Pristinmicrophor Tang, Shi, Wang & Yang

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 : 420-421

Pristinmicrophor Tang, Shi, Wang & Yang

Pristinmicrophor Tang, Shi, Wang & Yang, 2019: 2 . Type species: P. hukawngensis Tang, Shi, Wang & Yang, 2019 , by original designation.

Included species. Pristinmicrophor hukawngensis Tang, Shi, Wang & Yang, 2019 (Hukawng Valley, northern Myanmar; lowermost Cenomanian, Upper Cretaceous).

Remarks. The genus Pristinmicrophor was established to include a single species ( P. hukawngensis ) found from the amber of northern Myanmar ( Tang et al. 2019). The genus was not properly defined. The authors indicated three characters in their view that distinguished this taxon from other microphorines: pterostigma present, small cell br and vein M 2 absent. However, all these characters are present in other microphorines.

According to the original description, P. hukawngensis exhibits an interesting mosaic of characters. This species is relatively plesiomorphic in the following features: antenna placed near middle of head (fig. 2A), stylus two-articled, eyes bare, two pairs of scutellar setae, Sc fused to costa, bm-cu vein complete, long CuA+CuP (anal vein) extending almost to wing margin (fig. 2C), female tergite 10 with spine-like setae. However, the following characters are apomorphies: male eyes dichoptic, complete precoxal bridge, cell dm very narrow and almost parallel-sided, vein M 2 absent. In addition, the authors mentioned an incomplete costa ending at R 4+5 that, however, is not evident on the photos of figure 1 ( Tang et al. 2019: 2). The shape of the discal cell is probably an autapomorphy of Pristinmicrophor . In P. hukawngensis , the discal cell is unusually narrow and almost parallel-sided (versus distinctly broadened toward apex) ( Tang et al. 2019: fig. 2C).

A complete prothoracic precoxal bridge (prosternum fused laterally with proepisternum), described in P. hukawngensis , has never been found in microphorines. The prosternum is isolated in Microphor , Schistostoma and Meghyperiella , but its condition is unknown in Microphorites , Avenaphora and Curvus . Almost all recent Parathalassiinae (except Plesiothalassius Ulrich and Amphithalassius Ulrich ) and all Dolichopodidae sensu stricto have a precoxal bridge. In addition, this condition is present in Electrophorella Cumming & Brooks known from Baltic amber ( Cumming & Brooks 2002, 2019). Archichrysotus and Cretomicrophorus described by Negrobov (1978) from Cretaceous resins of Siberia (Taymyr) have a precoxal bridge as well. However, in Retinitus , described in the same paper, the condition of this character is unknown. The presence of the precoxal bridge is considered apomorphic ( Chvála 1983; Ulrich 1991; Cumming & Brooks 2002, 2019; Ulrich 2004). However, this character shows some variations in Dolichopodidae sensu lato and is homoplasious in the Empidoidea on the whole ( Ulrich 1991: 213, character 10; Sinclair & Cumming 2006: 30, character 30). In P. hukawngensis, Tang et al. (2019) describe the precoxal bridge as “complete, narrow”.

The male of P. hukawngensis has dichoptic head structure (there is a little confusion on this character between the description and discussion, but we follow the former), with eye margins converging toward antennae. Amongst microphorines, this condition was described in Avenaphora (Cumming & Grimaldi 1999) and, probably, in Curvus ( Kaddumi 2007) . Dichoptic eyes are present in all male Parathalassiinae (including fossils) and, with very few exceptions, in Dolichopodidae sensu stricto. Traditionally, the dichoptic head structure of the male in Microphorinae , Parathalassiinae and Dolichopodidae sensu stricto was viewed as apomorphic (versus holoptic) ( Hennig 1971; Chvála 1983; Cumming & Brooks 2002). Although, Ulrich (1991) considered that this character cannot be definitely appraised. In the remaining Empidoidea it is highly homoplasious ( Sinclair & Cumming 2006: 21, character 1), sometimes, even within one genus and subgenus (e.g., Empis ).

The wing of Pristinmicrophor hukawngensis has only two M veins beyond the discal cell. However, vein M 2 is absent, or M 1+2 unforked, in Meghyperiella (assigned to Microphorinae ), four genera of Parathalassiinae (extinct Archichrysotus and Retinitus , extant Chimerothalassius Shamshev & Grootaert and Neothalassius Brooks & Cumming ) and in Dolichopodidae sensu stricto (M 1+2 forked in Sciapodinae ). In addition, Ulrich (1991) noted that a tendency for the reduction of M 2 is present in Plesiothalassius flavus Ulrich. This pattern suggests that the reduction of M 2 has occurred several times within Dolichopodidae sensu lato. It is likely that even within microphorines this character evolved independently twice because there is no evidence of closer relationships between Meghyperiella and Pristinmicrophor .

To conclude, Pristinmicrophor shows closer affinities to Avenaphora and Curvus sharing dichoptic head structure of the male. In addition, this condition could be considered as a synapomorphy of Pristinmicrophor , Avenaphora , Curvus and Parathalassiinae + Dolichopodidae sensu stricto, i.e., the assemblage of Pristinmicrophor , Avenaphora and Curvus as the sister lineage to Parathalassiinae and Dolichopodidae sensu stricto ( Cumming & Brooks 2002). However, monophyly of the Pristinmicrophor + Avenaphora + Curvus lineage is uncertain. The presence of the precoxal bridge in Pristinmicrophor could provide additional evidence for close relationship with Parathalassiinae and Dolichopodidae sensu stricto. However, the condition of this character is unknown in Avenaphora and Curvus . Considering the plesiomorphic condition of the prothorax in the parathalassiine genera Plesiothalassius and Amphithalassius , the presence of the precoxal bridge in P. hukawngensis may suggest homoplasy and conclusion about closer phylogenetic relationships of this taxon with Parathalassiinae + Dolichopodidae sensu stricto would be premature.