Mesodiphthera grandis Tillyard, 1919

Lambkin, Kevin J., 2019, Mesodiphthera Tillyard, 1919, from the Late Triassic of Queensland, the oldest cicada (Hemiptera: Cicadomorpha: Cicadoidea: Tettigarctidae), Zootaxa 4567 (2), pp. 358-366 : 360-362

Mesodiphthera grandis Tillyard, 1919

( Figs 1–7 )

Mesodiphthera grandis Tillyard, 1919: 873 , text-fig. 7.

Material. Holotype tegmen GSQ213a (basal fragment with clavus), Denmark Hill ; 10 additional tegmina, Denmark Hill: GSQ192a/b (basal fragment without clavus); Dinmore: QMF 14311+, QMF 59846 (almost complete); QMF 59840+, QMF 59843 (basal fragments with clavus), QMF 59841, QMF 59842+, QMF 59845 (basal fragments without clavus), QMF 59844+ (almost complete, broken at nodal line), QMF 59847 (detached clavus). All specimens in the Queensland Museum.

Description. Tegmen c. 20–24 mm long, c. 6–8 mm wide (measurements from QMF59846 and QMF14311); branching pattern of RA2 variable ( Figs 4 , 5, 7 ); in most specimens the pre-nodal membrane and main veins (except claval veins) with a strong pattern of dark markings, post-nodal area apparently mostly hyaline except for dark markings in anterior radial field just beyond node, anterior margins of the M2+3, CuA1 and CuA2 cells, and more or less along the main veins and cross-veins ( Figs 2 , 5, 6 ); dark markings apparently less developed in QMF59846, only obvious along costal margin and R+RA, and in two broad transverse bands on the clavus, the proximal band much paler than the distal one ( Fig. 3 ).

Notes. The two most complete specimens (QMF59846 and QMF14311— Figs 3 , 6 ) vary a little in size, but the degree of difference is within the range of the tegmina of extant Tettigarcta crinita (specimens in the Queensland Museum), as well as the tegmina of extant Cicadidae of similar size. Two similarly sized Australian cicadids, Tryella burnsi Moulds and T. crassa Moulds , for example, have intraspecific differences in tegmen length of five and nine millimetres respectively ( Moulds 2003). It should also be noted that female cicadas are generally slightly larger than males. Another point of variation is the presence in QMF59846 ( Figs 3, 4 ) of a curved cross-vein between RP and M1+2 just proximal of the nodal line. Such a cross-vein was illustrated in the Jurassic Liassocicada mueckei ( Nel) (Nel 1996, fig. 2 ), but has not been recorded in any other living or extinct tettigarctid. As QMF59846 and QMF14311 also have slightly different tegmen shapes and possibly different colour patterns, it is possible that they have come from different species. For the present, however, in the absence of a good series of specimens for a comparative analysis, there seems little point in adding yet another specific name to the literature based on such minor differences in single specimens.

Nearly all specimens have a quite striking blotchy dark colour pattern, especially pronounced in the pre-nodal area. Such blotchy dark patterning, although differing in detail, has also been recorded in the Jurassic Liassocicada mueckei ( Nel 1996, fig. 1), Shuraboprosbole Bekker-Migdisova ( Wang & Zhang 2009, figs 1A, 4A), Maculaprosbole Zheng, Chen and Wang (Zheng et al. 2016 , fig. 1A), and Sanmai Chen, Zhang and Wang (Chen et al. 2016 , figs 3A, 4A1), and the Miocene Paratettigarcta Kaulfuss and Moulds (Kaulfuss & Moulds 2015, fig. 3B ). The tegmina of the two extant Tettigarcta species have a less striking speckly colour pattern, apparently providing good camouflage while they sit on lichen-covered eucalypt bark (see photographs in Popple 2018).

Figures

FIGURES 1–4. Mesodiphthera grandis Tillyard: 1, holotype, GSQ213a; 2, QMF59841; 3, QMF59846 (mirrored); 4, composite of QMF59845 (extreme base) and QMF59846; bc, basal cell; mm, marginal membrane; wcf, wing coupling fold.

FIGURES 5–7. Mesodiphthera grandis Tillyard: 5, QMF59844; 6, 7, QMF14311 (composite of part (top) and counterpart, counterpart mirrored), split and separation along claval suture recombined in the drawing.