IRONOMYIIDAE, McAlpine & Martin, 1966

Grimaldi, David A., 2018, Basal Cyclorrhapha In Amber From The Cretaceous And Tertiary (Insecta: Diptera), And Their Relationships: Brachycera In Cretaceous Amber Part Ix David A. Grimaldi, Bulletin of the American Museum of Natural History 2018 (423), pp. 1-97 : 1-97

FAMILY IRONOMYIIDAE

DIAGNOSIS: Relatively stout-bodied flies; male frons very narrow to partially holoptic, no differentiation of facets; eyes bare. Flagellomere 1 in some species cordate to reniform, basal margin deeply emarginate; in some Cretaceous species with deep basal seam. Arista apical to preapical, micropubescent to bare, 3-articled (with 2 small, ringlike basal articles); palp 1-segmented; vibrissa absent. Prescutellum present, lenticular; scutellum with 8 marginal setae (median ones longest), dorsal surface with or without small setae. Wing membrane glassy, entirely or largely without microtrichia; faint stigma between apices of Sc and R 1; Sc free at base and apex, fused with R 1 for most of its length. Sc long, ca. 0.50– 0.65× length of wing; R 4+5 ends at wing tip; C ends at tip of R 4+5; A present, incomplete.

COMMENTS: This diagnosis was made more inclusive in order to accommodate the Cretaceous fossils, the family definition previously applying just to the Recent type genus. There is one living genus of the family, Ironomyia White (in eastern Australia, below), and five fossil genera, all from the Cretaceous (Early [Berriasian] to Late [Santonian]): Cretonomyia J.F. McAlpine ( McAlpine, 1973) , Eridomyia Mostovski and Hermaeomyia Mostovski (Mostovski, 1995) , Palaeopetia Zhang (Mostovski, 1995, herein) and Proironia in Bur- mese amber (herein). With the exception of Cretonomyia , all the fossils are from central and eastern Asia. Interestingly, there is no fossil ironomyiid known from the Cenozoic, despite the wealth of insect fossils from this period. Perhaps by this time the occurrence of ironomyiids had already contracted into Australia.

The compression fossils seem to be well placed in this family, based on the unique condition whereby Sc and R 1 are fused for all but their base and apices, although in all of them veins M 1 and M 2 are plesiomorphically forked, with a stem attached to the apex of cell d (instead of each directly attached to d). Other plesiomorphic features of Palaeopetia are discussed below, based on my new observations of specimens in Burmese amber. Cretonomyia pristina , in Late Cretaceous amber from western Canada, is a

TABLE 3

Characters in the cladogram for Ironomyiidae (fig. 37)

1. Vein Sc joined to R 1 in middle, with both veins free basally and apically.

2. Labellum small, width barely greater than width of prementum.

3. Legs (especially tibiae) with large, long, stout setae that are nearly perpendicular to longitudinal axis of leg segment.

4. Basal flagellomere with groovelike seam on lateral and mesal surfaces.

5. Wing membrane entirely devoid of microtrichia, even at wing margins.

6. Antennal pedicel with fingerlike lobes extended into basal flagellomere, one on mesal and one on lateral surface.

7. Cell d apically acute (position of crossvein dm-cu is acute to veins it connects).

8. Veins M 1 and M 2 connected directly to cell d (no stem).

9. Fusion of veins Sc and R 1 short, less than 0.4× vein lengths (vs.>0.6×).

10. Eyes not holoptic or dorsally touching in males.

11. Veins R 2+3 and R 4+5 very close, nearly parallel.

12. Anal lobe of wing well developed, protruding.

13. Acrostichal setae on mesoscutum reduced to two rows (vs. abundant and scattered).

14. Dorsocentral setae small, reduced.

15. Proboscis slender, rigid, extended well beyond oral margin; labrum long.

16. Thorax and abdomen with dark, bold, sexually dimorphic markings of velvety black and silvery pruinescence.

definitive ironomyiid, its pedicel even with the fingerlike lobe extending into flagellomere one (on medial and lateral surfaces), and a short cup cell, as in Ironomyia . It differs from Ironomyia by the following, mostly plesiomorphic features: Proboscis shorter, labellum broader; postvertical setae more strongly developed; 3 (vs. 2) notopleural setae; fore- and midtibiae with preapical dorsal seta; wing with Sc fused with R 1 for only a short segment, cell dm apparently stout (though not well preserved in the unique fossil).

McAlpine (2008) disputed that Lebambromyia acrai Grimaldi and Cumming , in Early Cretaceous amber from Lebanon, was an ironomyiid. Indeed, it has many plesiomorphic features: Sc parallel and very close to but not fused with R 1 (though sclerotized between them), vein dm-cu not oblique; cell cup relatively large; wing membrane with microtrichia; M 1+2 unforked; flagellomere 1 with deep emargination, but cordate, and without fingerlike lobe of pedicel. Upcoming phylogenetic work will determine whether Lebambromyia is a very primitive stem group to Ironomyiidae , as previously suggested ( Grimaldi and Cumming, 1999).

Relationships of Ironomyia to other basal Cyclorrhapha have been extensively discussed, the consensus being that it is a close relative to the Phoridae sensu lato (including Sciadocerinae ) ( Griffiths, 1972; Sinclair et al., 2013; Wiegmann et al., 2011), although Brown et al. (2015) hypothesized an Ironomyiidae + ( Lonchopteridae + Phoridae ) relationship, and McAlpine (2008) was equivocal but seemed to favor a close relationship of Ironomyiidae with Eumuscomorpha ( Syrphidae + Pipunculidae + Schizophora). An ongoing study of mine will further explore the relationships of Ironomyiidae to other families. Given the extralimital fossils of ironomyiids in the northern hemisphere, the phylogenetically basal position of the family among Cyclorrhapha, and the very restricted distribution of the three Recent species, Ironomyia is clearly a highly relict genus.

A cladogram of relationships of the three genera of Ironomyiidae preserved in amber (all from the Cretaceous), plus the living genus, is presented in figure 37. It is based on 16 morphologi- cal characters, listed in table 3. Results are discussed under the respective genera.