Climacteris sp.

Nguyen, Jacqueline M. T., 2016, Australo-Papuan treecreepers (Passeriformes: Climacteridae) and a new species of sittella (Neosittidae: Daphoenositta) from the Miocene of Australia, Palaeontologia Electronica 11 (1), pp. 1-13 : 6-8

Climacteris sp. indet.

Figure 3.1, 3.3, 3.5

Material. QM F36276, a distal left tibiotarsus. Measurements (mm). Preserved length 4.9; distal width 2.9; length of condylus lateralis ca 1.9; length of condylus medialis ca 2.0; depth of condylus lateralis>2.4; depth of condylus medialis>2.3.

Locality and Horizon. Dirk’s Towers Site, Riversleigh World Heritage Area, northwestern Queensland, Australia; Faunal Zone B (early Miocene).

Description. The fossil tibiotarsus QM F36276 ( Figure 3.1, 3.3, 3.5 ) is referred to Passeriformes and Climacteridae because it possesses the above described features for these groups. This specimen is conservatively referred to Climacteris because it shows the following suite of features: tibiotarsus large and robust; pons supratendineus is situated proximally from condyles by a distance about equal to 50-60% of length of condylus medialis; sulcus extensorius relatively wider; lateral and medial bony ridges for attachment of retinaculum m. fibularis are long (except Cl. erythrops ); bony ridges for attachment of retinaculum m. fibularis about proximally level with or partly offset disto-laterally of tuberositas retinaculi extensoris lateralis (except Cl. erythrops , in which they are located proximally of this tuberosity).

QM F36276 is differentiated from other unrelated families of scansorial passerines by the above described character states. It is distinguished from the fossil tibiotarsus assigned to Cormobates because it is robust, the relative distance between the pons supratendineus and the condyles is smaller, and the lateral and medial bony ridges for the retinaculum m. fibularis are considerably longer and situated at about level with the tuberositas retinaculi extensoris lateralis ( Figure 4 ). The fossil tibiotarsus QM F36276 differs from extant species of Climacteris in the following features. It differs from all extant species of Climacteris in that the bony ridges for attachment of the retinaculum m. fibularis are less prominent. These ridges are situated slightly further distally with respect to the tuberositas retinaculi extensoris lateralis than in Cl. picumnus , Cl. rufa , and Cl. melanura . The fossil can be distinguished from Cl. affinis and Cl. erythrops in having slightly longer ridges for the retinaculum m. fibularis. The distinctiveness of QM F36276 allows its assignment to Climacteris , but the fragmentary nature of this fossil precludes its differentiation at the species level with confidence, pending recovery of more complete material.

The fossil tibiotarsus is comparable in size to the corresponding bones of Cl. picumnus . There is some damage to the edges of the condylus lateralis, but a distinctly thick rim along its distal edge is discernible in lateral aspect. As in extant climacterids, the epicondylus medialis is prominent and visible in cranial aspect. The impressio lig. intercondylaris is slightly deeper in the fossil than in extant climacterids. The tuberositas retinaculi extensoris lateralis is elongate and well developed. Although most of it is broken off, the distal edge of the tuberositas retinaculi extensoris medialis indicates that it is separated from its lateral counterpart by a distance about equal to the length of the former. The sulcus extensorius is broad, and the sulcus m. fibularis is long, wide and deep. Most of the cristae trochleae are broken off. The central ridge on the trochlea cartilaginis tibialis is very low. A very low ridge on the trochlea cartilaginis tibialis was also found in all specimens of Climacteris studied except for Cl. picumnus AM O. 59222, in which it was well developed.

It is possible that the three fossil tibiotarsi described here ( Figure 4 ) belong to extinct lineages in Neosittidae and Climacteridae , but the currently available material would not allow such new lineages to be identified with confidence. Until more complete material is discovered and studied, the fossils are conservatively referred to these extant families and genera.

Figures

FIGURE 3. Distal left tibiotarsus of Climacteris sp. QM F36276 (1, 3, 5) compared with that of Climacteris picumnus AM O.64841 (2, 4, 6). 1-2, cranial aspect; 3-4, caudal aspect; 5-6, lateral aspect. Abbreviations: cl, condylus lateralis; em, epicondylus medialis; lrf, lateral bony ridge of retinaculum m. fibularis; mrf, medial bony ridge of retinaculum m. fibularis; ps, pons supratendineus; rct, ridge on trochlea cartilaginis tibialis; rim, thickened rim of the condylus lateralis; trel, tuberositas retinaculi extensoris lateralis; trem, tuberositas retinaculi extensoris medialis. Scale bar equals 2 mm.

FIGURE 4. Comparison of fossil tibiotarsi of Daphoenositta trevorworthyi sp. nov. QM F57897 (1, 4), Cormobates sp. QM F57898 (2, 5) and Climacteris sp. QM F36276 (3, 6).1-3, cranial aspect; 3-6, lateral aspect. Characteristic features are as follows: a, pons supratendineus situated proximally of the condylus medialis by a distance about equal to one-third of the length of this condyle; b, sulcus extensorius narrow; c, bony ridges for attachment of retinaculum m. fibularis located disto-laterally of the tuberositas retinaculi extensoris lateralis; d, pons supratendineus situated proximally of condylus medialis by a distance greater than 50% of the length of this condyle; e, bony ridges for retinaculum m. fibularis long and prominent; f, condyles short and set widely apart; g, bony ridges for retinaculum m. fibularis long and low; h, condylus lateralis circular in shape; i, medial bony ridge for retinaculum m. fibularis short; j, thickened rim on condylus lateralis. Scale bar equals 2 mm.