Gusagrion coloratum, Nel, 2024

Nel, André, 2024, Two new damselflies from the Eocene Green River Formation (Odonata, Zygoptera, Dysagrionidae, Thaumatoneuridae), Zootaxa 5446 (4), pp. 588-594 : 589-591

Gusagrion coloratum sp. nov.

( Figure 1 )

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Material. Holotype IP.358925 (part and counterpart of a complete wing), stored at Invertebrate Paleontology Collection , Yale Peabody Museum, USA.

Age and outcrop. Eocene (Ypresian), Green River Formation, Parachute Creek member, Gus’ pit, two miles west of Rio Blanco store, Colorado, USA.

Etymology. Named after the colored distal third of wing.

Diagnosis. As for the genus. A dark brown area covering apical third of wing.

Description. A complete wing, with a dark brown area covering apical third, wing 28.8 mm long, 8.4 mm wide, broad and with numerous small cells; distance from base to arculus 3.6 mm, from arculus to nodus 3.2 mm; primary antenodal crossveins Ax1 and Ax2 well-defined; Ax1 2.2 mm from wing base, distance between Ax1 and Ax2 1.4 mm; Ax2 just distad arculus; no secondary antenodal crossveins; ca. 34 postnodal crossveins, not well aligned with postsubnodal crossveins; pterostigma rather short but broad, 2.4 mm long and 0.8 mm wide, covering four cells; distal edge of pterostigma more oblique than proximal one; pterostigmal brace absent; one row of crossveins between C and RA distal of pterostigma; posterior part of arculus (= basal discoidal crossvein) present, therefore discoidal cell basally closed; discoidal cell rectangular, elongate, narrow (1.6 mm long, 0.4 mm wide), and free of crossveins; origins of RP and MA separated in arculus; bend of ScP at nodus very abrupt and Z-like; nodal vein and subnodus oblique; subnodus aligned with nodal crossvein; no crossveins in antesubnodal area; median space free of crossveins; submedian space free of crossveins except for CuP-crossing; subdiscoidal cells free; anal area narrow (0.3 mm wide in middle), not wider than subdiscoidal cell, with one crossvein below subdiscoidal cell; cubito-anal area max. 2.0 mm wide in its broadest part, with rows of cells; CuA well-defined and curved; CuA not forked; area between MP and CuA progressively broadened; MP regularly curved, not distally zigzagged, and ending between nodus and pterostigma; basal half of postdiscoidal area between MA and MP narrow with only one row of cells, but greatly widened distally, and with two long secondary longitudinal veins; MA ending well basad pterostigma level; MA, RP3/4, and IR2 rather straight, but distally curved towards hind margin; no antefurcal crossveins between basal parts of RP and MA; area between RP3/4 and MA narrow with one row of cells between them in basal half, but area distally widened with two long secondary longitudinal veins; area between RP3/4 and IR2 progressively broadened, with two long secondary longitudinal veins; RP3/4 ending beneath pterostigma; base of RP3/4 1.8 mm basad subnodus; base of IR2 below nodus; RP1/2 straight at subnodus; base of RP2 very far from subnodus, at 13 cells distal from it; IR1 well-defined, long, and curved, originating four cells distad RP2; no lestine oblique vein ‘O’ between RP2 and IR2; RP2 and IR2 with only one row of cells between them until level of base of pterostigma; RP1 without distinct bend at pterostigmal brace; wings well petiolated, petiole 2.8 mm long.

Remark. This damselfly wing fits quite well with those of the two eodysagrionine genera and species Tynskysagrion brookeae Bechly, Garrouste, Aase, Karr, Grande & Nel, 2021 and Oreodysagrion tenebris Bechly, Garrouste, Aase, Karr, Grande & Nel, 2021 because of the elongate and narrow discoidal cell, long petiole, nodus situated in a very basal position, distal third of wing very broad. Eodysagrion has a shorter discoidal cell, the nodus situated in a more distal position, and much less postnodal crossveins ( Rust et al. 2008).

The new fossil differs from Tynskysagrion in the much narrower anal area below the subdiscoidal cell, at most as broad as subdiscoidal cell, as in Oreodysagrion vs. as broad as subdiscoidal plus discoidal cells in Tynskysagrion . The new fossil also has only one crossvein below subdiscoidal cell, vs. two in Oreodysagrion and 2–3 in Tynskysagrion . In Oreodysagrion , the nodus is situated in a very basal position, 14% of the distance between Ax2 and wing apex vs. 19% in the species of Tynskysagrion . In the new fossil, the nodus is situated at 10% of the distance between Ax2 and wing apex, which better fits with Oreodysagrion . But the wing of Oreodysagrion is more slender than in the new fossil and in Tynskysagrion . Thus the new fossil does not fit in these two genera.

Lastly, the color pattern of the new wing is strongly different from those of Oreodysagrion tenebris and Tynskysagrion brookeae . Oreodysagrion tenebris has a dark brown band between the base of RP2 and the basal side of pterostigma. Tynskysagrion brookeae has a completely darkened wings or with a narrow hyaline band in distal half of the wing.

Figures

FIGURE 1. Gusagrion coloratum gen. et sp. nov., holotype IP.358925. Photographs under alcohol of wing. A, part; B, xounterpart. Scale bars = 5 mm.