Frenguellia patagonica, Petrulevicius & Nel, 2003

Petrulevičius, J. F. & Nel, A., 2003, Frenguelliidae, a new family of dragonflies from the earliest Eocene of Argentina (Insecta: Odonata): phylogenetic relationships within Odonata, Journal of Natural History 37 (24), pp. 2909-2917 : 2911-2913

Frenguellia patagonica sp. n.

(figures 1–3)

Material. H   specimen MLP 6431, Departamento Científico Paleozoología Invertebrados, Museo de la Plata, La Plata, Argentina.

Stratum typicum. Earliest Eocene (52 Ma) (Wild et al., 2001), pyroclastic debries, La Huitrera Formation.

Locus typicum. Laguna del Hunco , province of Chubut, Patagonia Argentina, latitude 42°30∞S, longitude 70°W .

Presentation. Counter-imprint. The type specimen of Frenguellia patagonica is probably a fore wing because its discoidal cell is opened. This cell is generally closed in the Odonata (=Zygoptera+Epiproctophora).

Description. A nearly complete wing, but with the extreme base and apex missing; postero-median part, base and area between costal margin and RA distal of pterostigma deformed and partly broken; a wide dark zone present between the pterostigma and just distal of the nodus; wing base and apex hyaline; petiole short and broad, 1.8 mm long and 1.6 mm wide; wing 23.6 mm long, 8.5 mm wide; distance between base and arculus 2.9 mm, between arculus and nodus 4.8 mm, between nodus and pterostigma 12.1 mm, between pterostigma and apex 3.7 mm; nodus basally recessed; pterostigma long and broad, 2.9 mm long and 1 mm wide, covering four cells; pterostigmal brace reduced, anterior side of pterostigma not oblique, parallel to the postnodal cross-veins; no secondary antenodal cross-veins; Ax2 opposite arculus; Ax1 1 mm basally; no antesubnodal cross-veins; discoidal cell basally opened, very narrow, with an acute postero-distal angle; MP +CuA with a strong angle just distal of the base of CuP; CuP curved and looking like a secondary branch of AA; MA and MAb well aligned, not making an angle, composite vein [MA and MAb] curved to wing base; extreme base of RP not preserved; bases of RP 3/4 and IR2 between the arculus and nodus, that of RP 3/4 being nearer arculus than nodus and that of IR2 nearer to nodus than to arculus, distance between arculus and base of RP 3/4 1.4 mm, between arculus and base of IR2 2.7 mm; base of RP 2 three cells, 3 mm distal of subnodus; base of IR1 four cells, 2.4 mm distal of that of RP 2; nodal crossvein Cr and subnodus vertical, 1 mm (about one cell) distal of point of fusion of ScP with costal margin; distance between nodus and subnodus is 1.1 mm; posterior bent of CP not aligned with Cr but in a very distal position, at the point of fusion between ScP and costal margin (figure 3); point of fusion between CA +CP+ScP and ScP is in clear natural position (figure 3); a long and wide triangular zone limited by costal margin and ScP, distal of level of nodal Cr, basally opened, 1.02 mm long and 0.2 mm wide; fusion between ScP and costal margin well preserved, long (0.5 mm), nearly one cell long; ScP broken just basal of nodal Cr and aligned with distal part of RA; also part of RA basal of subnodus with a zigzag deformation (figures 2, 3); first postnodal cross-vein slightly basal of point of fusion of ScP with costal margin; 19–20 postnodal cross-veins between C and RA, not well aligned with the corresponding cross-veins between RA and RP 1; one ‘lestine’ oblique crossvein ‘O’, six cells distal to base of RP 2; cubito-anal area broad, with three rows of cells between CuA and posterior wing margin; CuA reaching posterior wing margin well distal (4.7 mm) of nodus level; area between MP and CuA distally greatly widened, with three rows of cells between MP and posterior wing margin and 14 rows of cells between these veins along posterior wing margin; postdiscoidal area with only one row of cells and distally narrowed; area between MA and RP 3/4 distally widened, with two long secondary longitudinal veins; area between RP 3/4 and IR2 narrow, with one row of cells; areas between IR2 and RP 2 and between RP 2 and IR1 distally widened with three long secondary longitudinal veins; area between IR1 and RP 1 with only one row of cells, broader than long; CuA distally zigzagged; MP, MA, RP 3/4, IR2 and RP 2 more or less straight or slightly curved; IR1 with a distinct but smooth curve opposite pterostigma, corresponding to a narrowing of the area between it and RP 1 and a broadening of the area between it and RP 2; no significant increase of spine-density at the apical costal margin.

Taphonomic remarks. The specimen shows some signs of deformation due to the taphonomic process of biostratinomy, before burial. This deformation is evident in the cubito-anal area and in the nodal area. Some veins show plastic deformation in the cubital area, CuA and the wing margin (figures 1, 2). This could be due to the preservation of the membrane, which maintains these veins in cohesion from external forces. Other veins are broken and folded in zigzag as RA in the nodal region. This could be due to the break of the membrane, which in these cases does not maintain these veins in position and produces their displacement (figures 2, 3). This is the case of RA in the nodal region whose basal portion is displaced distally (figures 2, 3).