Petrolestes inexpectatus, Nel, 2024

Nel, André, 2024, Two new damselflies from the Eocene Green River Formation (Odonata, Zygoptera, Dysagrionidae, Thaumatoneuridae), Zootaxa 5446 (4), pp. 588-594 : 591-592

Petrolestes inexpectatus sp. nov.

( Figure 2 )

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Material. Holotype IP.359116 (part and counterpart of a nearly 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 unexpected presence of a second species of Petrolestes in the Green River Formation.

Diagnosis. Wing characters only. Base of RP2 four cells distad subnodus; pterostigma covering two cells; presence of very long cells in cubito-anal area.

Description. Wings hyaline, distal third of wing deformed, thus its exact length is difficult to determine, wing ca. 27.8 mm long; max. width 6.8 mm, wing 6.2 mm wide at nodus level; a very short petiole, 2.3 mm long; anal area with one row of cells between AA and AP; subdiscoidal cell broad elongate, 1.7 mm long, 0.5 mm wide; distance from base to arculus 5.0 mm, from arculus to nodus 7.8 mm, from nodus to pterostigma ca. 10.0 mm; nodus in a basal position; pterostigma rather short but broad, 2.1 mm long, 6.2 mm wide, covering two cells; pterostigmal brace perpendicular to RA and RP1; distance from wing base to Ax1 3.4 mm, from Ax1 to Ax2 1.4 mm, Ax2 nearly aligned with arculus; no supplementary antenodal crossvein; discoidal cell unicellular, 1.1 mm long, 1.1 mm wide, distinctly broadened in its distal part, with basal side 0.3 mm, anterior side 0.9 mm, posterior side 1.1 mm, distal side MAb 1.1 mm; ScP not crossing through nodus as in Stenolestes Scudder, 1895 ; nodal crossvein very oblique; subnodus perpendicular to RA and RP with corresponding crossvein below (between RP1/2 and IR2) of inverted obliquity; ca. 14 postnodal crossveins preserved, not aligned with 14 postsubnodal crossveins; bases of RP3/4 and IR2 between arculus and nodus, closer to nodus than to arculus, base of RP3/4 4.6 mm from arculus and 3.2 mm from nodus; base of RP2 four cells, 3.0 mm distal of subnodus; base of IR1 two cells distally; oblique crossvein ‘O’ absent; cubito-anal area with three-four rows of cells between CuA and posterior wing margin, some of these being very long; CuA reaching posterior wing margin well distal of nodus level; CuA weakly curved; postdiscoidal area with one row of cells; area between RP3/4 and MA with two secondary longitudinal veins in between; three rows of cells between RP3/4 and IR2 and one row between RP1 and IR1; three rows of cells between IR1 and RP2 opposite pterostigma, but only one basally.

Remark. This wing is strongly similar to those of the two species of the genus Petrolestes , especially in the shape of the petiole, discoidal cell, subnodus, cubital veins, patterns of veins between main longitudinal veins, etc. ( Cockerell 1927; Garrouste & Nel 2015). It can be attributed to this genus, but differs from the two described species in the base of RP2 situated four cells distad subnodus vs. only two, in the pterostigma covering only two cells vs. four or more, and in the presence of very long cells in the cubito-anal area. Thus I consider it as a new species.

Figures

FIGURE 2. Petrolestes inexpectatus sp. nov., holotype IP.359116. Photographs under alcohol of wing. A, part; B, counterpart. Scale bars = 5 mm.