Lithoserix oublierus Viertler, 2024

Viertler, Alexandra, 2024, Another one bites the dust: A new Lithoserix species (Hymenoptera, Ichneumonidae, Pimplinae) from the early Oligocene in France, with an evaluation of wing morphometrics, Fossil Record 27 (1), pp. 135-145 : 135

Lithoserix oublierus Viertler sp. nov.

Fig. 2

Type material.

Holotype (PNRL-SIG-216, female, part, no counterpart available).

Etymology.

Oublierus - from the French word “oublier” (forgotten) because the fossil was in the collection for a long time under the label “wasp” and was overseen, until André Nel and Corentin Jouault saw the wing venation and identified it as a Darwin wasp. The name is dedicated to the possibly numerous Darwin wasp fossils that are overlooked in natural history collections.

Type locality.

South-eastern France, Calcaires de Campagne-Calavon Formation (Rupelian, 31-30 Ma).

Systematic placement.

Many characteristics indicate that the fossil belongs to Pimplinae : the stout and short T1 with a lateromedian carina present, a quadratic areolet in the fore wing, 2m-cu slightly bowed outwards and two bullae and a long 2R1 cell. Other strong arguments for this subfamily are found in the hind wing: a long 1Rs relatively to its short rs-m vein, as well as a nervellus that is intercepted clearly above the middle. While the ovipositor of this fossil is only weakly discernible, it appears to project posteriorly from the metasoma, providing further support for its placement in Pimplinae .

The fossil also shows some character combinations that are rare in Pimplinae , but that are found in the extinct genus Lithoserix : its rather extensive propodeum carination, the fore wing with an almost triangular areolet, a long 1Rs + M and a sinusoidal 4Rs vein, together with the lateromedian carina on T1 reaching to the posterior end.

Diagnosis.

There are currently two Lithoserix species described, which are both preserved from the dorsal side, while the new species is preserved more laterally. The new fossil specimen differs from both Lithoserix by having the vein 1cu-a strongly postfurcal, with 1Cu about 3-4 × longer than its width, having 3Cu much longer with twice the length of 2cu-a, 1Rs much longer than vein rs-m in the hind wing and by its narrower hind femurs (Table 1 ).

Additionally, the new fossil specimen differs from L. antiquus by having a nervellus that is intercepted very high up, not having smooth transverse bands on the hind margins of T2-T7 and its lateromedian carina on T1 reaching beyond the middle, maybe even until the posterior end, but this is difficult to interpret. Furthermore, L. antiquus has brightly-coloured legs (orange), whereas the new species appears to have dark legs.

Finally, the new fossil species differs from L. williamsi by having its antennal segments less stout, at least not in the basal segments. Furthermore, L. williamsi is around twice the body size and has strongly impressed notauli, whereas they are only weakly preserved in the new species.

The fossil specimen exhibits shallow notauli and weak pleural, lateral longitudinal and lateromedian carination on the propodeum. The fore wing has a strongly postfurcal nervulus, the nervellus in the hind wing is intercepted in its anterior 0.2 and T1 features lateromedian carinae which reach beyond the middle. The fossil specimen’s colouration is interpreted without having a counterpart or paratype, which would increase the certainty of the observed colours. However, the specimen shows both antennae and fore- and mid-coxae with a light colour, but a dark-coloured head, body and femurs. It appears that both hind tibiae have a bright base and a dark apex.

Description.

Preservation. Holotype in dorso-lateral view. Antenna, head and mesosoma well preserved, but some details are missing or obscured by the very well-preserved fore- and hind wings. Legs are partially preserved, including all femora and fore- and hind tibiae, as well as fore- and mid-trochanters. Propodeal carination visible. Metasoma difficult to interpret since hind coxa and first tergite seem to overlap and the metasoma is preserved rather compressed, which is probably an artefact. Ovipositor partially visible at base, but otherwise indiscernible or broken.

Body. 12-13 mm. Fossil dark in colour, either black or dark brown. Antennae seem bright, but scape appears dark. All femurs dark, front tibiae appear bright. Hind tibiae appear bright with lower 0.4 dark.

Head. Antenna 10.8 mm, 1.1 × fore wing length; without white band; dimensions of segments around 1.5-2.5 × longer than posteriorly wide; number of antennal segments unclear, but more than 20; antenna more or less of even thickness throughout.

Mesosoma. Dimension unclear. Scutellum with shallow and slightly converging notauli. Metapleuron appears as long as wide, with juxtacoxal carina present. Propodeum rounded posteriorly; about as long as high; with small oval spiracle; traces of pleural carina, lateral longitudinal and lateromedian carina present, at least anteriorly and posteriorly; posterior transverse carina present. Fore legs slender; hind femur 4.2 × as long as wide.

Wings. Fore wing 9.7 mm. Areolet closed, slightly petiolate almost triangular, 2-Rs same length as 2-rs-m, 4M 1.1 × 2-Rs and 2+3M 0.6 × 2-Rs. 2m-cu present, slightly bowed to straight, with two bullae. 4Cu 2 × 5Cu. 4Rs distally arched and slightly sinusoidal. 1Rs + M present, longer than width of surrounding veins. 1cu-a distal of 1M+1Rs by more than vein width. Pterostigma length 4.2 × width, 0.6 × vein 1R1. Cell 2R1 4.1 × longer as wide. 5M vein tubular through entire length. 2Cu 0.8 × 1M+1Rs, 1.17 × r-rs. 1m-cu&2Rs+M vein straight or weakly arched or angled. 3Cu 1.8 × 2cu-a. Hind wing with 1Cu very short, 0.15 × cu-a. Veins 2Rs and 2Cu tubular through entire length. 2Rs 2.4 × rs-m.

Metasoma. Dimension unclear, but stout in appearance. T1 broad and short, parallel-sided with slightly narrower base, with lateromedian carina more than half length of tergite. Dimension of T2 unclear, but appears transverse, as do T3-T6. Sternites strongly sclerotised, as dark as tergites. Ovipositor length unknown, but seems to reach past posterior end of metasoma.

Figures

Figure 2. Holotype of Lithoserix oublierus sp. nov. (PNRL-SIG- 216) A. Photograph of the holotype; B. Interpretative drawing, where dotted lines indicate uncertain interpretations. Scale bars: 5 mm.