Australotadorna, 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 : 428

GENUS AUSTRALOTADORNA GEN. NOV.

Type species: Australotadorna alecwilsoni sp. nov.

Diagnosis: Humerus more robust than other tadornines, ventral pneumotricipital fossa larger, and caudal margin of bicipital crest in ventral view forming a single plane from ventral tubercle to junction with shaft rather than forming a marked angle with the proximal section at near right angles to the shaft.

Etymology: For its inferred ancestral relationship to the shelduck Tadorna , and that it derives from Australia.

Description and comparison: Australotadorna gen. nov. shares with tadornines the above features and that the capital groove forms only a shallow notch in the proximal profile, not a deep one as in most oxyurines and all anatines. The ventral pneumotricipital fossa is large and, with its internal diameter at about 46% of proximal width, is broader than that of all other tadornines. It is highly pneumatic and thus differs from Miotadorna where bone struts fill the fossa inside of the median crest. The capital shaft ridge is better developed and farther separated from the dorsal tubercle than it is in Tadorna species , but is in this similar to Miotadorna from New Zealand. As in Miotadorna , it has the dorsal tubercle separated from the capital ridge by a flaring groove extending onto the dorsal surface. Alopochen differs with a dorsal tubercle about as wide as long, rather than elongate, and by the capital shaft ridge being more directed to the dorsal tubercle. The latter results from a deeper and broader dorsal pneumotricipital fossa that extends under the head. Chenonetta and Hymenolaimus , two genera often associated with tadornines, have a much wider dorsal pneumotricipital fossa with the capital shaft ridge more weakly developed and directed towards the dorsal tubercle. The well developed ectepicondylar prominence is better developed than in Tadorna but similar to the development in Miotadorna and Alopochen . The brachial fossa was secondly deepened distoventrally and did not extend closer than 3 mm of the dorsal shaft margin. Such a secondary deepened brachial fossa is seen in Miotadorna and Alopochen .