Archaehierax sylvestris Mather, Lee, Camens and Worthy

Mather, Ellen K., Lee, Michael S. Y., Camens, Aaron B. & Worthy, Trevor H., 2021, An exceptional partial skeleton of a new basal raptor (Aves: Accipitridae) from the late Oligocene Namba formation, South Australia, Historical Biology 34 (7), pp. 1175-1207 : 7-22

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; Land distal R ulna; Land distal R radius; L carpometacarpus; LR os carpi ulnare; Los carpi radiale; Rmanual phalanges, proximal fragment MI.1, proximal fragment MII.1 and MII.2; Lmanual phalanges MI.1, MII.2 with distal end eroded, and MIII.1; LR proximal femur fragments; Rtibiotarsus 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 most large elements fractured into many roughly articulated pieces, presumably by expansion and contraction associated with the wetting 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 fromthe Greek world ‘sylvas’, meaning forest, and the Latin suffix ‘-estris’, meaning ‘belonging to’.

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 in reasonably good condition. Morphology of its rostral tip, tomial margin, rostral marginof 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 the rostrum 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 most accipitrids, spanning just over half the rostrum depth. (4) The ossified section rostral to the incisura ventromedialis is of small to moderate 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 fromthe adjacent lateral margin creating a false incision. Asmall fragment of bone preserved between the pars maxillaris palatini is interpreted as a displaced fragment of the processus maxillopalatinus. (6) Damage precludes ascertaining the presence/form of the fenestra 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 members of Elaninae , Perninae (except Chondrohierax uncinatus , which is sharper), Buteoninae , and Gypaetinae have similar or shallower angled tips.

The rostrum maxillare is overall most similarto 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 lateral side ventrally, the medial side of the processus oticus, and loss of the processus orbitalis. Preservation of morphological detail isbest medially. On the processus oticus, only about half of the capitulum squamosum is preserved and the dorsal half of the crista medialis is lost. Of the processus orbitalis, only the well-preserved base remains. Both thecondylus pterygoideus and medialisare intact, butthe entire condylus lateralis and caudal half of the condylus caudalis are lost.

(Trait 1) The processus oticus ( Figure 3D : POt) is short and broad leading up to the capitulum squamosum. (2) The capitulum squamosum ( Figure 3D : CS), as preserved is relatively small, and has 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 is set entirely in the ventral half of the quadrate, creating a gentle, shallow sloping arc between the base of the processus and the capitulum. (5) Alarge and deep foramen pneumaticum basiorbitale ( Figure 3C : FPB) is present between the processus orbitalis and the condylus pterygoideus. (6) Breakage prohibits assessing the status of 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 sulcusruns along the ventral margin of the crista to connect to the foramen pneumaticum caudomediale. (9) A distinct, deep foramen pneumaticum caudomediale ( Figure 3C : 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, with a pointed medial margin that extends further medially than the condylus pterygoideus. (12) The portion of the condylus caudalis ( Figure 3C : CC) preserved indicates a facet of a similar size to the condylus 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 of Milvus and Haliaeetus (Haliaeetinae) where it is narrow and indistinct. (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) ; and deep 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 defined pit) in all species, and apneumatic in all species except in Pernis and Haliaeetus .

The quadrate is overall most similar to that of species of 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 to the 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 the centre, 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 in cranial 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 the neural 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) Ashort but caudally prominent projection is present dorsal to each facet ( Figure 3H : FA), measuring 2–2.5 mm in width. (11) There is no evidence of a bridge enclosing the incisurae caudales arcus ( Figure 3F, H : PAC).

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 species of 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) Aspina 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, is noticeably expanded from the width of the pila carinae immediately dorsal to it (3.0). (6) The apex carinae is rounded, with no hooked projection 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 no small, dispersed pneumatic foramina present dorsally in the body of the 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 the spina 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) Apila 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 in membersof allsubfamilies except Aegypiinae . (8) Theapex carinaelies directly ventral to the base of the spina externa, or projects more craniad, in species in all subfamilies except for Gypaetinae and Aegypiinae . (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 is thus 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 of both sternal ends of the coracoids of SAMA P.54998 were recovered. They reveal the following:

(Trait 1) Aforamen nervi supracoracoidei ( Figure 4G : FoNS) is present 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) Alarge (6 mm wide) pneumatic foramen is present in the sulcus m. supracoracoidei ( Figure 4F : SMS). The width of the sulcus is approximately 14.5 mm fromthe 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 the aforementioned 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 the processus procoracoideus and triangular shaped. (7) The facies articularis humeralis ( Figure 4G : FAH) is 7.7 mm wide and 12.8 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 the medial face to partly enclose the triosseal canal. (10) The best preserved sternal-end fragment shows that the angulus medialis is acute, forming a 30–45° angle. (11) The medial side of the facies articularis sternalis is 6.5 mm wide at its broadest point, and shallow, 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 of the 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 from the 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/cranially of the tuberculum coracoideum. (7) Minimum dorsoventral depth of the collum scapulae ( Figure 4E : ColS) is 6.3 mm. (8) While the extremitas caudalis is broken off, the corpus scapulae is elongate 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 and immediately 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 the caput humeri, crus dorsale fossae, fossa pneumotricipitalis, and the incisura 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 significant breakage and fracturing of the bone surface in this specimen, which has resulted in the loss of the tuberculum dorsale, the ventral marginof 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 the left humerus, is shallow and lacks secondary deepening. (2) There is 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 and dorsal 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, is preserved in its entirety in the left specimen. Preserved length is 42.7 mm from the assumed position of the tuberculum dorsale to its 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 in a 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 and tuberculum 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.

The proximal humerus is overall most similar to that of species of 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 the ventral margin of the cotyla ventralis contiguous with the olecranon, 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 and condylus 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 quadrangular in shape with a flattened dorsal tip between parallel equal-length 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, and a ridge descendingventrodistally fromthe base of the processus cotylaris dorsalis dorsally, is shallow. (6) Distal to the incisura radialis 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 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 end of 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 and blunt, or rounded, in dorsal and ventral view, (10) with a 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) when viewed 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 fromthe caudal margin to the incisura tendinosa, in caudodorsal view. (12) The caudal marginof the condylus 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 and the 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 in ventral 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 in elanines, 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).

Radius ( Figure 6 (A, B))

In SAMA P.54998, the left radius is complete, preserving most features 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:

Atuberculum 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 has a 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 is shallow 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 N. percnopterus (Gypaetinae) , species of Gyps (Aegypiinae) , and H. 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 of Haliaeetinae 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.

Ithasthefollowing features, terminologyfrom Mayr (2014): (1) The distoventralprojection ( Figure 7G : DVP) issmalland 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 for the musculus extensor carpi radialis ( Figure 7H : ECR) is shallow, forming a gentle curve at about a 160° angle between the ventral and dorsal ends. (5) A broad, deep fossa covers most of the ventral half of the cranial face ( Figure 7H : CVFos), which is open towards the proximo-ventral corner. (6) Asecond smaller and deep fossa is present on the dorsal half of the cranial face ( Figure 7H : DVF), and is apneumatic and 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 caudalmargin of the faciesarticularis metacarpalis formsa convex continuous curve from the ventral margin to the dorsal margin.

The os carpale radiale is overall most similar to that of species of Elaninae and Buteoninae (see SI.2 for more detailed differential comparisons).

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) Adistinct 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 equal in cranial height towards the crus breve ( Figure 7J : CB) and the crus longus ( Figure 7J : CrL). (3) The proximodorsal corner of 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 the face and positioned ventrally adjacent to the proximal end of the crus longus. (5) The crus breve is slightly shorter (8.7 mm long) in the right specimen, than total length (9.4 mm) from the 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 the rest of the distal face by a distinct but low crista that extends dorsoventrally across the face from the caudal projection ( 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 the crus breve. (11) Avery shallow sulcus is seen running along 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 the dorsalcranial facein allsubfamiliesexcept Accipitrinae . (3) There isno notchontheproximalendof thecruslongusin allsubfamiliesexceptin 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 more detailed 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) Arounded ridge extending from the processus pisiformis to the trochlear rim separates the fossa infratrochlearis from (3) an extremely deep sulcus ( Figure 7A : SV) between the processus pisiformis and the processus extensorius. This sulcus is elongate and extends from the trochlea carpalis ( Figure 7B : TrC) to adjacent to the processus alularis ( Figure 7B : PA). (4) The fossa supratrochlearis ( Figure 7B : FS), which is caudoventrally positioned on 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 just distal 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 and apneumatic. (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 the processus 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 the 19.6 mm proximal width of the carpometacarpus. (10) The proximodorsal margin of the processus extensorius forms a sharp crista that 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 is positioned 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 is occupied by a shallow sulcus that is bound by the os metacarpale minus in its distal half. (15) The synostosal region distal to the processus alularis is wider craniocaudally than it is long dorsoventrally. (16) The intermetacarpal tuberosity ( Figure 7A : ITR), which is the scar for the insertion of the m. extensor metacarpi ulnaris has almost no caudal projection and is positioned well distal of the proximal 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 the os 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, the carpometacarpus has a proximal craniocaudal width that is equivalent to 25% of the total length, which is moderately gracile.

Extant accipitrid subfamilies differ as follows

(Trait 1) The fossa infratrochlearisis shallow, except in Perninae (deep in Pernis apivorus and Chondrohierax uncinatus , the latter also pneumatic) and Gypaetinae (deep). (19) The proximal section of 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 of species 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 and fragment 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 into a thin crista that continues along the length of the preserved bone. (3) Asmall tuberculum is present on the caudal margin of 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 bone narrows 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 of depression or sulcus. Only the proximal end of the MII.1 is preserved, 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 expands notably with the presence a shallow sulcus extending to the distal end. (11) On the dorsal surface, a low ridge is present at the proximal end, with a small but deep fossa set into the caudal side of it. (12) Asimilar fossa is also set into the caudal side of this ridge in proximal view, just distal of the articular facet. (13) The ventral face has a deep depression lacking pneumatic foramina just distal of the proximal end.

The manus bones are overall most similar to those of species of Perninae (see SI.2 for more detailed differential comparisons).

Femur ( Figure 8 (A, B))

In SAMA P.54998, only the caput of both femora has been preserved, 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 the proximal 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 preservesthebase of thecnemial crestsand the entirecrista fibularis, butdamageto thedistal end obscuresthedetails of 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 elevated tuberculum on the medial face, measuring 4.5 mm wide and 8.9 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 for the ligament that connected to the distal end of the fibula is approximately 34.5 mm long and extends distally along the lateral margin of the shaft, from 38 mm distal to the crista fibularis. (7) Adistinct linea is visible on the medial margin of the shaft that extends approximately 77.4 mm proximodistally fromthe 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 the sulcus 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 the long 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 caudal tuberculum 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 gradual and 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 well medial 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 the margins 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 scar in 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 the retinaculum 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).

Fibula

The proximal ends of the left and right fibulae are preserved in Archaehierax sylvestris gen. et. sp. nov. Craniocaudal depth is about 10.2 mm, while width is 3.7 (right) and 4.0 mm (left).

(1) Ashallow fossa is present in the cranial half of the proximal lateral face. (2) The caudal face has a very shallow depression just distal 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 preserved in 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 the bone. The lateral half is thus undistorted from just proximal to the foramen 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 all features, but the proximal half is so badly fragmented that nearly all identifying features are lost. Only the crista medialis hypotarsi is recognisable. The specimens reveal the following features:

(1) Thelength of the tarsometatarsus is about 66–75% of the length of 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 is moderately elongate among accipitrids. (3) The cotyla medialis ( Figure 9D : CtM) is deep and with a notably convex dorsal margin. (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, and so 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 the depth of the medial hypotarsal crista 17.8 mm. (8) In medial view, themedialhypotarsal cristahaslittle or nohook distally. (9) Thesulcus 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 lateral side 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 pairof distinctlyprojecting cristae, withthe 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 distance distally along the shaft. (16) The medial half of the proximal 40% of the shaft is highly compressed as it is in many accipitrids, forming a crista 1.3 mm thick. (17) The crista plantaris lateralis ( Figure 9G : CPL) is well-developed, extending from the hypotarsus to level with thefossa metatarsi I. (18) In lateral aspect the cristaplantaris lateralisis markedly projecting plantarly, deepest just proximal to mid-length. (19) The foramen vasculare distale ( Figure 9A : FVD) has a diameter of about 1.6 mm and is positioned close to the incisura intertrochlearis lateralis. (20) The fossametatarsi I ( Figure 9B : FMI) issetlargelyon the plantar 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 tothe fossa metatarsi I, toopen plantarly between thefacet in metatarsi Iand 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) areextremely wide comparedto in other Accipitridae . (24) From distal view, the trochleae are arched dorsally. All trochleae are higher than they 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 right specimen). (26) Trochlea metatarsi III ( Figure 9H : TIII) is located comparatively 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 profileindistal view, with a short, robustplantarprojection on itsouter margin 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 the lateral margin. (31) The flange on trochlea metatarsi II is moderately projecting plantarly, (32) while the flange on trochlea metatarsi IV is quite prominent and plantar oriented. (33) The distal extent of the trochleae metatarsorum II and III is roughly equal and surpass distally the 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 the fossa metatarsi Iin all observed species. (23) In all subfamilies, the incisura intertrochleae are relatively narrower and the autapomorphically wide incisura in the fossil is one of its most characteristic features.

The tarsometatarsus is overall most similar to that of species of Elaninae (although more elongate), Aquilinae and Circaetinae (see SI.2 for more detailed differential comparisons).

DigitI ( Figure 10A )

The os metatarsale Iin SAMA P.54998 is fairly robust, with the proximal end attenuated to a thin point. In dorsal and plantar view, the region immediately proximal to the medial side of the articular surfacefor I.1 isinflated, creatinga> 90° anglejustdistal of themidlength 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 as a shallowattachment point to roughly midway on the corpusdistally. 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 are very 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 in right 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 and II.3. The species in Haliaeetinae and Ictinia are notable for such fusion (see Jollie 1976). The phalanx II.1 is quite short compared to phalanx 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 the digit does not appear in the sampled elanine genera ( Elanus , Gampsonyx ), species of Hieraaetus (though the section before the articular end is swollen) or Spizaetus , but appears to a lesser degree in the pernines, gypaetines, circaetines, aegypiines, species of Aquila , and species of Haliaeetus .

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; the vertebrae – elanines; the sternum – aegypiines; the coracoid – aegypiines, accipitrines, and buteonines; the scapula – elanines; the humerus – elanines, aegypiines, aquilines, haliaeetines and buteonines; the ulna – circaetines; the os carpi radiale – elanines and buteonines; the os carpi ulnare - elanines, pernines, gypaetines and aquilines; the carpometacarpus - buteonines; the tibiotarsus – buteonines; and the tarsometatarsus – elanines (fossil is more elongate), 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 incisurae intertrochleae 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 Asites ( Travouillon et al. 2006) that onbiochronological 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 distinguished from Archaehierax sylvestris by the following characters: the distal marginof thepons supratendineus isangled 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 end of the shaft. Aquila bullockensis from themid-Miocene Camfield Beds (12 Ma) of Bullock Creek ( Gaff and Boles 2010; Megirian et al. 2010) was described from a distal humerus – which was not preserved in Archaehierax sylvestris . However, A. bullockensis is very much (>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 features on other bone elements that exclude close affinity with both Aquila and the Aquilinae , so conspecificity with A. bullockensis can be ruled 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 are found in North America and Europe. Nearly all of them are described from a single skeletal element, making assessment of relationships with Archaehierax sylvestris difficult. The late Oligocene – early Miocene accipitrids from North America, including the relatively complete Palaeoplancus sternbergi , are all 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 incisura intertrochleae of Archaehierax sylvestris , and the flange on the trochlea 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 is oriented more medially ( Milne-Edwards 1863, Plate 183, Figures 1-10 ).

Aviraptorlongicrus 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 of Accipitrinae , 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 the dorsal condyle ( Kurochkin 1968, Figure 1 ).

Three fossil accipitrids are known from early Miocene deposits of Europe;

Promilio incertus ( Gaillard, 1939) was described from a right tarsometatarsus 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 from a tarsometatarsus, tibiotarsus and carpometacarpus, is from Auvergne, France. It is larger than P. gervaisii . Compared to Archaehierax sylvestris , the incisura intertrochleae are narrow and the 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 less distinct 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 from a 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, Figures 5-10 ).

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).

Figures

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 Sub- Basin. Lake Pinpa Sites 11 and 12, Ericmas Quarry, and Wells Bog Site located by black squares.

Figure 2. Exemplar accipitriform skeleton, Pandion haliaetus cristatus, derived from an 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.

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 in caudal (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. Scale bars are 10 mm.

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 in ammonium 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.

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.

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.

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 on ventral facies; TrC, trochlea carpalis. Scale bars 10 mm.

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) and caudal (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, incisura intercondylaris; 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.

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 distal right 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.

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.

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.

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.

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 directionality of 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.

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.