Microphorites Hennig, 1971

Shamshev, Igor V. & Perkovsky, Evgeny E., 2022, A review of fossil taxa of Microphorinae (Diptera, Dolichopodidae sensu lato), with redescription of the Eocene genus Meghyperiella Meunier, Zootaxa 5150 (3), pp. 411-427 : 418-420

Microphorites Hennig

Microphorites Hennig, 1971: 16 . Type species: Microphorites extinctus Hennig, 1971 , by monotypy.

Included species (alphabetically). Microphorites deploegi Nel, Perrichot, Daugeron & Néraudeau, 2004: 24 (Charentese amber, uppermost Albian, Lower Cretaceous, France); M. erikai Bramuzzo & Nel, 2017: 590 (lowermost Eocene, Oise amber, France); M. extinctus Hennig, 1971: 16 (Lebanese amber, Lower Cretaceous, Barremian, Jezzine, Lebanon); M. magaliae Perrichot & Engel, 2014: 31 (Vendean amber, Upper Cretaceous, France); M. moravicus Tkoč, Nel & Prokop, 2016: 185 (Studlov amber, Cretaceous (Cenomanian)/lower Paleogene, Moravia); M. oculeus Grimaldi & Cumming, 1999: 59 (Lebanese amber, Lower Cretaceous); M. pouilloni Ngô-Muller & Nel in Ngô-Muller et al., 2020: 2 (lowermost Cenomanian, Burmese amber, Myanmar); M. similis Grimaldi & Cumming, 1999: 57 (Lebanese amber, Lower Cretaceous); M. utrillensis Peñalver in Arillo et al., 2008: 31 (San Just amber, upper Albian, Lower Cretaceous, Spain).

Remarks. Hennig (1971) established this genus to include the single species M. extinctus described by him from Lebanese amber (Lower Cretaceous, Barremian, Jezzine, Lebanon (129.4–125 Ma)). Currently, Microphorites unites nine named species, which were found from different deposits dated over a very broad geological temporal range from Lower Cretaceous to lowermost Eocene: Lower Cretaceous—five species; Upper Cretaceous—three (?two); Eocene—one (?two). In terms of current geography, eight species are known from the Palaearctic Region ( Czech Republic, France, Lebanon, Spain) and one species from the Oriental Region ( Myanmar).

Grimaldi & Cumming (1999) described from Lebanese amber the next two species of Microphorites : M. similis (only female) and M. oculeus (only male). Two other Lower Cretaceous species of Microphorites are much younger. They were described from Charentese amber of France (Albian, 105.3–99.6 Ma) ( Nel et al. 2004) and from San Just amber of Spain (Albian, 112–105.3 Ma) ( Arillo et al. 2008): M. deploegi Nel, Perrishot, Daugeron & Néraudeau (male and female) and M. utrillensis Peñalver (only female), respectively.

The Upper Cretaceous fauna of Microphorites is known at least after two species. The first species was described from Vendean amber of France (Cenomanian to Turonian, 99.6–89.8 Ma) ( Perrichot & Engel 2014): M. magaliae Perrichot & Engel (only male). The second species was found in Burmese amber of Myanmar (lowermost Cenomanian, ~99 Ma): M. pouilloni Ngô-Muller & Neal (only male). Jouault et al. (2020) published a description of the female of M. pouilloni . However, the female described by these authors is not conspecific with M. pouilloni because of the differences with the male are beyond the range of sexual dimorphic variability in microphorines. Microphorites moravicus described after a female from Študlov amber of Czech Republic was dated from the Eocene (Lutetian, 47.8 Ma), although, the Upper Cretaceous age (upper Cenomanian, 91 Ma) cannot be precluded ( Tkoč et al. 2016; Bramuzzo & Nel 2017).

Finally, a species described from Oise amber of France (lowermost Eocene, 53 Ma) would support that Microphorites really occurred in the Eocene ( Bramuzzo & Nel 2017): M. erikai Bramuzzo & Nel (only female). Therefore, this species could be the youngest representative of the genus.

Hennig (1971) indicated the main features distinguishing Microphorites from Microphor (anal angle of wing strongly rounded) as well as from Microphorella and Parathalassius (antennae situated approximately in middle of anterior eye margin, arista two-segmented, basal crossvein of wing complete, eye lack hairs). Figure 21 ( Hennig, 1971: 17) shows that his expression “the anal angle of the wing is strongly rounded” means that in M. extinctus the anal lobe is weakly developed and the anal angle is obtuse (not right-angled as Microphor ). A review of available illustrations of the wing of other species assigned to Microphorites shows that the degree of curvature of the anal lobe is variable (anal lobe margin invisible in M. similis , M. oculeus and M. erikai ). It is especially clear in the case of Microphorites magaliae ( Perrichot & Engel 2014: fig. G2; Tkoč et al. 2016). In this species, the wing shape is the same as in the females of some Microphor species and in both sexes of many species of Schistostoma ; i.e., the anal lobe is strongly developed ( Brooks & Cumming 2022; Shamshev, unpubl. data).

Microphorites extinctus (as well as species of Microphor and Schistostoma ) differs from all species assigned later to Microphorites primarily by the complete (circumambient) costal vein (versus incomplete, i.e., ending at or just beyond R 4+5, or at M 1, leaving posterior margin of wing membranous). The costal termination is an important diagnostic character in higher level Empidoidea . Phylogenetically, it is probable undisputable that the circumambient costa is the plesiomorphic condition (e.g., Sinclair & Cumming 2006: 35, character 50). However, the reduction of the costa evolved independently in several groups of Empidoidea . This character has some “disadvantages” because, in some empidoids, the costa does not end abruptly (when incomplete) or it is weakened beyond meeting point with R 4+5 or M 1; i.e. along posterior margin of the wing (when complete) (see Sinclair & Cumming 2006 for some examples). Within the Microphorinae lineage, an incomplete costa was described in Avenaphora and Pristinmicrophor , within the Parathalassiinae + Dolichopodidae sensu stricto lineage—in extinct Cretomicrophorus , Archichrysotus and Retinitus , as well as in all Dolichopodidae sensu stricto.

In addition, Hennig (1971) noted that the ommatidia in M. extinctus are distinctly larger on the upper half of the eye and the mesonotum is fairly uniformly covered with fine hairs (besides macrosetae). Both features are unique for microphorines, but their phylogenetic value is unclear. The first character is applicable only to females because the male of M. extinctus remains unknown. An eye with enlarged upper ommatidia is a curious feature for females of microphorines, as Chvála (1983: 57) has already noted. In many species of these flies, the enlarged upper ommatidia are usually present in males (when compound eyes are holoptic), whereas in females they are uniformly small. Undifferentiated ommatidia (i.e., equally small) were described in males with holoptic eyes of all species assigned to Microphorites (Grimaldi & Cumming 19991; Nel et al. 2004; Perrichot & Engel 2014; Ngô-Muller et al. 2020), which is known in some recent species of Schistostoma as well ( Chvála 1987). Sinclair & Cumming (2006: 60) did not include the facet size character in their cladistic analysis.

In the remaining species assigned later to Microphorites , the costa is incomplete, as it follows from the original descriptions (a helpful summary, with some other characters, was provided by Tkoč et al. (2016)). However, the authors described somewhat different conditions of costal termination: costa ending at M 1 — M. utrillensis ; costa ending between R 4+5 and M 1 — M. deploegi , M. pouilloni ; costa ending at R 4+5 (or just beyond)— M. similis , M. oculeus , M. magaliae , M. moravicus , M. erikai . As far as we are aware, there are no similar examples of such broad variations in the costal termination among genera of empidoids possessing an incomplete costal vein.

Although the costal vein extends around the entire wing margin in species of Microphor and Schistostoma , its thickness is somewhat variable posteriorly. In Microphor , the costa becomes much thinner just beyond the apex of M 1 (including extinct M. rusticus ). In Schistostoma (including fossil species), the costa becomes thinner just beyond R 4+5 or, in some extant species, of nearly uniform thickness. It is somewhat curious but these features greatly resemble the distribution of costal termination in Microphorites summarised above.

A cladistic analysis of Microphorites is beyond the scope of our paper. Nevertheless, very provisionally, a complex of species including M. deploegi (Lower Cretaceous, uppermost Albian), M. magaliae (Upper Cretaceous, Cenomanian to Turonian) and M. moravicus (?Upper Cretaceous/Lower Paleogene) may be supported by the synapomorphic setation of the scutellum. These species share one pair of scutellar setae versus two pairs that are present in the oldest species of Microphorites , including M. extinctus , M. similis and M. utrillensis (unknown in M. oculeus )), as well as in potential outgroups. One pair of scutellar setae is present in some extant species of Schistostoma (two pairs in fossils).

The postpedicel of Microphorites varies considerably in shape and length. Although it is somewhat difficult to formalise it seems that the postpedicel of M. similis and M. utrillensis (as well as M. extinctus ) refers more or less to the plesiomorphic condition suggested by Chvála (1983): moderately long conical postpedicel and at most equally long stylus. However, it should be noted that the postpedicel of microphorines is often not quite conical and bilaterally symmetrical, which can lead to differences in the shape depending on angle of view (e.g., Hennig 1971: 5, figs 2, 3). In M. oculeus , M. deploegi , M. magaliae and M. moravicus , the postpedicel is abruptly tapered (broadened at base and constricted distally). Similar transformations of the shape of the postpedicel are present in species of Microphor and Schistostoma , as well as in some groups of Parathalassiinae .

It seems that Microphorites pouilloni from Burmese amber is placed somewhat aside among other species of the genus. Although M. pouilloni retains two pairs of scutellar setae, this species possesses a longer list of unique and potentially apomorphic features, including onion-shaped postpedicel, long basal section of M 2 (= m-cu), which is nearly as long as crossvein dm-m (= dm-cu), and some others ( Ngô-Muller et al. 2020).

Two species assigned to Microphorites ( M. moravicus and M. erikai ) share the wing with a brownish pterostigma.Amongst microphorines the pterostigma is present in Microphor , Meghyperiella and Pristinmicrophor ; in Schistostoma the pterostigma is usually present, but sometimes weakly so, or absent (in fossil species). The pterostigma is absent in Avenaphora and Curvus .

Microphorites moravicus is a distinct species with rather clear affinities to some Cretaceous species of Microphorites , as have been mentioned above. Microphorites erikai resembles more an extant species of Microphor or Schistostoma . It possesses even three pairs of scutellar setae that are usually present in Microphor and, sometimes, in Schistostoma . There are no characters suggesting closer relationships of M. moravicus and M. erikai . Therefore, in these species the pterostigma has probably evolved independently.

To conclude, an assemblage of the species known nowadays as the genus Microphorites cannot be precisely defined. The species assigned to Microphorites can be separated into two groups. The first group includes only M. extinctus (the type species) and, therefore, it is the genus Microphorites sensu Hennig’s original concept ( Hennig 1971). However, the question about monophyly of this genus remains open.

The second group ( M. similis species group) includes all other species assigned later to Microphorites . Provisionally, this group could be supported by the apomorphic state of the costal vein (incomplete) and would deserve a generic level status. However, a curiously broad variation of the costal termination has been described. Since it is unclear if this pattern has phylogenetic significance, a misinterpretation of the costal termination by the authors, as one of the possible explanations, cannot be precluded. Therefore, we retained provisionally the M. similis group within Microphorites as an assemblage of the species with questionable systematic position.