Systematic palaeontology

Order Odonata Fabricius, 1793

Suborder Zygoptera Selys-Longchamps, 1854

Superfamily Coenagrionoidea Kirby, 1890

Family Platycnemididae Yakobson & Bianchi, 1905

Subfamily Palaeodisparoneurinae Poinar et al.9

Yijenplatycnemis huangi gen. et sp. nov

(Figures 1, 2, 3, 4, 5).

Figure 2: Yijenplatycnemis huangi gen. et sp. nov. (A–F) Holotype (NIGP164757); (G–I) paratype (BA16200). Photograph of head (A); thorax (B); hindwing (C); foreleg (D); midleg (E); hindleg (F); left forewing and hindwing (G); left forewing base (H); hindwing apex (I). Full size image

Figure 3: Yijenplatycnemis huangi gen. et sp. nov. Paratype (SMNS Bu-137); Photograph of specimen (A), right forewing base (B) and left forewing apex (C). Full size image

Figure 4: Yijenplatycnemis huangi gen. et sp. nov. Paratype (BA16200); line drawing showing venation of left forewing (A) and hindwing (B) (drawn by DZ). Abbreviations: AA, anterior anal; Arc, arculus; Ax, primary antenodal crossvein; Cr, nodal crossvein; CuA, cubitus anterior; CuP, cubitus posterior; DC, discoidal cell; IR, intercalary radial vein; MA, median anterior; MP, median posterior; N, nodus; Pt, pterostigma; RA, radius anterior; RP, radius posterior; ScP, subcosta posterior; Sn, subnodal crossvein. Full size image

Figure 5 Reconstruction showing the courtship behaviour of huangi gen. et sp. nov. from the mid-Cretaceous tropical forest in Burma (drawn by DZ). Full size image

Etymology

The generic name is after Mr Huang Yijen, the donator of the type specimen, and the typical genus Platycnemis. The specific name is after Mr. Huang Yijen. Gender masculine.

Holotype

NIGP164757, head, thorax and abdomen base well preserved, forewing bases attached to thorax, one fragmentary hindwing near legs, all legs except for right hindleg well preserved; deposited in NIGPAS.

Paratype

BA16200, head missing, thorax and abdominal basal segments present, left forewing and hindwing complete, right wing bases badly preserved, only forelegs and midlegs present; temporarily housed at NIGPAS and will eventually be deposited in the Lingpoge Amber Museum in Shanghai. SMNS Bu-137, two forewings well preserved and attached to thorax, a fragmentary leg present; housed at State Museum of Natural History in Stuttgart (Germany).

Locality and Horizon

Hukawng Valley, Kachin Province, Myanmar; lowermost Cenomanian, lowermost Upper Cretaceous.

Diagnosis

Very small damselfly, complete wing length about 11–14 mm; DC closed and quadrangular with MAb perpendicular to MAa; five postnodal and five postsubnodal crossveins present, somewhat aligned; only one postnodal crossvein present distal of Pt; midfork slightly basal of N; RP1 with strong angle below very long pterostigmal brace; area between RA and RP1 greatly widened distal of Pt; IR2 aligned with Sn; IR1 short, originating below Pt; MA long, ending on posterior wing margin below base of RP2; MP short, one or two cells long; CuA reduced to oblique vein; Pt very small, less than half length of surrounding cells; all tibiae spectacularly expanded, covered with two brown bands, in pod-like sclerite except on metatibiae where of semi-circular shape.

Description

Specimen NIGP164757 (Figs 1A and 2A–F), body well preserved. Head dark (Fig. 2A), 2.74 mm long and 0.97 mm wide; eyes 0.89 mm wide, well separated by gap of 0.79 mm; ocelli located low between eyes; antenna three segmented, with segment 1 short and stout, segment 2 stout and 0.75 mm long, segment 3 slim and 0.76 mm long. Legs well developed, profemur 4.11 mm long and armed with long spines in basal part, protibia 2.66 mm long and 0.61 mm wide (Fig. 2D), tarsus 0.62 mm long (claws excluded); mesofemur 5.03 mm long, mesotibia 3.06 mm long and maximum 0.81 mm wide, tarsus 0.74 mm long (Fig. 2E); metafemur 9.02 mm long, metatibia 6.63 mm long and maximum 2.96 mm wide, tarsus 0.91 mm long (Fig. 2F); paired long spines present on tibia and tarsi; tibia armed with about ten pairs of spines; tarsi slightly curved, three segmented, with length of third tarsomere equal to first two tarsomeres combined; basal tarsomere armed with two pairs of long spines, second and third tarsomere armed with four pairs of spines; apical claws symmetrical, 0.12–0.16 mm long.

Specimen BA16200 (Figs 1C–D and 2G–I), left hindwing complete. Wing length 14.07 mm, width at level of N 1.42 mm; length from wing base to Arc 2.24 mm, from Arc to N 2.03 mm, from N to Pt 8.33 mm, from Pt to wing apex 1.45 mm. Primary antenodal crossveins present (Fig. 2H), Ax0 close to wing base, Ax1 1.29 mm distal of Ax0, Ax2 0.64 mm distal of Ax1; no secondary antenodal and antesubnodal crossveins present. Five postnodal and five postsubnodal crossveins present before Pt, somewhat aligned. One postnodal and one postsubnodal crossvein present distal of Pt, non-aligned (Fig. 2I). Arc angular and aligned with Ax2. DC basally closed, free and rectangular, 0.8 mm long and 0.18 mm wide. Subdiscoidal cell free and elongate, 0.81 mm long and 0.2 mm wide. Nodal structures well preserved, Sn aligned with Cr. Midfork (base of RP3/4) slightly basal of N; RP3/4 curved, reaching posterior wing margin just below base of Pt brace. Base of IR2 aligned with Sn, one cell and 0.93 mm distal of midfork; IR2 basally straight but distally zigzagged, ending on posterior wing margin just below Pt. RP2 originating three cells distal of Sn, equidistant between N and Pt, lying 3.6 mm distal of Sn. IR1 originating below end of Pt and six cells distal of base of RP2. RP1 with strong angle below pterostigmal brace. MA basally slightly curved but distally zigzagged, reaching posterior wing margin just below base of RP2. MP curved and short, covering two cells. CuA short, reduced to oblique vein. Pt quite small, rectangular and hyaline, 0.47 mm long and 0.22 mm wide.

Specimen SMNS Bu-137 (Fig. 3) shares all wing characters of specimen BA16200 (Fig. 4) besides following differences: wing short and 11.5 mm long; MP one or two cells long; IR1 originated below Pt base, and five cells distal base of RP2.

Remarks

Y. huangi has a short vein IR1 originating below the distal side of the pterostigma which is only present in a few damselflies, viz. the platycnemidid Palaeodisparoneura burmanica Poinar, Bechly and Buckley, 2010, the hemiphlebiid Burmahemiphlebia zhangi Zheng et al.27, the dysagrionid Burmadysagrion zhangi Zheng, Wang and Nel, 2016, and the recent perilestid genus Perilestes Hagen in Selys-Longchamps, 1862. Perilestes species have the base of RP3/4 and IR2 distal of the nodus, differentiating them from Y. huangi29. Burmadysagrion zhangi has a unique discoidal cell (anterior and posterior sides not parallel, and the basal side longer than the distal side), long MP and CuA, star-shaped Pt, and can thus be easily distinguished from Y. huangi30. Y. huangi has a rectangular discoidal cell, short CuA, RP1 with strong angle below Pt base as in both P. burmanica and Burmahemiphlebia zhangi23,30, but differs from the latter two in having only one postnodal crossvein distal of Pt, a smaller Pt, and expanded male tibiae. However, Burmahemiphlebia zhangi has a basally open discoidal cell in the forewing, closed in the hindwing, quite different from Y. huangi, while P. burmanica has a closed discoidal cell more like Y. huangi.

Very few modern male damselflies have expanded tibia, namely Platycypha Fraser, 1949 (Chlorocyphidae), Platycnemis Burmeister, 1839, Proplatycnemis Kennedy, 1920, Copera Kirby, 1890, Matticnemis Dijkstra, 2013 (tibiae weakly expanded) and Pseudocopera Fraser, 1922 (Platycnemidae: Platycnemidinae)32. Affinities of Y. huangi with Chlorocyphidae are excluded because of the different wing venation (numerous antenodals, long CuA, no angular RP1 in Chlorocyphidae)33.

The wing venation of Y. huangi is very similar to that of the fossil platycnemid P. burmanica. Platycnemididae, called white-legged damselflies, currently consist of over 400 species, widely distributed in the Old World34,35,36. They are currently divided into six modern subfamilies35 plus the Cretaceous Palaeodisparoneurinae Poinar et al.9. Despite the fact that the type specimen of P. burmanica is a male without expanded tibiae, Y. huangi has all the characters listed in the diagnosis of this subfamily23. On the other hand, Y. huangi strongly differs from modern Platycnemidinae in the very short veins IR1, MP and CuA (apomorphies of Palaeodisparoneurinae), and the broad area between RP1 and IR2. Here we establish a new genus for Y. huangi and place it in the Palaeodisparoneurinae. This attribution implies a convergent evolution in the expanded tibiae between Y. huangi and modern Platycnemidinae.