Australotadorna alecwilsoni, Worthy, 2009

Worthy, Trevor H., 2009, Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia, Zoological Journal of the Linnean Society 156 (2), pp. 411-454 : 429-432

SPECIES AUSTRALOTADORNA ALECWILSONI

SP. NOV. ( FIGS 5 , 6 )

Holotype: SAM P.43141 (formerly AMNH 11499 ), L humerus ( Fig. 5B, D, F ), reassembled from several fragments with plaster infill in areas of shaft so that distal end is distorted ventrally; dorsal margin of deltoid crest lost, a 7 by 5 mm hole in ventral part of intumescentia humeri, distal margin of bicipital crest worn, and craniodistally part of the shaft proximal to the attachment of the anterior ligament extending through the brachial fossa is lost; light brown in colour.

Diagnosis: As for genus. Etymology: For Alec Wilson, owner of Frome Downs Station who has freely allowed access to the fossil sites and helped palaeontologists over many years.

Type locality: Lake Pinpa (= Pine Lake ), 31° 8 ′ S, 140° 13 ′ E, Lake Eyre Basin , Callabonna (= Tarkarooloo) Sub-basin, SA , north-west side Pine Lake , near grid coordinates 317148 on the CURNAMONA (prov. ed.) sheet ( R. H. Tedford, pers. comm. 30 Aug 2006), collected by R . H. Tedford et al., 1971, collection code QMAM 74 .

Horizon: Stratigraphy/Age/Fauna: Namba Formation, Late Oligocene 24–26 Mya, Pinpa LF.

Distribution: Late Oligocene (24–26 Mya): Lake Pinpa, Namba Formation, Pinpa LF; possibly Lake Palankarinna, Etadunna Formation (see below).

Measurements of holotype: TL = 132.4 mm (as preserved bent), estimated restored TL = 134 mm, PW (maximum from dorsal tubercle) = 28.7 mm, SW = 10.2 mm, DW = 22.4 mm, depth dorsal condyle = 12.6 mm.

Paratype: Coracoid ( Fig. 6 ): SAM P.43137 (formerly AMNH 11497 ), cranial part R coracoid ( Fig. 6I ), Lake Pinpa, north-west side near CURNAMONA (prov. ed.) sheet grid co-ordinates 317148, R. H. Tedford, pers. comm. 30 Aug 2006, collection code QMAM 65 , R. H. Tedford et al., July 1971, Namba Formation, Pinpa LF. Measurements – preserved length = 38 mm, length humeral facet = 15 mm, SW = c. 7.5 mm .

Description and comparison

Humerus: As for genus.

Coracoid: SAM P.43137 preserves only the dorsal half of the cranial end so lacks the tip of the acrocoracoid, the ventral clavicle facet and the ventral half of the supracoracoidal sulcus. It is of appropriate size for Australotadorna , given the size of the humerus SAM P.43141. It has the following features: deep circular scapular cotyla, c. 7 mm in diameter; short supracoracoidal sulcus not undercutting the humeral facet; ridge separating supracoracoidal sulcus from humeral facet relatively short, broad and rounded; shallow fossa with small pneumatic foramina adjacent to the scapular cotyla on sulcus side of this ridge; dorsal clavicle facet markedly overhangs sulcus as sharp crest with pneumatic foramina under it; procoracoid short and robust, although tip lost; procoracoid lacking a foramen in it, although insufficient of the shaft, remains to determine if it had a notch as seen in Cereopsis ; supracoracoidal sulcus extended as a groove along ventral side of procoracoid; ventral facies apparently flattened adjacent procoracoid, not very deep as in Cereopsis .

Although SAM P.43137 is of similar size to coracoids of Anseranas , it differs as follows: it lacks a procoracoidal foramen; it has a sharp dorsal lobe of the clavicle facet and pneumatic foramina in the supracoracoidal sulcus penetrating the acrocoracoid (both lacking in Anseranas ). The pneumatic acrocoracoid suggests an affinity with anserines, but only Cereopsis has a similarly sharp overhanging dorsal clavicle lobe. Tadornines, e.g. Alopochen and Miotadorna also have pneumatic foramina under the clavicle facet, so their presence is a plesiomorphic feature. Whereas the fossil shares with Cereopsis a relatively broad, short, rounded ridge between the supracoracoidal sulcus and the humeral facet, a groove along the ventral side of the procoracoid is not seen in anserines but is in tadornines. The broad, rounded ridge craniad of the scapular cotyla differs from tadornines where it is narrower, but this may relate to the larger size of the fossil. Larger specimens of Miotadorna , e.g. NMNZ S.42315 have a short relatively inflated ridge approaching the condition seen in SAM P.43137. A shallow pneumatic fossa dorsally immediately craniad of the scapular cotyla in the fossil has its homologue in a small elongate pneumatic fossa on the supracoracoidal sulcus side of the ridge in tadornines, e.g. in Tadorna tadornoides and Miotadorna . The insertion on the shaft of the procoracoid is relatively shorter than in Tadorna and Miotadorna but breakage means its medial, ventral, and cranial extents are not determinable. In summary, SAM P.43137 is of appropriate size for Australotadorna and shares more features with tadornines than other groups of waterfowl, but it is distinguished by several apomorphies, such as a more circular scapular cotyla and shorter procoracoidal insertion. Their significance is obscure at present, but given that Australotadorna is several million years older than the next known tadornine, Miotadorna , such differences are likely to be plesiomorphic features.

Referred material: The following specimens are referred to Australotadorna alecwilsoni on the basis of their appropriate size and tadornine-like morphology. Coracoid ( Fig. 6 ): SAM P.24531, cranial part R coracoid ( Fig. 6G ), Tedford Locality, Lake Palankarinna, Etadunna Formation, Ditjimanka LF, Zone B. Measurements – SW = 5.8 mm, length humeral facet c. = 12.3 mm.

The specimen lacks the entire sternal blade, and the tip of the acrocoracoid including the clavicle facets. It has a standard anatid form: the scapular cotyla is circular and deep; procoracoid lacks a foramen; and the supracoracoidal sulcus does not have a secondary fossa below the humeral facet. Coracoids of Phoenicopteriforms, present in the Etadunna Formation, differ with a procoracoidal foramen. It is of similar size to coracoids of tadornines. The dorsal facies of the ridge leading from the humeral facet to the acrocoracoid is like that in SAM P.43137, short and broadly inflated. It is smaller than SAM P.43137; however, the size difference is within that seen in sexual dimorphism in modern anatids. SAM P.43137 is pneumatic below the dorsal clavicle facet but this cannot be determined in SAM P.24531. In summary, this specimen may be referred to Australotadorna alecwilsoni or a very similar taxon.

Carpometacarpus ( Fig. 6 ): All from Lake Pinpa, Site C, Namba Formation, Pinpa LF, collected by R. H. Tedford et al., 1971. AMNH 10728: pL carpometacarpus, PW = 16 mm. AMNH 10818, pL carpometacarpus ( Fig. 6B, D, E ), collection code QMAM 175, PW = 15.7 mm. AMNH 10864, worn pR carpometacarpus, collection code QMAM 175, PW = 14.6 mm.

These specimens preserve only the proximal half of the element. They are about the size of Tadorna tadornoides but have a shorter extensor process. They are tentatively referred to Australotadorna on the basis of size and that there is no evidence of another large anatid in the source fauna. They have the following features: shallow infratrochlear fossa, a deep cranial fossa, moderately deep cuneiform fossa, an elongate proximal synostosis, and the minor metacarpal is not grooved at the fornix. Only AMNH 10818 allows the morphology of the ligamental scars proximally on the dorsal surface. The proximal one is prominent, but a second, shallow and elongate distal scar usually found in tadornines is present only as an obscure elongate hollow, but polishing of the bone by windblown sand may have obscured its real form.

Scapula: UCMP 57156, R scapula, Lake Palankarinna, Tedford Locality Site 3, UCMP V-5762, R. H. Tedford 1957, collection code RHT#465, Etadunna Formation, Minkina LF, Zone A, Member 4, measurements – acromion to ventral margin of humeral facet = 14.7 mm, depth of collum scapulae (blade) = 5.9 mm. UCMP unreg., R scapula, Leaf Locality, Lake Abbreviations: SW, shaft width; CWD, caudal width distal condyle; HMC, height of medial condyle; DD, depth between distal condyles; F, female; M, male.

Ngapakaldi, UCMP V-6313, collection code RAS #5294, Wipajiri Formation, Early Miocene, Kutjamarpu LF, measurements – blade depth = 5.2 mm.

UCMP 57156 is missing most of the blade. It has the general shape of anatid scapulae, particularly a compressed dorsal margin to the blade, acromion extending craniad of tuberculum coracoideum, and the coracoid tubercle prominent of a line joining the humeral facet and acromion. It is distinguished from Anseranas and anserines by the lack of pneumatic foramina either laterally or medially. In size, it is similar to that of Tadorna tadornoides and thus larger than scapulae of Biziura , Oxyura , Dendrocygna , Malacorhynchus , Stictonetta , and Aythya and other anatines. UCMP unreg., worn and lacking most of the blade and the acromion, is similar to UCMP 57156, but preserves little of diagnostic value.

Tibiotarsus ( Fig. 6 ): SAM P.36762, dR tibiotarsus ( Fig. 6F ), White Sands/ SAM North, RV-7247, Lake Palankarinna, Etadunna Formation, Ditjimanka LF, Zone B, Member 6.

Of typical anatid shape, SAM P.36762 is smaller than tibiotarsi of Anseranas , but is slightly larger and has a stouter shaft than Tadorna tadornoides ( Table 3). It is thus smaller than anserines, e.g. Cereopsis , and larger than Biziura , Stictonetta , oxyurines, and all anatines. SAM P.36762 is also similar to tibiotarsi of Tadorna in qualitative features and differs from those of Anseranas as follows: short tendinal bridge; distal end with distal margin near right angles to the shaft (not sloped distally); medial condyle forming notch with shaft at proximo-anterior junction (rather than a wide angle); and medial prominence small and occluded by medial condyle in anterior view (large, protuberant). It differs from those of Dendrocygna by larger size and greater medial inflection of the medial condyle. As it has tadornine features it is tentatively referred to Australotadorna alecwilsoni .

Measurements: See Table 3.

Figures

Figure 5. Left humeri of tadornines in caudal (A, B), cranial (C, D) and ventral (E, F) views: A, C, E, modern T. tadornoides SAM B.39591; and B, D, F, Australotadorna alecwilsoni (SAM P.43141). The arrow points to the planar caudoventral margin of the bicipital crest compared to the angled margin in Tadorna. Scale bar = 10 mm. See main text for abbreviations.

Figure 6. Fossil tadornine bones compared with modern Tadorna tadornoides SAM B.39591. Tadorna tadornoides: A,C. proximal right carpometacarpus; and H, dorsal view cranial half coracoid. Fossils referred to Australotadorna alecwilsoni: B, D, E, proximal right carpometacarpus; F, distal right tibiotarsus SAM P.36762 in anterior view; G, cranial part right coracoid (SAM P.24531) in dorsal aspect; I, cranial part right coracoid (SAM P.43137) in dorsal aspect. Fossils referred to an undetermined tadornine from Alcoota: J, left radius UCMP 65985 in dorsal aspect; and right carpometacarpus NT P.2913 in K, ventral; L, dorsal; and M, caudal views. Scale bars = 10 mm. See main text for abbreviations.