Research Article |
Corresponding author: John T. Huber ( john.huber2@agr.gc.ca ) Academic editor: Petr Janšta
© 2023 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.
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
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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 compression 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 amber 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.
Chalcidoidea, Eocene compression fossil, Mymaridae
Parasitoid wasps of the family Mymaridae (Hymenoptera), almost all parasitic in eggs of other insects, are common and widespread, occurring on all continents except Antarctica, from 81°49'N (Hazen Camp, Canada) to 54°57'S (Bahía Aguirre, Tierra del Fuego, Argentina). They also occur on most islands, even those farthest 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 Baeomorphidae), represented almost entirely by inclusions in amber (
Measurements, in millimeters, were taken from the photographs as accurately as possible and converted into micrometers (μm). Given that the end points of a structure were not always clear, their measurements were rounded to the nearest 5 μm 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 micrometer measurements.
fu = funicle segment, mps = multiporous plate sensilla. The specimen is deposited in:
Eotriadomeroides abjunctus Huber, here designated.
Female. Antenna with funicle 8-segmented and clava 1-segmented (Figs
Male. Unknown.
From the Greek, eos, meaning early + Triadomerus (a compound 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).
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-segmented 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. Examination of the clava of Eotriadomeroides does not suggest it is 2- or 3-segmented but rather that it is clearly 1-segmented, i.e., entire (Fig.
Holotype
female (
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 (
Female. Color. Vertex, antenna except radicle, dorsum of body, except for scutellum, and ovipositor sheaths dark brown or almost black; face, radicle, scutellum, and mesosoma and metasoma ventrally apparently lighter brown (Fig.
From the Latin abjunctus, meaning disunited or separated, 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).
Chronologically, Eotriadomeroides (43–46 my), falls almost midway between Triadomerus (70–90 my) and Neotriadomerus (present day). Evidently, Triadomerini is an ancient lineage that occurs continuously throughout much of the geological history of Mymaridae as currently understood. A related lineage within Triadomerinae, the Aresconini, contains extant species in three genera (
The middle Jurassic and early Cretaceous had gymnosperm-dominant environments worldwide, which changed to angiosperm-dominant environments in the later Cretaceous (
The piece of shale that contained Eotriadomeroides also contained other synimpressions, 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.
We thank the United States Forest Service for allowing D. Greenwalt to collect compression 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.