Palaelodus aotearoa, Worthy & Tennyson & Archer & Scofield, 2010

Worthy, Trevor H., Tennyson, Alan J. D., Archer, Michael & Scofield, R. Paul, 2010, First Record of Palaelodus (Aves: Phoenicopteriformes) from New Zealand, Records of the Australian Museum 62 (1), pp. 77-88 : 80-83

Palaelodus aotearoa n.sp.

Figs 1–3

Holotype. NMNZ S.51799, a distal right tibiotarsus, collected 10 February 2009 by the University of New South Wales, NSW, Australia / Canterbury Museum, Christchurch, NZ/ Museum of New Zealand Te Papa Tongarewa, Wellington, NZ expedition.

Diagnosis. A Palaelodus species within the size range of P. wilsoni and P. ambiguus ( Tables 1, 2) but tibiotarsus with a relatively broader shaft for its distal width, a less concave medial margin above the medial condyle, and a broader extensor sulcus that is more widely separated from the medial margin.

Etymology. For Aotearoa, a Maori name for New Zealand.

Measurements of holotype. Distal width 13.9 mm, craniocaudal depth of lateral condyle 13.7 mm, craniocaudal depth of medial condyle 14.8 mm, shaft width proximal side tendinal bridge 10.2 mm, minimum shaft width 7.5 mm, preserved length 81.6 mm.

Paratype ( Figs 2 , 3 ). NMNZ S.51258, a distal right tibiotarsus, collected 12 January 2008 by the University of New South Wales, NSW, Australia / University of Adelaide , South Australia/ Canterbury Museum, Christchurch, NZ/ Museum of New Zealand Te Papa Tongarewa, Wellington, NZ expedition .

Measurements of paratype. Distal width 13.7 mm, craniocaudal depth of lateral condyle 13.9 mm, craniocaudal depth of medial condyle 15.0 mm, shaft width proximal side tendinal bridge 9.7 mm, minimum shaft width preserved 9.1 mm, preserved length 25.0 mm.

Holotype locality. Bed HH 1b, 9.5–9.58 m above base of the Bannockburn Formation, Trench Excavation, foot of hill 50 m across terrace from river bank at 44.90780° S; 169.85844° E, Manuherikia River, Home Hills Station , Otago, New Zealand; ca. 10–15 cm thick sand & cobble layer; Fossil Record Number in the archival Fossil Record File of the Geological Society of New Zealand H41/f0103.

Paratype locality. Bed HH 1a, 6.88–7.0 m above base of Bannockburn Formation, main quarry at 44.907944° S, 169.858222°E, Manuherikia River , Otago, New Zealand ; Fossil Record Number in the archival Fossil Record File of the Geological Society of New Zealand H41/f88.

Stratigraphy/Age/Fauna. Bannockburn Formation, Manuherikia Group, Early Miocene (Altonian); 19–16 Ma; St Bathans Fauna.

Description and comparisons. Both NMNZ S.51799 and NMNZ S.51258 are stained black and have slightly worn edges to the condyles ( Figs 1 , 2 ), consistent with the transported and disarticulated nature of specimens in both deposits and are inferred to have been accumulated in the sublittoral zone. Their distal widths are within the size range for the Australian P. wilsoni and the European P. ambiguus , indicating a medium-sized palaelodid ( Table 1). To capture the observation that in P. aotearoa the shaft expands in width more gradually towards the condyles and is relatively wider than in other taxa, three different width measurements were taken ( Table 2). A standard least shaft width measurement, only ascertainable for NMNZ S.51799, was 53.9% of distal width in P. aotearoa , a ratio higher than the ratio of the means for the European palaelodid species, and higher than values for P. ambiguus ( CM specimens), or for P. wilsoni individuals. Secondly, we measured width and depth values ( SW 1 and SD1) of the shaft where the distance to the proximal side of the supratendinal bridge was half that to the distal end ( Table 2). Thirdly, we measured shaft width at the proximal end of the supratendinal bridge ( SW 2; Table 2). Values for SW2 relative to distal width ( SW 2/DW) of 57.7 and 62.8% in specimens of P. ambiguus ( Table 2) are about 7–9% greater than SW1/DW. Equivalent ratios for P. wilsoni (57–65%) are similar to those for P. ambiguus but less than the values of 70.7 and 73.4% for P. aotearoa . In summary, the tibiotarsal shaft of P. aotearoa is both relatively stouter than that of the European and Australian Palaelodus species and widens much more gradually towards the distal end, rather than abruptly to create a step in anterior view. Palaelodus aotearoa is substantially larger than P. pledgei , as revealed by the condylar width of the paratype tarsometatarsus SAM P. 27997 and a here referred distal tibiotarsus SAM P.42002.

Tentatively referred specimen. An additional probable phoenicopteriform specimen was found in 2008 in bed HH1a. NMNZ S.51257 is a fragment of the cranial part of a sternum ( Fig. 4 ), 23.2 mm wide and preserving the base of the carina, about 14 mm of the left and 11 mm of the right sulcus articularis coracoidei, and dorsally the medial part of the pila coracoidea. On this fragment the left coracoidal sulcus overlaps above the right sulcus medially, the coracoidal sulci are roughly in the same plane as the adjacent labrum internum, a spina externa is inferred by the presence of a preserved base, the ventral margin of the coracoidal sulci slope caudally rather than being near right angles to mid-line, the anterior margin of the pila coracoidea lacks a spina interna and has a broad central notch, and the carina has a broad base. The caudal margin of the pila coracoidea drops abruptly down onto the pars cardiaca, but little of this facies is preserved. Compared with other large carinate birds found to-date in the St Bathans Fauna, accipitrid sterna have a similar general form to the preserved fragment but differ with the anterior margin of the labrum internum forming a face at an abrupt angle to the adjacent coracoidal articular facet. Anseriforms and gruiforms, with the exception of Balearica (Mayr & Clarke, 2003) , which differs markedly in shape from the fossil, differ markedly in having non-overlapping coracoidal sulci. Other large birds that might be expected in the New Zealand faunas all differ markedly. Some phalacrocoracids are similar with overlapping coracoidal sulci, but differ trenchantly by much thinner dorsoventral depth and that the labrum internum is developed as a prominent cranially directed facet to receive an opposing facet on the coracoid. In pelecanids, large procellariiforms, such as Macronectes, Thalassarche , and Diomedia , and in most ciconiids, the coracoidal sulci do not overlap and, in all these taxa, the labrum internum forms a large facet as seen in phalacrocoracids. The fragment is very similar in shape to the only published image of a palaelodid sternum that we are aware of, a cranial sternal fragment attributed to Palaelodus [= Megapaloelodus ] goliath by Milne-Edwards (1867 –1871: plate 87). It appears to be of appropriate size for Palaelodus aotearoa , based on relative sizes of Phoenicopterus distal tibia and sterna, so we tentatively refer it to the new taxon.

distal (C), lateral (D), and medial (E) views. Abbreviations as in Fig. 1 . Scale bar = 1 cm.

Figures

Figure 1. The holotype distal right tibiotarsus NMNZ S.51799 of Palaelodus aotearoa, in cranial (A), lateral (B), medial (C), posterior (D), cranial (E), and distal (F) views. Numbers refer to characters given in genus referral. Abbreviations: ltRET, lateral attachment of retinaculum extensorium tibiotarsi; es, extensor sulcus; ii, intercondylar incision; mtRET, medial attachment of retinaculum extensorium tibiotarsi; lc, lateral condyle; mc, medial condyle; tb, supratendinal bridge. Scale bars, upper = 5 cm, lower = 1 cm.

Figure 2. The paratype distal right tibiotarsus NMNZ S.51258 of Palaelodus aotearoa, in anterior (A), posterior (B),

Figure 3. Distal tibiotarsi of Palaelodus species compared in cranial views: A, P. wilsoni SAM P.22706; B, Palaelodus sp. indet. SAM P.25151; C, D, P. aotearoa NMNZ S.51258; E, P. ambiguus, CM Av11396; F, P. wilsoni, SAM P.27973; and G, P. aotearoa NMNZ S.51799. A and F illustrate size range in P. wilsoni. Scale bar = 1 cm. Abbreviations as in Fig. 1.

Figure 4. Views of NMNZ S.51257 in dorsal (A), cranial (B, C), left lateral (D), and ventral (E) views.Abbreviations:pc, pila coracoidea; sac, sulcus articularis coracoideus; li, labrum internum; se, base of spina externa. Scale bar = 1 cm.