Palaelodus Milne-Edwards, 1863

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 : 79-80

Genus Palaelodus Milne-Edwards, 1863

The new species described here for NMNZ S.51258 is referred to Palaelodidae because of the following unique combination of characters derived from Lydekker (1891), L. Miller (1950), Švec (1981), and Baird & Vickers-Rich (1998) ( Figs 1 , 2 ): (1) the lateral tuberosity for the attachment of the retinaculum extensorium tibiotarsi is approximately circular and prominent, located laterally to the pons supratendineus (supratendinal bridge) and separated from the lateral margin of the bone and from the proximal margin of the incisura intercondylaris; (2) the intercondylar incision is deep, broadens proximally and extends into proximo-medial face of medial condyle; (3) the sulcus extensorius is located centrally on the shaft, is narrow (a third of shaft width) and deep; (4) the proximal end of the supratendinal bridge is widely separated from the medial margin of the shaft by a robust rounded ridge; (5) the supratendinal bridge is not elongate; (6) the condyli lateralis et medialis have deep tendinal pits just caudad of their cranial projections; (7) the distal margins of the lateral and medial condyles are distinctly notched; (8) the distal cranial part of the medial condyle is markedly inflated medially; (9) the trochlea cartilaginis tibialis has a prominent medial ridge; (10) the medial edge of the supratendinal bridge is excavated in a furrow separating it from the medial margin; (11) the intercondylar incision lacks a prominent distally directed articular facet for the eminentia intercotylaris of the tarsometatarsus, i.e. the “anterior intercotylar tubercle” of Švec (1981).

We note the following additional tibiotarsal characters that further define this family: (12) the medial attachment for the retinaculum extensorium tibiotarsi forms a low rounded zone on the medial side of the sulcus extensorius just proximal to the tendinal bridge; (13) the lateral and medial condyles lack significant projection caudad of the shaft; (14) in cranial view, the cranial part of the medial condyle is displaced medially such that it is entirely mesad of the supratendinal bridge resulting in a relatively wide notch between the condyles.

Of these characters, we consider character 1 an autapomorphy of the Palaelodidae : in no other birds is the lateral attachment of the retinaculum extensorium tibiotarsi a prominent, near circular, tuberosity: it is usually elongate and located near the margin of the extensor sulcus. Baird & Vickers-Rich (1998) used three of these characters to distinguish flamingos from palaelodids as follows (character number above to which these relate): intercondylar incision, shallower, not so deeply extending into proximo-medial face of medial condyle (2); distal tendinal pits shallower (6); notches in distal margins of lateral and medial condyles shallower (7). However, we found the expression of these characters variable intra- and/or interspecifically, and so treat them as synapomorphies of Phoenicopteridae and Palaelodidae , rather than as autapomorphies of Palaelodidae . Further, while Baird & Vickers-Rich (1998) stated that the distal opening of the extensor canal is rounded and narrow in Palaelodus but rounded and broad in flamingos, we find this difference to be inconsistent. While the combination of characters 1–14 is unique to palaelodids, apart from character 1, individually, all the other characters are either present convergently in some other families or are plesiomorphic in palaelodids.

Flamingos differ from palaelodids including the new species described below as follows: the lateral attachment of the retinaculum extensorium tibiotarsi is an elongate crest, linked to, or closely approaching, an elevated, distally directed articular facet for the intercotylar eminence of the tarsometatarsus; the medial attachment for the extensor retinaculum is a prominent crest on the ridge medially of the extensor sulcus; the extensor sulcus is wider and more laterally located; the medial bounding ridge is narrower; the supratendinal bridge is more elongate; the lateral and medial condyles project significantly caudad of the shaft; the distal anterior part of the medial condyle is not inflated medially; the medial condyle is not so far offset medially, so it lies distad and in line with the tendinal bridge, resulting in a narrower anterior notch between the condyles; the trochlea cartilaginis tibialis lacks a prominent medial ridge.

In other large birds with some similarity to palaelodids, the lateral attachment for the extensor retinaculum, if present, is not circular (e.g., ardeids, pelecanids, threskiornithids, and ciconiids), but more elongate, and in those birds with elongate tibiotarsi (e.g., species of Grus, Ciconia, Ardeotis ), the lateral attachment for the extensor retinaculum is always associated with an intercondylar tubercle, an elevated distally directed prominent facet for articulation with the intercotylar eminence of the tarsometatarsus, see character 101 of Mayr & Clarke (2003), which is presumed to act as a locking mechanism in the tibial-tarsal joint.

The fossil is referred to Palaelodus as it does not differ from members of this genus to any significant degree ( Cheneval, 1983a; L. Miller, 1950; Baird & Vickers-Rich, 1998). Megapaloelodus connectens A.H. Miller, 1944 is a much larger species and was distinguished by deeper distal notches in the medial condyle (L. Miller 1950). The European species P. goliath was referred to Megapaloelodus solely on size, and if Mlíkovský’s (2002) synonymy of Megapaloelodus with Palaelodus is accepted, then the family had only one globally-distributed genus during the Miocene.

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),