Palaeomedeterus cambayensis Bickel, 2022

BICKEL, DANIEL J., MARTIN, JOHN, AGNIHOTRI, PRIYA & SINGH, HUKAM, 2022, Dolichopodidae (Diptera) from the Eocene amber deposits of Cambay and Kutch Basins, India, Palaeoentomology 5 (5), pp. 475-486 : 481-482

Palaeomedeterus cambayensis Bickel sp. nov.

( Fig. 3A–D )

Type material. Holotype: ♂, INDIA: Gujarat: Tadkeshwar Lignite Mine, Lower Eocene strata of the Cambay Shale formation, 21°21.400′N, 73°4.532′E, I/2009 – I/2012. D. Grimaldi & P. Nascimbene, Tad-476-B . Paratypes: ♂, same but Tad-476-A; ♂, same but KU-173-A; #f, same but Tad-124 (all AMNH) .

Additional material. Specimens that are obscured or damaged but possibly belong to this species. ♂, similar to holotype data, but Tad-483; ♂, same but Tad-448 ( AMNH) .

Etymology. The specific epithet cambayensis refers to this species presence as inclusions in Cambay amber.

Diagnosis. As for genus.

Locality and horizon. Cambay and Kutch basins, Gujarat State, India; Eocene.

Description. Male. Length: 1.7 mm; wing: 1.5 × 0.5 mm.

Head. Dorsal postcranium slightly concave; vertex not excavated between ocellar tubercle; frons apparently dark metallic green, without pruinosity; postorbital setae major setae black; short postvertical setae; strong ocellar and slightly weaker vertical setae present; face and clypeus slightly narrowed beneath base of antennae, and parallel sided; eye with anterior facets enlarged; palp brown, with strong apical seta; proboscis brown; scape and pedicel dark brown; scape bare; pedicel with ring of short subapical setae, and with stronger dorsal and ventral seta: postpedicel dull brown, rounded subrectangular, with dorsoapical arista arising in subapical notch; arista about as long as head height; ventral postcranium with black setae; dorsal postorbital setae short and black.

Thorax. Rather short and rounded in lateral view; posterior mesonotum not distinctly flattened and almost entirely dark brown with little apparent pruinosity; setae black; ac biseriate, 8–9 regular pairs; 6 strong dc, decreasing in size anteriorly; 1 postalar seta, 1 posterior supra-alar seta, 1 sutural intraalar and 1 shorter intraalar anteriad; 1 postpronotal seta, and 2 notopleural setae; scutellum with strong median setae and short hairlike lateral seta; ventral pronotum with strong seta projecting anteriorly just above base of CI.

Legs. Coxae and remainder of legs dark brown; setae black; CI with short basally and with 3–4 strong distolateral setae, CII distally with some short anterolateral setae; CIII with single strong lateral seta near 1/3; I: 2.0; 2.0; 0.9/ 0.6/ 0.4/ 0.3/ 0.2; FI bare; TI from ¼ to apex with dorsal row of 8 slanted and spaced subequal setae; II: 2.4; 2.6; 1.4/ 0.7/ 0.5/ 0.4/ 0.2; FII with distinct anterior subapical seta at 5/6; TII with short ad-pd setal pair at 1/5, very strong anterior seta near 1/3 and with subapical circlet of ad, pd, av, and ventral seta; III: 2.5; 2.9; 0.6/1.0/ 0.5/ 0.4/ 0.3; FIII also with anterior subapical seta at 5/6, but weaker than that of FII; TIII with ad setae at 1/5, with irregular dorsal row of 4-5 strong setae and shorter setae, and with subapical circlet of ad, av, ventral, and pd seta.

Wing. Hyaline; vein R 1 joining costa neat 1/3; R 2+3 joining costa at 7/8; vein R 4 + 5 in gentle curve with slight subapical anterior bend to join margin just anteriad of wing apex; vein M 1 unbranched, gently diverging from vein R 4+5, with flexion or bosse alaire halfway between crossvein dm-m and apex, then becoming subparallel with R 2+3 to join costa just posteriad of apex; crossvein dm-m straight; CuAx ratio: 0.6; anal vein weak; lower calypter brown with fan of black setae; halter yellow.

Abdomen. Entirely dark brown with some metallic green reflections; tergites 1–6 with short black vestiture and strong setae along tergite margins; sternite 4 slightly enlarged with row of setae along posterior margin, and forming hood to receive distal hypopygium; tergite and sternite 7 forming short peduncle; sternite 8 ovate with some marginal setae, and covering left lateral hypopygial foramen; hypopygium including cercus mostly dark brown; epandrium rather short and rounded, subrectangular; surstylus short and tapering with some short distal setae; cercus yellowish, broadly subtriangular, and with apical group of some 8 strong setae.

Female. Similar to male except as noted: eye facets uniform; podomere ratios and setation similar.

Remarks. Palaeomedeterus cambayensis is known from four distinct specimens and three obscured/damaged specimens and appears to be a common species in Cambay amber. The dark brown legs, tibia I with dorsal row of short, slanted setae, and the broad ovate cercus with its group of apical setae is diagnostic for this species.

This species is close to the also common Baltic amber species, Palaeomedeterus ignavus Meunier ( Fig. 3E ), and despite their separation in both time and space (see Discussion), they share the following diagnostic characters: a strong anterior seta near 1/3 on tibia II (see arrows on Fig. 3A and Fig. 3E ), sternite 4 slightly enlarged with row of setae along posterior margin, and a large subtriangular cercus with apical setae (cf. Fig. 3C, E ).

Figures

FIGURE 3. Palaeomedeterus cambayensis sp. nov. A, Male habitus, left lateral, (GIAM-012). B, Male postabdomen, left lateral (GIAM-012). C, Male postabdomen, left lateral (GIAM-014). D, Male habitus, dorsal (GIAM-011). E, Palaeomedeterus ignavus (Meunier), Baltic amber: male habitus, left lateral. (Photo from the collection of Jonas Damzen, Vilnius, Lithuania. Legend: cer, cercus; st4, sternite 4.