HISTORICAL BIOLOGY
https://doi.org/10.1080/08912963.2021.1966777

An exceptional partial skeleton of a new basal raptor (Aves: Accipitridae) from the late
Oligocene Namba formation, South Australia
Ellen K. Mathera, Michael S. Y. Leea,b, Aaron B. Camensaand Trevor H. WorthyaaCollege of Science and Engineering, Flinders University, Adelaide, SA, Australia; bEarth Sciences Section, South Australian Museum, North Terrace,
Adelaide, SA, Australia
ABSTRACTARTICLE HISTORY

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 fromthe 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 blackbreasted 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 wasadapted 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.
lsid:zoobank.org:pub:6A25C569-3E9F-43B8-AAF8-F36CE405C06E

Received 11 June 2021
Accepted 8 August 2021
KEYWORDS

Lake Pinpa; Accipitriformes;
Cenozoic fossil birds;
accipitrid evolution; Australia

Introduction
The Accipitridae and kin
The Accipitriformes comprises four extant families and 259 species:
the New-World vultures (Cathartidae, seven species), secretarybirds (Sagittariidae, one species), ospreys (Pandionidae, one species) and the eagles, hawks and Old-World vultures (Accipitridae,~250 species) (Dickinson and Remsen 2013). The accipitrids are themost widely distributed family in the order, being widespread on
every continent except for Antarctica, and play key roles as apex
predators and scavengers in many environments.
From the 19th to early 21st century, the Accipitridae were usuallyplaced in Falconiformes with the Falconidae (falcons), Cathartidae,
Sagittariidae and Pandionidae (Sharpe 1874; Ridgway 1874; Gadow
1891; Sushkin 1905; Peters 1934; Jollie 1976; Stresemann andAmadon 1979; Lerner and Mindell 2005; Hackett et al. 2008).
Molecular data justiﬁed recognising Falconidae and Pandionidae
as separate families from Accipitridae, though Pandion is very
closely related to the Accipitridae (Sibley and Ahlquist 1990;
Wink and Sauer-Gürth 2004; Lerner and Mindell 2005; Griﬃths
et al. 2007; Hackett et al. 2008). Accipitriformes was resurrected toinclude Accipitridae, Pandionidae, Sagittariidae and Cathartidae by
Christidis and Boles (2008) and this usage has been followed thereafter (Gill et al. 2010; Dickinson and Remsen 2013). Accipitridae isrecognised to include multiple subfamilies, though similarities inplumage and morphology (see Peters 1934; Amadon 1964; Jollie
1976) have obscured relationships and composition which are only
recently being revealed by analyses of molecular data (refer to
Ferguson-Lees and Christie 2001; Lerner and Mindell 2005;
Dickinson and Remsen 2013; Mindell et al. 2018). Here, we use

CONTACT Ellen K. Mather
math0083@ﬂinders.edu.au
Supplemental data for this article can be accessed here.
© 2021 Informa UK Limited, trading as Taylor & Francis Groupthe subfamilies Elaninae, Perninae, Gypaetinae, Aegypiinae,
Circaetinae, Harpiinae, Aquilinae, Accipitrinae, Haliaeetinae, andButeoninae, following Nagy and Tökölyi (2014). We diﬀer from
Mindell et al. (2018) in recognising the Haliaeetinae as distinct fromthe Buteoninae, and Aquilinae from Harpiinae, based on diﬀerences in morphology and ecology, and the lack of justiﬁcation
provided by Mindell et al. (2018) for merging them.
Australia has 17 resident breeding accipitrid species in 12 genera, two of which are monotypic and endemic, in ﬁve subfamilies(Debus 1998; Christidis and Boles 2008; Dickinson and Remsen2013).
Pre-Pleistocene Fossil Record of the Accipitridae
The fossil record of Accipitridae begins in the middle Eocene inEurope, although the fragmentary nature of the fossils prohibits
deﬁnitive identiﬁcation (Olson 1985; Mlíkovský 2002; Mayr2017). A further complication is the presence of lineages that
resemble Accipitridae, such as the Horusornithidae, thought tobe an extinct lineage of Accipitriformes (Mourer-Chauviré
1991), and the Messelasturidae, predators in a lineage now
thought to be related to stem-group parrots (Mayr 2006a,
2011). The Eocene raptor Masillaraptor parvunguis Mayr,
2006b, represented by several articulated skeletons, was considered to be either an accipitriform or a falconiform when ﬁrst
described (Mayr 2006b), but was later considered to bea falconid (Mayr 2009, 2017).
The Oligocene to Miocene record of accipitrids varies by continent. Africa is extremely poorly represented at the time of writing,with one indeterminate Oligocene fossil from Egypt bearing someCollege of Science and Engineering, Flinders University, Adelaide, SA 5000, Australia

2

E. K. MATHER ET AL.

similarity to Haliaeetus (Rasmussen et al. 1987); otherwise, African
fossils attributable to extant genera are known from the Miocene
onwards (Walker and Dyke 2006).
North America has numerous described species of late
Oligocene to early Miocene age: four species have been describedin the modern genus Buteo, (but see Mayr and Perner 2020 for
caveats), and nine species in six fossil genera (Brodkorb 1964; Mayr
2009, 2017; Mayr and Perner 2020). Most species are describedfrom a single bone, except for Palaeoplancus sternbergi Wetmore,
1933, which is represented by a partial skeleton with axial, pectoraland pelvic limb elements (Wetmore 1933). In contrast, SouthAmerica has no deﬁnitive fossil accipitrids from this time period,
possibly due to the dominance of the Cathartidae, Teratornithidae
and Phorusrhacidae in the avian predatory and scavenging guilds(Mayr 2017).
Two accipitrids, each based on single bones, are known from
Oligocene deposits of Asia: Buteo circoides Kurochkin, 1968 and
Venerator (Tutor) dementjevi (Kurochkin, 1968). Other indeterminate fossil accipitrids of early Oligocene age are known from
Mongolia and of late Oligocene age from Kazakhstan (Kurochkin1976). Four species of vulturine accipitrids are recorded from middle to late Miocene deposits of China: Mioaegypius gui Hou, 1984,
Mioneophron longirostris Li et al., 2016, Qiluornis taishanensis Houet al., 2000, and Gansugyps linxiaensis Zhang et al., 2010, each
represented by a partial or near complete skeleton.
Seven fossil accipitrids are known from the early Oligocene tothe early Miocene deposits of Europe, six of which are describedfrom single bones: Palaeohierax gervaisii (Milne-Edwards, 1863),
Promilio incertus (Gaillard, 1939), Aquilavus priscus (MilneEdwards, 1863), Aquilavus depredator (Milne-Edwards, 1871),
Aquilavus corroyi (Gaillard, 1939), and Aquilavus hypogaeus(Milne-Edwards, 1892). In contrast, Aviraptor longicrus Mayr and
Hurum, 2020, represented by a complete skeleton, is one of theoldest conﬁrmed accipitrids known from Europe.

The pre-Pleistocene fossil record of the Australian Accipitridae
is quite poor (Baird 1991; Vickers-Rich 1991). At the time ofwriting, Australia has two described pre-Pleistocene accipitrids,
the late Oligocene to early Miocene Pengana robertbolesi Boles,
1993 from the Riversleigh deposits in Queensland, and the middle
Miocene Aquila bullockensis Gaﬀ and Boles , 2010 from the Bullock
Creek Site in the Northern Territory (Worthy and Nguyen 2020).
The global fossil record, and molecular divergence dating, suggest that by the early Miocene, about 20 Ma, all extant subfamiliesof the Accipitridae had evolved (Walker and Dyke 2006; Zhang
et al. 2012; Nagy and Tökölyi 2014; Mindell et al. 2018).
The Namba Formation
The vast Kati Thanda–Lake Eyre catchment is approximately
1.2 million km2, extending over much of mid-central to northeastern inland Australia. Sedimentary deposition in the central/southern Australian section of the basin occurred in three major
phases; the ﬁrst phase resulted in the Late Palaeocene – Middle
Eocene Eyre Formation, which is comprised of sandstone andcarbonaceous conglomerates and clasts; the second phase resulted
in the Late Oligocene – early Miocene Etadunna, Namba,
Doonbarra and Cadelga Formations, which are comprised ofclays, silts, ﬁne sand, and carbonates; and the third phase saw the
Pliocene – Quaternary Wipajiri, Tirari, Kutjitara, Katipiri, Eurinilla,
Millyera Coomb Spring and Coonarbine Formations deposited,which are comprised of a variety of sediments including cobbles,
sands and clays from ﬂuvial or lacustrine deposition (Drexel andPreiss 1995; Alley 1998).
Our focus is the Namba Formation, located in the CallabonnaSub-basin of the Lake Eyre Basin, in South Australia to the east of
the Flinders Ranges (Alley 1998; see Figure 1). This is sometimes
referred to as the Tarkarooloo Basin (see Woodburne et al. 1994) or
the Frome Sub-basin (see Megirian et al. 2010). The age of thisformation is correlated with that of the Etadunna Formation, in the

Figure 1. (A) Map of South Australia with general location of Frome Sub-Basin fossil sites marked with a rectangle, (B) detailed map of the study sites in the Frome SubBasin. Lake Pinpa Sites 11 and 12, Ericmas Quarry, and Wells Bog Site located by black squares.

HISTORICAL BIOLOGY

Tirari Sub-basin of the Lake Eyre Basin (Alley 1998). The Namba
Formation contains three primary Local Faunas (LFs): the Pinpa
LF, the Ericmas LF, and the Tarkarooloo LF (Callen and Tedford
1976; Rich and Archer 1979; Rich et al. 1991; Thorn et al. 2021). The
Pinpa LF derives from beds of olive and orange mottled clay andwhite dolomitic mudstone stained with manganese at the top of thelower member of the Namba Formation, which crops out at Lake
Pinpa and Billeroo Creek (Tedford et al. 1977; Rich et al. 1991;
Thorn et al. 2021). The Ericmas LF derives from ﬂuvial sands
deposited in channels cut into the lacustrine units of the Namba
Formation, so is younger than the Pinpa LF, and derives from
Ericmas Quarry and South Prospect Quarries at Lake Nambaa few kilometres south of Lake Pinpa (Tedford et al. 1977; Richet al. 1991). There is much overlap of species composition between
Pinpa and Ericmas LFs suggesting broad similarity in age. While
Rich et al. (1991) recognised the Ericmas LF to occur at Lake Pinpa,
recent work by THW and ABC recognises only one local faunafrom Lake Pinpa and restricts the Ericmas LF to that derived from
Ericmas and South Prospect quarries at nearby Lake Namba (Thornet al. 2021). The Tarkarooloo LF derives from ﬂuvial sands in Tom
O’s Quarry by Lake Tarkarooloo about 10 kilometres west of Lake
Pinpa, but the temporal relationship to the Ericmas LF is unknown,
though co-occurrence of some species suggests a broadly similarage (Rich et al. 1991).
The accepted age of the Namba and Etadunna Formations hasvaried (see Pledge 2016). The Etadunna Formation, and therefore
by proxy the Namba Formation, was initially considered to be of
Oligocene age when it was ﬁrst identiﬁed (Stirton et al. 1961).
Subsequent analysis of the Pinpa and Ericmas LFs of the Namba
Formation considered their likely age to be middle Miocene (12–16 Ma) (e.g., Tedford et al. 1977; Woodburne et al. 1985) based on
the identiﬁcation of grass pollen in the basal Namba Formation in
Wooltana-1 bore that thereby indicated the presence of extensive
grasslands (Callen and Tedford 1976). However, later studies ofthe same pollen slides determined that grass pollen was exceedingly rare and that of Restionaceae or sedges, which occur wherever wetlands are present, was common along with a host of
rainforest taxa (Martin 1990). Therefore, Martin (1990) interpreted the palaeoenvironment as a rainforest surrounding swamps
and via correlation with ﬂoras elsewhere, inferred a late
Oligocene – early Miocene age for the basal Namba Formation.
Woodburne et al. (1994) detailed the biostratigraphy and revised
the age of the Etadunna Formation, using four lines of evidence: 1,
the presence of Oligocene age (28–24 Ma) foraminiferal fauna in the
Etadunna Formation (Lindsay 1987); 2, a reported Rb-Sr age of
25 Ma on an authigenic illite (Norrish and Pickering 1983); 3, thepresence of land mammal fossils consistent with those of known
Oligocene age; and 4, the magnetostratigraphic record, to conclude
that a late Oligocene age for the Etadunna Formation was most likely.
As Woodburne et al. (1994) determined that the Pinpa LF correlatedwith the most basal Zone A ‘Wynyardiid’ Fauna of the Etadunna
Formation, a late Oligocene age was also inferred for it. Woodburne
et al. (1994) did not cite Martin (1990) and were apparently unawareof it, as the pollen data provided compelling evidence to support theirinferred late Oligocene age. This work was accepted by Megirian et al.
(2010) who established a comprehensive land mammal biostratigraphy and advocated a late Oligocene age (28–24 Ma) for the Namba
Formation. Some of the ages accepted by Megirian et al. (2010) havebeen robustly conﬁrmed by direct dating of sites from Faunal Zones
B and C at Riversleigh, northwest Queensland, to the early andmiddle Miocene, respectively (Woodhead et al. 2016), supporting
the prior correlation of Faunal Zone B sites with the Kutjamarpu LF(Wipajiri Fm) from Lake Ngapakaldi, Lake Eyre Basin on biochronological grounds; the Kutjamarpu LF is slightly younger than the3uppermost Etadunna local fauna – the Ngama LF – on biochronological grounds (Megirian et al. 2010). Therefore, we use the age
range of 26–24 Ma advocated by Woodhead et al. (2016) for the
Pinpa + Ericmas Local Faunas.
Aquatic or semiaquatic vertebrates are common in both the
Pinpa and Ericmas LFs in the Namba Formation, including ﬁsh,turtles, crocodilians, and dolphins (Tedford et al. 1977; Fordyce
1983; Rich et al. 1991), revealing the presence of a permanent lakein the basin during this time period. The dolomitic layers at the site
suggest periods of time when sections of the lake would seasonally
dry out (Callen 1977). The afore-mentioned pollen record from the
Namba Formation reveals that the depositional environment was
dominated by a mix of rainforest and temperate forest surrounding
sedge-lined lakes in the late Oligocene to early Miocene when the
Pinpa LF was present (Martin 1990). The range in habitats resulted
in a diverse vertebrate fauna inhabiting this area in the late
Oligocene, resulting in a fossil fauna that is a key snapshot into
our understanding of the evolution of Australian animals.
The Pinpa LF, found at Lake Pinpa and Wells Bog Site at Billeroo
Creek (Rich et al. 1991; Thorn et al. 2021) (Figure 1), is extremely
diverse, comprising ﬁsh and both aquatic and terrestrial reptiles,
mammals, and birds (Rich et al. 1991). Reptiles are represented byan indeterminate species of chelid turtle (Emydura sp.), an unnamed
species of meiolaniid turtle (see Rich et al. 1991), the crocodilian
Australosuchus clarkae Willis and Molnar, 1991 (See Willis 1997),
and an ergerniine skink Proegernia mikebulli Thorn et al., 2021.
The mammals of the Pinpa LF are well-documented, see Richet al. (1991) or subsequently described; Monotremata:Ornithorhynchidae, Obdurodon insignis Woodburne and Tedford,
1975. Marsupialia, Vombatiformes: Phascolarctidae, Madakoala
devisi Woodburne et al., 1987a; Ilariidae, Ilaria illumidens Tedford
and Woodburne, 1987; Mukupirnidae, Mukupirna nambensis Becket al., 2020 (=Vombatoidea genus A of Tedford et al. 1977);
Diprotodontidae, Raemeotherium yatkolai Rich et al., 1978;
Wynyardiidae, Muramura pinpensis Pledge, 2003. Marsupialia,
Phalangeriformes: Pseudocheiridae, Pildra antiquus Woodburne
et al., 1987b; Pildra secundus Woodburne et al. , 1987b (listed asfrom Ericmas LF, Lake Pinpa); Pilkipildridae, Pilkipildra handae
Archer, Tedford and Rich, 1987; Miralinidae, Miralina sp. cf
M. minor; Ektopodontidae, Chunia sp. cf C. illuminata; undetermined
Petauridae;
undetermined
Macropodiformes,
Macropodidae/Potoroidae; Placentalia, Cetacea: an unnamed species of extinct rhabdosteid dolphin (Fordyce 1983).
Birds are also abundant in the Pinpa LF, with many semi-aquatictaxa, see Rich et al. (1991), as modiﬁed by Boles and Ivison (1999),
Worthy (2009, 2011), Boles et al. (2013) and De Pietri et al. (2016).
Presbyornithidae, Wilaru tedfordi Boles et al., 2013; Megapodiidae,
Ngawupodius minya Boles and Ivison, 1999 (listed as from theEricmas LF by Boles and Ivison 1999, but derives from the Southend of Lake Pinpa where only deposits preserving the Pinpa LF
occur (Thorn et al. 2021), and as a pigeon in Rich et al. [1991,
p. 1025]). Anatidae: Pinpanetta tedfordi Worthy, 2009; Pinpanetta
vickersrichae Worthy, 2009; Pinpanetta fromensis Worthy, 2009,
Australotadorna alecwilsoni Worthy, 2009. Phalacrocoracidae:
Nambashag billerooensis Worthy, 2011; Nambashag microglaucus
Worthy, 2011. Pelecanidae: Pelecanus tirarensis Miller, 1966. Other
taxa include undescribed species of rails (Rallidae), undeterminedﬂamingos (Phoenicopteriformes), grebes (Podicipedidae), and passerines (authors’ unpubl. data).
From the dolomitic beds of the Namba Formation exposed at Site
12 on Lake Pinpa (Figure 1), and hence forming part of the Pinpa LF,
a partial skeleton of an accipitrid was recovered in 2016 by a Flinders
University expedition, led by THW and ABC. Sixty-three recognisablebones are represented, spanning the tip of the rostrum to the pedal

4

E. K. MATHER ET AL.

University of Kansas Institute of Biodiversity, Lawrence, KS, USA(KU); Smithsonian Museum of Natural History, Washington DC,
USA (USNM); Natural History Museum, London, UK (NHMUK).
Anatomical
Pedal phalanges are identiﬁed by the digit ﬁrst (Roman numeral)and phalanx second (Arabic number), e.g., II.2 is digit II, phalanx 2;cmc, carpometacarpus; cor, coracoid; DW, distal width; L, left; PW,
proximal width; R = right; SW, shaft width; tmt, tarsometatarsus.
Manus digits are identiﬁed akin to the pedal phalanges, e.g., MI.1 ismanus digit I, phalanx 1.
Nomenclature
The anatomical nomenclature advocated by Baumel and Witmer(1993) is followed for all bones except for the os carpale radiale,
which follows Mayr (2014), and the quadrate, which follows
Elzanowski and Zelenkov (2015). Taxonomic nomenclature follows
Dickinson and Remsen (2013) and Gill et al. (2020) for composition of
Accipitriformes, and Nagy and Tökölyi (2014) for subfamilial
composition.
Measurements
Bones were measured with an accuracy of 0.1 mm using digitalcallipers.
Photography

Figure 2. Exemplar accipitriform skeleton, Pandion haliaetus cristatus, derived froman illustration in Eyton (1867), showing the bones preserved in the fossil accipitrid
specimen SAMA P.54998 shaded in grey. The illustrated taxon and fossil material
are not identical in terms of the morphology of individual elements.

digits (Figure 2). The pelvic limb elements are well preserved, except
for the femur for which only the caput is preserved. This skeleton
represents not only the oldest fossil representative of Accipitridae inAustralia but also the most complete (cf. Boles 1993; Gaﬀ and Boles
2010). This relatively complete state is also rare on a global scale, andonly observed in a handful of cases, such as the Miocene vultures ofChina which are near complete (Hou et al. 2000; Zhang et al. 2010; Liet al. 2016), Palaeoplancus sternbergi (see Wetmore 1933; Mayr andPerner 2020) and Aviraptor longicrus (see Mayr and Hurum 2020).
Besides the new skeleton, there are another two accipitrid fossils
recognised from the Namba Formation; a distal right humerus, fromthe dolomitic layers at Site 11, Lake Pinpa (also of the Pinpa LF) anda distal femur from Ericmas Quarry, Lake Namba, of the Ericmas LF.
It is the aim of this contribution to formally describe these fossils anddetermine their phylogenetic relationships in the Accipitridae.

Materials and methods
Abbreviations
Institutions
South Australia Museum, Adelaide, SA, Australia (SAMA);
Museums Victoria, Melbourne, VIC, Australia (NMV); Australian
National Wildlife Collection, Canberra, ACT, Australia (ANWC);

Photographs were taken using a focus stacking method usinga Canon 5DS-r digital camera 50.0 MP with either a Canon EF
100 mm or a 65 mm f2.8 IS USM professional macro lens withmultiple images then compiled into a single photo using the program Zerene Stacker. Some fossil specimens were whitened withammonium chloride powder before imaging (see Feldmann 1989)
to retain shape as the primary feature captured rather than variable
staining and reﬂective surfaces.
Comparative material
Skeletons of a broad range of accipitrids and outgroup taxa wereloaned from museums and other institutions from Australia andinternationally to compare to the fossil as follows.
Extant species (in taxonomic groupings)
Falconidae Falco berigora SAMA B55605; Falco longipennis
SAMA B49055; Falco peregrinus SAMA B32515.
Threskiornithidae Threskiornis spinicollis AMA B48351.
Ciconiidae Ciconia ciconia SAMA B49223, SAMA B11601.
Cathartidae Coragyps atratus SAMA B36873.
Sagittariidae Sagittarius serpentarius USNM 223836.
Pandionidae Pandion haliaetus SAMA B37096, NMV B30256.
Accipitridae Elaninae: Elanus axillaris NMV B34037;
Elanus scriptus NMV B8617, NMV B30263, ANWC 22680;
Gampsonyx swainsonii USNM 623110; Chelictinia riocourii
NHMUK S.1904.4.28.3. Perninae: Elanoides forﬁcatus USNM
622340; Chondrohierax uncinatus USNM 289784; Aviceda subcristata ANWC 22665, NMV B19826; Pernis apivorus SAMA B59278;
Lophoictinia isura NMV B18533, ANWC 44373; Hamirostra melanosternon ANWC (FALS-41), SAMA B36200. Gypaetinae:
Polyboroides typus USNM 430434; Neophron percnopterus SAMA
B11449; Gypohierax angolensis USNM 291316; Gypaetus barbatus

HISTORICAL BIOLOGYMNH S.1972.1.59, MNH S.1896.2.16.120, MNH S.1952.3.61.
Circaetinae: Spilornis cheela USNM 562001; Terathopius ecaudatus
NMV 18575; Pithecophaga jeﬀeryi MNH S.1910.2.11.1a, MNH
S.1961.23.1. Aegypiinae: Necrosyrtes monachus USNM 620646;
Gyps coprotheres ANWC 22724; Gyps fulvus NMV 18574, NMV
B30269; Aegypius monachus NMV R553; Sarcogyps calvus MNH
S.2013.22.1, MNH S.2007.30.1; Trigonoceps occipitalis MNH
S.1954.30.54; Torgos tracheliotos MNH S.1930.3.24.248, MNH
S.1952.1.172. Harpiinae: Harpia harpyja NHMUK S.1862.3.19,
NHMUK S.1909.8.18.1. Aquilinae: Stephanoaetus coronatus
NHMUK S.1954.30.42, NHMUK S.1862.3.14.19; Aquila audax
SAMA B46613, NMV B19228; Aquila chrysaetos NMV B32659,
ANWC 22682 (FALS-123); Aquila fasciata (formerly Hieraaetus
fasciatus) NMV B30575; Hieraaetus morphnoides SAMA B47128,
NMV B8643, NMV B20224; Hieraaetus (=Harpagornis) moorei,
casts of the original type material, NMV P33032 (tibiotarsus),
NMV P33031 (pedal phalanx), NMV P33030 (tarsometatarsus),
NMV P33029 (femur), NMV P33028 (humerus), NMV P33027(femur), NMV P33026 (ulna); Spizaetus tyrannus KU 35007;
Spizaetus ornatus KU 72077. Haliaeetinae: Haliaeetus leucogaster
NMV B8847, SAMA B49459; Haliaeetus leucocephalus ANWC
22723 (16,500), NMV B15601; Haliaeetus albicilla NMV B34417;
Haliastur indus ANWC 22719, NMV B13753; Haliastur sphenurus
NMV B11661, SAMA B33998; Milvus migrans SAMA B47130,
NMV B20404. Accipitrinae: Melierax metabates NHMUK
S.1954.30.29;
Kaupifalco
monogrammicus
NHMUKS.1869.10.19.28; Circus assimilis SAMA B56454, ANWC 22727;
C. approximans ANWC 22728, ANWC 22729; C. cyaneus ANWC
22735; C. aeruginosus NMV B12891; Accipiter fasciatus NMV
B13444, SAMA B36355; A. cooperii ANWC 22764, ANWC 22765;
A. striatus ANWC 22747, NMV B12666; A. novaehollandiae NMV
B18401; A. cirrocephalus NMV B16071, NMV B10346; A. nisus
NMV B12413, ANWC 22742; A. gentilis ANWC 22736, NMV
B12927. Buteoninae: Erythrotriorchis radiatus NHMUKS.1872.10.22.9;
Geranospiza
caerulescens
NHMUKS.1903.12.20.318; Ictinia mississippiensis ANWC 22681 (21,655),
NMV B13343; Buteo buteo SAMA B46558, NMV B24505;
B. nitidus NMV B13222; Buteo rufofuscus NMV B24503; Buteo
lagopus ANWC 22776 (21694), NMV B24884.
Phylogenetic methods
Morphological analysis
A total of 300 morphological characters were coded for both extant
and fossil specimens, from the following elements: cranium, sternum, coracoid, humerus, ulna, carpometacarpus, ossa carpi, ossa
digitorum manus, pelvis, femur, tibiotarsus, tarsometatarsus, andpedal phalanges (see SI.1). A total of 154 characters were derived
from Migotto (2013, unpublished thesis), two from Elzanowski and
Stidham (2010), two from Elzanowski and Zelenkov (2015), sixfrom Gaﬀ and Boles (2010), one from Worthy et al. (2016), three
from Mayr (2018) and three from Mayr (2014). The remaining 129
characters were novel traits derived from observations and comparisons between the extant and fossil specimens.
Molecular data
Molecular data from Burleigh et al. (2015) was added to the morphological data to improve estimated relationships between living
species (Lerner and Mindell 2005; Nagy and Tökölyi 2014; Burleighet al. 2015). This allows the fossil taxa to be placed phylogeneticallyaccording to the signal in the morphological data, but in the context
of a DNA-informed tree for living taxa which better accommodates
homoplasy in skeletal morphology (see Holdaway 1994; Griﬃths
et al. 2007). The following genes, well-sampled in accipitrids, were5

used: cytochrome b, cytochrome oxidase 1, NADH dehydrogenase
2, 12s RNA, RAG 1, and ﬁbrinogen B beta introns 6 and 7, for analigned matrix totalling seven gene regions and six loci.
Genomic data for the above gene regions from Burleigh et al.
(2015) were used for the following species: Ciconia ciconia,
Coragyps atratus, Sagittarius serpentarius, Pandion haliaetus,
Elanus caeruleus, Gampsonyx swainsonii, Elanoides forﬁcatus,
Chondrohierax uncinatus, Aviceda subcristata, Pernis apivorus,
Lophoictinia isura, Hamirostra melanosternon, Polyboroides typus,
Neophron percnopterus, Gypohierax angolensis, Gypaetus barbatus,
Spilornis cheela, Terathopius ecaudatus, Pithecophaga jeﬀeryi,
Necrosyrtes monachus, Gyps fulvus, Gyps coprotheres, Aegypius
monachus, Sarcogyps calvus, Trigonoceps occipitalis, Torgos tracheliotos, Harpia harpyja, Stephanoaetus coronatus, Aquila chrysaetos,
Hieraaetus morphnoides, Hieraaetus fasciatus/Aquila fasciata,
Hieraaetus moorei, Spizaetus tyrannus, Spizaetus ornatus,
Haliaeetus leucogaster, Haliaeetus leucocephalus, Haliaeetus albicilla, Milvus migrans, Melierax metabates, Kaupifalco monogrammicus, Circus aeruginosus, Circus cyaneus, Accipiter cooperii,
Accipiter striatus, Accipiter novaehollandiae, Accipiter gentilis,
Ictinia mississippiensis, Geranospiza caerulescens, Buteo buteo,
Buteo lagopus, Buteo rufofuscus, and Platalea leucorodia. To reduce
missing data, genetic data from Platalea leucorodia was paired withThreskiornis spinicollis, and Elanus caeruleus paired with Elanus
scriptus, as these species pairs consist of closely related taxa (seeCampbell and Lapointe 2009 regarding this method).
Phylogenetic analysis
Phylogenetic comparisons were aimed primarily at determining therelationships of the fossil specimen SAMA P.54998. A total of 47
species of Accipitridae, and one species each of Pandionidae,
Sagittariidae, Cathartidae, Threskiornithidae, and Ciconiidae were
sampled. The non-accipitrid species were selected for the following
reasons; Pandionidae, Sagittariidae and Cathartidae are successive
sister-taxa to the Accipitridae within the Accipitriformes; the species of Ciconiidae and Threskiornithidae (Ciconiiformes), areexamples of bird families outside of Accipitriformes that sharesimilar size and ﬂight morphology, as well as a history of grouping
with the Cathartidae in older phylogenies (see Sibley and Ahlquist
1990; Wink 1995).
Both parsimony and Bayesian analyses were used to explore thedata. The parsimony analyses of the morphological, molecular, andcombined morphological-molecular datasets used PAUP 4.0b10,
and heuristic searches. Each search was comprised of 1000 random
addition replicates, and enabled TBR branch swapping, with
NCHUCK set to 1000. Characters that were inapplicable toa specimen were coded using ‘-’, while missing data were coded as‘?’. The taxa Threskiornis spinicollis, Ciconia ciconia, Coragyps atratus, Sagittarius serpentarius and Pandion haliaetus were all deﬁned
as outgroup taxa in all analyses, with Threskiornis spinicollis andCiconia ciconia being the most basal outgroups. Once the heuristic
searches had generated a set of most parsimonious trees (MPT),
a strict consensus tree was created from them. The support forclades on these trees were then assessed using bootstrapping, with
1000 replicates, and majority-rule consensus trees set to conlevel 50(support shown if >50%) (see SI.3).
For the Bayesian analyses, MrBayes 3.2.7 was used via the
CIPRES platform (Miller et al. 2010). The morphological partition
used the standard (Lewis) model for discrete data, with correction
for non-sampling of invariant characters. The among-character ratevariability was modelled using the gamma parameter, with distribution approximated using four categories. The molecular partitioning scheme and substitution models were identiﬁed using
PartitionFinder (Lanfear et al. 2016), using BIC. The data was6

E. K. MATHER ET AL.

thus treated as three partitions: morphological data (morph); molecular partition 1 (pﬁnder Molec1), which contains Cyt-B codons 1
and 2, CO1 codons 1 and 2, ND2 codons 1 and 2, 12s, Rag-1 codons
1, 2 and 3, and FGBint67; and molecular partition 2 (pﬁnder
Molec2), which contains Cyt-B codon 3, CO1 codon 3, and ND2
codon 3. The Molec1 and Molec2 partitions each had a GTR modelusing a Dirichlet prior for the state frequencies. The amongcharacter rates were set to InvGamma, with the gamma distribution
approximated as above. All substitution parameters were unlinked
across these molecular partitions (see SI.4).
Each analysis entailed four runs, each run comprising four
MCMC chains (incrementally heated to 0.1), the number ofgenerations set to 50,000,000, the sample and print frequency
set to 5000. Burnin was set to 20% (and conﬁrmed suﬃcient
using PSRF and SDSF values in MrBayes) and the majorityrule consensus tree was obtained from all post-burnin samples.
During the MrBayes runs, Ciconia ciconia was set as the soleoutgroup taxon, due to limitations of MrBayes, but trees werelater rerooted so that both Ciconia ciconia and Threskiornis
spinicollis were the most distal outgroup clade. The Bayesiananalyses were performed twice: with morphological and molecular branch lengths linked or unlinked.

Ecomorphological analyses
Measurements of selected elements for a sample of extant
accipitrids were used to correlate morphology with ecology
of living forms and so to retrodict the ecology and feeding
strategy of the fossil taxon. Measurements used reﬂected theiravailability in the fossil: height of the quadrate; length andproximal width of the carpometacarpus; length, shaft widthand distal width of the ulna; length, shaft width, distal width,height of the condylus lateralis, depth of the condylus lateralis,height of the condylus medialis and depth of the condylus
medialis of the tibiotarsus; length, shaft width, distal width,
and width and height of trochleae metatarsorum 2, 3 and 4 of
the tarsometatarsus; length of the ﬁrst phalanx of pedal digit 1;
and the length of the ﬁrst and second phalanges of pedal digit
2. The fossil species was compared to Elanus scriptus,
Hamirostra melanosternon, Pernis apivorus, Lophoictinia
isura, Neophron percnopterus, Aegypius monachus, Gyps
coprotheres, Spilornis cheela, Haliaeetus leucogaster, Aquila
audax, Hieraaetus morphnoides, Spizaetus tyrannus, andCircus assimilis in Principal Components Analysis (PCA).
These species were chosen as they were considered to beeither, exemplars of the diﬀerent hunting strategies ofAccipitridae, or were potential analogues for the fossil. The
PCA was performed on measurements of the wings and legs:
raw, log-transformed, and standardised for size by division by
the height of the quadrate in each individual (as this was
possible for the fossil). The extant taxa were classed based on
their preferred habitat (open, woodland, or forest) as determined from the literature (Brown and Amadon 1968;
Ferguson-Lees and Christie 2001).
Widths of the distal femur, distal humerus, proximal humerus
and distal tibiotarsus were measured for both extant and fossil
specimens so that the relationships between these values could be
used to predict the width of the distal humerus and distal femur for
SAMA P.58917, and thereby to assess whether size precluded theisolated distal humerus from Site 11 Lake Pinpa and the distal
femur from Ericmas Quarry from being the same taxon as SAMA
P.58917.

Results
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, withunbranched 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 andlaterally, 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 theother families of Accipitriformes (Cathartidae, Sagittariidae,
Pandionidae) by the morphology of the tarsometatarsal hypotarsus
cristae and sulcus. The cristae are fused or partially fused together toenclose 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 arefound: 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 theprocessus 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 thatare 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: therostral 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.
Type species: Archaehierax sylvestris sp. nov.
http://zoobank.org/urn:lsid:zoobank.org:act:8C4B01F2-12CE46F4-A444-C63B18C90BAE
Etymology
Archaehierax is derived from the Greek words ‘archaios’, meaning
ancient, and ‘hierax’, meaning hawk. Gender masculine.
Diagnosis
An accipitrid distinguished by the combination of the following
features; Rostrum. (1) The nares are large and fully open, (2)processus maxillopalatini not fused; Quadrate. (3) the condylus

HISTORICAL BIOLOGY

pterygoideus projects less medially than the condylus medialis, (4)a deep, distinct fossa caudomedialis with a small amount of pneumatism; Sternum. (5) The apex carinae is displaced caudally fromthe base of the spina externa, (6) the medial crista on the carina
does not extend to the spina externa; (7) The pila medialis on thedorsal face separates two deep fossae (autapomorphy); Humerus.
(8) The caput humeri is only slightly elevated proximally past the
tuberculum ventralis (autapomorphy); Os carpale ulnare. (9)Deepened depression on ulnaris face; Tarsometatarsus. (10) The
trochleae metatarsorum are splayed and separated by wide incisurae, especially laterally, with the individual trochleae themselves
quite narrow in width (autapomorphy); (11) The incisura forthe m. ﬂexor hallucis brevis tendon is large, distinct, and extends
distal to the fossa metatarsi I (autapomorphy); Phalanx IV.4. (12)The distal articular end that articulates with phalanx IV.5, is considerably wider than the shaft.
Type Locality/Stratigraphy/Age
31° 07.499ʹ S; 140° 12.755ʹ E. Site 12a, Lake Pinpa, Frome Downs
Station, Callabonna Sub-Basin, S.A. Dolomite bed of Namba
Formation, Pinpa LF, late Oligocene, 26–24 Ma.
Archaehierax sylvestris Mather, Lee, Camens and Worthy gen. et
sp. nov. (Figures 3-10)
http://zoobank.org/urn:lsid:zoobank.org:act:092140CA-E93743B3-B3F1-7127C97094F4
Holotype
SAMA P.54998, 63 elements and associated fragments of a single
skeleton (see Figure 2) as follows:
Fragments of mandible; rostral majority of rostrum;
R pterygoid; L quadratojugal; L quadrate; ceratohyal; atlas vertebra; axis vertebra; partial cervical vertebra #3; caudal vertebrae x3(position in tail indeterminate); cranial part sternum; LR scapulae;
cranial and sternal parts LR coracoids; proximal LR humeri; L anddistal R ulna; L and distal R radius; L carpometacarpus; LR os
carpi ulnare; L os carpi radiale; R manual phalanges, proximal
fragment MI.1, proximal fragment MII.1 and MII.2; L manualphalanges MI.1, MII.2 with distal end eroded, and MIII.1; LR
proximal femur fragments; R tibiotarsus reconstructed in two
parts; L tibiotarsus; fragmented LR ﬁbulae; LR tarsometatarsi; LR
ossa metatarsalia; pedal phalanges: RI.1, RII.1, RII.2, RIII.1, RIII.2,
RIII.3 (partial), RIII.4, LI.1, LI.2 (fragmented), LII.1, LII.2, LIII.1,
LIII.2, LIII.3 (partial), LIII.4, LIV.1, LIV.2, LIV.3, LIV.4, LIV.5.
The skeleton was found eroding out on the surface with surviving
elements recovered in a semi-articulated state from within dolomitic clays (equivalent to layer 5 of Thorn et al. 2021), with mostlarge elements fractured into many roughly articulated pieces,presumably by expansion and contraction associated with thewetting and drying of the clays. The fragments for each element
were, where possible, separated, cleaned and reassembled
by THW.
Measurements (mm)See Appendix 1 Table S1.
Etymology
The species name ‘sylvestris’ is derived from the Greek world‘sylvas’, meaning forest, and the Latin suﬃx ‘-estris’, meaning‘belonging to’.

7

Type locality/Stratigraphy and age
As per genus.
Diagnosis
As for genus.
Descriptions
Rostrum maxillare (Figure 3(A, B)).
The rostral section of the rostrum maxillare is preserved inreasonably good condition. Morphology of its rostral tip, tomial
margin, rostral margin of the nares, and the palatines is visible.
The rostrum has a preserved length of 32.6 mm from the rostral
tip to the posterior base of the nares, and a preserved depth of
17.3 mm from the tomial margin to the dorsal side of the rostrum
taken at the rostral end of the nares. (Trait 1) The rostral tip of therostrum is hooked, descending below the tomial margin at a 30–40°
angle. (2) The lateral tomial margin (Figure 3A: CT), positioned
distal to the nares, is ventrally convex. (3) The nasal aperture(Figure 3A: N) is large (height 8.7 mm) and fully open as in mostaccipitrids, spanning just over half the rostrum depth. (4) The
ossiﬁed section rostral to the incisura ventromedialis is of small tomoderate size (10.1 mm preserved length) relative to the total
length of the rostrum. (5) In ventral aspect, an incisura ventromedialis (Figure 3B: IV) (sensu Livezey and Zusi 2007) is present(sediment ﬁlled) extending from where damage destroys it rostrally
to the preserved caudal end of the palate; it is narrow and widens
caudally, rather than being closed forming a fenestra. The pars
maxillaris palatini (Figure 3B: PM) are unfused and diverge slightly
caudally, the left being least fragmented although it has broken
from the adjacent lateral margin creating a false incision. A small
fragment of bone preserved between the pars maxillaris palatini isinterpreted as a displaced fragment of the processus maxillopalatinus. (6) Damage precludes ascertaining the presence/form of thefenestra ventrolaterale.
Other accipitrid subfamilies diﬀer as follows:(Trait 1) Compared to the fossil, the tip of the rostrum is much
more sharply hooked ventrally in most subfamilies. Only membersof Elaninae, Perninae (except Chondrohierax uncinatus, which is
sharper), Buteoninae, and Gypaetinae have similar or shallower
angled tips.
The rostrum maxillare is overall most similar to that of species of
Buteoninae (see SI.2 for more detailed diﬀerential comparisons).
Quadrate (Figure 3(C, D))
The left quadrate has considerable breakage aﬀecting the lateralside ventrally, the medial side of the processus oticus, and loss of theprocessus orbitalis. Preservation of morphological detail is best medially. On the processus oticus, only about half of the capitulum
squamosum is preserved and the dorsal half of the crista medialis islost. Of the processus orbitalis, only the well-preserved base remains.
Both the condylus pterygoideus and medialis are intact, but the entire
condylus lateralis and caudal half of the condylus caudalis are lost.
(Trait 1) The processus oticus (Figure 3D: POt) is short andbroad leading up to the capitulum squamosum. (2) The capitulum
squamosum (Figure 3D: CS), as preserved is relatively small, andhas a tuberculum subcapitulare forming a distinct hook projecting
ventrally on its cranial margin. (3) The processus orbitalis(Figure 3C: POr) is dorsomedially oriented. (4) The processus isset entirely in the ventral half of the quadrate, creating a gentle,
shallow sloping arc between the base of the processus and the8E. K. MATHER ET AL.

Figure 3. Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998 rostrum in lateral (A) and ventral (B) view; quadrate in medial (C) and lateral (D) view; atlas vertebra incaudal (E), lateral (F) and cranial (G) view; and axis vertebra in caudal (H), lateral (I) and cranial (J) view. Specimens in A-D are coated in ammonium chloride. Abbreviations:Arc. At., arcus atlantis; CC, condylus caudalis; CM, condylus medialis; CP, condylus pterygoideus; CS, capitulum squamosum; CT, crista tomialis; FA, facies articularis; FAA,
facies articularis axialis; FC, fossa condyloidea; FPB, fossa pneumaticum basiorbitale; FPC, fossa/depressio pneumaticum caudomediale; IAC, incisura caudalis arcus; IF,
incisura fossae; IV, incisura ventromedialis; N, nasale; PAC, processus articularis caudalis; PM, pars maxillaris palatini; POr, processus orbitalis; POt, processus oticus. Scalebars are 10 mm.

capitulum. (5) A large and deep foramen pneumaticum basiorbitale(Figure 3C: FPB) is present between the processus orbitalis and thecondylus pterygoideus. (6) Breakage prohibits assessing the statusof the foramen rostromediale. (7) The ventral section of the crista

medialis is preserved and is quite broad and ﬂat with no projecting
ridge. (8) A thin, distinct sulcus runs along the ventral margin of thecrista to connect to the foramen pneumaticum caudomediale. (9)A distinct, deep foramen pneumaticum caudomediale (Figure 3C:

HISTORICAL BIOLOGY

FPC) is present just medial of the ventral-most point of the crista
medialis. (10) The condylus pterygoideus (Figure 3D: CP) is distinct, high-set and well separated from the condylus medialis. (11)The condylus medialis (Figure 3C: CM) is well preserved, showing
a large (4.0 mm wide by 2.8 mm deep), semi-ovular facet, witha pointed medial margin that extends further medially than thecondylus pterygoideus. (12) The portion of the condylus caudalis(Figure 3C: CC) preserved indicates a facet of a similar size to thecondylus medialis, with a semicircular shape.
Other accipitrid subfamilies diﬀer as follows (variable characters excluded):(Trait 8) The sulcus running along the ventral crista is
broad and indistinct in all other taxa except in species ofMilvus and Haliaeetus (Haliaeetinae) where it is narrow andindistinct. (9) The fossa caudomediale is practically absent in
the subfamilies Circaetinae and Aegypiinae, as well as the
species in Hamirostra, Lophoictinia (Perninae), Neophron(Gypaetinae), and Haliaeetus (Haliaeetinae); shallow in
Aquilinae and species of Elanoides, Chondrohierax(Perninae), Polyboroides and Gypohierax (Gypaetinae); anddeep in Elaninae, Accipitrinae and Buteoninae, as well as
species in Pernis (Perninae). The depressio was indistinctly
shaped (i.e. a gradually deepened area rather than a deﬁnedpit) in all species, and apneumatic in all species except in
Pernis and Haliaeetus.
The quadrate is overall most similar to that of speciesof Aegypiinae (see SI.2 for more detailed diﬀerential
comparisons).
Vertebrae (Figure 3E-J)
The atlas vertebra of SAMA P.54998 is 10.7 mm wide by
10.7 mm high (from the proximal margin of arcus atlantis tothe distal margin of fossa condyloidea). (Trait 1) The arcus
atlantis (Figure 3G: Arc. At.) forms a low, ﬂat arch, which
dorsally has a maximum proximodistal width of 3.2 mm at thecentre, overhanging the fossa condyloidea cranially. (2) The
incisura fossae (Figure 3G: IF) is shallow and broad, forming
a semicircular shape in cranial aspect. (3) The fossa condyloidea (Figure 3G: FC) is 4.3 mm wide by 4.2 mm long. (4) The
dorsolateral eminences of the fossa condyloidea are small. (5)The ventral margin of the fossa forms a rounded point incranial aspect and is prominent cranially in lateral aspect.
(6) The zygopophyses caudales are badly worn and diﬃcult
to assess, but what is preserved indicates they were distinct
and caudally projected from the rest of the arcus atlantis. (7)The incisurae caudales arcus (Figure 3E: IAC) are very shallow. (8) The facies articularis axialis (Figure 3E: FAA) is
5.7 mm wide by approximately 3.8 mm long. (9) The rest of
the distal corpus atlantis is worn away and cannot be assessed,
but what is present suggests that few additional structures
were present, and that there was some asymmetry in the
shape of the lateral fossa condyloidea.
The axis vertebra is quite fragmented, with most of theneural spine, facies articularis atlantica, dens, facies articularis
caudalis, processus ventralis and the area of incisurae caudales
arcus broken away. Its width is 12.7 mm across the processus
articulares caudales and mid-line length of the corpus vertebra
is 8 mm. The facies articularis on zygopophyses caudales are
3.1 mm wide by 3.8–4.1 mm long. (10) A short but caudally
prominent projection is present dorsal to each facet (Figure 3H:FA), measuring 2–2.5 mm in width. (11) There is no evidenceof a bridge enclosing the incisurae caudales arcus (Figure 3F,
H: PAC).

9

The three known caudal vertebrae are too broken to identify
their position in the caudal series.
The vertebrae are overall most similar to that of speciesof Elaninae (see SI.2 for more detailed diﬀerential
comparisons).
Sternum (Figure 4(A, B, C))
The cranial section of the sternum of SAMA P.54998 is preserved, retaining the structure of the spina externa, pila carinae,
crista medialis carinae, apex carinae, the left sulcus articularis
coracoideus, and the left labrum internum. It is characterised by:(Trait 1) A spina interna is absent; a small notch exists in its
place. (2) The spina externa (Figure 4B: SE) is 6.4 mm wide at its
base, 4.7 mm wide at its blunt tip and 4.2 mm long. In cranial view,
the spina externa is triangular as a medial crista forming a lobe
projecting 3.6 mm ventrally. The base of the spina externa is broader
than the apex carinae (4.0 mm). (3) The crista medialis carinae(Figure 4A: CMC) is short, extending dorsally from the apex carinae
to mid-height of the pila carinae with a low proﬁle in lateral view.
More dorsad, the pila carinae is smooth to the base of the spina
externa. (4) The pila carinae (Figure 4A: PC) is robust for its size,
measuring 5.2 mm at mid-depth. It is 23.3 mm long from the ventral
margin of the carina sterni to where the pila carinae meets the spina
externa. (5) The apex carinae (Figure 4A: AC) at 4.0 mm wide, isnoticeably expanded from the width of the pila carinae immediately
dorsal to it (3.0). (6) The apex carinae is rounded, with no hookedprojection extending cranially. (7) The maximum carina depth
below the sternal basin is roughly equivalent to basin depth below
the costal margin, typical of most accipitrids except for certain
vulture species (Aegypiinae). (8) The apex carinae is set well caudally[assuming the junction of the carina with the pars cardiaca is aligned
horizontally] from the base of the spina externa. (9) There are nosmall, dispersed pneumatic foramina present dorsally in the body ofthe sternum. (10) The small part of the carina sterni preserved
narrows caudally from the pila carinae. (11) The left sulcus articularis coracoideus (Figure 4B: SAC) is 4.3 mm dorsoventrally deep,and extends to the midline of the sternum, directly dorsal to thespina externa, where it does not overlap the right sulcus. (12) The
left labrum internum (Figure 4A: LI) is maximally 4.2 mm deep and
2.8 mm wide in dorsal view as preserved. (13) A pila medialis(Figure 4C: PM), 2.1 mm wide, on the dorsal face of the sternum
separates two deep, pneumatic fossae in the pars cardiaca.
Extant accipitrid subfamilies diﬀer as follows:(3) The crista medialis extends to the base of the spina externa inmembers of all subfamilies except Aegypiinae. (8) The apex carinae lies
directly ventral to the base of the spina externa, or projects morecraniad, in species in all subfamilies except for Gypaetinae andAegypiinae. (11) The sulci articularis coracoidei overlap in all species
except for Gampsonyx swainsonii (Elaninae) and Sarcogyps calvus(Aegypiinae). (13) No species in any subfamily has a distinct pila
medialis separating pneumatic fossae in the pars cardiaca, which isthus an autapomorphy suggesting subfamilial distinction for the new
species.
The sternum is overall most similar to that of species of
Aegypiinae (see SI.2 for more detailed diﬀerential comparisons).

Coracoid (Figure 4(F, G, H, I))
The well-preserved left and right omal ends and fragments ofboth sternal ends of the coracoids of SAMA P.54998 were recovered. They reveal the following:

10

E. K. MATHER ET AL.

Figure 4. Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998 partial sternum in cranial (A), left lateral (B) and dorsal (C) view; right scapula in lateral (D) and medial (E)view; omal fragments of the left coracoid in medial (F) and lateral (H) view and of the right coracoid in dorsal (G) and medial (I) view. Specimens in A, B, and F-I are coated inammonium chloride. Abbreviations: AC, apex carina; Ac, acromion; CMC, crista medialis carinae; CtS, cotyla scapularis; ColS, collum scapulae; FAC, facies articularis
clavicularis; FAH, facies articularis humeralis; FoNS, foramen nervi supracoracoidei; ILA, impressio ligamenti acrocoracohumeralis; LI, labrum internum; MD, margo dorsalis;PC, pila carinae; PM, pila medialis; P. Procor., processus procoracoideus; SAC, sulcus articularis coracoideus; SE, spina externa; SMS, sulcus m. supracoracoidei; TC,tuberculum coracoideum. Scale bars are 10 mm.

(Trait 1) A foramen nervi supracoracoidei (Figure 4G: FoNS) ispresent and located adjacent to the shaft rather than near the medial
margin of the processus procoracoideus; (2) The foramen lacks an

opening into the corpus; and (3) it is small, about 1 mm in width,and positioned just sternal of the cotyla scapularis. (4) A large(6 mm wide) pneumatic foramen is present in the

HISTORICAL BIOLOGY

sulcus m. supracoracoidei (Figure 4F: SMS). The width of the sulcus
is approximately 14.5 mm from the ventrosternal corner of the
facies articularis clavicularis to the facies articularis humeralis,and 12.8 mm from the medial margin to the laterodorsal margin
immediately cranial to the cotyla scapularis. (5) The facies articularis clavicularis (Figure 4F: FAC) is large, broad, and clearly delineated sternally by a crista that dorsally overhangs theaforementioned foramen, and ventrally is a low non-overhanging
crista. The sternal margin of this facet is straight with no notch nor
dorsal or ventral projections directed sternally. (6) The cotyla
scapularis (Figure 4G: CtS), preserved on the right omal fragment,
is deep and large (6.7 mm wide by 5.7 mm long) in relation to theprocessus procoracoideus and triangular shaped. (7) The facies
articularis humeralis (Figure 4G: FAH) is 7.7 mm wide and12.8 mm long. (8) The impressio lig. acrocoracohumeralis(Figure 4H: ILA), best seen on the left specimen, forms a distinct
sulcus ~7 mm wide by 18.1 mm long on the processus acrocoracoideus, although this may be exaggerated by damage to the fossil.
(9) The processus procoracoideus (Figure 4I: P. Procor.) forms
a short projection medially, barely as long again as the cotyla
scapularis width, with its tip sharply angling ventrally towards themedial face to partly enclose the triosseal canal. (10) The best
preserved sternal-end fragment shows that the angulus medialis isacute, forming a 30–45° angle. (11) The medial side of the facies
articularis sternalis is 6.5 mm wide at its broadest point, andshallow, with little deepening towards the dorsal margin.
Extant accipitrid subfamilies diﬀer as follows:(Trait 5) The sternal margin of the facies articularis clavicularis
does not form a crest overhanging the sulcus supracoracoideus in
Elaninae, Perninae (except Chondrohierax uncinatus), Gypaetinae(except Polyboroides typus), Aegypiinae, Haliaeetinae, Accipitrinae,
and Buteoninae. (8) The impressio lig. acrocoracohumeralis is shallow in Elaninae, Perninae, Gypaetinae, Accipitrinae, and Buteoninae.
(9) In all subfamilies, the processus procoracoideus does not, or
barely, angles ventrally towards the medial face.
The coracoid is overall most similar to that of species of
Aegypiinae, Accipitrinae and Buteoninae (see SI.2 for more detailed
diﬀerential comparisons).
Scapula (Figure 4(D,E))
Both the left and right scapulae of Archaehierax sylvestris gen. et.
sp. nov. are almost complete, lacking only the distal third or less ofthe corpus scapulae. In total, the preserved craniocaudal length of
the scapulae is 56.8 mm (left) and 53.3 mm (right).
The proximal dorsoventral width of the scapula is 14.4 mm fromthe acromion to the ventral side of the facies articularis humeralis.
(1) The tuberculum coracoideum (Figure 4E: TC) is low and barely
cranially prominent dorsal of the facies articularis humeralis. (2)The acromion (Figure 4D: Ac) has a distinct cranio-laterally
oriented crista lig. acrocoracoacromiali dorsally, and a robust
rounded medial prominence. (3) There are no pneumatic foramina
or fossae present in the acromion cranially, (4) nor on the lateral or
medial facies between the acromion and the facies articularis
humeralis. (5) The facies articularis humeralis (Figure 4D: FAH)
is quite large and broad, measuring 6.3 mm dorsoventrally by
10.8 mm craniocaudally on the left specimen; 6.3 mm by 10.4 mm
on the right. (6) The acromion barely projects proximally/craniallyof the tuberculum coracoideum. (7) Minimum dorsoventral depthof the collum scapulae (Figure 4E: ColS) is 6.3 mm. (8) While theextremitas caudalis is broken oﬀ, the corpus scapulae is elongate

11

and moderately narrow, (9) but it greatly increases in depth caudal
to the margo dorsalis ridge (Figure 4D: MD), attaining a maximum
dorsoventral depth of 8.1 mm. (10) The lateral face dorsal to andimmediately posterior to the facies articularis humeralis is ﬂat. (11)The ligamental attachment on the margo dorsalis has a very small
prominence and is not elevated dorsally above the rest of the margo
dorsalis.
Extant accipitrid subfamilies diﬀer as follows:(Trait 6) The acromion strongly projects cranially in all species
except in pernines (Chondrohierax uncinatus, Pernis apivorus,
Aviceda subcristata), and Ictinia mississippiensis (Buteoninae).
The scapula is overall most similar to that of species of Elaninae(see SI.2 for more detailed diﬀerential comparisons).
Humerus (Figure 5).
The humeri are poorly preserved in SAMA P.54998. Only thecaput humeri, crus dorsale fossae, fossa pneumotricipitalis, and theincisura capitis of the proximal end of the right humerus is preserved. The left humerus is more complete, preserving about 60mm
of proximodistal length of the proximal end including the caput
humeri, crus dorsale fossae, fossa pneumotricipitalis, incisura capitis, sulcus lig. transversus, facies bicipitalis, crista deltopectoralis,and some of the proximal shaft. However, there is also signiﬁcantbreakage and fracturing of the bone surface in this specimen, which
has resulted in the loss of the tuberculum dorsale, the ventral
margin of the crista bicipitalis, tuberculum ventrale, and sulcus n.
coracobrachialis. These specimens reveal the following:(1) The incisura capitis (Figure 5A: IC), as best observed in theleft humerus, is shallow and lacks secondary deepening. (2) Thereis no visible ligamental scar in the distal incisura capitis. (3) The
caput humeri (Figure 5A: CH) is quite ﬂattened, projecting proximal to the incisura capitis only a few millimetres. (4) The fossa
pneumotricipitalis (Figure 5A: FP) was large and deep, although
breakage precludes assessing its former width. The betterpreserved left specimen shows it was minimally 7.7 mm wide.
(5) The crus dorsale fossae (Figure 5A: CDF) is broad, measuring
4.0 mm wide, and is caudally convex. (6) The sulcus lig. transversus (Figure 5C: SLT), best seen in the left humerus, is shallow but
well deﬁned, and seems continuous between the ventral anddorsal sections. Ventrally, the sulcus is deep and round, measuring
6.3 mm wide by 4.5 mm long cranial to the incisura capitis. The
crista deltopectoralis (Figure 5B: CrD), while quite fractured, ispreserved in its entirety in the left specimen. Preserved length is42.7 mm from the assumed position of the tuberculum dorsale toits distal end. (7) The proﬁle of the proximal section of the dorsal
margin of the crista between its origin near the tuberculum dorsale and the angulus cristae of the crista deltopectoralis is ﬂat ina ventro-cranial view. (8) The angulus cristae of the crista deltopectoralis is very prominent and distinctly triangular in dorsal
view. (9) Distally, the crista deltopectoralis, while fractured, projected mainly cranially (shaft margin visible proximal to the distal
point of crista).
Extant accipitrid subfamilies diﬀer as follows:(Trait 1) In all subfamilies except Aegypiinae and Spilornis
cheela in Circaetinae, species have a deep incisura capitis; (3) The
caput humeri is more elevated proximal to the incisura capitis andtuberculum ventrale, ranging from a moderate (Elaninae) to a large
proximal projection (all other subfamilies) so a low ﬂattened caput
is identiﬁed as an autapomorphy of the species.

12

E. K. MATHER ET AL.

Figure 5. Proximal humerus fragments of Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998: right, in caudal view (A); left, in dorsal (B) and cranial (C) views. Specimens
in B and C are coated in ammonium chloride. Abbreviations: CD, crista deltopectoralis; CDF, crus dorsale fossae; CH, caput humeri; CVF, crus ventrale fossae; FP, fossa
pneumotricipitalis; IC, incisura capitis; IH, intumescentia humeri; SLT, sulcus ligamenti transversus. Scale bars are 10 mm.

The proximal humerus is overall most similar to that of speciesof Elaninae, Aegypiinae, Aquilinae, Haliaeetinae and Buteoninae(see SI.2 for more detailed diﬀerential comparisons).
Ulna (Figure 6(C, D, E))
SAMA P.54998 preserves a near-complete left ulna, reassembled
from fragments, that is only missing the olecranon, parts of theventral margin of the cotyla ventralis contiguous with theolecranon, and the caudodorsal margin of the cotyla dorsalis. The
distal right ulna is also preserved with the condyles mostly intact,with only the ventrocaudal margin of the condylus dorsalis andcondylus ventralis worn away. They reveal the following features:(1) The ulna is largely straight in dorsal and ventral view, with
only very slight caudal curvature towards the proximal and distal
ends. The processus cotylaris dorsalis projects distally of the cotyla
ventralis (Figure 6E: PCD), is 5.8 mm wide, and (2) is quadrangularin shape with a ﬂattened dorsal tip between parallel equal-length

HISTORICAL BIOLOGY

13

Figure 6. Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998 left radius in ventral (A) and dorsal (B) view, and left ulna in ventral (C), cranial (D) and caudal (E) view.
Abbreviations: CD, condylus dorsalis; CrI, crista intercotylaris; CtV, cotyla ventralis; CV, condylus ventralis; DL, depressio ligamentosa; DR, depressio radialis; FAR, facies
articularis radiocarpalis; FAU, facies articularis ulnaris; IB, impressio brachialis; IR, incisura radialis; IST, impressio scapulotricipitis; IT, incisura tendinosa; ITC, incisura
tuberculum carpalis; PCD, processus cotylaris dorsalis; SI, sulcus intercondylaris; ST, sulcus tendineus; T, tuberculum; TAV, tuberculum aponeurosis ventralis; TBR,
tuberculum bicipitale radiale; TCr, tuberculum carpale; TLCV, tuberculum ligamentum collateralis ventralis. Scale bar 10 mm.

proximodorsal and distoventral sides. (3) The cotylae are shallow,
separating by a moderately proximally protruding crista intercotylaris (Figure 6D: CrI). Breakage precludes assessing if a pneumatic
fossa or foramen was present caudal of the cotylaris dorsalis. (4)The impressio scapulotricipitis (Figure 6E: IST) is shallow. (5) The
incisura radialis (Figure 6D: IR), deﬁned by the margin of the cotyla
ventralis proximoventrally, the tuberculum cranialis distally, anda ridge descending ventrodistally from the base of the processus
cotylaris dorsalis dorsally, is shallow. (6) Distal to the incisuraradialis two tubercula are present, one on the cranial face is large
and round (3.8 mm wide) and distinctly projects from the shaft(Figure 6D, E: T), the other smaller (1.9 mm wide) and ﬂatter
positioned adjacent to it on the ventral face. (7) The impressio
brachialis (Figure 6C: IB) is shallow, with the base ﬂat and not14

E. K. MATHER ET AL.

depressed relative to the shaft and is 12 mm long proximodistally.
The midshaft of the left specimen is 7.7 mm craniocaudally wide in
dorsal aspect. (8) The papillae remigales caudales form low, barely
prominent scars, which is typical of most accipitrids. The distal endof the ulna measures 12.9 mm wide (left) and 12.2 mm wide (right)
between the cranial point of the tuberculum carpale (Figure 6C:TCr) and the caudal margin of the condylus dorsalis (Figure 6C:CD) in ventral aspect. (9) The tuberculum carpale is short andblunt, or rounded, in dorsal and ventral view, (10) witha ﬂattened facet directed ventrodistally. (11) The incisura tuberculum carpale (Figure 6C: ITC) forms a distinct notch separating the
tuberculum carpale and condylus ventralis (Figure 6C: CV) whenviewed in dorsal aspect. The condylus dorsalis (left specimen) is
13.5 mm long proximodistally along its caudal margin in ventral
aspect, and 9.3 mm deep from the caudal margin to the incisura
tendinosa, in caudodorsal view. (12) The caudal margin of thecondylus dorsalis forms a continuous curve in the proximal half,
best visible in either craniodorsal or caudodorsal view, interrupted
only by a small notch for the incisura tendinosa (Figure 6E: IT).
(13) The incisura tendinosa lies between the condylus dorsalis andthe condylus ventralis (dorsal aspect), though it does not quite
separate the two proximodistally. (14) The depressio radialis(Figure 6C: DR) is shallow and not pneumatized. (15) The sulcus
intercondylaris (Figure 6C: SI) forms a relatively deep v-shape inventral aspect. (16) The condylus ventralis distinctly projects distocranially, and measures 5.7 mm wide (in ventral aspect) by
11.2 mm deep (in cranial aspect).
Extant accipitrid subfamilies diﬀer as follows:(Trait 1) The proximal shaft is notably curved cranially inelanines, most pernines (except Aviceda subcristata, Lophoictinia
isura and Hamirostra melanosternon), and buteonines (except species of Circus).
The ulna is overall most similar to that of species of Circaetinae(see SI.2 for more detailed diﬀerential comparisons).

N. percnopterus (Gypaetinae), species of Gyps (Aegypiinae), andH. morphnoides and A. chrysaetos (Aquilinae). (7) The depressio
ligamentosa is shallower in Perninae (except E. forﬁcatus),
Gypaetinae, Circaetinae, Aquilinae, Haliaeetinae, and Buteoninae.
The radius is overall most similar to that of species ofHaliaeetinae and Gypaetinae (see SI.2 for more detailed diﬀerential
comparisons).
Os carpale radiale (Figure 7(G, H))
The left os carpale radiale is complete in SAMA P.54998.
Measurements: proximodistal length 8.6 mm, dorsoventral
width 12.3 mm, and depth 5.4 mm.
It has the following features, terminology from Mayr (2014): (1) The
distoventral projection (Figure 7G: DVP) is small and pointed, oriented
at an angle between 45° and 60°. (2) The notch for the musculus
ulnometacarpalis ventralis (Figure 7H: NMUMV) is distinct, but shallow. (3) The facies articularis metacarpalis (Figure 7H: FAM) slightly
projects distally from the cranial face in cranial view. (4) The sulcus forthe musculus extensor carpi radialis (Figure 7H: ECR) is shallow,
forming a gentle curve at about a 160° angle between the ventral anddorsal ends. (5) A broad, deep fossa covers most of the ventral half ofthe cranial face (Figure 7H: CVFos), which is open towards the proximo-ventral corner. (6) A second smaller and deep fossa is present on
the dorsal half of the cranial face (Figure 7H: DVF), and is apneumaticand oriented more craniodorsally. (7) The facies articularis radialis(Figure 7G: FARad) is broad (depth ~5.7 mm, dorsoventral width
11.0 mm) and strongly marked on the caudal face. (8) The caudal
face has a small but deep fossa (Figure 7G: FAUF), set in the facies
articularis ulnaris (Figure 7G: FAU) close towards the ventral end. (9)The caudal margin of the facies articularis metacarpalis forms a convex
continuous curve from the ventral margin to the dorsal margin.
The os carpale radiale is overall most similar to that ofspecies of Elaninae and Buteoninae (see SI.2 for more detailed
diﬀerential comparisons).

Radius (Figure 6(A, B))
In SAMA P.54998, the left radius is complete, preserving mostfeatures of the proximal (cotyla humeralis slightly worn ventrocaudally) and distal ends.
The cotyla humeralis is large, measuring 5.5 mm deep dorsoventrally, and 4.1 mm wide. It shows the following:
A tuberculum bicipitale radiale (Figure 6A: TBR) is located
5.4 mm distal of the facies articularis ulnaris on the dorsal face.
The tuberculum has (1) a large, deep, non-pneumatic fossa(2.6 mm wide by 3.8 mm proximodistal length) on it, and (2)has a distinct proﬁle in cranial view as a low, quadrangular ridge.
(3) The sulcus tendineus (Figure 6B: ST) is very shallow, barely
diﬀerentiated from the corpus. (5) The tuberculum aponeurosis
ventralis (Figure 6A: TAV) projects ventrally at approximately 60–
70°, and its tip is rounded. (6) The facies articularis radiocarpalis(Figure 6A: FAR) is quite ﬂat in dorsal view, but slightly curves
out distally from the tuberculum aponeurosis ventralis to the
opposite margin. (7) The depressio ligamentosa (Figure 6A: DL)on the ventral face of the distal end is deep but lacks pneumatism.
(8) The facies articularis ulnaris (Figure 6(A, B): FAU) forms
a prominent bulb that projects out ventrally, and which hasa deep notch on the proximal margin that gives it a doublepeaked appearance.
Extant accipitrid subfamilies diﬀer as follows:(Trait 1) The fossa associated with the tuberculum bicipitalis isshallow in all species except some pernines e.g., Elanoides forﬁcatus(absent) and Pernis apivorus (deep). (5) The tuberculum aponeurosis ventralis projects at a more abrupt angle in all taxa except

Os carpale ulnare (Figure 7(I, J))
Both the right and left os carpale ulnare are complete in
SAMA P.54998. Measurements (mm) right/left: dorsoventral
width 12.2/11.8, craniocaudal depth (excluding cranial projection) 4.4/4.6, and proximodistal length 9.9/9.2. They show:(1) A distinct projection, roughly in the centre of the
cranial face (Figure 7J: CrPro), extends well cranially above
the margin of the proximal ligament attachment, and lacks
a prominent ridge that makes it contiguous with the proximodorsal corner. (2) The rest of the cranial face is roughly equalin cranial height towards the crus breve (Figure 7J: CB) andthe crus longus (Figure 7J: CrL). (3) The proximodorsal cornerof the crus longus is distinctly notched by a deepened apneumatic fossa (Figure 7J: PDF). (4) The proximal margin of the
cranial face has a distinct ligament attachment point(Figure 7J: PLA), projecting slightly proximally above theface and positioned ventrally adjacent to the proximal end of
the crus longus. (5) The crus breve is slightly shorter (8.7 mmlong) in the right specimen, than total length (9.4 mm) fromthe proximal point of the crus longus to the distal margin, (6)and has a ﬂattened, ventral face. (7) On the caudal face, a very
low projection is present on the proximal margin immediately
adjacent to the ventral crus breve (Figure 7I: PVP). (8)A distinct, deep impression is present in the caudal surface(Figure 7I: CaD). (9) This depression is separated from therest of the distal face by a distinct but low crista that extends
dorsoventrally across the face from the caudal projection

HISTORICAL BIOLOGY

15

Figure 7. Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998 left carpometacarpus in ventral (A) and dorsal (B) view, manual phalanx digiti majoris II.1 broken distally (C),manual phalanx digiti majoris II.2 (D), manual phalanx digiti alularis I.1 (E), manual phalanx digiti minoris III.1 (F), os carpale radiale in caudal (G) and cranial (H) view, and os
carpale ulnare in caudal (I) and cranial (J) view. Carpometacarpus coated with ammonium chloride. Abbreviations: CaD, caudal fossa; CB, crus breve; CCr, caudal crista; CrL,
crus longus; CLF, crus longus fossa; CLS, crus longus sulcus; CrPro, cranial projection; CVFos, cranial ventral fossa; DSyn, distal synostosis; DVF, dorsal ventral fossa; DVP,
distoventral projection; ECR, extensor carpi radialis; FADMaj, facies articularis digitalis major; FADMin, facies articularis digitalis minor; FAM, facies articularis metacarpalis;
FARad, facies articularis radialis; FAU, facies articularis ulnaris; FAUF, facies articularis ulnaris fossa; FCCr, fovea carpalis cranialis; FCCd, fovea carpalis caudalis; FI, fossa
infratrochlearis; FS, fossa supratrochlearis; IM, incisura metacarpalis; ITR, intermetacarpal tuberosity; NMUMV, notch for musculus ulnometacarpalis ventralis; OMMa, os
metacarpale majus; OMMi, os metacarpale minus; PA, processus alularis; PDF, proximodorsal fossa; PE, processus extensorius; PLA, proximal ligament attachment; PrPis,
processus pisiformis; PS, proximal sulcus; PSyn, proximal synostosis; PVP, proximoventral projection; SpI, spatium intermetacarpale; ST, sulcus tendineus; SV, sulcus onventral facies; TrC, trochlea carpalis. Scale bars 10 mm.

(Figure 7I: CCr), connecting to both the crus breve and crus
longus. (10) The incisura metacarpalis is deep and broadly

v-shaped (Figure 7J: IM), with the peak oﬀset towards thecrus breve. (11) A very shallow sulcus is seen running along16

E. K. MATHER ET AL.

the proximodistal extent of the caudal face of the crus longus(Figure 7I: CLS), (12) which terminates in a shallow fossa on
the distal point of the crus (Figure 7I: CLF).
Extant accipitrid subfamilies diﬀer as follows:(Trait 2) The ventral cranial face is higher set cranially than thedorsal cranial face in all subfamilies except Accipitrinae. (3) There is nonotch on the proximal end of the crus longus in all subfamilies except in
the genera Aquila (Aquilinae), Haliaeetus (Haliaeetinae) and Buteo(Buteoninae), which have a shallow notch. (8) There is no deepened
depression on the caudal face in all subfamilies except Aquilinae,
Aegypius monachus (Aegypiinae), Accipitrinae, and the genus Buteo(Buteoninae). (9) There is no raised crista on the caudal face in all
subfamilies except in the genus Buteo (Buteoninae).
The os carpale ulnare is overall most similar to that of species of
Elaninae, Perninae, Gypaetinae and Aquilinae (see SI.2 for moredetailed diﬀerential comparisons).
Carpometacarpus (Figure 7(A, B))
For SAMA P.54998, the left carpometacarpus is almost complete, missing only the cranial section of the facies articularis
digitalis majus.
(1) The fossa infratrochlearis (Figure 7A: FI) is deep and lacks
pneumatisation. (2) A rounded ridge extending from the processus
pisiformis to the trochlear rim separates the fossa infratrochlearis
from (3) an extremely deep sulcus (Figure 7A: SV) between theprocessus pisiformis and the processus extensorius. This sulcus iselongate and extends from the trochlea carpalis (Figure 7B: TrC) toadjacent to the processus alularis (Figure 7B: PA). (4) The fossa
supratrochlearis (Figure 7B: FS), which is caudoventrally positionedon the ventral face of the proximal end, is shallow and lacks
pneumatisation. (5) There is a shallow sulcus on the ventral face,on the proximal margin at the base of the processus extensorius justdistal to the trochlea carpalis (Figure 7A: PS). (6) The fovea carpalis
cranialis (Figure 7A: FCCr) is shallow and apneumatic. (7) The
fovea carpalis caudalis (Figure 7B: FCCd) is very shallow andapneumatic. (8) The ventral rim of the trochlea carpale projects
strongly caudally and distally is short, terminating slightly distal to
the level of the processus pisiformis. (9) The proximal margin of theprocessus extensorius (Figure 7A: PE) and the trochlea carpale
forms an approximately 120° angle, with the proximal margin
slightly upturned proximally. From base to tip, the processus extensorius measures 7.7 mm in craniocaudal width, and is 39% of the19.6 mm proximal width of the carpometacarpus. (10) The proximodorsal margin of the processus extensorius forms a sharp cristathat dorsally overhangs the dorsal face of the processus. (11) The
processus alularis protrudes slightly cranially in a triangular bulge,
with a single curved articular facet distally. (12) The processus
alularis is separated from the caudal surface of the shaft by a small
notch on the dorsal face. (13) The processus pisiformis (Figure 7A:
PrPis) strongly projects ventrally in caudal and cranial view, and ispositioned central on the ventral face between the processus extensorius and the caudal margin of the trochlea carpalis. It is separated
from the spatium intermetacarpale (Figure 7A: SpI) by
a dorsoventral length of 10.5 mm. (14) This region of separation
between the processus pisiformis and spatium intermetacarpale isoccupied by a shallow sulcus that is bound by the os metacarpale
minus in its distal half. (15) The synostosal region distal to theprocessus alularis is wider craniocaudally than it is long dorsoventrally. (16) The intermetacarpal tuberosity (Figure 7A: ITR), whichis the scar for the insertion of the m. extensor metacarpi ulnaris has

almost no caudal projection and is positioned well distal of theproximal synostosis (Figure 7A: Psyn). (17) The sulcus tendineus(Figure 7B: ST) is primarily located on the dorsal face of the shaft.
(18) The sulcus tendineus is broad. (19) The proximal region of theos metacarpale minus has a distinct groove on the caudal face,which lacks any pneumatisation. (20) The os metacarpale minus(Figure 7B: OMMi) is slightly arched caudally when viewed in
ventral and dorsal aspect. (21) The facies articularis digitalis
minor (Figure 7B: FADMin) projects further distally than the preserved facies articularis digitalis major (Figure 7A: FADMaj). (22)The length between the distal point of the facies articularis digitalis
minor and the spatium intermetacarpale is approximately equal to
the width of the spatium. (23) The distal synostosis (Figure 7A:DSyn) is very short. (24) The os metacarpale majus (Figure 7A:
OMMa) has a markedly ﬂattened cranial face and is dorsoventrally
deeper than it is craniocaudally wide. (25) The sulcus interosseus
positioned in the distal synostosis is slightly deepened.
Measurements – see Appendix 1 Table S1; overall, thecarpometacarpus has a proximal craniocaudal width that isequivalent to 25% of the total length, which is moderately
gracile.
Extant accipitrid subfamilies diﬀer as follows(Trait 1) The fossa infratrochlearis is shallow, except in Perninae(deep in Pernis apivorus and Chondrohierax uncinatus, the latteralso pneumatic) and Gypaetinae (deep). (19) The proximal sectionof the os metacarpale minus has a shallower groove, except in
P. typus (Gypaetinae, deep) and Haliaeetus leucocephalus(Haliaeetinae, deep), or in Elaninae (ﬂat, ungrooved).
The carpometacarpus is overall most similar to that ofspecies of Buteoninae (see SI.2 for more detailed diﬀerential
comparisons).

Manus (Figure 7C, D, E, F)
The manus bones are moderately well-preserved in SAMA
P.54998, with a mostly intact left phalanx digiti alulae (L MI.1),
complete left phalanx digiti minoris (L MIII.1) and left phalanx digiti
majoris 2 (L MII.2), and a mostly intact R MI.1, partial R MII.1 andfragment of the R MII.2.
(1) The proximal L MI.1 has a dorsoventral width of
6.6 mm and a craniocaudal depth of 6.5 mm, and from proximal view is triangular. (2) The cranial margin is tapered intoa thin crista that continues along the length of the preservedbone. (3) A small tuberculum is present on the caudal marginof the ventral face, close to the proximal end. (4) The dorsal
margin and face of the proximal end is much more protruding
than the ventral margin and face and has two ligament attachment points on its dorsal surface. (5) The width of the bonenarrows distally. (6) The L MIII.1 is 14.2 mm long and has
a prominent caudal projection slightly less than halfway distally along its length, the tip of which is oriented caudoproximally. (7) Both the dorsal and ventral face lack any sort ofdepression or sulcus. Only the proximal end of the MII.1 ispreserved, which is 8.3 mm wide by 6.9 mm deep. (8) The
caudal margin projects caudally into a thin crista, and a deep
depression is visible just distal of the projecting point. The left
MII.2 is 24.1 mm long and proximally has a dorsoventral
height of 5.8 mm and a craniocaudal depth of 4.8 mm. (9)The caudal margin forms a thin crista. (10) The proximal
quarter of the cranial margin is also ﬂattened, but then

HISTORICAL BIOLOGY

17

Figure 8. Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998 proximal left and right femoral fragments in medial (A) and cranial (B) view, left tibiotarsus in cranial (C) andcaudal (D) aspect, and distal right tibiotarsus (E-G) in medial (E) lateral (F) and cranial (G) view. Abbreviations: CExt, canalis extensorius; CrF, crista ﬁbularis; CL, condylus
lateralis; CM, condylus medialis; CrTRMF, cranial tuberculum retinaculi musculus ﬁbularis; DEL, depressio epicondylaris lateralis; DEM, depressio epicondylaris medialis;
DREM, distal insertion retinaculum extensorium tibiotarsi; ECM, epicondylus medialis; FAAce, facies articularis acetabularis; FLC, fovea ligamenti capitis; II, incisuraintercondylaris; ILCM, impressio ligamenti collateralis medialis; PTREM, proximal insertion scar retinaculum extensorium tibiotarsi; PS, pons supratendineus; SExt, sulcus
extensorius; SELC, lateral crista beside sulcus extensorius. Scale bars 10 mm.

expands notably with the presence a shallow sulcus extending
to the distal end. (11) On the dorsal surface, a low ridge ispresent at the proximal end, with a small but deep fossa set

into the caudal side of it. (12) A similar fossa is also set into
the caudal side of this ridge in proximal view, just distal of thearticular facet. (13) The ventral face has a deep depression
lacking pneumatic foramina just distal of the proximal end.

18

E. K. MATHER ET AL.

The manus bones are overall most similar to those of species ofPerninae (see SI.2 for more detailed diﬀerential comparisons).
Femur (Figure 8(A, B))
In SAMA P.54998, only the caput of both femora has beenpreserved, preserving the articularis acetabularis face and the
fovea ligamenti capitis. The width of the caput is 7.6 mm. The
fovea ligament capitis (Figure 8A: FLC) is shallow and set in theproximal margin of the caput. The articularis acetabularis face
(Figure 8B: FAAce) is not well deﬁned from the medial face.
Tibiotarsus (Figure 8(C, D, E, F, G))
Both the right and left tibiotarsi are preserved in SAMA P.54998.
The left tibiotarsus is almost complete with only the proximal articular surfaces missing. It preserves the base of the cnemial crests and theentire crista ﬁbularis, but damage to the distal end obscures the detailsof the pons supratendineus, the tuberculum retinaculum m. ﬁbularis,and the distal insertion scar for the retinaculum extensorium tibiotarsi. The right tibiotarsus is missing the entire proximal end, and the
distal end could not be reconnected to the shaft but is very wellpreserved revealing most features of interest.
As observed on the left element, (1) the impressio lig.
collateralis medialis (Figure 8C: ILCM) is a slightly elevatedtuberculum on the medial face, measuring 4.5 mm wide and8.9 mm long. (2) The crista ﬁbularis (Figure 8C: CrF) is
approximately 33.3 mm long, or roughly 24% of the preserved
length (135.7 mm). (3) The crista ﬁbularis is prominent,
maximally projecting 2.4 mm, or approximately 26% of shaft
width (9.3 mm) at the same point. (4) The width of the crista
ﬁbularis is greatest distally. (5) The cranial face directly adjacent to the crista ﬁbularis is slightly convex. (6) The scar forthe ligament that connected to the distal end of the ﬁbula isapproximately 34.5 mm long and extends distally along thelateral margin of the shaft, from 38 mm distal to the crista
ﬁbularis. (7) A distinct linea is visible on the medial margin of
the shaft that extends approximately 77.4 mm proximodistallyfrom the distal base of the impressio lig. collateralis medialis.
(8) The cross-section of the shaft at mid length is roughly
circular. (9) The sulcus extensorius (Figure 8G: SExt) is medially positioned on the distal third of the shaft and is approximately 5 mm wide at broadest, compared to a shaft width of
10.5 mm at the same section. (10) The lateral margin of thesulcus is bordered by a raised crista (Figure 8G: SELC). (11)The canalis extensorius (Figure 8G: CExt) is deep, and both
openings are quite large. (12) The pons supratendineus(Figure 8G: PS) is obliquely angled at roughly 45° to thelong axis, and (13) is distinctly arched cranially. (14) The
distomedial margin of the pons supratendineus lies close(1.3 mm) to the medial shaft margin. (15) The cranial tuberculum retinaculi m. ﬁbularis (Figure 8G: CrTRMF) is craniolaterally
prominent.
(16)
The
caudaltuberculum
retinaculi m. ﬁbularis is low and barely projecting, but preservation is poor in this region of the bone. (17) The proximal
scar (tuberositas retinaculum extensoris medialis, Figure 8G:
PTREM) is separated proximally from the pons supratendineus
by a distance equal to the proximodistal width of the pons.
(18) The distal/lateral attachment of the extensor retinaculum(Figure 8: DREM) is marked by a deep, round fossa. (19)Distal width (17.5 mm) is greater than the maximum distal
depth (13.4 mm) by roughly 24% (right element). (20) The
increase in width from the shaft to the distal end is gradualand symmetrical either side. (21) The condyles have roughly

equal craniocaudal depth in distal view, (22) with a deep
incisura intercondylaris roughly 25% of depth of the distal
end, (23) and the impression in the trochlea cartilaginis tibialis in caudal view forms an inverted v-shape. (24) The epicondylus medialis (Figure 8E: ECM) is large and projects wellmedial to the condylus medialis, being visible in cranial view,
and is of moderate robustness. (25) The epicondyle is surrounded by a deep depressio medialis (Figure 8E: DEM),
which is bordered by a thin but prominent crista on themargins of the condyle. (26) The depressio lateralis(Figure 8F: DEL) is shallow, and bordered by a ﬂattened,broad crista on the distal margin of the lateral condyle. The
trochlea cartilaginis tibialis is diﬃcult to assess due to breakage, (27) but appears largely ﬂat.
Extant accipitrid subfamilies diﬀer as follows:
The medial side of the pons supratendineus is more widely
separated from the medial shaft margin (Trait 14) in elanines,
pernines except E. forﬁcatus, gypaetines, aegypiines, circaetines,
aquilines, and haliaeetines. (10) There is no crista on the lateral
margin of the sulcus extensorius in elanines, gypaetines, aegypiines,
circaetines, aquilines, haliaeetines, accipitrines or buteonines. (18)
No species in any subfamily has the lateral/distal retinaculum scarin a deep fossa; it ranges from a shallow fossa (pernines, aegypiines,
circaetines, aquilines, haliaeetines), to ﬂat (elanines, some pernines,
gypaetines), or slightly elevated rugose surface (accipitrines, buteonines), identifying the deep pit for the distolateral insertion of theretinaculum extensoris medialis as an autapomorphy of the fossil.
The tibiotarsus is overall most similar to that of species of
Buteoninae (see SI.2 for more detailed diﬀerential comparisons).
FibulaThe proximal ends of the left and right ﬁbulae are preserved inArchaehierax sylvestris gen. et. sp. nov. Craniocaudal depth is about
10.2 mm, while width is 3.7 (right) and 4.0 mm (left).
(1) A shallow fossa is present in the cranial half of the proximal
lateral face. (2) The caudal face has a very shallow depression justdistal to the caudal projection. (3) The medial face has a broad but
shallow sulcus that extends from near the proximal margin down
the shaft.
Tarsometatarsus (Figure 9)
The right and left tarsometatarsi are both imperfectly preservedin SAMA P.54998. The left tarsometatarsus preserves the original
length of the bone, though the medial half and the proximal end,
from mid-length on the medial side to and including the area
proximal to the foramen vasculare proximale laterale, has been
dorsolaterally twisted approximately 90° relative to the rest of thebone. The lateral half is thus undistorted from just proximal to theforamen vasculare proximale laterale distally. The cotyla lateralis is
missing with about half of the eminentia intercotylaris. The foramen vasculare proximale mediale is obscured by the distortion on
both the dorsal and plantar side.
The right specimen has the distal half preserved well with allfeatures, but the proximal half is so badly fragmented that nearly all
identifying features are lost. Only the crista medialis hypotarsi isrecognisable. The specimens reveal the following features:(1) The length of the tarsometatarsus is about 66–75% of the lengthof the tibiotarsus (uncertainty allows for the missing proximal end of
the tibiotarsus). (2) The length to distal width (maximal across trochleae) ratio is approximately 1:6 and shows the tarsometatarsus ismoderately elongate among accipitrids. (3) The cotyla medialis(Figure 9D: CtM) is deep and with a notably convex dorsal margin.

HISTORICAL BIOLOGY

19

Figure 9. Tarsometatarsi of Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998, left in dorsal (A), plantar (B), proximal end plantar (D) and proximal E) view, and distalright in dorsal (C), medial (F), lateral (G), and distal (H) view. Abbreviations: CLFHL, crista lateralis ﬂexoris hallucis longus; CtM, cotyla medialis; CMFDL, crista medialis ﬂexoris
digitorum longus; CPL, crista plantares lateralis; CPM, crista plantares medialis; EI, eminentia intercotylaris; FLCo, fovea ligamentosa collateralis; FMI, fossa metatarsi I; FVD,
foramen vasculare distale; FVP, foramen vasculare proximale; IIL, incisura intertrochlearis; IIM, incisura intertrochlearis medialis; IMFHB, incisura musculus ﬂexor hallucis
brevis; SExt, sulcus extensorius; SF, sulcus ﬂexorius; T, tuberculum; TII, trochlea metatarsi II; TIII, trochlea metatarsi III; TIV, trochlea metatarsi IV. Scale bars 10 mm.

(4) The eminentia intercotylaris (Figure 9D: EI) projects a few millimetres proximally to the rim of the cotyla medialis. (5) The crista
lateralis ﬂexoris hallucis longus (sensu Mayr 2016) (lateral hypotarsal
crista) and the crista medialis ﬂexoris digitorum longus (medial hypotarsal crista) (Figure 9E: CMFDL) are not fused together plantarly, andso form a wide monosulcate hypotarsus. (6) The medial hypotarsal
crista is distinctly proximodistally longer (8.9 mm from proximal
margin to distal hook, 11.4 mm from proximal margin to distal
termination point) than the lateral hypotarsal crista (6.0 mm). (7)The plantar depth of the lateral hypotarsal crista is 13.6 mm (76%) of20

E. K. MATHER ET AL.

the depth of the medial hypotarsal crista 17.8 mm. (8) In medial view,the medial hypotarsal crista has little or no hook distally. (9) The sulcus
ﬂexorius (Figure 9B: SF) is moderately deep, with the cristae plantares
lateralis and medialis quite distinct and projecting plantarly. (10) The
tuberositas m. cranialis (Figure 9A: T) is positioned towards the lateralside of the shaft, moderately projects dorsally to the adjacent laterodorsal margin, (11) is short and oval shaped, (12) and is positioned
well distal (5.2 mm) of the lateral foramina vascularia proximalia. (13)The impressio retinaculi extensorii, preserved on the dislocated cotyla
medialis, are a pair of distinctly projecting cristae, with the retinaculum
itself unossiﬁed, which is the typical state among the accipitrids. (14)The fossa infracotylaris dorsalis is shallow in the undamaged section
distal to the eminentia intercotylaris and towards the retinaculi. (15)There is a distinct sulcus extensorius (Figure 9A: SExt) at mid-length,
which opens to the medial face around two-thirds of the distancedistally along the shaft. (16) The medial half of the proximal 40% of
the shaft is highly compressed as it is in many accipitrids, forminga crista 1.3 mm thick. (17) The crista plantaris lateralis (Figure 9G:
CPL) is well-developed, extending from the hypotarsus to level withthe fossa metatarsi I. (18) In lateral aspect the crista plantaris lateralis ismarkedly projecting plantarly, deepest just proximal to mid-length.
(19) The foramen vasculare distale (Figure 9A: FVD) has a diameter ofabout 1.6 mm and is positioned close to the incisura intertrochlearis
lateralis. (20) The fossa metatarsi I (Figure 9B: FMI) is set largely on theplantar face, though partially faces medially, and measures 6.7 mm
long by 3.5 mm wide. (21) The incisura m. ﬂexor hallucis brevis(Figure 9F: IMFHB) is very distinct, passing dorsally above and distal
to the fossa metatarsi I, to open plantarly between the facet in metatarsi
I and trochlea metatarsi II. This state of the incisura was rarely seen in
our comparative sample, with a similar but shallower incisura in
species of Haliaeetus and Harpia harpyja (slightly deeper) that ends
just proximal to the fossa metatarsi I. (22) The fossa supratrochlearis
plantaris is very shallow. (23) The incisura intertrochlearis medialis(Figure 9A: IIM) and incisura intertrochlearis lateralis (Figure 9A: IIL)
are extremely wide compared to in other Accipitridae. (24) From distalview, the trochleae are arched dorsally. All trochleae are higher thanthey are wide (excluding extension from ﬂanges). (25) The plantar
extent of trochleae metatarsorum II (Figure 9H: TII) and IV are almost
identical (9.1 mm and 9.5 mm respectively, measured from rightspecimen). (26) Trochlea metatarsi III (Figure 9H: TIII) is locatedcomparatively much higher dorsally, and while it has a depth of
7.7 mm, the plantar-most point of it is separated from that of trochlea
metatarsi IV by about 6.6 mm. (27) Trochlea metatarsi II has a robust
proﬁle in distal view, with a short, robust plantar projection on its outermargin and a deep fovea ligamentosa collateralis. (28) Trochlea metatarsi III has a robust proﬁle in distal view and has a shallow medial
groove dorsodistally. (29) Trochlea metatarsi III is laterally directed
relative to the shaft axis. (30) Trochlea metatarsi IV is the narrowest of
the trochleae in distal view, with a short, thin plantar projection on thelateral margin. (31) The ﬂange on trochlea metatarsi II is moderately
projecting plantarly, (32) while the ﬂange on trochlea metatarsi IV isquite prominent and plantar oriented. (33) The distal extent of thetrochleae metatarsorum II and III is roughly equal and surpass distallythe distal margin of IV.
Extant accipitrids diﬀer across all subfamilies as follows:(9) The sulcus ﬂexorius is shallower, with the cristae plantares
lateralis and medialis relatively low in elanines, gypaetines, circaetines, haliaeetines, and buteonines. (21) The incisura m. ﬂexor hallucis brevis is shallower and shorter ending at or proximal to thefossa metatarsi I in all observed species. (23) In all subfamilies, theincisura intertrochleae are relatively narrower and the autapomorphically wide incisura in the fossil is one of its most characteristicfeatures.
The tarsometatarsus is overall most similar to that of species of
Elaninae (although more elongate), Aquilinae and Circaetinae (seeSI.2 for more detailed diﬀerential comparisons).

Digit I (Figure 10A)
The os metatarsale I in SAMA P.54998 is fairly robust, with theproximal end attenuated to a thin point. In dorsal and plantar view,the region immediately proximal to the medial side of the articularsurface for I.1 is inﬂated, creating a > 90° angle just distal of the midlength point along the ‘shaft’. The attachment facet for the tarsometatarsus is quite long, extending to be adjacent with the previously
mentioned inﬂation, but is not prominent in lateral view. The sulcus
for a tendon on the distal dorsal face is bordered by a reduced crest
that is positioned slightly medial of centre in the metatarsal. The
phalanx I.1 is long and moderately robust, with the enlarged proximal end much wider than the corpus. Plantarly, the tubercula
ﬂexoria are enlarged, enclosing a broad sulcus that extends asa shallow attachment point to roughly midway on the corpus distally.
The lateral side of the face dorsalis of the proximal end is slightly
inﬂated into a ligamental attachment point, forming a modest,rounded mound. The foveae lig. collaterales on the distal end arevery deep, and there is only a very shallow indentation set between
the two foveae on the dorsal face. The ungual phalanx I.2 (as seen inright side) is slightly larger than the ungual phalanx II.3, with mild
curvature along the ungual phalanx. The phalanx I.1 and ungual I.2
exhibit notable hypertrophy in contrast to digits III and IV, a trait
that is present in almost all Accipitridae (Fowler et al. 2009).

Digit II (Figure 10B)
Like most accipitrids, there is no fusion of the phalanges II.1 andII.3. The species in Haliaeetinae and Ictinia are notable for suchfusion (see Jollie 1976). The phalanx II.1 is quite short compared tophalanx II.2, being just under half its length and considerably
shortened lengthwise (not compressed lateromedially), which is
a common trait in Accipitridae. All phalanges are notably hypertrophied compared to those in digits III and IV.

Digit III (Figure 10C)
Four phalanges are present. The medial face of the ungual
phalanx (III.4) lacks the central ridge present in most accipitrids
and falconids, though it is possibly that this feature has been poorly
preserved.

Digit IV (Figure 10D)
The midshaft width of phalanx IV.4 is 3.2 mm, compared to the
3.8 mm of phalanx I, and the distal end of phalanx IV.4 is distinctly
widened, measuring 4.6 mm. This dramatic shift in width along thedigit does not appear in the sampled elanine genera (Elanus,
Gampsonyx), species of Hieraaetus (though the section before thearticular end is swollen) or Spizaetus, but appears to a lesser degreein the pernines, gypaetines, circaetines, aegypiines, species of
Aquila, and species of Haliaeetus.

HISTORICAL BIOLOGY

21

Figure 10. Image showing left pedal phalanges and os metatarsale 1 of Archaehierax sylvestris gen. et. sp. nov. SAMA P.54998, digit 1 (A), digit 2 (B), digit 3 (C) and digit 4(D) with RI.2 added given the left counterpart was broken. Scale bar 10 mm.

Summary
Archaehierax sylvestris shares a mosaic of characters across a broad
range of taxa and thus the above comparisons do not reveal clear
aﬃnity with any one taxon. Diﬀerent elements in the fossil skeleton
diﬀer markedly as to which subfamilies they most closely resemble:
the rostrum maxillare – buteonines; the quadrate – aegypiines; thevertebrae – elanines; the sternum – aegypiines; the coracoid –aegypiines, accipitrines, and buteonines; the scapula – elanines;
the humerus – elanines, aegypiines, aquilines, haliaeetines andbuteonines; the ulna – circaetines; the os carpi radiale – elaninesand buteonines; the os carpi ulnare - elanines, pernines, gypaetinesand aquilines; the carpometacarpus - buteonines; the tibiotarsus –22

E. K. MATHER ET AL.

buteonines; and the tarsometatarsus – elanines (fossil is moreelongate), aquilines and circaetines. There are several autapomorphies which further diﬀerentiate it from all extant subfamilies.
Notably these include the sternal basin having a medial bar separating deep pneumatic fossae, humerus with very low proximal
projection of the caput, and tarsometatarsus with broad incisuraeintertrochleae and the incisura for the m. ﬂexor hallucis brevis
tendon extending distal to the fossa metatarsi I. Together, these
support diﬀerentiation of this taxon with separate subfamilial status, consistent with the phylogenetic results discussed below.
Comparison with fossil accipitrids
Australia has only two described pre-Pleistocene accipitrids. Pengana
robertbolesi is from Sticky Beak Site in the Riversleigh World
Heritage Area, of ? Late Oligocene – Early Miocene age, which is
now considered one of the Faunal Zone A sites (Travouillon et al.
2006) that on biochronological grounds are slightly younger than the
Pinpa LF (Woodhead et al. 2016). It is represented by a distal tibiotarsus (Boles 1993), and while of similar size, is easily distinguishedfrom Archaehierax sylvestris by the following characters: the distal
margin of the pons supratendineus is angled less steeply, ~30° relative
to the long axis; the condyles have ﬂattened sides in cranial aspect
and are not medially and laterally expanded relative to the distal endof the shaft. Aquila bullockensis from the mid-Miocene Camﬁeld
Beds (12 Ma) of Bullock Creek (Gaﬀ and Boles 2010; Megirian
et al. 2010) was described from a distal humerus – which was notpreserved in Archaehierax sylvestris. However, A. bullockensis is verymuch (>10 Ma) younger than Archaehierax sylvestris, much larger,
and the morphology of the distal humerus was interpreted to be
typical of species of Aquila. Archaehierax sylvestris has many featureson other bone elements that exclude close aﬃnity with both Aquila
and the Aquilinae, so conspeciﬁcity with A. bullockensis can beruled out.
In relation to Oligocene-age fossil accipitrids from elsewhere in the world, the geographic isolation of Australia
makes it unlikely that any described species are closely related
to Archaehierax sylvestris. As reviewed in the Introduction,
most late Oligocene and early Miocene accipitrid species arefound in North America and Europe. Nearly all of them aredescribed from a single skeletal element, making assessment ofrelationships with Archaehierax sylvestris diﬃcult. The late
Oligocene – early Miocene accipitrids from North America,
including the relatively complete Palaeoplancus sternbergi, areall easily distinguished from Archaehierax sylvestris by size,and by morphology of the distal tarsometatarsus; speciﬁcally,trochlea metatarsi II is relatively broader and/or the intertrochlear incisions are much narrower.
Four Oligocene fossil accipitrids are described from Europe, all
but one of which is based on a single bone:
Aquilavus hypogaea (Milne-Edwards, 1892), from the Quercy
ﬁssure ﬁllings, is incomparable as it is based on a femur.
Aquilavus corroyi (Gaillard, 1939), also from Quercy ﬁssure
ﬁllings, was described from a tarsometatarsus that resembles
Milvus according to Mayr (2009). It lacks the wide incisuraintertrochleae of Archaehierax sylvestris, and the ﬂange on thetrochlea metatarsi II is oriented more medially (Gaillard 1939,
Figure 1).
Palaeohierax gervaisii (Milne-Edwards, 1863), late Oligocene
France, is described from a tarsometatarsus and is larger than ‘A.’
corroyi. Compared to Archaehierax sylvestris, the incisura intertrochleae are narrow and the ﬂange on trochlea metatarsi II isoriented more medially (Milne-Edwards 1863, Plate 183, Figures
1-10).

Aviraptor longicrus Mayr and Hurum, 2020, of early Oligocene age
from Poland, is described from a complete skeleton. It is a very small
accipitrid with highly elongate legs like those seen in species ofAccipitrinae, which clearly distinguishes it from Archaehierax
sylvestris.
There are two Middle Oligocene species from Mongolia; Buteo
circoides Kurochkin, 1968 (distal ulna), and Venerator (‘Tutor’)dementjevi (Kurochkin, 1968) (distal humerus). Only B. circoides
can be directly compared to Archaehierax sylvestris, with images
indicating the tuberculum carpale is less prominent of the ventral
condyle, and the ventral condyle has greater distal extent than thedorsal condyle (Kurochkin 1968,Figure 1).
Three fossil accipitrids are known from early Miocene depositsof Europe;
Promilio incertus (Gaillard, 1939) was described from a righttarsometatarsus from Chavroches, France, which lacks the wide
incisura of Archaehierax sylvestris, the ﬂange on the trochlea
metatarsi II is oriented more medially, and the hypotarsal crests
are of roughly equal craniocaudal depth (Gaillard 1939,
Figure 9).
Aquilavus priscus (Milne-Edwards, 1863), described froma tarsometatarsus, tibiotarsus and carpometacarpus, is from
Auvergne, France. It is larger than P. gervaisii. Compared toArchaehierax sylvestris, the incisura intertrochleae are narrow andthe ﬂange on trochlea metatarsi II is oriented more medially(Milne-Edwards 1863, Plate 184, Figures 1-4). On the carpometacarpus, the os metacarpale minus is ﬂat, the processus alularis is lessdistinct from the distal processus extensorius, and the facies articularis digitalis major has less distal extent than the facies articularis
digitalis minor (Milne-Edwards 1863, Plate 184, Figures 14-16).
The tibiotarsus seems to lack a distinct scar or rugosity for the
distal retinaculum extensorium (Milne-Edwards 1863, Plate 184,
Figures 11-13).
Aquilavus depredator (Milne-Edwards, 1871), described froma tarsometatarsus, is from Saint-Gérand le Puy, France. Compared
to Archaehierax sylvestris, the incisura intertrochleae are narrow
and the ﬂange on trochlea metatarsi II is oriented more medially(Milne-Edwards 1871, Plate 183 Figures 11-14; Plate 184, Figures5-10).
The middle Miocene accipitrids from Asia are all aegypiine
vultures (Hou et al. 2000; Zhang et al. 2010, 2012; Li et al. 2016)
and so are not closely related (see phylogenetic analysis below).

Family Accipitridae Vigors, 1824
Subfamily indet. Gen. et sp. indet.
Material
Distal right humeral fragment, preserving a relatively unworn distal
end and 16.2 mm of shaft, and some associated fragments of the
shaft, SAMA P.58917.
Measurements (mm)Distal width 15.4, least shaft width 8.3, total depth 8.5, condylus
dorsalis depth 8.3, condylus dorsalis width 5.2, condylus ventralis
depth 5.1, condylus ventralis width 7.3, epicondylus ventralis
depth 7.0.
Locality, stratigraphy and age
31° 07.568ʹ S; 140° 12.737ʹ E. Site 11, Lake Pinpa, Frome Downs
Station, South Australia, Namba Formation, Pinpa LF, late
Oligocene. Collected by A. Camens, T. Worthy and W. Handley,
24–26 September 2015.

HISTORICAL BIOLOGY

23

Figure 11. Accipitrid distal right humerus SAMA P.58917 in cranial (A), caudal (B), dorsal (C) and ventral (D) view. Abbreviations: CD, condylus dorsalis; CDCS, condylus
dorsalis caudal scars; CV, condylus ventralis; EV, epicondylus ventralis; FB, fossa brachialis; FO, fossa olecrani; II, incisura intercondylaris; MECR, m. extensor carpi radialis
insertion scars; MFCUS, musculus ﬂexor carpi ulnaris scars; PF, processus ﬂexorius; PSD, tuberculum supracondylare dorsale; PSI, pronator superﬁcialis insertion; SHT, sulcus
humerotricipitalis; SST, sulcus scapulotricipitalis; TSV, tuberculum supracondylare ventrale. Scale bar 10 mm.

Remarks
The fossil can be excluded from other raptor families on the following features:
Falconidae (falconid state in brackets): the condylus dorsalis is
thickened and rounded distally (consistently narrow and rectangular); the processus ﬂexorius ends proximal to the condylus ventralis(equidistant).
Pandionidae (state for Pandion haliaetus in brackets): a shallow
fossa m. brachialis (deep); a ﬂat epicondylus dorsalis (prominently
projecting); a ﬂat epicondylus ventralis (prominent); the fossa olecrani is shallow (deep); the sulcus scapulotricipitalis is shallow (deep).
Cathartidae (cathartid state in brackets): a shallow
fossa m. brachialis (deep); a lack of pneumatisation in the
fossa m. brachialis (present); a ﬂat epicondylus ventralis (prominent).
Sagittariidae (sagittariid state in brackets): the two fossae marking the attachment points for the lig. collaterale dorsale are positioned roughly adjacent to each other (cranial-most fossa slightly
proximal to and abutting caudal fossa in sagittariids).
The fossil is broadly similar to accipitrids and displays the following features: (1) The tuberculum supracondylare dorsale (Figure 11A:
PSD) is located well-proximal to the condylus dorsalis (Figure 11A:

CD) and is small, barely projecting dorsally of the shaft, but projects
slightly cranially as a proximodistally elongate rugosity; (2) the dorsal
face/shaft margin between the tuberculum supracondylare dorsale
and the epicondylus dorsalis is mildly inﬂated; Two shallow scars
for the m. extensor carpi radialis are present on the tuberculum
supracondylare dorsale (Figure 11C: MECR), (3) the larger palmar
attachment scar on the cranial face adjacent to the dorsal margin isoval (4) and the smaller dorsal scar is located on the dorsal face of theprocessus. (5) In caudal view, the processus ﬂexorius (Figure 11: PF)
terminates proximal to the condylus ventralis (Figure 11A: CV) but isprominent ventrally. (6) The sulcus scapulotricipitalis (Figure 11B:
SST) forms a shallow but broad notch roughly 2 mm wide on thecaudal face. (7) The fossa olecrani (Figure 11B: FO) is moderately
deep, deﬁning well the dorsal margin to the processus ﬂexorius but
does not create a discontinuity with the sulcus humerotricipitalis. (8)The sulcus humerotricipitalis (Figure 11B: SHT) is very shallow, andat 5.3 mm wide extends over half of shaft width of 9.7 mm at thesame point. (9) The fossa m. brachialis (Figure 11A: FB) is shallow
but distinct, with a proximodistal length of 13.8 mm extending well
proximal to the tuberculum supracondylare dorsale, and a maximum
dorsoventral width of 7.3 mm level with the proximal margin of the24

E. K. MATHER ET AL.

tuberculum supracondylare dorsale. In contrast, the shaft width
measures 10.1 mm at the same point. Within the fossa, theimpressio m. brachialis is slightly deeper. (10) The fossa is well
separated (3 mm) from the dorsal margin of the shaft. (11) The
epicondylus ventralis (Figure 11A: EV) is indistinct from the ventral
margin and does not project ventrally past the processus ﬂexorius.
(12) A single distinct, shallow insertion scar is present on the ventrodistal section of the epicondylus ventralis, with a very faint andshallow second insertion ventrally adjacent to it. These insertions
serve as the attachment point for the m. ﬂexor carpi ulnaris. (13)The tuberculum supracondylare ventrale (Figure 11A: TSV) projects
cranially but not ventrally from the shaft. (14) A shallow insertion
scar for the pronator superﬁcialis is present just proximal to the
tuberculum on the dorsal face. (15) The condylus dorsalis(Figure 11A: CD) is 5.9 mm proximodistally long, 4.7 mm dorsoventrally wide and 8.6 mm craniocaudally deep. (16) Two small, very
shallow insertion scars are present on the caudal section of the dorsal
face of the condylus dorsalis by the distal margin (Figure 11C:
CDCS), directly craniocaudally adjacent to each other. (17) The
condylus ventralis is 4.5 mm proximodistally long, 7.3 mm dorsoventrally wide and 5 mm craniocaudally deep. (18) The condylus dorsalis
is separated by a distinct notch from and set well proximal to the
distal margin of the condylus ventralis in cranial view. (19) The
incisura intercondylaris (Figure 11: II) is narrow, roughly 1.1 mm
wide, but distinct. (20) The processus ﬂexorius is surpassed distallyby the condylus ventralis in caudal view, and strongly projects ventrally in caudal view. (21) The ventral margin of the condylus
ventralis is not separated by a notch from the processus ﬂexorius in
cranial view.
Extant accipitrids diﬀer as follows: (Trait 1) The tuberculum
supracondylare dorsale projects much further dorsally in all subfamilies and species except Pernis apivorus (Perninae), Polyboroides
typus (Gypaetinae, non-projecting), Aquilinae, Accipitrinae andspecies of Buteo (Buteoninae). (16) The insertion scars towards
the caudal margin of the condylus dorsalis are both deep in all
subfamilies except Elaninae and Accipitrinae, with the latter having
the cranial-most insertion being shallow and the caudal-most deep.
The fossil has the most similarities to species from the subfamily
Elaninae (see SI.2 for more detailed diﬀerential comparisons), but
diﬀers markedly in regards to the inﬂation of the dorsal face
between the tuberculum supracondylare dorsale and the epicondylus dorsalis, the size and shape of the palmar and dorsal attachment
scars for the m. extensor carpi radialis, the distinct depression in thesection of dorsal face caudal to the tuberculum supracondylaris andthe epicondylus dorsalis, the sulcus humerotricipitalis width, thefossa m. brachialis length, the conﬁguration of the insertion scars
on the distal epicondylus ventralis, the position of the distal marginof the condylus dorsalis relative to that of the condylus ventralis incranial view, the ventral projection of the processus ﬂexorius, andthe connectivity of the condylus ventralis and entepicondyle incranial view.
As the Archaehierax sylvestris specimen SAMA P.54998 lacksa preserved distal humerus, it cannot be compared to SAMA
P.58917. However, it is not believed to belong to the same species
due to the signiﬁcantly smaller size of SAMA P.58917 from thehumerus size predicted for SAMA P.54998 (see comparative measurements below).

Family Accipitridae Vigors, 1824
Subfamily indet. Gen. et sp. indet.
Material
NMV P.222435, distal left femur preserving intact distal end and15.5 mm of shaft.
Measurements (mm)Preserved length 26, DW 13.3, least SW 7.3, preserved condylus
medialis depth 9.7, condylus medialis width 5.6, condylus lateralis
depth 11.0, condylus lateralis width 6.1.
Locality, stratigraphy and age
31° 11.237’S 140° 13.944ʹE Ericmas Quarry, Lake Namba, Frome
Downs Station, South Australia, Namba Formation, Ericmas LF,
late Oligocene. Collected by T. Flannery, 7/4/83.
Remarks
The specimen can be excluded from the Pandionidae andCathartidae by the presence of a single muscular attachment on
the planum popliteum, and from Falconidae and Sagittariidae by
the linea intermuscularis caudalis remaining level and visible on the
medial margin of the caudal face.
The femur is consistent with accipitrids and has the following
morphology.
(Trait 1) The linea intermuscularis caudalis (Figure 12C: LIC) is
highly distinct, running along the medial border of the caudal shaft
face in a raised line, (2) but is not continuous with the
tuberculum m. gastrocnemialis medialis, so there is no crista supracondylaris medialis. (3) The secondary origin point for the ligamentum collateralis lateralis is very faint and shallow, barely distinct
from the surface of the bone. (4) The fovea tendineus m. tibialis
cranialis is shallow. (5) The fossa poplitea (Figure 12B: FPop) is
shallow, deepening slightly towards the distal end immediately proximal to the condyles. (6) The attachment scar on the planum popliteum (Figure 12B: PPAP) is positioned medially. (7) The
impressio m. gastrocnemialis lateralis (Figure 12D: IG) is large andshallow. (8) The epicondylus lateralis (Figure 12A: EL) is short andvery robust but has little projection from the condylus lateralis.
The distal femur NMV P.222435 is from an accipitrid which
exhibits the most similarity to those of species in Buteoninae,
Aegypiinae, and most of Elaninae (see SI.2 for more detailed
diﬀerential comparisons). It mainly diﬀers from species in thesesubfamilies in lacking a prominent crista supracondylaris medialis, the position and shape of the attachment point on theplanum popliteum, and the weak projection of the epicondylaris
lateralis.
As the distal femur is not a highly diagnostic section of theaccipitrid skeleton, and the distal femur is not preserved inArchaehierax sylvestris specimen SAMA P.54998, NMV
P.222435 is regarded as gen. et. sp. indet. The size diﬀerence
between NMV P.222435 and the predicted size of the distal
femur of SAMA P.54998 is greater than would be predictedfrom typical sexual dimorphism, which makes it unlikely thetwo are representatives of the same species (see comparative
measurements below).

HISTORICAL BIOLOGY

25

Figure 12. Distal left femur NMV P.222435 depicted in cranial (A), caudal (B), medial (C) and lateral (D) view. Abbreviations: CM, condylus medialis; EL, epicondylus lateralis;FPop, fossa poplitea; IG, impressio m. gastrocnemialis lateralis; ILCC, impressio lig. cruciati cranialis; LIC, linea intermuscularis caudalis; PPAP, planum popliteum attachment
point; SP, sulcus patellaris; TF, trochlea ﬁbularis; TMGM, tuberculum muscularis gastrocnemialis medialis. Scale bar 10 mm.

Size comparisons of the three fossils
The width measurements of the proximal humerus, distal humerus,
distal tibiotarsus and distal femur of extant taxa were compared (seeAppendix 1, Table S2) and showed that the distal width of thehumerus was between 80% and 90% of the proximal width of thehumerus, while the distal width of the tibiotarsus was between 75%
and 110% the distal width of the femur in extant accipitrids. If thebones of Archaehierax sylvestris had similar ratios, then it can bepredicted that the width of the missing distal humerus should fall in
the range 23.4–26.4 mm, while that of the missing distal femur
should be between 15.8 and 22.0 mm broad. Based on this, both theisolated distal femur NMV P222435 and the isolated distal humerus
SAMA P.58917 are too small to belong to an individual the size of
the A. sylvestris holotype. However, sexual dimorphism is known tobe considerable and common in accipitrids (Brown and Amadon
1968; Marchant and Higgins 1993) and raises the possibility thatthese isolated fossils may belong to a smaller sex of the one species ifthey fall within a certain size range. Field et al. (2013) devised
multiple algorithms for predicting body mass from skeletal measurements, while Campbell and Marcus (1992) predicted body mass
based on the femur and tibiotarsus circumference. Using these, themass of the bird for the Archaehierax sylvestris holotype is estimated as 3.7 kg based on the length of the coracoid facies articularis
humeralis, 4.6 kg by the least shaft diameter/width of the tarsometatarsus, and 3.2 kg based on tibiotarsus least shaft circumference.
The mass of the bird represented by the distal femur is calculated at
2 kg based on femur shaft width/diameter, or 1.6 kg based on shaft
circumference. The mass of the bird represented by the distal
humerus is calculated at 1.5 kg based on shaft width/diameter, or
1.6 kg based on circumference. Assuming these predictions areaccurate, the femur represents a bird 46–67% smaller than theskeleton specimen, and the humerus one 60–67% smaller. This
would be pushing accipitrid sexual dimorphism to its extreme
limits, making it unlikely that the fossils represent a single species.

26

E. K. MATHER ET AL.

Figure 13. PCA plots using length measurements of the carpometacarpus, ulna, humerus, tibiotarsus, tarsometatarsus, pedal digit 1 and pedal digit 2 treated in three ways.
(A) Absolute data, (B) log-transformed data, (C) size standardised data with variables proportional to quadrate height. Directional arrows at top right indicate directionalityof limb length (S, short and L, long) along the PC axes. Note: axes in A and B have been scaled for better visualisation, so 2D distances do not represent true 2D distances in
PCA space. Abbreviations: Ae. mon., Aegypius monachus; Ar. syl., Archaehierax sylvestris; Aq. au., Aquila audax; Ci. as., Circus assimilis; El. scr., Elanus scriptus; Gy. cop., Gyps
coprotheres; Ham. mel., Hamirostra melanosternon; Hal. leug., Haliaeetus leucogaster; Hi. mor., Hieraaetus morphnoides; Lo. isu., Lophoictinia isura; Ne. per., Neophron
percnopterus; Pe. api., Pernis apivorus; Spl. ch., Spilornis cheela; Spz. tyr., Spizaetus tyrannus. Dark green, forested habitat; light green, woodland/open forest; orange, open
habitat (grassland, savannah etc.). Fossil (Archaehierax) indicated by black square.

However, these mass predictions use diﬀerent elements, limiting
their comparability. Nevertheless, while considering it likely that atleast two accipitrids are represented, we consider it unwise todescribe the smaller as a second species when size would be theonly distinguishing factor and their congeneric status cannot be
assessed.

HISTORICAL BIOLOGY

27

Figure 14. Analysis 4a: combined molecular and morphological data (ordered) analysed with Bayesian methods; molecular and morphological partition branch lengths
unlinked. Node values show posterior probability.

PCA analysis of limb measurements
Length data for a range of post cranial measurements were visualised in PCA plots to determine if there was any correlation between
them and preferred habitat. All PCAs used a variance-covariancematrix, iterative imputation for missing data (in the case of I.2
length of Gyps coprotheres), and 1000 bootstrap replicates. See
Appendix 2 for datasets, scree plots, biplots, PCA values.
The ﬁrst PCA used absolute length measurements of the carpometacarpus, ulna, tibiotarsus, tarsometatarsus, pedal digit 1 andpedal digit 2 (Figure 13A). In the resulting scatterplot PC1 (92.1%
variance) was most strongly driven by the ulna, with some inﬂuence
from the carpometacarpus (wings), the tarsometatarsus and tibiotarsus and PC2 (7% variance) by the tarsometatarsus and tibiotarsus (legs). Archaehierax sylvestris was positioned as a long-legged,
short-winged taxon, well separated from other species. BothSpizaetus tyrannus and Spilornis cheela grouped closely together,creating a cluster for forest-habitat accipitrids. Circus assimilis,
which inhabits grassland and open woodland, was positioned intermediate between Archaehierax sylvestris and the forest taxa.
A second PCA was run after log-transforming the measurements. In the resulting scatterplot (Figure 13B) PC1 (91.4% variance), was driven by almost all measurements, with those of thetibiotarsus and tarsometatarsus having slightly more inﬂuence thanthose of the wings and digits, and PC2 (3.3% variance) revealed thatspecies were separated most strongly based on the tarsometatarsus
length, with lesser inﬂuence from the digit lengths and tibiotarsus
length. Archaehierax sylvestris grouped with the long-legged andshort-winged taxa, but the distribution of the extant taxa changed.
Spizaetus tyrannus and Spilornis cheela were more widely separated,with the open-habitat taxon Circus assimilis positioned more closely to Spizaetus tyrannus.
As size dominated the ﬁrst two PCAs, a third PCA was performed with measurements standardised for size, by division of
postcranial data by the height of the quadrate, an element whichcorrelates strongly with skull size and therefore body size
(Elzanowski et al. 2001). In the resulting scatterplot (Figure 13C),
PC1 (67.2%) was most strongly driven by ulna length and to a lesser
degree by carpometacarpus length, while PC2 (28.9%) was moststrongly driven by tibiotarsus length and tarsometatarsus length.
Archaehierax sylvestris occupied a more negative position on PC2
relative to Circus assimilis as the peak of the long-legged, shortwinged taxa, and Spizaetus and Spilornis clustered together closely
once more. Archaehierax sylvestris fell intermediate between Circus
assimilis and the forest accipitrid cluster.

28

E. K. MATHER ET AL.

Phylogenetic analyses
We performed phylogenetic analyses of morphological data only, andcombined morphological and molecular data, using parsimony andBayesian methods. We discuss all analyses below, but have most conﬁdence in the analyses combining morphology and molecules, inparticular the unlinked Bayesian analyses, for reasons discussed at
the end.
Analysis 1: Parsimony, morphology only, unordered characters
The ﬁrst analysis used only morphological data, with no ordering,
constraints or weighting applied to the characters. The resulting 30
most parsimonious trees (hereafter MPTs) had a tree length of 1686
steps (SI.5Figure 1). Coragyps atratus, Ciconia ciconia, Threskiornis
spinicollis, and Sagittarius serpentarius were rooted as the outgroup(PP = 97%), while Pandion resolved as sister to Accipitridae witha support value of 97%. This is broadly concordant with independent molecular phylogenetic studies.
Within Accipitridae, the tree is less congruent with DNA trees.
The Accipitridae as a family had strong support (87%) with the
non-Australian Perninae resolved as the most basal clade, which
was strongly supported (87%) but had species left in a polytomy.
The fossil Archaehierax sylvestris n. gen. et sp. resolved asa branch between the Circaetinae-Harpiinae-Aquilinae clade andall other subfamilies higher up the tree. However, support for thisposition was very weak (<50%).
Analysis 2: Parsimony, morphology only, ordered characters
Analysis 2 diﬀered from Analysis 1 by ordering certain multistatecharacters which formed morphoclines (see SI.1). This generated
four MPTs with a tree length of 1720. The resulting strict consensus
tree (SI.5Figure 2) is largely the same as for analysis 1, but with thefollowing diﬀerences. The Accipitridae resolved with strong support slightly higher than the previous analysis (PP = 88%).
The fossil Archaehierax sylvestris was resolved as being between
the Elaninae and the Australian endemic Perninae on the phylogenetic tree, though support for this position was very weak (<50%).
Analysis 3: Parsimony, morphology and DNA, ordered characters
As the analyses based on morphology failed to resolve the taxa ina way that reﬂects strongly supported clades based on comprehensive molecular data, and the primary aim of the analysis was toassess how the fossil related to the well-corroborated clades ofmodern taxa, molecular data from six genes was added for 47 taxa
(see Methods) forming a combined morphology and molecular data
matrix used in Analysis 3. Parsimony analysis of this matrix produced three MPTs with a tree length of 1831 (See SI.5Figure 3).
Given the molecular data largely constrains the tree to therelationships dictated by molecular data alone, relationships
were mostly the same as those in recent molecular studies(Nagy and Tökölyi 2014; Mindell et al. 2018).
The position of the fossil Archaehierax sylvestris varied
between the strict consensus tree and the bootstrap majority
consensus tree of the same analysis. In the strict consensus
tree (SI.5) the fossil resolved as nested within the Circaetinae,
sister to Pithecophaga jeﬀeryi. However, the bootstrap consensus tree resolved the fossil as its own branch between the
Perninae-Gypaetinae and the Circaetinae-Aegypiinae cladeswith moderate (68%) support.
Analysis 4: Bayesian inference, morphology + DNA, ordered
The Bayesian analysis with molecular and morphologicalbranch lengths unlinked produced a broadly similar tree forliving taxa to the bootstrap consensus of the corresponding

parsimony analysis, but with overall much stronger supports
for higher-level clades (Figure 14). All subfamilies resolved as
monophyletic, and the divergence nodes for all subfamilies
and major clades were greater than 70% except for one.
The fossil Archaehierax sylvestris resolved as a lineage between
the Elaninae and the Perninae-Gypaetinae clades (i.e. non-elanine
accipitrids). Support for Archaehierax plus a clade of all nonElanine accipitrids was weak (44%), but there was moderate support (73%) for monophyly of all other non-elanine accipitrids
excluding Archaehierax.
When the branch lengths for the molecular and morphological data were linked (SI.5Figure 4), the position of the fossilchanged. Archaehierax sylvestris moved up the phylogeny andresolved as an independent branch above the CircaetinaeAegypiinae clade but below the Harpiinae and relatives.
Support for this node was stronger than that of the position
resolved by the unlinked analysis, but still weak (56%).
Summary
All phylogenetic analyses resolved Archaehierax sylvestris with
the Accipitridae, consistent with the conclusions drawn fromthe morphological descriptions, though its precise position
within that family varied. Some analyses found it deeply
nested within Accipitridae, closely related to, but outside
buteonines, haliaeetines and accipitrines. These analyses
include the morphology-only parsimony analyses, morphology+molecularparsimonyandmorphology+molecular
Bayesian analysis with linked branch lengths. However, as
discussed below, these deeply nested aﬃnities for
Archaehierax are problematic, and appear less plausible than
the topology retrieved in the Bayesian analysis with branch
lengths unlinked – where it was one of the most basal accipitrid lineages, with only Elaninae diverging before it(Figure 14).
A more precise and robust position for Archaehierax sylvestris isperhaps prohibited by missing data. Even with the 63 preserved
elements, there is still a signiﬁcant amount of missing data. The
mandible and cranium, most of the sternum, the distal ends of thehumeri, the pelvis, and most of the femora were not preserved.
Thus, only 45% (135/300) of phylogenetic characters could beassessed in SAMA P.54998.

Discussion
Pengana robertbolesi was previously the only accipitrid raptor
known from the late Oligocene in Australia (Boles 1993; Worthy
and Nguyen 2020), being slightly younger than Archaehierax sylvestris at 24–20 Ma (Travouillon et al. 2006; Woodhead et al. 2016),
and represented only by a distal tibiotarsus making relationships
within Accipitridae diﬃcult to establish. The specimens from thelate Oligocene Namba Formation are the oldest accipitrids inAustralia and extend the fossil record of the Australian
Accipitridae to 26–24 Ma, when Australia was much warmer andheavily forested.
Relationships with fossil and extant Australian Accipitridae
Archaehierax sylvestris is unambiguously an accipitrid based on
many skeletal features, but notably the morphology of the tarsometatarsal hypotarsus, the lack of a spina interna on the sternum, andthe shortened second and third phalanges of the fourth digit.
Unsurprisingly, Archaehierax sylvestris has multiple unique featuresof its skeletal morphology that distinguish it from other accipitrids,
such as the low caput humeri (humerus), the two fossae in the parscaudale separated by a pila medialis (sternum), and the wide

HISTORICAL BIOLOGY

incisurae intertrochleares (tarsometatarsus). However, as summarised above, the diﬀerent elements of Archaehierax sylvestris do
not reveal a consistent closer relationship to the species in any one
subfamily. Some elements, such as the rostrum, carpometacarpus
and tibiotarsus, show much similarity to species in more derived
subfamilies like the Buteoninae, while others, such as the quadrate,
vertebrae, and sternum resemble those of more basal subfamilies
like Elaninae and Aegypiinae. Other elements, like the humerus,
ossa carpalia and the tarsometatarsus, share features with multiple
subfamilies. The scapula, ulna, radius, carpometacarpus, carpal
phalanges, ﬁbula and pedal phalanges do not align well with thespecies of any one subfamily. The morphology of the os carpi
radiale also excludes the fossil from an accipitrid clade comprising
Harpiinae, Aquilinae, Haliaeetinae, Buteoninae and Accipitrinae(see Mayr 2014). This mix of aﬃnities among characters contributes
to understanding why the fossil does not group robustly in any
subfamily in the phylogenetic analyses. This typiﬁes many
Palaeogene fossil bird species across multiple families (see Mayr2009) and, along with the phylogenetic results, supports the ideathat Archaehierax does not belong to an extant subfamily. Missing
data probably exacerbates the problem as about 55% of characters
could not be coded.
In our parsimony analysis using combined morphological andmolecular data SI.5, Archaehierax sylvestris resolved either deeply
nested within Circaetinae as sister to Pithecophaga jeﬀeryi (strict
consensus tree) or as a stem lineage situated between the clade
Gypaetinae-Perninae and Aegypiinae-Circaetinae (bootstrap consensus tree). The Bayesian analysis of combined morphological andmolecular data with morphology and molecular branch lengths
linked had A. sylvestris resolved as above the AegypiinaeCircaetinae clade but lower than the Harpiinae and Aquilinae. In
contrast, the Bayesian analysis of combined morphological andmolecular data, with unlinked molecular and morphological branch
lengths, resolved Archaehierax sylvestris near the base of the
Accipitridae, immediately above the Elaninae. The topology of theunlinked molecular and morphology branch lengths tree
(Figure 14, analysis 4a) is preferred for several reasons; ﬁrstly,
given the age of the fossil, a more basal position on the accipitrid
phylogenetic tree is more plausible. Dated molecular phylogenies
imply that most of the extant accipitrid subfamilies had notdiverged by the late Oligocene, with only the Elaninae, which
diverged at 33.7 Ma (Mindell et al. 2018), likely present, as thePerninae +Gypaetinae clade diverged at 23.8 Ma from remaining
accipitrids (Mindell et al. 2018). Other lineages emerged during or
after the middle Miocene (Nagy and Tökölyi 2014; Oatley et al.
2015; Prum et al. 2015; Mindell et al. 2018). Secondly, while many
analyses of combined morphological and molecular datasets link
branch lengths between these data types (e.g. Ronquist et al. 2012),
this might be justiﬁable only under certain circumstances. Duchéne
et al. (2020) compared the eﬀects of linking branch lengths of geneloci trees and demonstrated that partitioning and linking loci tocreate proportionate branch lengths gave the strongest support,
while analyses that had unlinked loci, or loci that were linked to
produce identical branch lengths, received weaker support.
Goloboﬀ et al. (2019) explored the question of whether assuming
a common mechanism of evolution to both all genetrees andmorphological data was warranted and concluded that morphological data was generally not compatible with the common clock
assumption used when linking branch lengths, producing low levelsof branch length correlation. Similarly, Barba-Montoya et al. (2021)
found a poor linear relationship between branch lengths for morphological and molecular data, consistent with the idea that themorphological traits were evolving at much more variable rates

29

compared to the molecular ones. Based on this, the results estimated by linking morphological and molecular branch lengths (SI.
5) should be regarded with caution.
The molecular-based divergence dates for Aquilinae (Nagyand Tökölyi 2014; Mindell et al. 2018) suggest that Aquila
bullockensis, at 14–12 Ma (Woodhead et al. 2016), pre-dates
the inferred age of the Aquila genus by at least 5 Ma.
Morphologically the holotype distal humerus has several distinct diﬀerences from Aquila audax, including a reduced distal
projection of the processus ﬂexorius, a tuberculum supracondylare ventrale with less cranial projection and no proximal
narrowing, little to no convexity between the processus supracondylare dorsale and epicondylus dorsalis, and the dorsal
insertion for the m. extensor radii is positioned oﬀset fromthe processus supracondylare dorsale. This does not necessarily mean that A. bullockensis is not an aquiline, but rather
that it is unlikely to be a member of the crown Aquila or any
other extant aquiline genus, and that the initial comparativedescriptions were too limited to support referral of the species
to Aquila. Since the description of the holotype, more fossilmaterial that likely belongs to A. bullockensis has been discovered and is awaiting description, which may change interpretations of the relationship of A. bullockensis to the extant
Aquilinae.
In relation to size, it is clear that Archaehierax sylvestris wasa large accipitrid, smaller than the wedge-tailed eagle Aquila audax
and the white-bellied sea eagle Haliaeetus leucogaster but larger
than the black-breasted buzzard Hamirostra melanosternon
among the extant Australian fauna. It is tempting to assume fromthis that it must belong to a lineage of large accipitrids. However,while size is sometimes useful in diagnosing clade membership,
there are notable exceptions. Haast’s eagle Hieraaetus moorei, oneof the largest eagles ever known at an estimated 15 kg (Worthy andHoldaway 2002), is most closely related to the little eagle Hieraaetus
morphnoides (Bunce et al. 2005; Knapp et al. 2019), which weighs
under 1 kg, the two diverging from a common ancestor approximately 1 million years ago (Knapp et al. 2019). Another example isseen among extant species; the Philippine eagle Pithecophaga jeffreyi is morphologically convergent on the Harpiinae in terms oflarge body size, prey preference, and preferred habitat, but groups
molecularly with the Circaetinae, most of which are medium-sized
reptile specialists.
Regardless of its closest extant relative, Archaehierax sylvestrisdemonstrates the presence of Accipitridae in Australia since the late
Oligocene and that there were at least two divergent clades(A. sylvestris and Pengana robertbolesi) in Australia around the
Oligo-Miocene boundary. All well-sampled Australian faunas
from the late Oligocene onwards are now known to have contained
accipitrids (Baird et al. 1991; Boles 1993; Gaﬀ and Boles 2010; Richand van Tets 1982; Louys and Price 2015; Worthy and Yates 2018).
However, the geographic origin of these austral accipitrids is diﬃcult to infer, given the presence of accipitrids across multiple continents at this time and a lack of phylogenetic analyses of them withfossils elsewhere.
Conspeciﬁcity of the isolated distal humerus and femur specimens from other sites in the Namba Formation with
Archaehierax sylvestris could not be excluded based on morphology given the holotype lacks these elements, although theirmuch smaller size makes this unlikely, exceeding diﬀerences
attributable to sexual dimorphism. However, in the absence ofoverlapping skeletal elements, establishing whether they arecongeneric or not is impossible, so we refrain from describing
them as a new species.

30

E. K. MATHER ET AL.

Palaeobiology
Archaehierax sylvestris is inferred to have inhabited forested areas,
based on the pollen records from the Namba Formation (Martin
1990) and the associated fauna in the Pinpa LF, which contains
many arboreal taxa such as koalas (phascolarctids), and members offour families of possums and kin (phalangeriforms) (see above;
Rich et al. 1991). Our principal component analyses show the fossil
taxon grouped most closely to species with relatively shorter wings
and longer legs. This body form is observed in forest dwelling eagles
and hawks, such as species of Spizaetus, Spilornis, Harpia harpyja
and Pithecophaga jeﬀreyi, which are adapted to ﬂying through moreconstricted spaces among the trees and vegetation (Brown andAmadon 1968; Holdaway 1991 unpublished thesis). However, it isalso present in the spotted harrier Circus assimilis, which
Archaehierax sylvestris was also closely associated with in PCA
plots, which favours open grassland and lightly wooded areas for
its habitat (Brown and Amadon 1968; Marchant and Higgins 1993;
Debus 1998). In the case of Circus assimilis, however, wingspan toleg length proportion is less the result of the wings being shortened,but more the product of the legs being hyper-elongate compared toother accipitrids, especially in the tarsometatarsus, to facilitatea specialised hunting strategy. Circus assimilis is known to forage
by slowly ﬂying less than ﬁve metres above vegetation (Aumann2001) and has been documented pursuing small prey such as lizards
on foot (Buij 2014). It is likely that the high ratio between the wing
and leg length in C. assimilis is therefore being driven by a need toreach into grass cover to quickly grab small vertebrates before theycan escape. As Archaehierax sylvestris does not exhibit the extreme
elongate tarsometatarsus morphology observed in C. assimilis, andmore closely resembles that of the crested serpent-eagle Spilornis
cheela and the black hawk-eagle Spizaetus tyrannus, it can beinferred that the ecology of Archaehierax sylvestris was more akinto the latter species.
With its shorter wings allowing manoeuvrability, Archaehierax
would not have been a particularly fast ﬂier, but would have beencapable of more agile twists and turns in ﬂight than an accipitrid of
its size with a typical wingspan. If we use extant forest eagle species
such as those in Spizaetus as a morphological analogue, it can beassumed that Archaehierax sylvestris was likely an ambush hunter,waiting on a perch within forest cover until prey came into range,
and then attacking with a quick burst of speed (Whitacre and Jenny2013).
The potential diet of Archaehierax can be inferred based on thatof living analogues, such as species in Spizaetus. A female ornate
hawk-eagle Spizaetus ornatus was recorded feeding on the remains ofan estimated 3.2 kg Central American agouti (Dasyprocta punctata)and later, on a great curassow (Crax rubra), which can weighbetween 3.1 and 4.8 kg (though it was not directly observed killingthese animals). Whitacre and Jenny (2013) recorded a male with anadult great tinamou (Tinamus major) around 1 kg in weight, whichis also the average weight for male Spizaetus ornatus. Archaehierax
sylvestris is notably larger than the species of Spizaetus observed inthis project (Spizaetus ornatus, Spizaetus tyrannus), and assuming
similar prey hunting abilities, would have been quite capable ofpreying on many of the mammals and birds known from the
Pinpa Local Fauna.
Based on its larger physical size, phylogenetic position, and the
proportions of the tibiotarsus to the tarsometatarsus, it is unlikelythat Archaehierax sylvestris was restricted to preying on large
invertebrates and small vertebrates as seen in the elanines andsome of the pernines. The extant Australian elanines, the letterwinged kite Elanus scriptus and the black-shouldered kite Elanus

axillaris, primarily feed upon small mammals (typically mousesized), lizards, and large insects such as beetles, grasshoppers andlocusts (Brown and Amadon 1968; Marchant and Higgins 1993).
The pernine kite Hamirostra melanosternon feeds upon small
mammals (rabbit-sized at largest), reptiles, and birds, and has
been observed to break open eggs of large ground-dwellingbirds using either stones or its beak (Brown and Amadon 1968;
Marchant and Higgins 1993). The square-tailed kite Lophoictinia
isura preys on a wide array of small birds, reptiles, large insects,
and even bird eggs from nests (Brown and Amadon 1968;
Marchant and Higgins 1993).
However, Archaehierax sylvestris also lacks the robustness oflegs seen in the species of aquilines and harpiines that feed onlarger birds and small to medium mammals. The morphology andtibiotarsus-tarsometatarsus ratio of the fossil are also slenderer
compared to the ﬁsh eagles/haliaeetines, which require the sturdiness to strike through water and the grip to maintain a hold on
struggling prey, so despite living near a lake this bird likely did not
ﬁsh like these species. Aquila audax feeds on mammals ranging insize from rabbits to small wallabies, and is also a frequent scavenger of roadkill, while Haliaeetus leucogaster near exclusively preys
on large ﬁsh and sea-snakes (Brown and Amadon 1968; Marchantand Higgins 1993). Hieraaetus morphnoides, a smaller bird that isclosely related to Aquila, preys upon small rabbits and othermammals of a similar size, as well as small ground birds (Brown
and Amadon 1968; Marchant and Higgins 1993). Archaehierax islarger than H. morphnoides, but its more gracile morphology may
have restricted it to prey of a similar size to that preferred by thisspecies.
The reduced size of the ﬂange on trochlea metatarsi II in
Archaehierax sylvestris, as well as its strongly plantar orientation,
diﬀers greatly from most Accipitridae. As this marks the point where
the musculature for digit II connects to the tarsometatarsus, this
could indicate a reduced ability to manoeuvre this digit in theplantar-medial direction, which is the orientation present in mostaccipitrids. However, the wider spacing of the trochleae could indicate a greater foot span when the toes are extended for prey capture,
which might compensate for the loss of potential manoeuvrability.
The Pinpa Local Fauna contains a diverse array of animals (seeabove), some of which would have been potential prey for
Archaehierax sylvestris. If a diet of small to medium birds andmammals ranging in habitat from arboreal, terrestrial and littoral
is inferred, prey species may have included Wilaru tedfordi (apresbyornithid), Ngawupodius minya (a dwarf megapode), smaller
individuals and juveniles of Madakoala devisi (an early koala),a huge diversity of possums and many of the waterbirds that appear
in abundance in the Local Fauna.

Acknowledgments
We would like to thank Phillipa Horton, Maya Penck and Mary-Anne Binnie(SAMA), Judith White and Joanne Cooper (NHMUK), Chris Milensky(Smithsonian), Mark Robbins (KU), Tim Ziegler and Karen Roberts (NMV), and
Leo Joseph and Alex Drew (ANWC) for allowing access to collections and loans ofspecimens, without which this project could not have been done. We would also liketo thank Warren Handley for his input regarding mass allometry, Elizabeth
Scharsachs and her family for providing accommodation in Tring, and the PhD
students of Flinders Palaeontology for their support and willingness to talk overthoughts and concerns.
We thank the Mark Mitchell Foundation for a grant to T. H. Worthy,
A. B. Camens that funded some of the ﬁeldwork component. For assistance in theﬁeld, we thank Amy Tschirn and Warren Handley. We acknowledge the support ofAndrew Black (Blackie), manager, for access to Frome Downs Station that allowed
this work.

HISTORICAL BIOLOGY

We also thank Gerald Mayr, Nikita Zelenkov, and an anonymous reviewer
for looking over the manuscript before publication and providing valuable
feedback and corrections.

Authors contributions
EKM and THW designed the study. EKM collected all data, compiled themorphological matrix and performed all analyses. MSYL assisted with analysisof the molecular data and the combined analyses of morphological and molecular data. THW and MSYL contributed to data interpretation. EKM wrote themanuscript, and all authors edited the manuscript. THW and ABC collected thefossil material of Archaehierax sylvestris while on ﬁeld work.

Disclosure statement
No potential conﬂict of interest was reported by the author(s).

Funding
This work was supported by the Sir Mark Mitchell Research Foundation [NA].

ORCID
Ellen K. Mather
http://orcid.org/0000-0001-9437-1395
http://orcid.org/0000-0002-3905-0887
Michael S. Y. Lee
http://orcid.org/0000-0003-0464-0665
Aaron B. Camens
Trevor H. Worthy
http://orcid.org/0000-0001-7047-4680

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