Palaeoapsilocephala kishenehnensis Hauser and Greenwalt, 2022

Greenwalt, Dale E., Amorim, Dalton De Souza, Hauser, Martin, Kerr, Peter H., Fitzgerald, Scott J., Winterton, Shaun L., Cumming, Jeffrey M., Evenhuis, Neal L. & Sinclair, Bradley J., 2022, Diptera of the Middle Eocene Kishenehn Formation II, Palaeontologia Electronica (a 22) 25 (2), pp. 1-52 : 28-33

Palaeoapsilocephala kishenehnensis Hauser and Greenwalt sp. nov.

zoobank.org/ CDF58467-53D2-47C7-9265-9C700DF9E1E2

Holotype. Male, USNM 717195 , deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Locality and horizon. Park site, Middle Fork of the Flathead River (Pinnacle, Montana, USA). Middle Eocene Coal Creek Member, Kishenehn Formation.

Etymology. The generic name is from the prefix “palaeo” (from the Greek palaios for ancient, old) an indication that this is an extinct genus, and “apsilocephala”, which refers to the type genus of this family. The species epithet is derived from the name of the Kishenehn Formation, where the specimen was found.

Differential diagnosis. This species is smaller (3.8 mm) than P. vagabunda (5.6 mm) and P. pusilla (5 mm). In addition, P. kishenehnensis has a much shorter Sc (ending at r-m) than does P. vagabunda ( Hauser and Irwin, 2005) and the basal flagellomere of the stylus of P. kishenehnensis is quadrate whereas that of P. pusilla is three times as long as wide ( Hennig, 1967).

Description (male). Body 3.8 mm long ( Figure 16A ); head dark brown, distorted due to fossilization process; antenna 0.33 mm long, shorter than head; scape and pedicel short, lighter in color than postpedicel, pedicel 66 μm wide, wider than long with short, dark setae; postpedicel dark brown, length 0.18 mm, maximum width 80 mm, gradually tapered, not pyriform. Stylus 2-segmented, 0.55 times length of postpedicel, basal section very short, wider than long (13 μm long, 17 μm wide); terminal segment of stylus conical, 89 μm long ( Figure 16 B-C). Thorax black to brown, 1.1 mm long, without bristles. Wing 2.28 mm long, 0.8 mm wide with dense microtrichia, with long narrow pterostigma surrounding terminal portion of R 1; R 4 parallel for long distance with R 5; R 5 meeting margin exactly at apex of wing; vein M 3 complete, cells m 3 and cua closed ( Figure 16 D-E). Legs pale yellow, femora darker, twice as wide as tibiae; hind tibia 1.07 mm long, with longer setae at apex (part of circlet of apical setae?) ( Figure 17 ); hind tarsus 0.94 mm long. Abdomen elongate, length 2.2 mm, maximum width 0.71 mm, dark brown with posterolateral margins of tergites cream-colored; sparsely setose ( Figure 17A ). Genitalia partially torn; elongate cerci surrounded laterally by triangular extensions of epandrium; without articulated surstyli; other parts not discernable ( Figure 17 B-C).

Female. Unknown.

Synimpressions. Chaoborid ( Diptera ) pupae (3), Notonectidae ( Hemiptera ) and chaoborid adults (2)

Remarks. The family Apsilocephalidae , as established in 1991, contained three species in three genera: Apsilocephala Kröber, 1914 , Clesthentia, White, 1914 and Clesthentiella, Nagatomi ,

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Saigusa, Nagatomi and Lyneborg, 1991. Apsilocephala and Clesthentia had previously been assigned to different families ( Therevidae and Rhagionidae , respectively ( Nagatomi et al., 1991a)). The family was diagnosed based in part, on vein R 5 ending before or at wing apex, first flagellomere round-triangular or pyriform with pointed 1- or 2- segmented stylus, frons concave and narrow, scutum strongly arched, apex of tibiae with circlet of setae and no spurs, empodium bristle like and male with posterolateral epandrial surstylus ( Nagatomi et al., 1991b; 1991c). Because only the genus Apsilocephala possesses articulated surstyli, they are not considered a synapomorphy for the family, and their homology with the surstyli of the Empidoidea has been questioned ( Sinclair et al., 1994). Another character for this family would be the absence of acanthophorite spines in the females, which is clearly a secondary loss, because they are found in most related families. Although Nagatomi and Yang (1998) later synonymized Apsilocephalidae under the fossil family Rhagionempididae Rohdendorf, 1951 , this change was never followed by other dipterists. This is partially due to the uncertain position of Rhagionempididae , for which the absence or presence of pulvilli or a pad like empodium as well as the male and female genitalia are unknown. The position of Apsilocephalidae in the therevoid clade of Asiloidea has been confirmed by molecular and morphological evidence (Yeates et al., 2003; Yeates and Wiegmann, 2005; Trautwein et al., 2010, Wiegmann et al., 2011; Winterton and Ware, 2015; Shin et al., 2017). In the molecular phylogenies of Winterton and Ware (2015) and Shin et al. (2017), Evocoidae is the sister to Apsilocephalidae , while Therevidae and Scenopinidae form a clade that is the sister to Apsilocephala and Evocoidae .

The extremely relictual fauna that constitutes Apsilocephalidae currently consists of four extant described species in three genera: The monotypic Apsilocephala with A. longistyla Kröber, 1914 in western North America (with several undescribed closely related species in the southwestern USA); Clesthentia , with the two species from Tasmania: C. aberrans White, 1914 and C. crassioccipitis (Nagatomi, 1991) . The latter were originally described in the genus Clesthentiella Nagatomi, 1991 and synonymized with Clesthentia by Winterton and Irwin (2008); the monotypic Kaurimyia Winterton and Irwin, 2008 with K. thorpei Winterton and Irwin, 2008 from New Zealand. The authors have seen images of an undescribed Apsilocephalidae from southern Australia.

Extant Apsilocephalidae Genera and Their Characters

Because of the rarity of both specimens and species in this family, the characters used to distinguish genera and species have been contentious. The genus Apsilocephala is characterized by the epandrial surstylus as well as the very long last flagellomere and the long and thin legs (especially the hind femur). Vein M 3 is present in Apsilocephala and Kaurimyia , but variable in Clesthentia . Nagatomi et al. (1991a) described Clesthentia with M 3 but C. crassioccipitis without M 3 while Winterton and Irwin (2008) reported specimens of Clesthentia with an incomplete M 3. The absence or reduction of a wing vein can affect only part of a population and should not be used for classification purposes if only very few specimens are available. Vein R 5 was originally reported to terminate before or at the wing apex of Apsilocephala but was figured ending just below the apex (figure 5 in Nagatomi et al., 1991a), while R 5 in Clesthentia it ends before the apex (the partial wing of C. crassioccipitis did not contain the terminus of R 5); R 5 terminates at the wing apex in Kaurimyia ( Winterton and Irwin, 2008) . It is sometimes difficult to evaluate if R 5 terminates at, or slightly below or above the wing apex, and it is, therefore, not a good character for generic limitation; unfortunately, this character is often used in the even more difficult task of describing fossil taxa. However, it is a good character to distinguish this family from the closely related Therevidae , which has R 5 always distinctly ending below the wing apex (the wing apex is always between R 4 and R 5). In a limited study of intraspecies variation, examination of seven specimens of Apsilocephala longistylus housed at the NMNH from six different sites in four western North American states, R 5 terminated either at or slightly below the wing apex (data not shown). These preliminary data support the statement by Winterton and Irwin (2008) that this character, by itself, should not be justification for generic separation.

While Apsilocephala was originally reported as not having a pterostigma, Apsilocephala and Evocoa Yeates, Irwin and Wiegmann, 2006 —a replacement name for preoccupied Ocoa Yeates, Irwin and Wiegmann, 2003 —in the family Evocoidea , both have a distinct darkening between the R 1 and Sc veins. Nagatomi et al. (1991a) reported a female specimen of Clesthentia sp. with a pterostigma very much like that of Apsilocephala and Kaurimyia ; White (1914) figured Clesthentia as having a long dark pterostigma that filled cell sc but the depicted intensity of the pigmentation may have been an artifact of printing. Clestenthia crassioccipitis was originally reported with an area that “may be brown” at the apex of sc ( Nagatomi et al., 1991a). It seems that all Apsilocephalidae and Evocoidae have a similar pterostigma.

The antennal flagellum of Apsilocephala , Clesthentia and Kaurimyia were all reported to have three segments although C. crassioccipitis was originally described as having only two segments. The only specimen of C. crassioccipitis could not be located (it is not in the collection in Copenhagen, where it should be), and therefore whether or not the antenna has only two flagellomeres or if the third one is broken off, can not be verified. The second flagellomere in Apsilocephala and Clesthentia is much shorter than the terminal third flagellomere. In Kaurimyia , the terminal segment of the flagellum is figured as about 1/8 the length of the “deflexed” part of the antenna, which consisted of the last two flagellomeres. In the key, it states “apical segment [of flagellum] greatly elongate”, but there is no description of the proportions of the last two flagellomeres in the description ( Winterton and Irwin, 2008). It is likely that the illustration is incorrect, and Kaurimyia has the same configuration as the other apsilocephalid genera, with the second flagellomere being the shortest. The diagnosis of the genus Kaurimyia lists two antennal characters: “Antennal style approximately equal length to base of flagellum, deflexed ventrally at base”. According to the key to genera in Winterton and Irwin (2008), the antennal style is “approximately equal length of basal segment of flagellum” in Kaurimyia , while “less than half the length of basal segment of flagellum” in Clesthentia , a character also adopted in the key by Zhang et al. (2018). Ratios of length of last two flagellomeres to the first flagellomere is 0.8 in Kaurimyia when measured from the figure in Winterton and Irwin (2008), 0.7 (female) to 0.4 (male) in Clesthentia sp. , 0.15 in C. crassioccipitis , and 1.4 (female) to nearly 3 (male) in Apsilocephala ( Nagatomi et al., 1991a; Winterton and Irwin, 2008). This indicates that use of the antennal length ratio to separate Kaurimyia and Clesthentia in the keys of Winterton and Irwin (2008) and Zhang et al. (2018) are not practical. Winterton and Irwin (2008) stated that “Considering also, the variability in the length and number of flagellar segments at genus and species level in related Therevidae , this character (and wing venation) by itself should not be justification for generic separation.” It is therefore surprising that Winterton and Irwin (2008) synonymized Clesthentiella with Clesthentia , even though Clesthentiella is the only apsilocephalid with a two segmented flagellum (and a significantly enlarged occiput) and then erected the new genus Kaurimyia by using even more subtle antennal characters to diagnose it. In addition, the deflexed last flagellomere is listed as an important character, but from photographs of the type of Kaurimyia , the angle is not 90° as in the drawing, and a ventral deflexion is also found in Clesthentia and Apsilocephala . This deflexion could be a postmortem artifact. The synonymy of Clesthentiella might have been a bit hasty, considering the strange antennal character of Clesthentiella and the enlarged occiput, but a final decision has to await additional material. Kaurimyia is clearly a separate genus from Clesthentia , by the characters of the male genitalia, the number of spermathecae and the unusual hindlegs. Its description mentions that the “hind legs are distinctly longer and thicker than mid and fore legs”, but the authors failed to mention that the hind tibia is club-shaped and twice as thick apically as basally. Even the tarsal segments, especially the basitarsus, are significantly thickened. Unfortunately, the size of the specimens and the configuration of the palps (one or two segmented) are not mentioned in the description.

The Fossil Record of Apsilocephalidae

Several fossil species of Apsilocephalidae have been reported (See Zhang et al., 2018 for overview and key). Fossils of Cretaceous age include Burmapsilocephala cockerelli Gaimari and Mostovski, 2000 , Burmapsilocephala evocoa, Grimaldi, 2016 , Kumaromyia burmitica Grimaldi et al., 2011 , Myanmarpsilocephala grimaldii Zhang et al., 2018 , Irwinimyia spinosa Zhang et al., 2018 , and Cascomixticus tubuliferous Poinar and Vega, 2021 ( Gaimari and Mostovski, 2000; Grimaldi et al., 2011; Grimaldi, 2016; Zhang et al., 2018; Poinar and Vega, 2021). Solórzano Kraemer and Cumming (2019) added the genus Kuhwahldyia as family incertae sedis, near Apsilocephlidae, and compared it with all known genera in Zhang et al., 2018. Noteworthy is the description of Cretothereva antiqua Carmo et al., 2021 , the oldest Therevidae fossil. We will discuss these taxa and their taxonomic placements.

Cretothereva Carmo, Lamas and Ribeiro, 2021 . C. antiqua is a beautifully preserved species from the Crato Formation (115 Ma), which was described as a Therevidae . The open cell m 3 is a character state not found in the more basal Therevidae lineages Phycusinae and Xestomyzinae , but it is present in the Therevinae and Agapophytinae . The absence of a hypandrium, which is present and large in all Xestomyzinae and present in many Phycusinae , indicates that this genus is not part of these subfamilies. As Carmo et al. (2021) stated, it is not possible to place the genus in one of the recent four subfamilies of Therevinae , and it displays several characters which do not indicate a basal position in the Therevidae . We don’t know where this fossil should be placed, but it might not have a close relationship with Therevidae or even the therevoid clade.

Kuhwahldyia Solórzano Kraemer and Cumming, 2019 . The head of Kuhwahldyia is much higher than broad in lateral view compared to the more spherical head shape of other Apsilocephalidae , a character shared only with Irwinimyia Zhang, Li, Wang and Yeates, 2017 ; the pterostigma is absent, as it is in Kumaromyia Grimaldi and Hauser, 2011 ; scape and pedicel are lacking setae as in Kumaromyia ; the frons seem to be relatively broader than the rather narrow frons in most Apsilocephalidae ; the last abdominal segment appears to be much smaller (more narrow in dorsal view and thinner in lateral view) than in other Apsilocephalidae ; the one segmented female cercus in Kuhwahldyia is cylindrical and not flat and triangular as in the modern Apsilocephalidae genera. The illustration of the wing (figure 6 in Solórzano Kraemer and Cumming [2019]) has an additional crossvein in cell br, which is not visible in the photograph of the fossil, and the cell bm has an unusually pointed extension leading into vein M 4, which is not present in the photograph of the wing. We agree that this fossil has a certain similarity with Apsilocephalidae , and that the best placement for the moment is in incertae sedis, near Apsilocephalidae .

Cascomixticus Poinar and Vega, 2021 . The unique species C. tubuliferous differs from all known Apsilocephalidae by its long mouthparts. Although the wing venation resembles that of an apsilocephalid, it is also a rather plesiomorphic venation, which is similar even to families outside the Asiloidea clade. If the interpretation of the antennal structures is correct, the antenna has an unusually elongate pedicel. In the description of the antennae, the authors state that the flagellum is only two segmented, but this needs to be confirmed. The empodium is described as “spine-like”, which is different from the empodium of Apsilocephala , Evocoa and Therevidae , in which the unguitractor plate has only a modest anterior extension. We consider Cascomixticus to be insertae sedis within Asilomorpha, likely not close to the Asiloidea .

Burmapsilocephala Gaimari and Mostovski, 2000 and Myanmarpsilocephala Zhang, Li, Wang and Yeates, 2017 . From the descriptions of Burmapsilocephala and Myanmarpsilocephala it is evident to us that these two genera belong in the family Evocoidae Yeates, Irwin and Wiegmann, 2006 . Evocoidae is a monotypic family including Evocoa chilensis (Yeates, Irwin and Wiegmann, 2003) , which is endemic to Chile (Yeates et al., 2003, 2006). This family is characterized by its long legs, a postpedicel with a bulbous base and a long threadlike terminal element, M 3 lacking, tibial spurs absent, anterior surface of hind coxa with a strong, knoblike, bulbous projection; the epandrium divided into two sickle-like halves, gonostyli articulate in a horizontal plane, female with acanthophorite spines and hypoproct with ventrally projecting needlelike setae. Evocoa differs from Burmapsilocephala and Myanmarpsilocephala by having the cell cua open and M 3 absent. These differences are discussed in Grimaldi (2016) under the genus Burmapsilocephala . Despite recognition of a close relationship between the three genera— as indicated by the species epithet evocoa — B. evocoa was placed in Apsilocephalidae and not Evocoidae . Burmapsilocephala evocoa was described after a male which has the typical sickle-like epandrium of Evocoa as well as the bulbous postpedicel with the long threadlike terminal. It differs by being holoptic, while Evocoa is dichoptic in both sexes. The genus itself was described by Gaimari and Mostovski (2000) based on a female specimen of Burmapsilocephala cockerelli and, although the structures at the end of the abdomen are not visible, the antenna and the wing venation is very similar to Burmapsilocephala evocoa . The two Burmese amber genera and Evocoa share vein M 4 originating from the cell dm and not bm, as it is the case in all Apsilocephalidae . We consider this character more important than the open cua cell (and/or the reduction of M 3). A convergent system of wing venation can be found in the Vermileonidae : M 3 can be reduced ( Vermileo Marquart, 1834 ) or present and cell m 3 can be open ( Isalomyia Stuckenberg, 2002a ) or closed ( Namaquamyia Stuckenberg, 2002b ). The general habitus of Evocoa as a gracile, long-legged fly is strikingly similar to Burmapsilocephala and Myanmarpsilocephala . The configuration of the female abdominal tip with acanthophorite spines and long ventral setae in the holotype of Myanmarpsilocephala grimaldii Zhang et al., 2018 (figures 3C and D in Zhang et al., 2018) is nearly identical with Evocoa (figure 14 in Yeates et al., 2003). None of the other Apsilocephalidae have acanthophorite spines, except an undescribed fossil in Cretaceous amber from Wealden ( UK) mentioned by Grimaldi et al. (2011) and depicted by Chandler (2010). Because of the great similarities between Evocoa , Burmapsilocephala and Myanmarpsilocephala we are transferring these two fossil genera from Apsilocephalidae to Evocoidae .

The undescribed Wealden-fossil has been associated with Apsilocephalidae ( Grimaldi et al., 2011) , and the wing venation is very indicative of this placement. However, it has short, thick acanthophorite spines and lacks a circlet of apical setae on the tibia, both characters that differ from modern Apsilocephalidae . While the antennal proportions are very similar to Kumaromyia , the tip of the abdomen of Kumaromyia was not discernible, and therefore it is not clear if there are acanthophorite spines present. We agree with Grimaldi et al. (2011) that “It is quite possible that Kumaromyia is a stem-group taxon for the therevid-family group, not necessarily belonging within Apsilocephalidae or Therevidae ” a statement which might also be true for the undescribed Wealden amber fossil and even for Kuhwahldyia .

Irwinimyia Zhang, Li, Wang and Yeates, 2017 . The genus Irwinimyia is a very interesting and unusual taxon, with its distinct spines on the hind femur and a two segmented palpus. The head shape and the crossvein r-m located in the middle of the discal cell are conditions also found in Kuhwahldyia . The scape is longer in Irwinimyia than in Kuhwahldyia , but the proportions of the three flagellomeres are similar, and both species seem to possess a very small bristle on the apex of the last flagellomere. This is not included in the description of Irwinimyia or in the drawing of the antenna which is wrongfully depicted with numerous short setae covering all flagellomeres (figure 6A in Zhang et al., 2018); the bristle is visible in the photograph of the head (figure 5B in Zhang et al., 2018). Cell m 3 is closed and petiolate in Irwinimyia , while it is open in Kuhwahldyia . Solórzano Kraemer and Cumming (2019) gave an extensive comparison between the Kuhwahldyia and all other Apsilocephalidae genera.

Palaeoapsilocephala Hauser and Greenwalt, 2022 . Two species, Psilocephala pusilla Hennig, 1967 described from Baltic amber, and Rueppellia vagabunda Cockerell, 1927 from the 34 Ma Florissant Formation in western North American, are Eocene in age ( Cockerell, 1927; Hennig, 1967; Hauser and Irwin, 2005; Hauser, 2007). Both species have been placed in the genus Apsilocephala ( Hauser and Irwin, 2005; Hauser, 2007). A number of morphological features characteristic of extant Apsilocephala are not shared in the fossil species assigned to this genus (e.g., antennal stylus very elongate). As a result, we conclude that the fossil species A. pusilla and A. vagabunda do not belong in Apsilocephala as the last flagellomere is much shorter, the femora are thicker and the epandrium is without articulated surstyli. Consequently, these two species, together with the new species described herein, are placed in the new genus Palaeoapsilocephala .

Figures

FIGURE 16. Palaeoapsilocephala kishenehnensis Hauser and Greenwalt gen. and sp. n., USNM 717195, Male. A, Habitus; B, Antennae; C, Drawing of antennae; D, Right wing; E, Drawing of right wing. Scale bars equal 2.0 mm (A), 0.15 mm (B), and 1.0 mm (D).

FIGURE 17. Palaeoapsilocephala kishenehnensis Hauser and Greenwalt sp. n., USNM 717195. A, Hind tibia spurs; B, Genitalia. C, Drawing of genitalia. Scale bars equal 0.5 mm (A, B).