the insertion for m. pseudotemporalis superficialis on the facies orbitalis. A sternum with (7) distinct and prominently projecting processus labrum internum; (8) a spina externa that is narrower than the apex carinae; (9) a crista medialis carinae that does not extend to the base of the spina externa. A humerus with (10) a weakly ventrally projecting epicondylus ventralis; (11) the distance between the interior margin of the tuberculum supracondylare ventrale and the proximal tip of the condylus dorsalis is equal to that between the tip of the condylus dorsalis and the dorsal margin; and (12) a deep insertion pit for the distal head of the m. pronator profundus. An ulna with (13) a tuberculum carpale that has little prominence cranioventrally. A tarsometatarsus that (14) is robust; (15) has a trochlea metatarsi II that is broad and more distally elongate than trochlea metatarsi III; (16) has the trochleae metatarsorum II and IV with robust plantar flanges and with (17) the plantar openings of the foramen vasculare proximale medialis positioned on the lateral side of the crista medialis hypotarsi; and (18) has the medial side of the shaft deeply excavated caudally by the fossa parahypotarsalis medialis such that the medial margin is very thin.

Etymology: The genus name is a combination of the ancient Greek words δῠνᾰτός (dynatós), meaning strong, mighty, or powerful, and ᾱ̓ετός (āetós) meaning eagle.

Dynatoaetus gaffae gen. et sp. nov.

Etymology: The name ‘gaffae’ honours Priscilla Gaff, who first discussed the fossil material of this species in her 2002 thesis revising Australian accipitrids.

Ellen K. Mather, Michael S. Y. Lee, Aaron B. Camens and Trevor H. Worthy. 2023. A Giant Raptor (Aves: Accipitridae) from the Pleistocene of southern Australia. Journal of Ornithology.  DOI: 10.1007/s10336-023-02055-x