During sorting of extensive samples of amber from the mid-Cretaceous (Albian–Cenomanian: Grimaldi et al., 2002 and Shi et al., 2012) deposits of northern Myanmar, a single individual of the family was recovered. The inclusion was discovered in a deep reddish-orange piece of amber and initially was obscured from the left side of the wasp. The wasp was separated carefully from the remaining inclusions by trimming with a fine water-fed saw and the resulting chip was finely polished close to the specimen, so that it could be examined under both compound and stereomicroscopes (Fig. 1 and Fig. 2a). The individual is exceedingly well preserved and despite various particulates in the amber, is not generally obscured from view. There are minor fracture planes around the apices of the wings (which at first give them a fringed appearance), but these do not detract from observing the structures. The right antenna, particularly the more apical flagellomeres, has separated from the amber slightly along an internal fracture within the amber, and thereby results in an altered view of the feature. The body does have various small bubbles or micro-bubble froths in places that obscure the integument, but these are relatively minor. The only major detriment in preservation is a prominent fracture plane in the amber near the wasp that obscures portions of the left lateral, ventral oblique view (Fig. 2a). The format and terminology for the descriptions follow those used by Engel et al. (2013), and these authors also provide a general account of spathiopterygid relationships and morphology for the family. The description is provided to further document diversity within the family and to expand our knowledge of potential patterns of relationships (Grimaldi and Engel, 2007). Photomicrographs were prepared using a Canon EOS 7D digital camera attached to an Infinity K-2 long-distance microscope lens.

Family Spathiopterygidae Engel and Ortega-Blanco

Diagnosis (refer to Engel et al., 2013, for complete description of family): Compound eyes of moderate size, circular, with coarse ommatidia; ocelli present; occipital carina absent. Antennal toruli widely separated from clypeus, positioned on weakly protrudent antennal shelf, not overhung by frontal lamella; frons without depressions or grooves; antenna slender, 14-segmented, anellus absent, without placoid sensilla, with distinct curved trichoid sensilla apically on flagellomeres. Mesosoma higher than wide; pronotum with posterolateral corner nearly reaching tegula, posterior margin deeply concave, lateral surface fused to mesopleuron; prepectus absent. Mesoscutum with percurrent or indistinct notauli, lateral borders slightly converging posteriorly, transscutal sulcus complete; mesoscutellum about as long as wide, axilla not produced. Legs long with respect to body length; tibial spur formula 1-1-1; pretarsal claws simple, arolium large. Forewing distinctly larger than body, extending well beyond metasomal apex, spatulate, with or without well-defined marginal fringe, when present fringe setae not greatly elongate; venation represented by weakly nebulous or largely spectral lines on membrane, membrane with scattered short setae, hyaline, smooth to reticulate or wrinkled, pterostigma absent; venation greatly reduced, without C, single basal stem branching into spectral trace of A running to posterior wing margin and anteriorly with R running to anterior wing margin; Cu branching shortly after A, diverging to posterior margin of wing; Rs + M not contacting directly with Cu. Hind wing reduced or absent. Metasoma inserted low on mesosoma, between metacoxae; terga laterally covering lateral margins of sterna; without visible syntergites or synsternites; first metasomal segment reduced to small petiole and mostly obscured; second and third metasomal segments largest, the latter larger.

Diaspathion Engel and Huang, gen. nov.

Type species: Diaspathion ortegai Engel and Huang, new species.

Diagnosis: Head imbricate and impunctate. Compound eyes slightly bulging, with a reduced number of coarse ommatidia (ca. 40). Scape longer than compound eye; pedicel not rimmed; flagellomeres I–IV much longer than wide, thin, distinctly longer than remaining flagellomeres. Mesoscutum imbricate, with notauli slightly impressed, percurrent, converging posteriorly. Pronotum laterally with weak, transverse striation. Forewing membrane distinctly roughened and wrinkled, without marginal fringe of setae; venation as described for family (Engel et al., 2013). Hind wing completely absent. Metasoma about as long as remainder of body.

Etymology: The new generic name is composed of the Greek terms dia (meaning, “between”) and the diminutive of spathe (meaning, “paddle”). The gender of the name is neuter.

Diaspathion ortegai Engel and Huang, sp. nov.

Fig. 1 and Fig. 2

Diagnosis: As for the genus (vide supra).

Description: ♂: Total length 0.84 mm; forewing length 0.94 mm; integument reddish brown, lighter on antennae and legs. Head imbricate and impunctate, more weakly so in malar area; malar area well developed, about as long as compound eye; occipital carina absent; ocelli small, well separated from compound eyes; compound eyes prominent, berry-like in appearance (Fig. 1b), composed of around 40 coarse ommatidia. Antenna arising upward from a distinct but not prominent frontal shelf, with sparse, minute, fine setae, and such setae becoming longer and more numerous on successively more apical flagellomeres; scape relatively straight (Fig. 1c); pedicel about one-half scape length; flagellomeres I–IV thinner than pedicel (Fig. 1c); flagellomeres I and II shorter than scape and slightly longer than pedicel; flagellomeres III and IV about as long as pedicel; remaining flagellomeres shorter than pedicel, except apicalmost flagellomere, which is about as long as pedicel. Mesosoma imbricate, more finely and weakly so on mesopleura. Forewing membrane roughened (Fig. 1 and Fig. 2), not covered by setae or microtrichia, marginal setae absent; venation spectral but distinct, pattern of veins (R, Rs, M, a portion of Rs + M, Cu, and A present, Fig. 2b), as described for family (Engel et al., 2013). Legs elongate, with sparsely scattered, minute, fine setae; tibia without inner row of setae; probasitarsus much shorter than remainder of protarsus, meso- and metabasitarsomeres just slightly shorter than remainder of corresponding tarsomeres. Metasoma faintly imbricate, about as long as combined lengths of prosoma and mesosoma.

♀: Unknown.

Holotype: ♂, NIGP160526, Albian–Cenomanian boundary, Hukawng Valley, northern Myanmar; deposited in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China.

Etymology: The specific epithet is a patronym for our dear friend and colleague, Dr. Jaime Ortega-Blanco, authority on fossil Hymenoptera from the Universitat de Barcelona and formerly of the University of Kansas. Jaime was the first to hypothesize spathiopterygids in Burmese amber and we are delighted to validate his speculation.

Key to genera of Spathiopterygidae.

It is both exciting and expected to discover a spathiopterygid in Burmese amber. Given the broad geographical and temporal distribution of the previous records, it is unsurprising to find an individual in a deposit of more intermediary age. The Burmese species also extends the distribution of this family, expanding the known range into southern Eurasia and along the northern shores of the Tethys Ocean. Given these points, these minute wasps should be carefully sought in other Mesozoic sites such as those in France, North Carolina, Canada, Siberia, Alaska, and even Lebanon, albeit some are slightly outside of the known temporal range, but not dramatically so. Indeed, given their size and ease with which they ‘disappear’ among flow lines or reflective fractures, they may already have been collected among samples from these localities and perhaps have understandably been overlooked. Alternatively, to the uninitiated they may have also been passed over, because at a quick glance the wings are not distinctively ‘hymenopteran’ and could superficially suggest the wings of a male aleyroid or coccoid hemipteran.

The new genus is fascinating in that it, at least in some features, seems to bridge the morphological disparity between the Spanish and New Jersey taxa. Admittedly, there is a relatively minor diversity known thus far and few characters from which to work, but it would appear that Mymaropsis is the most basal member of the family based on its more developed hind wing. In this genus, the hind wing is certainly reduced and vestigial but is still present with some minor membranous area. In Spathiopteryx, the hind wing is reduced to a simple veinal stub, without a membrane of any kind (Engel et al., 2013), and in Spathopria and Diaspathion, the hind wing is clearly absent. Interestingly, this small transition series also correlates with geological age, with the two younger taxa being apparently more closely related based on an apomorphic loss of the hind wing. Naturally, a larger suite of character data is needed and hopefully more taxa will be discovered for a more extensive exploration of relationships within the family. Nonetheless, for the time being it seems safe to conclude, based on the aforementioned transition series, that familial relationships may be summarized as [Mymaropsis (Spathiopteryx [Diaspathion + Spathopria])] in advance of a cladistic analysis.

Documenting these tiny wasps certainly represents a major advance in understanding the diversity of parasitoids during various stages of the Late Mesozoic and refines our knowledge of relationships and the evolution of biological traits (Grimaldi and Engel, 2007). Nonetheless, one of the long-standing challenges will be to more fully understand the biology and ecology of these wasps, and this will be enhanced greatly by the discovery of females. Today parasitoids are critical in virtually all terrestrial ecosystems, as they regulate and influence populations of their hosts, which in turn impacts downstream taxa such as particular floral species, and are integral to host-parasite coevolution. Naturally, fossils representing crown groups with known biology are easily understood, but the more important revelations will come from knowledge of host-parasite relationships among those extinct clades more basal among the diversifications of particular superfamilies, perhaps spanning important host shifts or biological transformations (e.g., transitions to specializing in egg parasitoidism and the concomitant anatomical and physiological changes). Discovering the particular biology of these taxa will require either rare or uniquely preserved material, such as syninclusions with some indication of behavior, or novel methods of inference. Either way, overcoming this tremendous difficulty will reap broad-reaching rewards for understanding the phases of parasitoid evolution.