Okanagrion threadgillae Archibald & Cannings, 2021

Archibald, Bruce, Cannings, Robert A., Erickson, Robert J., Bybee, Seth M. & Mathewes, Rolf W., 2021, The Cephalozygoptera, a new, extinct suborder of Odonata with new taxa from the early Eocene Okanagan Highlands, western North America, Zootaxa 4934 (1), pp. 1-133 : 43-44

Okanagrion threadgillae Archibald & Cannings , new species

Figs. 19–20 .

Diagnosis. Wings separated from those of O. beardi , O. dorrellae by MP, CuA sub-parallel at terminus on posterior margin [ O. beardi : distinctly wider, O. dorrellae : widening, but less distinctly as CuA zigzagged distally ( O. angustum , not known); from O. dorrellae by MP linear to margin [ O. dorrellae : zigzagged near margin]; from O. angus- tum, O. beardi by IR2 origin between RP1-2, RP3-4 [ O. angustum , O. beardi : origin on RP1-2]; from O. dorrellae by wider wing: length (arculus to apex)/ maximum width, 3.1 [ O. dorrellae : 3.7], nodus to apex 2.5 times maximum width [although the wing of O. angustum is less complete, it is distinctly narrower, compare angle of posterior margin to anterior margin preserved between levels of nodus, origin of RP2]; width at level of two cells proximal to origin of RP 2 in O. angustum 75% that of O. threadgillae ; from O. liquetoalatum by wing shape: while length of arculus to nodus is equivalent, arculus to apex is about 2 mm longer in O. threadgillae ; from O. liquetoalatum , O. dorrellae by wing shape: length (arculus to apex) / maximum width 3.1 [ O. liquetoalatum : 2.6; O. dorrellae 3.7; others similar to O. threadgillae ( O. lochmum , O. worleyae , O. angustum not comparable by preservation)]; wing length (arculus to apex) / maximum width, O. dorrellae 3.7; from O. hobani by main veins less deeply curved near margin; from O. worleyae further by shape: posterior margin more deeply curved; from O. lochmum by RA–RP1 space becomes two cells wide about two cells proximal to pterostigma [ O. lochmum over seven cells proximal].

Further separated by colouration (sex unknown): proximal approx. 2/5 hyaline, dark apical to this except narrow lighter fascia just distal to mid-way between nodus, pterostigma, extending from anterior margin to mid-wing; size and extent of light fascia differs from: O. hobani about three times as wide, extending to or almost to posterior margin; O. angustum apparently similar to O. hobani as preserved; O. beardi , O. lochmum , wider than in O. threadgillae by small but definite amount, extending closer to posterior margin; O. dorrellae similar width as O. beardi , O. lochmum , probably extending to mid-wing (but damage in this region); O. liquetoalatum : hyaline throughout; O. worleyae : lightly infuscate throughout known wing.

Type material. Holotype: SR 98-12-10 (Republic A0307 , collected by Carolyn Threadgill 8.iv.1998): two well preserved, complete wings; disarticulated, in close association; with colour patterning clearly preserved; housed in the Stonerose Interpretive Center collection.

Description. Holotype, SR 98-12-10, forewing ( Figs. 19A , 20A ): distal to nodus rather wide-oval, symmetrical around longitudinal line from apex; posterior margin slightly widens about level of quadrangle; 30.5 mm long, 27.6 mm arculus to apex, 22.5 mm nodus to apex; 18.0 mm origin of RP2 to apex, 21.5 mm arculus to base of pterostigma, 16.5 mm nodus to base of pterostigma; 9.0 mm wide. Nodus at 28% wing length. Colouration as in diagnosis. Pterostigma anterior, posterior margins oblique; length 3.5 times width; subtends 5.5 cells; no oblique brace vein. 40 crossveins in postnodal space (complete), the distal-most one joining pterostigma (hyperstigmal crossvein); not aligned with postsubnodal crossveins. Maximum three cells wide in much of costal space distal to pterostigma. RA meets margin at apex; RA–RP1 space narrows near margin. RP1–IR1 space goes to two cells wide 10 cells distal to origin of IR1. Cells in apical portion increasingly dense, many small cells along margin. IR1 origin nine cells distal to origin of RP2; IR1–RP2 space becomes two cells wide about ten cells distal to origin. RP2 origin 6.5 cells distal to origin of IR2. No crossvein O. IR2 origin at subnodus. R3-4 origin less than 2/3 distance between arculus, nodus. Arculus immediately proximal to Ax2. Ax0 not detected. All main veins linear except proximal portion of IR1. MP, CuA slightly divergent at terminus on posterior margin. CuA ends at level about half way between nodus, pterostigma; CuA–A space maximum five cells wide.

Hind wing ( Figs. 19B , 20B ): As for forewing, except: Posterior margin evenly curved about level of quadrangle, does not slightly widen; 26.5 mm arculus to apex, 21.7 mm nodus to apex, 17.7 mm origin of RP2 to apex, 20.6 mm arculus to base of pterostigma, 15.7 mm nodus to base of pterostigma; 8.5 mm wide. Nodus at 30% wing length. Pterostigma length 3.5 times width; subtends six cells. 35 crossveins preserved (presume 36 total) in postnodal space, distal-most three hyperstigmal. One column four cells wide, mostly three in costal space distal to pterostigma. RP1–IR1 space goes to two cells wide 11 cells distal to origin of IR1. IR1 origin six cells distal to origin of RP2; IR1–RP2 space becomes two cells wide eleven cells distal to origin. RP2 origin probably five cells distal to origin of IR2. Origin of RP3-4 slightly proximal to position in forewing. MP, CuA sub-parallel at terminus on posterior margin. CuA–A space maximum six cells wide.

Etymology. The specific epithet is a patronymic formed from the surname of Carolyn Threadgill, the collector of the holotype, recognising her contribution.

Range and age. Republic locality A0307 of the Tom Thumb Tuff Member of the Klondike Mountain Formation; latest Ypresian.

Discussion. We presume the top wing of Figs. 19A and 20A to be a forewing and the bottom wing of these ( Figs. 19B and 20B ) to be a hind wing, as discussed above.

Figures

FIGURE 19. Okanagrion threadgillae holotype, SR 98-12-10. Photograph. A and B refer to drawings in Fig. 20. Scale bar is 5 mm.

FIGURE 20. Okanagrion threadgillae holotype, SR 98-12-10. A, drawing of wing A of Fig. 19; B, drawing of wing B of Fig. 19. Both to scale, 5 mm.