Nambashag billerooensis, Worthy, 2011

Worthy, Trevor H., 2011, Descriptions and phylogenetic relationships of a new genus and two new species of Oligo-Miocene cormorants (Aves: Phalacrocoracidae) from Australia, Zoological Journal of the Linnean Society 163 (1), pp. 277-314 : 284-292

NAMBASHAG BILLEROOENSIS SP. NOV. ( FIGS 1 , 2 )

Holotype: SAM P.29079, right tarsometatarsus.

Diagnosis: A species of Nambashag about the size of P. carbo with the sulcus for the origin of M. flexor hallicus longus on the femur proximal to the trochlea fibularis shallow with little craniocaudal depth.

Etymology: After Billeroo Creek in South Australia, where many of the fossils described here were collected.

Type locality: White Sands Basin, Lake Palankarinna , South Australia, Australia. Collected by M. Fuller on 9.vii.1987 .

Horizon: Stratigraphy/age/fauna: Zone B, Etadunna Formation, Late Oligocene 24–26 Mya, Ditjimanka LF.

Distribution: Late Oligocene (24–26 Mya), South Australia, Australia: Lake Palankarinna, Etadunna Formation, Minkana LF, Zone A, and Ditjimanka LF, Zone B; Lake Pinpa, Namba Formation, Pinpa LF; Billeroo Creek, Namba Formation; Lake Yanda, Namba Formation, Yanda LF.

Measurements of holotype: Length 48.7 mm, proximal width 11.1 mm, proximal depth 15.4 mm, mid shaft width 6.1 mm, mid shaft depth 4.7 mm, maximum distal width 13.6 mm, width trochlea III 5.2 mm, depth trochlea III 6.6 mm, length of distal foramen 2.0 mm, distance foramen to intertrochear notch 4.1 mm.

Paratypes: Site 2 Billeroo Creek, Frome Downs Station , 31°06.205 ′ S, 140°13.912 ′ E, Namba Formation, Late Oligocene, all collected THW & A. Camens 5–6.vi.2007 – SAM P.32566, shaft R tarsometatarsus; SAM P32565, L tibiotarsus; SAM P.32567, L femur; SAM P.32568, R femur; SAM P.32569, proximal L humerus; SAM P.32571, distal R ulna; SAM P. 32574, L carpometacarpus; SAM P.32580, R quadrate; SAM P.32572, posterior part R side mandible; SAM P.32573, posterior part L side mandible; Site 7, 31°07.837 ′ S, 140°12.636 ′ E, Lake Pinpa , South Australia, Namba Formation, Late Oligocene, Pinpa LF – SAM P.43135, proximal L tarsometatarsus, collected THW et al. 29.v.2007 .

Referred material: Site 2, 31°06.205 ′ S, 140°13.912 ′ E, Billeroo Creek, Frome Downs Station, South Australia, Namba Formation, Late Oligocene, all collected THW & A. Camens 5–6.vi.2007 – SAM P.32570, fragment distal L humerus; SAM P. 32575–577, three cervical vertebrae; SAM P. 32579, R fibula; SAM P. 32578, distal R radius. Billeroo Creek , Frome Downs Station, collection data THR 1977–229 , grid 319151 CURNAMONA sheet (? = Site 2 Worthy & Camens) – MV P.222423, proximal R humerus; MV P.222422, proximal R ulna.

Lake Pinpa , Frome Downs Station, SA , Namba formation, Pinpa LF, Late Oligocene – SAM P.32581, L humerus in unjoined proximal and distal parts, Site 8, 31°08.167 ′ S, 140°12.636 ′ E, collected THW & Camens vi.2007; SAM P.43022, a very fragmented R humerus, Site 10, 31°08.088 ′ S; 140°12.622 ′ E, collected THW & Camens vi.2007; MV P.230791, distal R tibiotarsus, Lake Pinpa , immediately south of the east-west track across the floor of the lake, resting on the Namba Fm, collected Tom Rich et al. 4.vii.1980, THR 1980–16 (= PVR 80–1 ) .

Lake Palankarinna, SA, Etadunna Formation, Late Oligocene – SAM P.41275, distal L tarsometatarsus, Steve’s Site, south of Tedford Locality (RV-8447), Ditjimanka LF, Zone B, collected 6.vii.1987 ; SAM P.42008, very worn distal R humerus, White Sands Basin, Ditjimanka LF, Zone B, collected N.S. Pledge 11.viii.1995 ; SAM P.41264, proximal R ulna, White Sand Locality, Ditjimanka LF, Zone B ; SAM P41289, complete L coracoid assembled from a cranial end collected from Mother Lode (RV-8504) in ix.1992 and a sternal part collected at Neville’s Nirvana on 4.viii.1999 (these sites are 20 m apart, pers. comm., J. McNamara, South Australia Museum , 19.viii.2009) , Minkana LF, Zone A; UCR 16097, distal R ulna, Turtle South (RV-7252), Minkana LF, Zone A .

Lake Yanda, Yanda LF, Namba Formation, Upper Oligocene – MV P.222430, anterior sternum, MV P.222420, L quadrate.

Measurements: See Table 2.

Description: Numbers in parentheses refer to characters in Appendix 1.

Mandible ( SAM P. 32572, SAM P.32573; Fig. 2A, B ). The mandible, indeed the whole bill, is represented only by these two caudal fragments. The right fragment (P.32572) is more complete anteriorly with the os surangular preserved to and including the angulus mandibulae and the os prearticulare preserved to a few millimetres anterior of this point, but the caudal part of the cotyla lateralis, the crista transversa fossae, and the proc. mandibulae medialis are missing. The left fragment (P.32573) is less complete anteriorly, but the cotyla lateralis and crista transversa fossae are complete and it lacks the proc. medialis ( Fig. 2A, B ). Both specimens show that the crista intercotylaris is a prominent caudomedially directed boss, separated from the cotyla lateralis (23) typical of phalacrocoracids. A large tubercle is present dorsally at the anterior end of the cotyla lateralis (24): it is present in all phalacrocoracids, but is reduced and low in some taxa such as those included in Leucocarbo . Breakage obscures the form of the fossa caudalis, but the medial facies below the anterior end of the cotyla medialis is deeply concave (26). The fossa aditus canalis mandibulae was an extensive fossa extending close to the ventral margin of the mandible, which lacked a caudal pocket (27). The proc. coronoideus has a well-developed tuberosity dorsal to the anterior end of the fossa aditus canalis mandibulae, about 10 mm anterior of the tubercle adjacent to the cotyla lateralis (28).

Quadrate ( SAM P.32580, MV P.222420; Fig. 2C, D ). SAM P. 32580 has a maximum height of 16.2 mm and width of 11.1 mm and MV P.222420, a height of 13.8 mm. These agree with the general form of crown group phalacrocoracids with an obsolete proc. orbitalis, widely separated condyli medialis et lateralis with a deep notch between, condylus caudalis elevated c. 5 mm relative to the other condyles, the capitulum squamosum about twice as large as the capitulum oticum, from which it is separated by a shallow notch. The tubercle, laterally, below the capitulum squamosum is broken but its remaining extent indicates it would have been anteriorly prominent (21). Medially, a small foramen pneumaticum is present at mid height (22).

Humerus ( MV P.222423, SAM P.42008, SAM P.32569, SAM P.32581, SAM P.32570, SAM P.43022; Fig. 2E–G ). The available humeral fragments are similar to those of phalacrocoracids in their proportions and reveal the following features. The tuber. dorsale is discrete and elevated from the surrounding facies; the crista deltopectoralis is concave dorsally; there is a prominent margo caudalis directed towards the centre of the caput humeri and linked to the crus dorsale fossae. The incisura capitis is broad with a round ligamental attachment for the M. subscapu- laris ( Owre, 1967: 24) at its dorsal end abutting the end of the margo caudalis, resulting in the dorsal end of the incisura being elevated to enclose a sulcus in the middle of the incisura, which varies in depth intraspecifically. The insertion of the coracobrachialis posterior is a shallow round sulcus on the dorsal side of the tuber. ventrale. The fossa pneumotricipitalis extends deeply under the tuber. ventrale (31) and is floored by an osseous lamina that is penetrated by several small pneumatic foramina. The incisura capitis interrupts the proximal profile as a shallow notch (32). The sulcus lig. transversus extends ventrally from adjacent to the caput humeri as a shallow groove that in ventral view only makes a shallow notch less than half the depth of the crista bicipitalis, and whose ventral end is partly blocked by a thin osseous wall (33). The crista deltopectoralis in SAM P.32569 is 34.5 mm long and extends only 12 mm distal of the crista bicipitalis (34). The width of the ventral fossa pneumotricipitalis is greater than the width dorsally of the crus dorsale fossa to the base of the tuber. dorsale (35). The ventral facies immediately distal of the sulcus ligamentum transversus is convex, not with a distinct groove as seen in some phalacrocoracids (36). The impressio coracobrachialis is a broad and deep sulcus smoothly rising to the intumescentia humeralis ventrally, i.e. not emarginated by a distinct crest (37) that narrows distally (38). The tuber. supracondylare ventrale is directed cranially (39), rather than being rotated ventrally as in most phalacrocoracids. Although in the best preserved distal humerus ( SAM P.32581), the cranioproximal sides of both condyles are broken, the broken end of the proc. flexorius is equally ventrally prominent with the epicondylus ventralis indicating that when complete it would have been more prominent (40) as in all phalacrocoracids, but unlike Anhinga . The proc. supracondylaris dorsalis is a rounded prominence (preserved in SAM P.32570) located distal to the proximal margin of the condylus dorsalis (41), again as in phalacrocoracids and unlike Anhinga . The fossa M. brachialis extends diagonally from the dorsal margin of the shaft as a parallel sided impression distally to abut the tuber. supracondylare ventrale, where it is relatively deeper than proximal parts of the fossa (42). The proc. flexorius and condyli ventralis et dorsalis have a similar distal projection, and the fossa olecrani is broad and deep.

Ulna ( MV P.222422, SAM P.32571, SAM P.41264, UCR 16097; Fig. 2H, I ). The proximal fragments MV P.222422 and SAM P.41264 reveal that the proc. cotyla dorsalis is prominent cranially and, although about 4.0 mm long proximodistally, does not form a marked distally directed hook (43); the tuber. lig. collateralis ventralis is separated from the cotyla by a shallow groove, is not ventrally prominent of the cotyla (44), is elongate and separated from the cotylar margin (45), the attachment of the M. bicipitis below the cranial lip of the cotyla ventralis is elongate; the impressio brachialis is 26 mm long and undercuts the ventral facies in its proximal half; the incisura radialis is shallow, bound by a single elevated ligamental attachment aligned at about 45 degrees to the shaft axis and extending proximoventrally from the base of the cotyla dorsalis; the cranial facies is flat and roughly at right angles to the adjacent impressio brachialis; and the cranial intermuscular line is not prominent. The olecranon is broken, so its extent proximal to the cotyla dorsalis cannot be ascertained. The distal fragments SAM P.32571 and UCR 16097 reveal that the tuber. carpale is robust and shorter than crown phalacrocoracids, for example P. carbo , and is more like Anhinga ; the incisura tuber. carpale forms a distinct notch that is proximally offset from the sulcus intercondylaris in ventral view, more like Anhinga than Phalacrocorax ; the condylus ventralis ulnaris has a ventrally prominent tubercle at the distal margin of the depressio radialis whose cranial face is visible in ventral view, as in P. carbo ; the condylus ventralis ulnaris projects only slightly cranially of this tuberculum, rather than projecting cranially a distance equal to tuberculum width as in crown phalacrocoracids, e.g. P. carbo ; caudally, the condylus dorsalis has an oval sulcus in its cranial half from which the incisura tendinosa emanates, which is bound cranially by a more robust ridge compared with P. carbo (more like Anhinga ), but unlike both Anhinga and P. carbo , the most proximal part of this sulcus is terminated by a triangular prominence related to greater angularity of the shaft in Nambashag .

Carpometacarpus ( SAM P.32574; Fig. 2J ). This specimen preserves the complete length, but is missing the proc. extensorius, part of the ventral rim and cranial end of the trochlea carpalis, and the os metacarpale minus. The length of the proximal synostosis, between the proc. alularis and the spatium intermetacarpale, is longer (6.5 mm) than wide (4.5 mm) (47). The fovea carpalis caudalis is deep, short, and wide (width approximates length) (49). The width of the os metacarpale minus at the proximal synostosis is much less than that of the os metacarpale majus (50), but it is broken at the synostosis precluding the determination of whether it was grooved immediately distal to that point. The groove extending proximally from the spatium intermetacarpale is short and does not link to the sulcus cranial to the proc. pisiformis (52). The ventral rim of the trochlea carpalis joins to the shaft well distal to the proc. pisiformis (53) not adjacent to as in Anhinga .

Coracoid ( SAM P.41289; Fig. 2M, N ). Medial length 59.8 mm, maximum dorsoventral depth through facies artic. humeralis 9.7 mm, length from cotyla scapularis to tip of the proc. acrocoracoideus 20.1 mm. This generally well-preserved specimen, reassembled from two halves collected about seven years apart, lacks the entire proc. lateralis and the tip of the proc. medialis. The proc. acrocoracoideus only slightly overhangs the ventrolateral facies (55), not markedly so as in Anhinga . It has the pelecaniform apomorphy of the facies artic. clavicularis being ovate and on the ventral facies of the proc. acrocoracoideus (56), but this facies is similar to those of phalacrocoracids in being craniosternally elongate (8.1 by 6.6 mm), rather than lateromedially elongate as in Anhinga . The sulcus M. supracoracoidei lacks pneumatic foramina and does not undercut the ridge linking the facies artic. humeralis and the proc. acrocoracoideus (57), as it does in crown group phalacrocoracids. The area between the facies artic. humeralis and the tip of the proc. acrocoracoideus is excavated in a shallow parallel-sided groove (58), rather than a deep groove narrowing ventrally because of a ridge running from the tip, as in crown group phalacrocoracids. The proc. acrocoracoideus does not extend medially over the sulcus M. supracoracoidei, is deeper than wide, and the facies artic. humeralis is elongate (11.3 ¥ 5.3 mm) and projects laterally. The cotyla scapularis has a shallow but distinct sulcus, rather than being flat or convex as in crown group phalacrocoracids (59). This depression is bound by a row of pneumatic foramina separating the cotyla from the sulcus M. supracoracoidei. The articular facet is continuous with the facies artic. humeralis medially and, laterally, extends onto the proc. procoracoideus. A distinct, cranially directed prominence defines the mediodorsal margin of the cotyla, which itself is directed craniolaterally. This contrasts with crown group phalacrocoracids, where the cotyla is more elongate, directed more laterally, and somewhat sloped sternally. The proc. procoracoideus is stout, short, not extending above the cotyla, and lacks a foramen nervi supracoracoidei. The shaft is narrow and elongate as typical of phalacrocoracids. Ventrally, the linea muscularis ventralis is prominent, laterally enclosing a shallow sulcus, and straight, not recurved medially near the sternal end as in P. carbo , and joins the facies artic. sternalis no less than 13 mm from the angulus medialis. As it is most improbable that this articular facet was 26 mm wide, it is inferred that the linea joins the facet in its lateral half (60). The facies artic. sternalis dorsalis has a prominent boss 9.0 mm long and, maximally, c. 3 mm wide, which is estimated to occupy less than half the width of the sternal articulation (61). The facies artic. sternalis ventralis is worn but lacked a prominent lip such as seen in P. carbo , and thus is more like M. melanoleucos in this feature.

Sternum ( MV P.222430). This tentatively referred anterior fragment preserves part of the coracoidal sulci and the base of the carina, revealing a wide notch between the labri interni and so the absence of a spina interna rostri, and a wide flattened spine externa.

Femora ( SAM P. 32567, P. 32568; Fig. 2O–Q ). There is damage to the femoral ball and the condylus medialis in P.32567, and P.32568 has the distal parts of both condyles lost, but the following features are determinable. The dorsal pretrochanteric surface is excavated in a shallow sulcus below the facies artic. antitrochanterica (69). Distally of this sulcus, the insertion for the M. psoas forms an obvious oval area centred on the pretrochanteric facies, rather than being located close to the medial side (70). The insertion for the M. femorotibialis internus on the medial facies is ovate and not raised into a prominent tubercle (71). The crista trochanteris is slightly shorter than proximal width and is low. The femoral ball does not extend proximal to the crista trochanteris. The linea intermuscularis cranialis connects to the medial side of the crista trochanteris smoothly, without a distinct rugosity as in most phalacrocoracids (72). The lateral facies between the impressions for the M. obturator internus and the M. ilio-trochantericus medialis ( Owre, 1967) is smooth with no deep sulcus (73), such as seen in Leucocarbo chalconotus . Caudally, there is a broad shallow fossa adjacent to the facies artic. antitrochanterica (74). There is a short ovate rugosity slightly proximal to the nutrient foramen for the insertion of M. caudofemoralis, which is separated by c. 5.0 mm in both specimens from the crista for M. flexor ischiofemoralis more proximally (75). The latter insertion extends around onto the lateral facies. This arrangement is seen in Anhinga and other pelecaniforms, but not in any phalacrocoracids. In Microcarbo taxa, the insertions for M. caudofemoralis and M. flexor ischiofemoralis are separated by a short gap and in remaining crown group taxa the insertions form a continuous crista, so the wide separation of the insertions in Nambashag is plesiomorphic. The tuber. M. gastrocnemialis lateralis is located distinctly proximal to the condylus fibularis and is elongate at c. 7.0 mm long (76). The origin of M. flexor hallicus longus ( Owre, 1967) forms a small shallow sulcus just proximal to the condylus fibularis, which does not extend as far as the tuber. M. gastrocnemialis lateralis and is restricted to the caudal half of shaft depth, but which is emarginated cranially by a low crest (77). The fossa poplitea is broad and shallow. The caudal parts of both the condylus lateralis and the condylus medialis are not preserved. Although the shaft is caudally deflected slightly in its distal third of length, as it is to varying degrees in all phalacrocoracids, it was definitely not markedly caudally rotated as in some modern phalacrocoracids (80). The tuber. M. gastrocnemialis medialis is triangular, abuts the medial margin of the shaft, is proximally separated from the condylus medialis (82), and is integrated as a single tuberosity with the crista supracondylaris medialis (81), rather than the latter passing mesad of it. Despite the distal parts of the condylus medialis not being preserved, the remaining parts suggest that the condyle did not extend mesial to the shaft (83). Overall, the femora are relatively elongate compared to phalacrocoracids and their length exceeds the length of associated tarsometatarsi (84), unlike the situation in most phalacrocoracids where femur length is equalled or exceeded by tarsometatarsi length.

Tibiotarsus ( SAM P.32565, MV P.230791; Fig. 2K, L ). SAM P.32565: Total length 89.6 mm, length from proximal articular surface 84.6 mm, mid shaft width 6.96 mm, mid shaft depth 5.0 mm, distal width 10.9 mm, length fibular crest 23 mm, maximum width of shaft through fibular crest 9.5 mm. This bone is relatively robust. The crista cnemialis lateralis has its tip thickened and formed on a plane with the rest of crest (85), as in Anhinga , not displaced anteriorly of the crista as in all phalacrocoracids; slightly so in Microcarbo and P. neglectus , but markedly so in all other Phalacrocorax species. The crista cnemialis lateralis is not greatly elongated proximally, so that the tip proximodistally overlaps the area interarticularis (86). The crista cnemialis cranialis is prominent anteriorly and extends down the medial margin of the shaft overlapping the fibular crest. The fossa flexoria has a distinctly broad lateral part with the medial part obsolete (87). The impressio lig. collateralis medialis is not medially prominent and comprises two distinct impressions (88), one for the insertion of M. flexor cruris lateralis towards the caudal side of the medial facies and, well separated from the latter, a more elongate one for M. flexor cruris medialis on the anterior margin ( Owre, 1967: 80–81). This is similar to the state in Microcarbo and P. gaimardi , but differs from all other phalacrocoracids where they are both in the anterior half of shaft depth and close together. Some breakage and loss of the facies artic. lateralis obscure the structure, but the length from its distal side to the crista fibularis is about 10.5 mm, much greater than shaft width at this point (7.0 mm) (89). The epicondylus medialis forms a prominent tuberosity on the medial facies (90). The tuber. retinaculi M. fibularis extends about 5.5 mm proximal of the pons supratendineus and is prominent laterally with no anterior elevation (contrasts with Microcarbo species that are prominent anteriorly) so that the lateral margin of the sulcus extensorius is separated from the lateral margin of the tuberculum by a rounded ridge (91). The condylus medialis has slightly greater anterior projection than the condylus lateralis, but its projection anterior to the incisura intercondylaris is much less than the depth posterior of that point (92). The distal extent of the condyli medialis et lateralis are equal (93), unlike all crown group phalacrocoracids where the condylus medialis has markedly more distal extent. The sulcus extensorius is positioned laterally of centre on the shaft (94), and its width at right angles to the axis on the proximal side of the pons supratendineus is 3.8 mm, much wider than the proximodistal 2.1 mm length of the pons supratendineus (95). The shape of MV P.230791 conforms to the above in all aspects.

Tarsometatarsus ( SAM P.29079, P.43135, P.41275, P.32566; Fig. 1 ). The plantar depth of the proximal end is significantly greater than proximal width (99) as in all members of Phalacrocoracidae , but contrasting with Anhinga , Fregata , Sula , and Morus . Nambashag billerooensis has an arrangement of tendinal canals similar to that seen in all phalacrocoracids and which differs from anhingids. The tendinal canal for M. flexor hallicus longus (fhl) is the most laterally and dorsally placed of the three main canals and is closed plantarly (97) by a osseous bridge that bears a shallow sulcus for more plantar tendons; seen in SAM P.43135, broken in SAM P.29079. The canal for M. flexor digitorum longus (fdl) lies medially to and slightly plantar of fhl adjacent to the large robust crista medialis plantaris (as in all phalacrocoracids) and is not quite closed in its lateroplantar zone (96). The tendinal canal for M. flexor perforatis digiti 2 (fp2) is a broadly open laterally directed groove located plantar of and slightly laterad of fdl (98) unlike in Anhinga where it is enclosed. The plantar facies of the hypotarsus is a flattened oval plate forming a distally directed hook in lateral view (102). The eminentia intercotylaris has a similar proximal extent as the plantar cotylar margins (100), rather than exceeding them as in Anhinga . The groove marking the track of the M. extensor hallicus longus over the dorsal medial margin of the shaft is 7.6 mm wide (measured as length down shaft), which is significantly greater than shaft width (101), unlike all crown phalacrocoracids where the trace width is equal to or less than shaft width. The fossa parahypotarsalis medialis is obsolete (103), but a small crest lies on the medial facies extending about 7 mm proximally from the groove for M. extensor hallicus longus. The impressiones retinaculi extensorii are low crests, a medially placed one medial to the foramen vascularis proximalis medialis and the other on the dorsomedial margin of the sulcus extensorius with the intervening surface flat and sloping and much elevated above the base of the sulcus extensorius (104). The tuberositas M. tibialis cranialis comprises two discrete tuberosities that are lateromedially adjacent to each other and separated by a shallow groove, with both lying immediately distal to the foramina vascularia proximalia. The sulcus extensorius extends distal to mid length but is separated from the foramen vasculare distale by c. 7 mm. In anterior view, the lateral margin is slightly concave distal to the foramina vascularia proximalia (105), not planar as in Anhinga and Microcarbo taxa. In lateral view, the sulcus for M. abductor digiti IV is broad and bound dorsally by the crista plantar lateralis that is parallel and close to the dorsal facies over the whole shaft length (106), as in Anhinga and Microcarbo species , but unlike all other phalacrocoracids where the crista plantar lateralis is more widely separated from the dorsal surface at mid length than it is either more proximally or more distally. The shaft is wider than it is dorsoplantarly deep (107). Distally, trochlea metatarsi II has equal distal extent as trochlea metatarsi IV, with both ending slightly proximal to trochlea metatarsi III. Trochlea metatarsi II, however, ends only slightly proximal to trochlea metatarsi III (108), rather than distinctly so as in most phalacrocoracids other than Microcarbo . Similarly, trochlea metatarsi IV ends only slightly proximal to trochlea metatarsi III (109), not markedly so as in Anhinga and Microcarbo . Trochlea metatarsi IV is longer than it is wide at its base (110). The foramen vasculare distale is relatively small (2.04 mm long) and well separated from the incisura intertrochlearis lateralis by 4.12 mm (111), more like the small foramen seen in Leucocarbo taxa than in other phalacrocoracids. The fossa metatarsi I is obvious in plantar aspect and c. 9 mm long, but it barely impinges on the medial profile of the shaft in anterior view.

Comparisons with fossil taxa

Borvocarbo guilloti is much smaller than N. billerooensis and distinguished by a circular and deeply concave cotyla scapularis and a convex, not flattened, facies articularis clavicularis ( Mourer-Chauviré et al., 2004).? Borvocarbo stoeffelensis is also small, and shares several plesiomorphic features with Nambashag , e.g. distal end of the proc. cotylaris dorsalis on the ulna not forming a hook, the omal portion of the facies artic. humeralis directed essentially laterally rather than dorsolaterally with its ventral margin projecting laterally as in crown group phalacrocoracids, the thickened tip of the crista cnemialis lateralis on the tibiotarsus forming a plane with the rest of the crest (character 9 in Mayr, 2007) and, on the tibiotarsus, the condylus medialis protruding only slightly distal to the condylus lateralis. It is distinguished from Nambashag by the shorter crista bicipitalis, which meets the humeral shaft at a steeper angle (as in Oligocorax and Nectornis ), a deeper cup to the cotyla scapularis on the coracoid ( Mayr, 2007: fig. 5A), and the sulcus extensorius being located centrally on the tibiotarsus ( Mayr, 2007).

? Borvocarbo tardatus is of similar size to N. billerooensis but is distinguished by a less hooked proc. cotyla dorsalis on the ulna, the tip of the crista cnemialis lateralis being displaced cranially of the crista, a centrally located sulcus extensorius, a more proximodistally elongate and more horizontally aligned pons supratendineus, and the condylus medialis projecting more distally on the tibiotarsus ( Göhlich & Mourer-Chauviré, 2010: figs 4, 5).

Oligocorax littoralis , the only species in the genus, is of similar size to N. billerooensis . The coracoid has the scapular articular surface forming a mediodistally directed point on the proximal side of the proc. procoracoideus and the proc. procoracoideus is robust and globular (fide Mourer-Chauviré et al., 2004), which are features shared with N. billerooensis , but it differs by having the cotyla scapularis more deeply concave, the facies artic. clavicularis much more craniosternally elongate, and the linea intermuscularis ventralis located more laterally (Milne-Edwards, 1867–71b: pl. 43, figs 5–7). The humerus differs from that of Na. billerooensis by its relatively narrower impressio coracobrachialis, which is more sharply defined on its ventral margin and a relatively shorter crista bicipitalis (Milne-Edwards, 1867–71b: pl. 44, figs 1, 2). The ulna of O. littoralis shares with Na. billerooensis the absence of a distal hook to the cotyla dorsalis (Milne-Edwards, 1867–71b: pl. 44, figs 6, 7), distinguishing both from crown group phalacrocoracids. The tibiotarsus of Oligocorax has the proximodistal width of the condylus medialis narrower than in extant Phalacrocorax species (see Milne-Edwards, 1867–71b: pl 42, fig. 7), and the crista medialis hypotarsi on the tarsometatarsus protrudes less plantarly, and the distal margin of the crista medialis hypotarsi is near vertical rather than sloping distally as in Phalacrocorax (Milne-Edwards, 1867–71b: pl. 42, fig. 7; Mayr, 2001). The tarsometatarsus of O. littoralis is further distinguished from that of Na. billerooensis by the tendinal canal for M. flexor hallicus longus (fhl) being plantarly open (Milne-Edwards, 1867–71b: pl. 44, fig. 8).

Both Nectornis species are much smaller than Na. billerooensis . Both are similar in having a slightly concave cotyla scapularis, but differ from Na. billerooensis and all crown group phalacrocoracids by: the humerus having a short crista bicipitalis with a very convex medial profile (caudal view) and that abruptly, not gradually, joins to the shaft; the scapular articular surface of the coracoid extends over the proximal surface of the proc. procoracoideus and forms a mediodistally directed point; and the proc. procoracoideus is more pointed (Mourer-Chauviré, in Paicheler et al., 1978; Cheneval, 1984). In Nectornis , the trochlea metatarsi II extends as far distally as trochlea metatarsi III, as in Na. billerooensis and Microcarbo species , but unlike Phalacrocorax species , in which it is shorter ( Mayr, 2001; data herein). Nectornis anatolicus differs from Na. billerooensis by having a foramen nervi supracoracoidei, a hollow in the sulcus M. supracoracoidei that undercuts the ridge leading from the facies artic. humeralis to the acrocoracoid tip (Mourer-Chauviré, in Paicheler et al., 1978).

The Phalacrocorax intermedius humerus appears to have a more projecting tuber. dorsale than Na. billerooensis , which may relate to a more cranially directed crista deltopectoralis (Milne-Edwards, 1867– 71b: pl. 43, figs 8, 9).

Limicorallus saiensis is a very small species based only on a distal humerus of distal width 8.6 mm ( Kurochkin, 1968), which apart from size, differs from Na. billerooensis by a ventrally inclined tuber. supracondylare ventrale ( Mlíkovský & Švec, 1986) and also by the fossa m. brachialis not extending alongside the tuber. supracondylare ventrale, as judged from the depiction in Kurochkin (1968).

? Limicorallus carbunculus is the smallest fossil cormorant taxon, with a tarsometatarsus two-thirds the length of that for M. pygmaeus , and was referred to cf. Phalacrocoracidae ( Mayr, 2009) . It differs from Na. billerooensis and all crown group phalacrocoracids by: (1) having the sulci for the tendons of M. flexor perforatus digiti II and M. flexor hallicus longus on the same dorsoplantar plane and separated by a low ridge, rather than the former being displaced plantarly and separated from the latter by a more protruding crista; (2) having the lateroplantar edge adjacent to these sulci not protruding as strongly proximally; (3) having the furrow for the tendon of M. extensor hallicus longus passing over the dorsomedial margin of the shaft relatively closer to the proximal end. However, as in Na. billerooensis , this furrow is wide, such that its breadth, as measured where it crosses the medial shaft margin, is wider than the shaft width. Nambashag billerooensis shares with? L. carbunculus , Microcarbo taxa, and Anhinga a deep sulcus for M. abductor digiti IV, such that it extends close to the dorsal shaft margin near mid length, although in Na. billerooensis and all extant phalacrocoracids this sulcus extends further proximally than in? L. carbunculatus , being excavated closer to the cotyla lateralis. In addition, Na. billerooensis shares with? L. carbunculatus the plesiomorphic features of a straight lateral shaft margin (concave in crown group phalacrocoracids more derived than Microcarbo ), relatively small foramen distale such that its length is less than half the length of the bone separating it from the incisura lateralis (greater than half in extant phalacrocoracids except in Leucocarbo taxa), and a distally elongate trochlea metatarsi II with near equal distal extent as trochlea metatarsi III (relatively shorter in crown group phalacrocoracids more derived than Microcarbo ).

The remaining six Miocene fossil cormorants all derive from the Late Miocene and were described in Phalacrocorax , in which genus they remain unchallenged ( Table 1; Bocheński, 1997; Mlíkovský, 2002). Most are known from sparse remains, so afford little comparison. Phalacrocorax femoralis differs from Na. billerooensis by the derived condition of a distally elongate condylus medialis to the tibiotarsus even though it shares the plesiomorphic condition of a femur longer than the tarsometatarsus. Phalacrocorax marinavis was considered most similar to P. carbo by Shufeldt (1915) and has the hooked proc. cotylaris dorsalis (= radial process) on the ulna characteristic of crown group phalacrocoracids and a large foramen distale on the tarsometatarsus as seen in, e.g. P. carbo . The remaining taxa have not been examined, but being from the Late Miocene are likely to belong in Phalacrocorax .

Figures

Figure 1. Holotype tarsometatarsus of Nambashag billerooensis sp. nov. SAM P.29079, in dorsal (A), plantar (B), medial (C), lateral (D), and proximal (E) views. Plantar wall of fhl broken in this specimen. Scale bar = 10 mm. Abbreviations: cl, cotyla lateralis; cm, cotyla medialis; ehl, groove for the M. extensor hallicus longus; ei, eminentia intercotylaris; fdl, tendinal canal for M. flexor digitorum longus; fhl, tendinal canal for M. flexor hallicus longus; fmI, fossa metatarsi I; fp2, tendinal canal for M. flexor perforatis digiti 2; fpm, fossa parahypotarsalis medialis; fvd, foramen vasculare distale; fvp, foramen vascularis proximalis lateralis; ire, impressiones retinaculi extensorii; saIV, sulcus for M. abductor digiti IV; tmt, tuberositas M. tibialis cranialis; II, trochlea metatarsi II; III, trochlea metatarsi III; IV, trochlea metatarsi IV.

Figure 2. Nambashag billerooensis sp. nov.: left ramus of mandible (SAM P.32573) in dorsal (A) and medial (B) views; right quadrate (SAM P.32580) in cranial (C) and caudal (D) views; humeri, left (SAM P.32581) in cranial view (E), proximal left (SAM P.32569) in cranial (F) and caudal (G) views; ulnae, proximal right (SAM P.41264) in ventral aspect (H), distal right (UCR16097) in dorsal aspect (I); left carpometacarpus (SAM P.32574) in dorsal aspect (J); left tibiotarsus (SAM P.32565) in cranial (K) and proximal (L) aspects; left coracoid (SAM P.41289) in dorsal (M) and ventral (N) aspects; left femur (SAM P.32567) in cranial (O), caudal (P), and lateral (Q) aspects. Scale bars = 10 mm. Abbreviations: ccl, crista cnemialis lateralis; cd, crista deltopectoralis; ci, crista intercotylaris; cl, cotyla lateralis; co, capitulum oticum; coc, condylus caudalis; col, condylus lateralis; com, condylus medialis; cs, capitulum squamosum; ct, crista transversa fossae; fac, facies artic. clavicularis; fb, fossa M. brachialis; fcc, fovea carpalis caudalis; fp, fossa pneumotricipitalis; ic, impressio coracohumeralis; Mc, insertion for M. caudofemoralis; mc, margo caudalis; Mfhl, origin for M. flexor hallicus longus; Mfi, insertion for M. flexor ischiofemoralis; Mp, insertion for M. psoas; omm, os metacarpale minus; pa, proc. acrocoracoideus; pcd, proc. cotyla dorsalis; po, proc. orbitalis; pp, proc. procoracoideus; ps, pons supratendineus; sc, cotyla scapularis; tc, tuber. carpale; tcv, tuber. lig. collateralis ventralis; tsv, tuber. supracondylare ventrale; tub, tuberculum.