JHR 96: 657-666 (2023) age Sy” JOURNAL OR Shen wntemicetiente doi: |0.3897/jhr.96. 107379 RESEARCH ARTICLE () Hymenopter a 9 https://jhr.pensoft.net The Inarasional Society of Hymenopreriss, RESEARCH A new compression fossil, Eotriadomeroides abjunctus Huber, gen. & sp. nov. (Hymenoptera, Mymaridae), in Eocene shale from the Kishenehn Formation, USA John T. Huber!, Dale E. Greenwalt? | Natural Resources Canada clo Canadian National Collection of Insects, Arachnids and Nematodes, K.W.- Neatby Building, 960 Carling Ave., Ottawa, ON, KIA 0C6, Canada 2 Department of Paleobiology, National Museum of Natural History, MRC 121, Smithsonian Institution, 10” & Constitution Ave. NW, Washington, D.C., 20013-7012, USA Corresponding author: John T. Huber (john. huber2@agr.gc.ca) Academic editor: Petr Janta | Received 1 June 2023 | Accepted 31 July 2023 | Published 15 August 2023 Attps://zoobank.org/D3EF3F05-9185-41 B9-A524-1 CAC7BIC2D6B Citation: Huber JT, Greenwalt DE (2023) A new compression fossil, Eotriadomeroides abjunctus Huber, gen. & sp. nov. (Hymenoptera, Mymaridae), in Eocene shale from the Kishenehn Formation, USA. Journal of Hymenoptera Research 96: 657-666. https://doi.org/10.3897/jhr.96.107379 Abstract A new fossil genus and species of fairyfly, Eotriadomeroides abjunctus Huber & Greenwalt, gen. and sp. nov. (Hymenoptera: Chalcidoidea: Mymaridae), is described and illustrated from a female preserved as a compres- sion fossil in middle Eocene shale from the Kishenehn Formation, Montana, USA. It is compared to extant species of Neotriadomerus Huber, known only from Australia, and Triadomerus Yoshimoto, a Cretaceous am- ber fossil from Canada. It is suggested that these three genera, classified together in Triadomerini, likely the most ancestral lineage of Mymaridae, are evidence of the Middle or perhaps Late Jurassic origin of the family. Keywords Chalcidoidea, Eocene compression fossil, Mymaridae Introduction Parasitoid wasps of the family Mymaridae (Hymenoptera), almost all parasitic in eges of other insects, are common and widespread, occurring on all continents ex- cept Antarctica, from 81°49'N (Hazen Camp, Canada) to 54°57'S (Bahia Aguirre, Tierra del Fuego, Argentina). They also occur on most islands, even those farthest Copyright John T. Huber & Dale E. Greenwalt. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 658 J.T. Huber & D. E. Greenwalt / Journal of Hymenoptera Research 96: 657-666 (2023) from continents, e.g., the Hawaiian Islands, St. Helena, and French Polynesia, or those with harsh climates, e.g., Greenland, Iceland, Auckland Islands, Campbell Island and South Georgia; the latter three more than 50°S. Mymaridae are also one of the two best represented families of Chalcidoidea in the fossil record (the other is Baeomorphi- dae), represented almost entirely by inclusions in amber (Yoshimoto 1975; Poinar and Huber 2011; Engel et al. 2013). Very few Mymaridae are described from compression fossils (Huber and Greenwalt 2011). The fossil records for the family are from the Cretaceous to the Pleistocene, a duration of at least 100 my, though with a large time gap of about 40 my between the Cretaceous and Tertiary fossils records. A compression fossil specimen from the Kishenehn Formation in Montana, USA, representing a new genus and species, is described here. Methods Huber and Greenwalt (2011) described the methods of collecting and photographing insect compression fossils from the Kishenehn Formation. ‘The fossil described below was collected in accordance with the United States Forest Service Special Use Permit HUN465. Greenwalt et al. (2015) described the taphonomy of the Kishenehn Formation. Measurements, in millimeters, were taken from the photographs as accurately as possible and converted into micrometers (um). Given that the end points of a struc- ture were not always clear, their measurements were rounded to the nearest 5 um and should be treated as approximate only. Length/width ratios of the antennal segments were calculated from the millimeter measurements, not from the rounded-off microm- eter measurements. Abbreviations used fu = funicle segment, mps = multiporous plate sensilla. The specimen is deposited in: NMNH Department of Paleobiology, National Museum of Natural History, Washington, DC, USA. Results Eotriadomeroides Huber, gen. nov. https://zoobank.org/3A127582-2F52-40DF-BDA3-ECDB8FBA27A3 Figs 1-8 Type species. Eotriadomeroides abjunctus Huber, here designated. Diagnosis. Female. Antenna with funicle 8-segmented and clava 1-segmented (Figs 2-5); fore wing with venation extending almost to wing apex, with postmarginal New genus and species of compression fossil 659 vein as wide as marginal vein or parastigma and ~2.7x as long as parastigma + marginal + stigmal veins (Fig. 7); tarsi 5-segmented (Fig. 8); fore wing microtrichia apparently extending to base of parastigma; hind wing relatively narrow, with acute apex; oviposi- tor extending ventral to mesosoma almost to level of head and not exserted posterior to apex of gaster (Fig. 1). Other details are apparently the same as for Neotriadomerus Huber, morphologically the genus most similar to Eotriadomeroides. Male. Unknown. Derivation of genus name. From the Greek, eos, meaning early + Triadomerus (a com- pound word derived from Greek, tries, meaning three, and meros, meaning part, referring to the 3-segmented clava) + the suffix -oides, meaning like, resembling. Eotriadomeroides (gender masculine) is therefore an “early Triadomerus-like” genus, referring to its geological age (the Eocene) and morphological similarity to the two other, evidently related genera: Neotriadomerus (with all its species extant) and Triadomerus (with its single species extinct). Relationships. Genera of Mymaridae are usually divided formally into subgenera if females of different species within a given genus have either a 1- or 2-segmented clava, or either a 2- or 3-segmented clava, and the other morphological features are essentially identical. So far, no genus is known to have its included species with either a 1-segment- ed or a 3-segmented clava but none with a 2-segmented clava. Only one genus (Anaphes Haliday) possibly has its included species with a 1-, 2-, or 3-segmented clava but so far Anaphes species with 3-segmented clava have yet been described and named. Examina- tion of the clava of Eotriadomeroides does not suggest it is 2- or 3-segmented but rather that it is clearly 1-segmented, ie., entire (Fig. 5). For comparison, the species of Eoan- aphes Huber and Eoeustochus Huber from the same formation and apparently with the same quality of preservation, are clearly 3-segmented whereas those of Gonatocerus Nees are just as clearly 1-segmented (Huber and Greenwalt 2011). If the clava of E. abjunctus were 2- or 3-segmented then it could be classified as a subgenus of Neotriadomerus, given that all other features, except relative lengths of postmarginal vein to the rest of the vena- tion, are almost the same in both taxa. Eotriadomeroides would then key to Neotriado- merus in the key to Cretaceous genera of Mymaridae (Poinar and Huber 2011). Another possibility would be to treat £. abjunctus as a subgenus within Triadomerus Yoshimoto, described from amber from Cedar Lake, Manitoba (Yoshimoto 1975), which is only about 1000 km away from the type locality (the Kishenehn Basin, Montana) of E. ad- junctus. According to McAlpine and Martin (1969) the actual source of the Cedar Lake amber is more likely to be upstream, along the Saskatoon River either near Saskatoon, Saskatchewan, or Medicine Hat, Alberta, respectively about 650 km and ~280 km from the type locality of E. abjunctus as determined from the present day configuration of the localities (essentially unchanged from 46 my years ago). Triadomerus does not have the ovipositor extending anteriorly ventral to the mesosoma and it has a relatively short postmarginal vein compared to length of stigma + marginal + parastigmal veins, so we treat E. abjunctus as belonging to a new genus, different from both Neotriadomerus and Triadomerus, both of which have a 3-segmented female clava and are known, respec- tively, from seven extant and one extinct species. Eotriadomeroides is best classified in Tri- adomerini (Huber 2017) but exact relationships among the genera still need resolution. 660 J. T. Huber & D. E. Greenwalt / Journal of Hymenoptera Research 96: 657-666 (2023) Eotriadomeroides abjunctus Huber, sp. nov. https://zoobank.org/ FOBF8666-43A7-4DFA-A7F9-5ED9 16490407 Figs 1-8 Material examined. Holotype female (NMNH), on 18 x 14 x 0.15 cm piece of oil shale (Fig. 9), labelled “Holotype Eotriadomeroides abjunctus Huber. USNM # PAL 620738”. The circle/square scratched onto the surface of the shape indicates the holotype location. The specimen was collected in 2012 at locality #43946, Park site, Kishenehn Formation, Montana, USA. Diagnosis. Eotriadomeroides abjunctus is the only described species in the genus. Its diagnosis is therefore the same as for the generic description. Comparing it with species of morphologically similar genera, it differs from all the described species of Neotriadomerus (Huber 2017) as follows: clava 1-segmented (clava 3-segmented in Neotriadomerus species); postmarginal vein ~2.7x as long as parastigma + marginal vein + stigmal veins (postmar- ginal vein at most 0.90x as long in Neotriadomerus species); hind wing narrow and apically acute (hind wing wide and apically blunt in Neotriadomerus species). The apparent absence of a straight setal line extending from apical margin of fore wing about halfway towards the parastigma + marginal veins (Fig. 7) is an additional feature that may separate E. abjunctus from Neotriadomerus but the wing surface of E. abjunctus is not clear enough to be sure if the setal line is absent. Fotriadomeroides abjunctus differs from Triadomerus bulbosus Yoshi- moto by the clava 1-segmented (3-segmented in 7’ bulbosus), ovipositor extending ventral to mesosoma as far as head (ovipositor not extending anteriorly ventral to mesosoma in 77 bulbosus), and relatively longer postmarginal vein (relatively shorter in 7’ bulbosus). Description. Female. Color. Vertex, antenna except radicle, dorsum of body, except for scutellum, and ovipositor sheaths dark brown or almost black; face, radicle, scutel- lum, and mesosoma and metasoma ventrally apparently lighter brown (Fig. 1). Total body length ~2850. Head. Head length ~205, head width ~600; mid ocellus diameter ~35. Antenna (Figs 2—5). Three (possibly 4) mps are visible on the right clava and one on fu, of the left antenna (Fig. 5); the mps that most likely should occur on the remaining funicle segments are not visible. Length/width measurements: range (ratios) of anten- nal segments: radicle? ~85/~12 (2.08), scape excluding radicle ~230/~90 (2.53), pedicel -751-50 (1.47), fu, -170/-45 (3.85), fu, ~160/-40 (3.83), fu, ~150/-40 (3.67), fu, -150/-45 (3.33), fu, ~140/-40 (3.08), fu, ~150/-40 (3.60), fu, ~135/40 (4.00), fu, ~125/-150 (2.57), clava ~325/~85 (3.76). Mesosoma. Mesosoma length ~900, metano- tum with dorsellum almost certainly triangular (Fig. 6). Wings. Fore wing (Fig. 7) with microtrichia uniformly covering entire surface, apparently to base of parastigma and ap- parently with one row of a few microtrichia posterior to apex of submarginal vein; fore wing length/width ~1930/~560, length/width 3.50, longest marginal setae ~80; hind wing length ~ 1150, width ~45, longest marginal setae ~115, with wing apex acute. Legs. Tarsi 5-segmented, the tarsomeres becoming shorter towards apex of tarsus (legs seg- ments mostly unrecognizable except two tibiae in part and two tarsi visible, with the end points of basal tarsomeres unclear). Metasoma. Petiole (Fig. 6) evidently short; gaster with terga apparently about equal in length. Metasoma length ~1875; ovipositor length ~2640, with sheaths extending anteriorly ventral to mesosoma to level of pronotum. New genus and species of compression fossil 661 ey cheers 1000 pm pe my ia ps: z atic eal Sa i mi: ae a ee ae Figures |, 2. Eotriadomeroides abjunctus Huber, holotype female | habitus (except most legs not visible) 2 pronotum + head + partly disarticulated antennae. Derivation of species name. From the Latin abjunctus, meaning disunited or sep- arated, refers both to the strongly disjunct geographic distribution of this 40 my old fossil from extant members of Neotriadomerus, the most similar looking genus, and to the fact that some of the fossil’s appendages are broken into parts (the antennae) or are separated from the body (the legs). 662 J. T. Huber & D. E. Greenwalt / Journal of Hymenoptera Research 96: 657-666 (2023) transverse” trabecula as Figures 3-5. Eotriadomeroides abjunctus Huber, holotype female 3 head + part of antennae 4 left an- tenna (pedicel—fu,) 5 fu, + clava of both antennae. New genus and species of compression fossil 663 am propedeum " base’of} submarginal) ey Figures 6, 7. Eotriadomeroides abjunctus Huber, holotype female 6 mesosoma 7 wings + metasoma. 664 J.T. Huber & D. E. Greenwalt / Journal of Hymenoptera Research 96: 657-666 (2023) nily : vTap % Calvert Marine Museum Fossil Club “% [| Solomons, MD www.calvertniarinemuseum.com ) f ra5 tb OL 6 shu tinl uutlunituilinstistiustisl it -) Wha hii iy\'} 4 e } ‘ ie “4 pe ns Ip NBL G \ t Tevth ae tes aan ie at ¢ hams j f ta + 4 2 Re - Le | 8 , 9 s £ z wWOo;- WW i, iI wil wtuilig tility wll il A, (9) ‘ ¥ t ee Sy ahs "i Ha Figures 8, 9. Eotriadomeroides abjunctus Huber, holotype female 8 tibiae and tarsi of one? pair of legs 9 shale piece containing holotype (circled) of Eotriadomeroides abjunctus Huber. New genus and species of compression fossil 665 Discussion Amorim and Greenwalt (2020) described Synneuron (Diptera: Canthyloscelidae) from the wings of two fossil specimens, one from the Kishenehn Formation and one from the Koonwarra Fossil Bed in Australia. Given their strongly disjunct (perhaps worldwide) distribution, they suggested the Cretaceous as the minimum age for Synneuron, but, more likely, based on their phylogenetic analysis of the tribe it is classified in, they proposed the Middle Jurassic as the minimum age of the genus. Synneuron has two extant species, one Palaearctic and the other Nearctic. The case of Eotriadomeroides and Neotriadomerus may be similar. Although they are classified in different genera, they, together with the Cretaceous genus Triadomerus, are best classified in the same lineage, the Triadomerini (Huber 2017), with only the species of Neotriadomerus extant. This tribe is likely the most ancestral lineage within Mymaridae, based on its morphology, and its included genera were possibly worldwide in distribution early in the existence of Mymaridae as a recognizable taxon, just as the present day Mymaridae are worldwide. And, as with Syn- neuron and its relatives, the Triadomerini may also have originated as a Pangaean clade. More likely, however, Triadomerini originated more recently, in the middle Jurassic, as estimated by Peters et al. (2018). Regardless of the actual age of origin, Mymaridae are small wasps easily capable of being dispersed aerially for long distances, as evidenced by their current existence on remote islands. So, if they did originate well after the breakup of Pangaea, dispersal worldwide from one or other of those putative centres of origin, either Laurasia or, much more likely, Gondwana would certainly have been possible. Chronologically, Eotriadomeroides (43-46 my), falls almost midway between Triado- merus (70-90 my) and Neotriadomerus (present day). Evidently, Triadomerini is an ancient lineage that occurs continuously throughout much of the geological history of Mymari- dae as currently understood. A related lineage within Triadomerinae, the Aresconini, con- tains extant species in three genera (Huber 2017), and one extinct species in one genus, Myanmymar, from 100 my Burmese amber (Poinar and Huber 2011).One hopes that the large time gaps will eventually be filled as more fossils deposits containing Mymaridae are discovered and better evidence for the age of origin of the family will be found. The middle Jurassic and early Cretaceous had gymnosperm-dominant environ- ments worldwide, which changed to angiosperm-dominant environments in the later Cretaceous (Wing 2000). This change in flora, presumably accompanied by a similar change in fauna (including perhaps the hosts of Mymaridae), may partly explain why two of the genera (Eotriadomeroides and Triadomerus) of Triadomerini are extinct and only one genus (Veotriadomerus) is extant and found only in the southern Hemisphere, which is where many of the archaic taxa of extant Hymenoptera seem to occur. The piece of shale that contained Fotriadomeroides also contained other synim- pressions, as follows: 2 Aphididae and 22 Corixidae (Hemiptera), 16 Chaoboridae, 1 Culicidae and 3 other flies (Diptera), 1 Chalcididae, 1 Chalcidoidea, 1 Formicidae and 1 other wasps (Hymenoptera), 1 Thysanoptera, and 1 plant (Cupressoideae). These insects together suggest they occurred in moist habitat near water. 666 J. T. Huber & D. E. Greenwalt / Journal of Hymenoptera Research 96: 657-666 (2023) Acknowledgements We thank the United States Forest Service for allowing D. Greenwalt to collect com- pression fossils from the Kishenehn Formation under the auspices of United States Forest Service Special Use Permit HUN465. We gratefully acknowledge the help of Jennifer Read (Canadian National Collection of Insects, Arachnids and Nematodes, Ottawa, Canada) for labelling the figures and compiling them into plates. 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