Accipitridae

Aquilavus sp.: une phalange distale (Coll. JR).

This fossil is readily distinguished from the following similar-sized birds likely to be encountered in Pleistocene Australian fossil sites. - From Ciconiidae (Ephippiorhynchus asiaticus) by the following characters (ciconiid state in brackets): The tuberculum supracondylare dorsale is strongly projecting (little to no projection); the dorsal sulcus of the m. humerotricipitalis is narrow, just under a third of the shaft width (broad, roughly half the shaft width); the ventral sulcus of the m. humerotricipitalis is broad, twice the width of the dorsal sulcus (narrow, half the width); the epicondylus ventralis and the tuberculum supracondylare ventrale are distinctly separated from each other (continuous / overlapping); the dorsal insertion of the m. extensor metacarpi radialis is oval restricted to the dorsal facies (circular with a ventrally projecting line leading onto the cranial facies). - From Pelecanidae (Pelecanus conspicillatus) by the following characters (pelecanid state in brackets): The tuberculum supracondylare dorsale is strongly projecting (little to no projection); the origin of m. extensor digitorum communi is a small, circular pit on the dorsal facies between the tuberculum supracondylare dorsale and the epicondylus dorsalis (large, oval-shaped attachment scar); the tuberculum supracondylare ventrale is weakly projecting cranially (cranially flattened); there is no pneumatism of the distal end (pneumatic region present on cranial facies adjacent to tuberculum supracondylare ventrale); the epicondylus ventralis strongly projects ventrally (weak projection); the distal margin of the fossa brachialis is positioned distal to the tuberculum supracondylare dorsale (positioned proximal to the processus). - From Phoenicopteriformes (Phoenicopterus ruber) by the following characters (phoenicopterid state in brackets): the epicondylus ventralis projects prominently ventrally (little to no projection), the dorsal sulcus for the m. humerotricipitalis is under a third of the shaft width (half of shaft width), the ventral sulcus for the m. humerotricipitalis is twice the width of the dorsal sulcus (half the width of the dorsal sulcus), the tuberculum supracondylare ventrale is weakly projecting cranially (cranially flattened), the condylus dorsalis and condylus ventralis are separated by a distinct, deep incisura (narrow, shallow incisura). - From Ardeidae by the following characters (ardeid state in brackets): A deep fossa m. brachialis (shallow); a broad fossa m. brachialis, approximately two thirds of shaft width or more (narrow, one third of shaft width); a narrow sulcus for the dorsal belly of the m. humerotricipitalis (broad). Several features of the bone, notably its large size, are only matched by Aquila audax and Haliaeetus leucogaster in the Australian fauna. However, the combination of a narrow dorsal part of sulcus humerotricipitalis, a markedly prominent epicondylus ventralis, the dorsally inflated facies between the tuberculum supracondylare dorsale and the epicondylus dorsalis, and a distally short processus flexorius, distinguish it from all other accipitrids. As this humerus is unambiguously identifiable as that of an accipitrid and is distinguished from all known genera and species, ‘ Taphaetus’ lacertosus is confirmed as a distinct taxon. However, it requires a new genus, as Taphaetus de Vis, 1905 is a junior homonym of Taphaetus de Vis, 1891, and the latter is a junior synonym of Uroaetus Kaup, 1844 and so of Aquila Brisson, 1760. As the quadrate QM F 5508 was inaccessible at the time of this study, we instead used the descriptions and illustrations in de Vis (1905) to assess if the original identification was valid. QM F 5508 differs distinctly from quadrates of accipitrids, instead being similar to those of Ardeidae, particularly species in the genera Ardea and Egretta, by the following characters (accipitrid state in brackets): A large foramen pneumaticum caudomediale is positioned ventral to the capitulum oticum articular surface (no foramen pneumaticum, though a depressio caudomediale is present in some species); the capitulum oticum is positioned further dorsally relative to the capitulum squamosum (capitulum squamosum further dorsal); the width of the capitula and the width of the shaft are very similar, with little narrowing between the dorsal and ventral ends (shaft distinctly narrower than dorsal end); in caudal view, the condylus mandibularis medialis is positioned level with the condylus mandibularis lateralis, with both being equally visible (condylus mandibularis medialis set back rostrally, less visible than the condylus lateralis); the condylus mandibularis caudalis is prominently projecting caudally (projecting medially); the condylus mandibularis lateralis barely extends laterally from the shaft (extends prominently caudally); the condylus mandibularis medialis extends prominently medially from the shaft (little to no extension); a prominent secondary facet is present on the condylus mandibularis medialis (no secondary facet); in ventral view, the condyles project rostrally past the rostral margin of the articular surface (roughly in line with margin). The reported dorsal height of 22 mm is distinctly larger than that observed in the Australasian Bittern Botaurus poiciloptilus (~ 15 – 16 mm). While the morphology of QM F 5508 is a better match for a heron, it is much larger than compared specimens of White-faced Heron Egretta novaehollandiae and Grey Heron Ardea cinerea but could potentially be a match in size to that of the Great-billed Heron (Ardea sumatrana). As QM F 5508 is not of an accipitrid, it is not considered further here.

The lectotype of ‘ Taphaetus’ lacertosus de Vis, 1905, a distal right humerus, QM F 5507, is identified as an accipitrid based on the presence of the following characters: The distal margin of the fossa brachialis extends distal to the tuberculum supracondylare dorsale; a distinct sulcus scapulotricipitalis; the proximal margin of the condylus dorsalis is roughly level with the ventral tip of the epicondylus ventralis; a distinct circular dorsal insertion for the m. extensor metacarpi radialis on the dorsal projection of the tuberculum supracondylare dorsale; a distinct pit for the insertion of the m. pronator superficialis ventrally adjacent to and slightly proximal to the tuberculum supracondylare ventrale; and the epicondylus ventralis is markedly ventrally prominent.

Throughout most of Australia, the Pleistocene (2.56 Ma – 11.7 Ka) epoch was marked by arid climatic conditions, with the environment dominated by grasslands, open woodland (Sniderman et al. 2007) and desert (Hesse et al. 2004), similar to the present day. The Australian megafauna, which included at least 20 genera of large mammals, four of large birds, and three of large reptiles (Wroe et al. 2013; Johnson et al. 2021), inhabited these environments until most of them went extinct between 50 – 40 Ka (Roberts et al. 2001; van der Kaars et al. 2017). The raptor guild of the Pleistocene can be assumed to have comprised most of the living Australian species, with fossil material of Aquila audax (Latham) (Wedge- tailed Eagle) at least 500 – 200 Ka old (Baird 1991; EKM, THW unpublished data). However, two extinct species that represent potential additional diversity have been described from this epoch; Aquila brachialis (de Vis, 1889) and “ Taphaetus ” lacertosus de Vis, 1905 (Gaff 2002 unpublished thesis; Boles 2006, 2017; Worthy & Nguyen 2020).

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 olecraniis shallow (deep); thesulcus 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 epicondylusventralis (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 11 A: PSD) is located well-proximal to the condylus dorsalis (Figure 11 A: 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 11 C: MECR), (3) the larger palmar attachment scar on the cranial face adjacent to the dorsal margin is oval (4) and the smaller dorsal scar is located on the dorsal face of the processus. (5) In caudal view, the processus flexorius (Figure 11: PF) terminates proximal to the condylus ventralis (Figure 11 A: CV) but is prominent ventrally. (6) The sulcus scapulotricipitalis (Figure 11 B: SST) forms a shallow but broad notch roughly 2 mm wide on the caudal face. (7) The fossa olecrani (Figure 11 B: 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 11 B: SHT) is very shallow, and at 5.3 mm wide extends over half of shaft width of 9.7 mm at the same point. (9) The fossa m. brachialis (Figure 11 A: 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 tuberculum supracondylare dorsale. In contrast, the shaft width measures 10.1 mm at the same point. Within the fossa, the impressio 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 11 A: EV) is indistinct from the ventral margin and does not project ventrally past the processus flexorius. (12) Asingle distinct, shallow insertion scar is present on the ventrodistal section of the epicondylus ventralis, with a very faint and shallow 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 11 A: TSV) projects cranially but not ventrally from the shaft. (14) Ashallow insertion scar for the pronator superficialis is present just proximal to the tuberculum on the dorsal face. (15) The condylus dorsalis (Figure 11 A: 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 11 C: 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 distally by 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 and species 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.

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.

Subfamily indet. Gen. et sp. indet.

Remarks The fossil can be excluded from other raptor families on the following features:

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 the section of dorsal face caudal to the tuberculum supracondylaris and the epicondylus dorsalis, the sulcus humerotricipitalis width, the fossa m. brachialis length, the configuration of the insertion scars on the distal epicondylus ventralis, the position of the distal margin of the condylus dorsalis relative to that of the condylus ventralis in cranial view, the ventral projection of the processus flexorius, and the connectivity of the condylus ventralis and entepicondyle in cranial view. As the Archaehierax sylvestris specimen SAMA P. 54998 lacks a 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 the humerus size predicted for SAMA P. 54998 (see comparative measurements below).

Locality, stratigraphy and age 31 ° 07.568 ʹ S; 140 ° 12.737 ʹ 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.

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) 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.

Subfamily indet. Gen. et sp. indet.

The femur is consistent with accipitrids and has the following morphology. (Trait 1) The linea intermuscularis caudalis (Figure 12 C: 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 12 B: FPop) is shallow, deepening slightly towards the distal end immediately proximal to the condyles. (6) The attachment scar on the planum popliteum (Figure 12 B: PPAP) is positioned medially. (7) The impressio m. gastrocnemialis lateralis (Figure 12 D: IG) is large and shallow. (8) The epicondylus lateralis (Figure 12 A: EL) is short and very 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 these subfamilies in lacking a prominent crista supracondylaris medialis, the position and shape of the attachment point on the planum popliteum, and the weak projection of the epicondylaris lateralis. As the distal femur is not a highly diagnostic section of the accipitrid skeleton, and the distal femur is not preserved in Archaehierax 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 predicted from typical sexual dimorphism, which makes it unlikely the two are representatives of the same species (see comparative measurements below). 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 (see Appendix 1, Table S 2) and showed that the distal width of the humerus was between 80 % and 90 % of the proximal width of the humerus, while the distal width of the tibiotarsus was between 75 % and 110 % the distal width of the femur in extant accipitrids. If the bones of Archaehierax sylvestris had similar ratios, then it can be predicted 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 the isolated distal femur NMV P 222435 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 to be considerable and common in accipitrids (Brown and Amadon 1968; Marchant and Higgins 1993) and raises the possibility that these isolated fossils may belong to a smaller sex of the onespecies if they 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, the mass 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 are accurate, the femur represents a bird 46 – 67 % smaller than the skeleton 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. However, these mass predictions use different elements, limiting their comparability. Nevertheless, while considering it likely that at least two accipitrids are represented, we consider it unwise to describe the smaller as a second species when size would be the only distinguishing factor and their congeneric status cannot be assessed.

PCA analysis of limb measurements

Remarks The specimen can be excluded from the Pandionidae and Cathartidae 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.

Locality, stratigraphy and age 31 ° 11.237 ’ S 140 ° 13.944 ʹ E Ericmas Quarry, Lake Namba, Frome Downs Station, South Australia, Namba Formation, Ericmas LF, late Oligocene. Collected by T. Flannery, 7 / 4 / 83.

Material NMV P. 222435, distal left femur preserving intact distal end and 15.5 mm of shaft.

Description. Neither bone is diagnosable at the species level but both compare well with A. cooperi in size and shape.

Remarks. See above.

Material. USNM PAL 641996, pedal phalanx, entire, with the articular cotyla slightly crushed; collected in the 1990 s. USNM PAL 641983, ungual phalanx, entire; collected Sept 22, 1994.

Craspedorrhynchus tubulus Buteo jamaicensis (Gmelin) Craspedorrhynchus sp. Degeeriella fulva Buteo plagiatus (Schlegel) Craspedorrhynchus sp. Buteo swainsoni Bonaparte Craspedorrhynchus sp. Haliaeetus leucocephalus (Linnaeus) Craspedorhynchus platystomus Parabuteo unicinctus Temminck Degeeriella fulva Geranospiza caerulescens nigra (Du Bus) Craspedorrhynchus genitalis Rupornis magnirostris griseocauda Ridgway Craspedorrhynchus brevicapitis