Daphoenositta trevorworthyi, Nguyen, 2016

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 : 4

Daphoenositta trevorworthyi sp. nov.

Figure 1.1, 1.3, 1.5

zoobank.org/ A82EDE52-2D67-47D2-B8F0-2CE42FD6D9B5

Etymology. The new species is named in honour of my mentor Dr. Trevor Worthy, who has significantly contributed to our knowledge of Australasian fossil birds. It is suggested that this new species be informally known as Trevor's Sittella.

Holotype. QM F57897 , a distal left tibiotarsus.

Type Locality and Horizon. Rick’s Sausage Site, Faunal Zone C deposits, Riversleigh World Heritage Area, Queensland, Australia. Rick’s Sausage Site is an isolated deposit that occurs on the southern section of the Gag Plateau ( Travouillon et al., 2014; Cooke et al., 2015). Based on stage-of-evolution biocorrelation, Rick’s Sausage Site is part of Riversleigh’s Faunal Zone C and is regarded as middle Miocene in age ( Archer et al., 1989, 1997; Travouillon et al., 2006, 2011; Arena et al., 2015).

Diagnosis. Daphoenositta trevorworthyi sp. nov. is distinguished from Da. chrysoptera by the following combination of features: distinctly larger in size; depth of condylus lateralis relatively greater; in medial view, condylus medialis relatively longer with respect to condyle depth and is subsequently more circular in shape; tuberositas retinaculi extensoris lateralis prominent and situated relatively more distally on proximo-lateral part of pons supratendineus; and bony ridges for attachment of retinaculum m. fibularis less prominent and, as a result, sulcus m. fibularis very shallow. Specimens of Da. miranda were unavailable for comparison, but Da. miranda falls within the reported size range of Da. chrysoptera ( Higgins and Peter, 2002; Noske, 2007b). Therefore, Da. trevorworthyi would have also been considerably larger than Da. miranda .

Measurements (mm). Preserved length 23.5; distal width 3.8; length of condylus lateralis 3.1; length of condylus medialis 3.1; depth of condylus lateralis 3.6; depth of condylus medialis 3.7.

Description. QM F57897 ( Figure 1.1, 1.3, 1.5 ) preserves a distal tibiotarsus with small patches of dendritic crystal growth and minor breakage to the trochlea cartilaginis tibialis. There is a series of moderately deep transverse scratches on the cranial and caudal surfaces of the proximal shaft ( Figure 1.1, 1.3 ). Also present on the caudal shaft surface is a longitudinal scratch that is situated slightly laterally of the shaft midpoint ( Figure 1.3 ). In addition to the features that characterise Neosittidae and those used to diagnose the new species, Daphoenositta trevorworthyi sp. nov. exhibits the following features. The distal end of the tibiotarsus is slightly narrower in width relative to its length than in Da. chrysoptera . The proximal edges of both condyles are about proximo-distally level. In the fossil specimen and Da. chrysoptera AM O. 60956, the condyles are about equal in distal extent, whereas in other specimens of Da. chrysoptera examined the condylus lateralis extends slightly further distally. The length of the incisura intercondylaris is greater than its width. Within the incisura intercondylaris, the impression for the attachment of the lig. tibiometatarsale intercondylare is shallow. The length of the pons supratendineus is about equal to its width, and the sulcus extensorius is wide and centred on the shaft. The tuberositas retinaculi extensoris lateralis is situated on the proximo-lateral part of the pons supratendineus and extends beyond the proximal margin of the latter. The proximo-distal distance between the tuberositas retinaculi extensoris medialis and its lateral counterpart is about equal to the length of the former. This was also observed in some specimens of Da. chrysoptera (AM O.62397, AM O.67631, AM O.68254), but in AM O.64965 the relative distance between the tuberosities is about twice the length of the tuberositas retinaculi extensoris medialis. The sulcus m. fibularis is narrow and very shallow. As in all scansorial passerines examined, the bony ridges that bound the sulcus and serve as attachment points for the retinaculum m. fibularis are more laterally displaced on the distal tibiotarsus than in non-scansorial passerines. The lateral bony ridge for attachment of the retinaculum m. fibularis is very low due to wear. The epicondylus lateralis is indistinct. In caudal view, there is a very faint ridge on the centre of the trochlea cartilaginis tibialis. The trochlea cartilaginis tibialis is wide, and the cristae trochleae are long and gently converge proximally. In distal view, the condyles slightly converge caudally. Despite the considerable size difference in the tibiotarsi of Da. trevorworthyi and Da. chrysoptera , their overall morphology is similar.

Figures

FIGURE 1. Distal left tibiotarsi of Daphoenositta trevorworthyi sp. nov. QM F57897 (1, 3, 5) compared with that of Da. chrysoptera AM.O.64965 (2, 4, 6). 1-2, cranial aspect; 3-4, caudal aspect; 5-6, lateral aspect. Abbreviations: cl, condylus lateralis; cm, condylus medialis; 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; trel, tuberositas retinaculi extensoris lateralis; trem, tuberositas retinaculi extensoris medialis. Arrows indicate scratch marks. Scale bar equals 2 mm.