Systematic palaeontology
Class Insecta Linnaeus, 1758
Order Hymenoptera Linnaeus, 1758
Superfamily Tenthredinoidea Latreille, 1802
Family Xyelotomidae Rasnitsyn, 1968
Aethotoma gen. nov.
Type and only species. Aethotoma aninomorpha sp. nov.
Etymology. The generic name is a combination of the Greek prefix “aeth-,” meaning unusual and unique, and “-toma,” a suffix from Xyelotoma Rasnitsyn, 1968. The gender of the name is feminine.
Diagnosis. Antenna 10-segmented, enlarged first flagellomere about 4 times as long as remaining flagellomeres combined, much thicker than remainder of flagellum. Tarsomere V longer than combined length of tarsomeres III and IV. Forewing with Sc simple, terminating into R, lacking a separate crossvein-like distal part; pterostigma fully sclerotized; first abscissa of Rs (Rs1) about 1/5 of that of M (M1). Hind wing Sc with two branches.
Remarks. The new genus is placed in Xyelotomidae based on the antenna with the 3rd segment very long and thick but much fewer flagellomeres. It differs from other genera of the family by the simple Sc in the forewing and Sc with two branches in the hind wing. Xyelotomidae are likely a paraphyletic assemblage and not a natural group, representing a potential stem-group to Tenthredinoidea [8]. Should this be conclusively established in future studies, then Xyelotomidae will require division into multiple groups. In additional, even the monophyletic clade of Tenthredinoidea is challenged recently, and further research is needed [9].
Aethotoma aninomorpha sp. nov.
(Figs. 1 and 2)
urn:lsid:zoobank.org:act:BC73BF5C-3922-4C56-8A9D-0B3AB7028090
Etymology. “Aninomorphus” means “different shape”, referring to the unique venation of the forewings.
Holotype. CNU-HYM-NN2012003p/c; the fossil is complete except for the apical segments of the abdomen (the 6th segment onward); sex unknown.
Type locality and horizon. Collected from the Jiulongshan Formation of Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia, China, the late Middle Jurassic (Bathonian-Callovian boundary, 165 million years ago [Mya]) [10, 11].
Description. Body length 10.2 mm as preserved (Fig. 1). Head nearly trapezoidal, 2.8 mm wide, 1.8 mm high, compound eyes (1.2 mm high) relatively small, oval. Three ocelli present, round, together forming an equilateral triangle, closely spaced. Antenna (3.5 mm long) (Fig. 2a) much longer than width of head, scape (0.5 mm long) slightly thicker than pedicel (0.2 mm in length), twice as long as latter; first flagellomere (2.1 mm long) about 4 times as long as remaining 7 flagellomeres combined (0.6 mm), remaining flagellomeres somewhat equal in length and width, each about 1/3 width of first flagellomere.
Forewing (Fig. 2d) Sc simple (without branches), merging into R much prior to separation of Rs from R, probably shorter than half of C in length; veins C and R markedly thickening before pterostigma (length 1.8 mm, widest part 0.4 mm), latter fully sclerotized. First abscissa of Rs (Rs1, 0.2 mm) about 1/5 length of M (M1, 1.0 mm). M + Cu slightly bent, Rs + M (0.9 mm long) nearly three times as long as 1r-rs (0.3 mm long), latter equal to section of Rs nearest it (Rs2, 0.3 mm long); 2nd abscissa of M (M2, 0.6 mm) slightly shorter than 1m-cu (0.7 mm); 2r-rs of left forewing forking into 2 short braches reaching Rs (Fig. 3a, b and e), right forewing with 2r-rs forming a small loop, then forking into 2 long braches reaching Rs (Fig. 3a, c and f). Crossvein 3r-m distinctly bent at middle, about twice as long as 2r-m. In the right forewing, a free vein (about 0.2 mm) extending from middle point of 2m-cu (Fig. 3a, d and g). Hind wing partially preserved (Fig. 2c), with Sc two-branched, Sc2 short; at least 12 basal hamuli visible at about 1/6 of hind wing length near basal part of vein C, traces of distal and intermediate group hamuli visible (but details not clear).
Thorax (3.1 mm wide at the widest point, about 4.1 mm long) slightly wider than head; where observed, thoracic dorsum with rough sculpture (densely areolate or tuberculate); pronotum (2.2 mm wide) short; mesoscutum large, anterior edge arched. Protibia with two spur present, one long and one short (Fig. 2b) (0.4 mm long); protibia 1.4 mm long, probasitarsus equal to protarsomeres II and III combined, protarsomere V longer than combined lengths of protarsomeres III and IV, pretarsus with strong claw (0.2 mm long), with sharp tooth extending from inner side of each pretarsal claw; all legs covered by numerous fine setae, each tarsus with some stiff setae apically; lengths of individual protarsomeres (mm): 0.76, 0.27, 0.20, 0.17, 0.38; metatarsomeres: 1.01, 0.53, 0.35, 0.24, 0.49; metapretarsal claws relatively short, without teeth.