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Review of wing morphology in fossil and modern species of humpbacked flies (Diptera: Phoridae)

BMC Biology volume 23, Article number: 298 (2025) Cite this article

Abstract

Background

The wing veins of known fossil and living phorids are reduced, making them difficult to homologise. Consequently, different interpretations have led to much confusion over the years. However, veins are crucial for phylogenetic and taxonomy studies, especially for fossils. We addressed these challenges by studying Cretaceous specimens, which exhibit fewer reductions in wing veins compared to modern fauna, along with post-Cretaceous specimens that display recent wing patterns. Furthermore, we examined related families such as Ironomyiidae, Platypezidae, Opetiidae, and Lonchopteridae to show wing similarities to the Phoridae.

Results

We propose two wing models that include the majority of veins found in each taxon. The early model (Phoridae sensu lato, including Sciadocerinae + “†Prioriphorinae”) consists of most Cretaceous species, except †Metopina goeleti from New Jersey amber, which displays a recent pattern. The recent model (Phoridae sensu stricto, i.e. Euphorida) is present in the majority of recent phorids. Based on this new interpretation, we re-evaluate three holotypes of Phoridae: †Euliphora grimaldii, †Prioriphora schroederhohenwarthi, and †Ulrichophora lobata. Additionally, we described a Phoridae specimen belonging to †Prioriphora in the Fouras-Bois Vert amber (France) and a new genus within the Ironomyiidae family in the San Just amber (Spain).

Conclusion

The newly proposed wing models facilitate rapid identification of Phoridae wing veins based on their degree of reduction. The two newly described specimens are the first records of these taxa in their respective localities.

Background

Species of the family Phoridae Curtis, including the subfamily Sciadocerinae Schmitz [1,2,3,4], are commonly known as “humpbacked flies” or “scuttle flies”. Phorids are small cyclorrhaphan flies, between 0.4 and 6 mm, with an astonishing diversity. Although far from being completely known, they already contain 4464 extant described species [5], but the estimate is much higher, probably between 40 and 50,000 species [6]. Conversely, the fossil record is much less rich.

Wing venation plays an essential role in the identification and study of cyclorrhaphan families, especially in the study of fossil remains due to the abundance of wings which, besides showing distinct characters, are easy to describe [7,8,9,10,11,12,13,14,15,16]. However, the history of vein terminology is extensive and has been the subject of considerable debate. The first comprehensive model for dipteran wing structures was established by Comstock and Needham [17]. The groundplan for Diptera was comprehensively revised by McAlpine et al. [8] in terms of the medial and cubital veins, and several changes were made afterwards (i.e. [18,19,20]). The last standard terminology was created by Cumming and Wood [13], which was built upon an unpublished handout by Saigusa [21] distributed at the 6th International Congress of Dipterology. In recent years, new research employing microtomographic x-ray scanning (µ-CT) has clarified the identity of the main postcubital vein (PCu vein) [22] and an intercalary longitudinal vein (fiv vein) in all Neoptera and especially Diptera, resulting in yet further refinements to wing venations terminology [16].

Adult Phoridae are easily identifiable by their modified wing venation, primarily due to the reduction of their radial and costal veins. The characters used for the classification of fossil specimens within the family are essentially based on the wing morphological structures [23,24,25]. Thus, despite vein reduction, wings are essential structures to hypothesise phylogenetic relationships between living and fossil phorids and their outgroups Platypezidae Fallén, Ironomyiidae McAlpine and Martin, Opetiidae Rondani, and Lonchopteridae Macquart [25].

Establishing a terminology for homologous wing veins, not only for the fossil phorids but also for the living ones, is a special challenge due to their highly derived wing venation, which is the result of a significant reduction of wing venation compared to other families of Diptera. The preferred labelling system for venation has been debated for many years, revealing inconsistencies across various authors [25,26,27,28,29,30]. The difficulties arise from two main problems. The first involves applying nomenclature derived from the wing venation ground plan of Diptera to Phoridae [8, 11, 13, 17,18,19,20,21], resulting in multiple interpretations of wing terminology (Table 1), particularly concerning the posterior part of the wing [1, 3, 23, 26, 28, 31]. The second involves reduced wing venation, especially the vanishing of the proximal parts of the medial, cubital, and anal veins, resulting in the absence of connections. These problems, coupled with considerable variability, especially in extant genera, present a challenge for the consistent labelling of phorid veins and establishing a terminology reflecting wing venation homologies.

Table 1 Wing vein terminology is used for Diptera and within Diptera specific for Phoridae. In italic: Diptera wing vein terminology also used for Phoridae. Not italicised: Phoridae wing vein terminology used in the description of species from various authors. In bold black: the new combination terminology model. X: it is not considered as a vein; ?: vein no mentioned; /: vein not present
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The homogenisation of the wing vein terminology presented here is the result of the observations of many fossil specimens and the analytical literature research on the wings of Diptera with emphasis on Phoridae. In this study, we present a new interpretation of the wing terminology through the creation of two models—an early and a recent one—that represent the majority of the wing vein diversity found on the fossil and living species. Within the recent model, we also added an example of a wing with extreme vein reduction. We applied this new terminological interpretation to three Phoridae holotypes, which were examined and re-evaluated: †Euliphora grimaldii Arillo and Mostovski, †Prioriphora schroederhohenwarthi Solórzano-Kraemer and Perrichot, and †Ulrichophora lobata Brown. In addition, we described two isolated wings, one Phoridae and one Ironomyiidae, representing the first records of these families in the respective Cretaceous deposits, Fouras-Bois Vert amber (included in Charentese amber, France), and San Just amber (Spain).

Results

The study of the wings of the fossil has evidenced: (1) a low number of species described in contrast to the fossils discovered and, for those described, limited morphological information is provided; (2) sexual dimorphism occurs in the modern fauna but not in the fossil record; (3) high variability of interpretations in the wing vein terminology; and (4) the need to create standardised wing models and a new proposal of primary homology of venation in phorids.

Number of extinct species described

Only 307 specimens of fossil Phoridae have been studied so far. These belong to 119 described species in 41 genera (23 are extinct genera), 68 of them in Cretaceous amber, belonging to 22 species and 15 genera. Moreover, 82.1% of these were published before 2000, and only 21 species have been described in the last 24 years. Closely related families are much less abundant in the fossil record, such as the Platypezidae or the Ironomyiidae, which have 26 described species belonging to 17 genera (15 are extinct genera) and 28 described species belonging to only six genera (all are extinct genera), respectively. The Lonchopteroidea (including Lonchopteridae) have five described species belonging to four genera (three are extinct genera) and the Opetiidae have six species belonging to four genera (three are extinct genera) (Fig. 1).

Fig. 1
figure 1

Overview of Phoridae, Ironomyiidae, Lonchopteridae, Platypezidae, and Opetiidae in fossil resins. Filled black circles, at least one species has been described in the literature. Empty black circle, no species has yet been described, but there are known specimens in collections

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Sexual dimorphism

To date, no Cretaceous female phorid with a significant reduction of wing venation has been reported. In addition, the Cretaceous specimens examined for the present work, from various deposits, show no significant dimorphism and both have well-developed wing venation. However, it is important to note that only a few species in the amber fossil record are preserved together in a single piece representing both sexes.

Variability of interpretations in the wing vein terminology and new models

Homogenisation of wing vein terminology of the phorids is critical for understanding the evolutionary history of this family over time. In an effort to standardise the various terminologies used in the study of the family Phoridae sensu lato, which includes “sciadocerines”, and in the study of the related families, two models have been established: an early model and a recent model (Fig. 2a,c), which serve as a valuable tool for describing both extinct and extant specimens. These models aid in distinguishing between species with more wing veins and those with a significant reduction in venation. The early model is derived from the wing venation pattern observed in Cretaceous specimens, while the recent model is based on species that emerged after the Cretaceous period, with a reduced wing venation pattern. An example of the recent model with even more reduced veins has also been made, to assist with the labelling of phorid wings with significant vein reduction (Fig. 2d). To achieve this, we have conducted a comprehensive investigation that combines the analysis of a large number of phorid wings from the existing literature with a thorough re-examination of selected extant specimens and the study of Cretaceous fossil specimens. The result of all these observations has led to a new interpretation of wing veins that applies to the entire family (Table 1).

Fig. 2
figure 2

Representation of the new ground-plan wing venation models of Phoridae with new combined terminology. a and b represent the wing venation of the early model based on fossil specimens: a full wing; b proximal part of the wing. And c and d represent the recent wing venation: c the recent model based on modern specimens; d an example of a recent model with an important reduction of wing venation

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The establishment of this new terminology interpretation of Phoridae wing veins (Fig. 2 and Table 1) is further supported by comparison with other terminologies of dipteran wing venations such as Comstock and Needham [17], McAlpine et al. [8], Wooton and Ennos [18], Chapman [19, 20], Saigusa [21], Cumming and Wood [13], and Schubnel [16], and the different terminologies of phorid wing venation from Schmitz [26], McAlpine and Martin [28], Grimaldi [23], Disney [1, 31], and Brown et al. [3] (Table 1). The revision of the wing veins recognises that the radial veins have a distal division, with vein R bifurcating into two branches, namely RA and RP as in the interpretation of Schubnel [16], modified after the general wing venation model of Kukalová-Peck [32]. The RA commonly called R1 for Diptera is the anterior branch of the radial vein. The RP is the posterior branch of the radial vein commonly referred to in the literature as Rs and is divided into RP1+2 (in literature known as R2+3 or Rs1+2) and RP3+4 (known as R4+5 or Rs3+4). Some modern genera, e.g. Chonocephalus Wandollek, Postoptica Disney, Triphleba Rondani, Phora Latreille, and Conicera Meigen show only two branches of the radial vein. The current data were inadequate for the resolution of the last modification or modifications of the RP vein reduction (Figs. 2 and 3). Thus, to prevent different interpretations of the reduction, disappearance, or fusion of the second radial vein, we have chosen to maintain one anterior and one posterior radial vein, a feature consistently found in all Phoridae species (Figs. 2 and 3; Table 1). This approach ensures homogenisation of terminology across the family.

Fig. 3
figure 3

Hypothesis of reduction of Phoridae radial veins. a Proximal wing, long fork of RP fork ①. b Recent wing, short fork of RP vein ②. c Wing with an important reduction of venation, lost fork of RP vein ③, and distal reduction of RA vein ④. d Zoom of possibility of reduction of RP1+2, lost of RP1+2 vein either distally or proximally Ⓐ, or by the fusion of RP1+2 and RP3+4 veins Ⓑ

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Chapman [20] proposed the division of the medial veins into anterior and posterior, but when MA cannot be distinguished, he proposed to use only medial veins. Schubnel [16] also separates the medial veins into the anterior and posterior, but he does not make a distinction when anterior or posterior is absent. However, these suggestions are not followed here because the presence or absence of MA is not homogeneous across all Phoridae. In some Phoridae genera, the MA is present but very difficult to observe (e.g. some species of Myriophora Brown, Phora, Chaetopleurophora Schmitz, Sciadocera White, Archiphora Schmitz). Nevertheless, in the majority of Phoridae genera, this vein is absent (e.g. Anevrina Lioy, Chonocephalus, Darwiniphora Schmitz, Triphleba). When MA is present, it is a short vein running along R ending before R divides into two distinct branches (RA and RP). The remaining medial veins retain the name M and are divided into M1+2 and M3+4, which in turn further subdivide into M1, M2, M3, and M4 (Figs. 2 and 3). The classification of the M4 vein is a subject of debate in the literature, primarily due to reduced wing venation and its lack of connection to the proximal vein, with various interpretations depending on the authors. The M4 is also referred to as CuA1 [8] and used in phorid descriptions (e.g. [8, 23, 26]). The revision of the literature and new specimens of various Cretaceous deposits demonstrate that M3 is present as a long vein (e.g. †Prioriphora n. sp.) (Fig. 2a,b), a short vein (e.g. †Euliphora Arillo and Mostovski) (Fig. 2c), or as an absence of microtrichia in the zone between M2 and M4 (e.g. Chonocephalus, Trophithauma Schmitz) (Fig. 2d). M3 in the referred genera is connected with the third long M vein, which has had a lot of labelling (i.e. CuA1, MP2, vein 6, A1; see Table 1), herein, thus this third long M vein is considered as M4.

The observations of the posterior part of the wing fit the interpretation of Schubnel [16]. The CuA vein is short and posteriorly curved. The CuP is predominantly transparent and can be difficult to observe and is often confused with the intercalary vein (i.e. the fiv). The fiv is thin and runs either beneath or along the CuP vein. Proximally, fiv connects to the proximal cell and extends distally to the wing edge. The fiv is not fused with other veins and is referred to in the literature by a variety of terms: A1, A1 + CuA2, A2, CuP, CuA + CuP (Table 1). The PCu vein is observed in the wing of Cretaceous specimens and early modern phorids, but it is absent in the majority of modern phorid species with reduced wing venation. The A1 vein is difficult to distinguish, runs along the posterior side of the PCu vein, and ends in the alular part of the wing. The A2 runs along the edge of the alula and sometimes extends into the anal part. For the terminology of cells and crossveins, we decided to keep and follow Cumming and Wood’s [13] nomenclature.

Description of the veins in the two wing models

Costal vein

In both models, the tubular C is variable in length and usually ends before the wing apex at the level of RP3+4 (Additional file 1: Figs. S1c; S2b). However, in rare species, such as Anevrina sp. or Postoptica continentalis Lengyel and Papp, C continues slightly beyond RP3+4. In some others, such as Neopleurophora kungi Ament and Amorim, Termitophilomyia Schmitz, or Javanoxenia Schmitz, C is shorter than RP ([33]: figs. S25, S27, S33).

Subcostal vein

In the early model, the tubular Sc is short and fuses with the RA at mid-length in most cases (Fig. 2a) such as †Agaphora iunior Mostovski (Additional file 1: Fig. S3), except for †Ulrichophora lobata (Fig. 4a). In †U. lobata, the Sc does not fuse directly with the RA; instead, it runs towards the RA and eventually fuses with the C. However, it is important to note that in †U. lobata the Sc does not diverge from the RA distally, unlike the Ironomyiidae. In the recent model, the Sc is shorter and gradually ends vanishing before reaching the RA (Additional file 1: Figure S2; [33]: figs. S25–S26).

Fig. 4
figure 4

Wing of †Ulrichophora lobata, holotype LACM ENT 159890. a Zoom of the base of the left wing. b Drawing of the left wing. c Complete left wing. Scale 0.5 mm

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Radial veins

The tubular R is divided into the RA and RP after the h crossvein. Typically, the tubular RA fuses with the C, except in a few species such as Postoptica continentalis, or Chonocephalus fletcheri Schmitz, in which the RA vanishes before reaching C (Additional file 1: Fig. S2). In the early model, the tubular RP undergoes a proximal division into the RP1+2 and RP3+4, which occurs either slightly before or after the r-m crossvein such as †Agaphora iunior (Additional file 1: Fig. S3). This division results in the formation of a long fork (Figs. 2a and 3a). The tubular RP1+2 fuses with the C, while the tubular RP3+4, does not. However, in a few species such as †Ulrichophora lobata (Fig. 4), Sciadocera rufomaculata White; and Archiphora patagonica Schmitz, the RP3+4 fuses with C (Additional file 1: Fig. S1); and thus, it is considered as a distinguishing character of the Sciadocerinae. In the recent model, the RP exhibits a distal division into two branches, forming a short fork (Figs. 2c and 3b,d; Additional file 1: Fig. S2a). This character is observed in taxa such as Dohrniphora Dahl, Kuenburgia Schmitz, Megaselia Rondani, and Spiniphora Malloch. In certain taxa (e.g. Aenigmatistes Shelford, Conicera, Gymnoptera Lioy, Phora), the RP is undivided (Figs. 2d and 3c; Additional file 1: Fig. S4b,c); in such cases, it does not fuse with the C. The RP1+2 may fuse with the C, or if it is unfused, but the veins are much more distally forked; this can be observed in a few species such as Chaetopleurophora rhomboidea Nakayama. In some instances, a portion of the RP1+2 remains fused to the C, but is no longer attached to the RP, as observed in species like Coniceromyia riccardiae Ament, Kung and Brown or Coniceromyia strongyla Ament, Kung and Brown. The RP3+4 does not fuse with the C. In both models, the presence of the longitudinal RP4 varies. In cases where the RP4 projection is present, it may manifest as a thin vein or as a vestigial or spectral projection vein. This can be distinguished by a parallel line with the anterior wing margin, often represented by a line of concentrated microtrichia or a darker-coloured line on the wing surface (Figs. 2 and 5; Additional file 1: Figs. S2; S4a; S5).

Fig. 5
figure 5

Wings of †Euliphora species. a–c Wing of †Euliphora grimaldii, holotype MCNA 8648: a proximal part of the left wing; b proximal part of the right wing; c draw of the left wing; d right wing of †Euliphora n. sp. 1, MCNA 12734, Álava (Peñacerrada I); e isolate left wing of †Euliphora n. sp. 2, MCNA 15469, from Álava (Peñacerrada I) distorted in proximal. Scales 0.2 mm

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Medial system (veins and crossveins)

The medial veins differ greatly between the early and recent models. The MA may be present in both models. If present, it starts from the base of the wing, is relatively narrow, and extends along the R to the base of the RP (Figs. 2a and 3a). However, it may be completely absent. In the early model, the r-m crossvein is located either at the same level or slightly beyond the RP fork and at the same level or slightly beyond the m-m crossvein (Fig. 2b). In the recent model, r-m crossvein is mostly absent (Fig. 2d).

In the early model, the M is present and splits into the M1+2 and M3+4 (Fig. 2a,b), but M3+4 is not connected to M (Fig. 2b). The M1+2 splits into M1 and M2 beyond the RP fork (Fig. 2a,b). The M1 is connected to M1+2 in some cases but in others, M1 is spectral at its proximal part (Additional file 1: Fig. S6a). The M2 is connected or not to M1+2. The M3+4 is short and slightly swollen and splits into the M3 and M4 behind the m-m (known as dm-m) crossvein (Fig. 2b; Additional file 1: Fig. S1b). The M3 is rather infrequent, short, narrow, and rapidly disappearing (Fig. 2a), or present only as a short vestigial vein. The M4 usually reaches the wing margin, but sometimes disappears just before. The M1, M2, and M4 are always posteriorly curved (Additional file 1: Fig. S1a).

In the recent model, the M is absent (Fig. 2c). The M1+2 is represented by a narrow vein running closely along the RP or as a short remnant vein at its base (Fig. 2c), or the vein is completely absent (Fig. 2d). In any case, it is difficult to observe. The bifurcation of M1+2 into M1 and M2 is not visible. The M1 and M2 are straight, anteriorly curved, or proximally anteriorly curved and distally posteriorly curved such as in †Agaphora iunior (Additional file 1: Figs. S3; S6b). The M1 never fused with RP. The M1 may run a little along the RP reaching RP3+4, or ends when the vein is very close to RP3+4 (Fig. 2c; Additional file 1: Fig. S6b). However, for a few species such as Chonocephalus sp. or Metopina sp. (Additional file 1: Fig. S2c,d), the proximal part of M1 is reduced and does not reach RP3+4 but conserves the direction towards RP3+4 (Fig. 2c). The proximal part of M2 is vanishing and runs slightly along RP or ends near RP about halfway between the R fork and RP fork or the end of RP if the RP fork is absent (Fig. 2c). The M3+4 is represented by a swollen short vein (Fig. 2c), or it is completely absent (Fig. 2d). The M3 can be absent or present, sometimes also represented by a line without microtrichia (e.g. Coniceromyia megalosoma Ament, Kung and Brown, or Metopina sp.) (Additional file 1: Fig. S5c). The M4 is straight, posteriorly curved, or slightly anteriorly curved, derived from the M3+4; however, if the M3+4 is absent, the M4 is vanishing proximally such as in Chonocephalus sp. (Additional file 1: Fig. S2d).

The longitudinal m-m crossvein is located between the M1+2 and M3 (Fig. 2b). It is a small tubular crossvein, almost transparent, and sometimes difficult to observe when the M1+2 and M3 are close together. The crossvein m-cu is present; it is more-or-less long and is located between the M3+4 and the CuA (Fig. 2b); but if both veins are absent, m-cu is also completely absent (Fig. 2d). Crossveins m-m and m-cu are present in the early model, whereas the crossveins m-m are absent and m-cu are present or absent in the recent model.

Proximal cells

In the early model, br, bm, and d (known as dm, e.g. [1, 3]) cells are represented through the proximal medial system (Fig. 2b; Additional file 1: Fig. S6a). The length of the br cell varies depending on the position of r-m, with it either opening proximal or being enclosed by the MA. The bm and d cells are not merged but are separated by the M3+4, with the d cell slightly opening towards the distal side to bm. The boundary between br and bm is defined by the M, while the separation between br and d is marked by the M1+2. In the recent model, there is a reduction of the proximal part of wing veins (Fig. 2c,d). There are three observable cases. First, the two cells br and bm + d are present. M and M1+2 are present, br cell present but M3+4 absent, bm and d cells are fully open and form a unique cell bm + d. Second, only one cell br + bm + d is present. This is the result of the proximal reduction of medial veins. M, M1+2 and M3+4 are absent, but the surrounding veins are present, bounded anteriorly by a base of radial s, distally by the medial veins and the m-m crossvein, and posteriorly by the cubital veins and the m-cu crossvein. Third, all cells are absent. This is observable when the wing has an important wing vein reduction.

Cubital veins

In the early model, the CuA is short, distally posteriorly curved, and dips rapidly towards CuP (Fig. 2a). If CuP is reduced or absent, CuA dips towards the fiv at the level of m-cu crossvein. The CuA is mainly spectral before joining fiv. In the recent model, the cubital veins are present or absent (Fig. 2c,d); if they are present, the CuA and CuP are shorter than in the early model. The CuA is distally posteriorly curved and reaches the CuP or the fiv just after m-cu crossvein, or it ends on the contact with crossvein m-cu. The CuP is represented by a spectral vein, usually transparent and difficult to observe. The CuP is distally vanishing before, or slightly after, the ends of the CuA, running closely along the anterior margin of fiv.

Intercalary vein

In the early model, the intercalary vein known as fiv is present. It appears as a narrow vein located between the alula and the CuP in the anal region of the wing. The fiv does not connect another vein, from the proximal cell of the wing, but runs proximally closely along the posterior margin of the CuP until it reaches the wing margin (Fig. 5a,c; Additional file 1: Fig. S1). In the recent model, when proximal cells are present, the fiv maintains a similar configuration to that of the early model. However, when the proximal cells are absent, the proximal fiv either vanishes and terminates just before the wing margin or is completely absent.

Postcubital

In both models, the PCu may be present or absent. The PCu is short and wide (Additional file 1: Fig. S1b), with one or two branches [22].

Anal veins

The A1 is short, ends in the alular part of the wing, and is difficult to distinguish from the PCu. The A1 runs closely along the posterior margin of the PCu (Fig. 2). The PCu and the A1 appear to be fused. In the early model, the A2 is long, runs along the margin of the alula and continues into the anal part of the wing (Fig. 2a). In the recent model, the A2 is short and ends in the alula, or it is absent (Fig. 2c,d).

Comments

The majority of Cretaceous species show characters fitting only the early model, with the exception of †Agaphora Mostovski species and †Metopina goeleti Grimaldi. The †Agaphora species have a wing pattern that fits with both models, an early radial system and a recent medial system. We refer to this group as the “Agaphorine-group”. The species †M. goeleti has a reduced wing pattern, with a reduced radial and medial system as in the recent model. The †Agaphora species and †M. goeleti have not been revised; thus, the characters discussed here are exclusively from the literature. Only two Tertiary species from the Baltic amber (†Ulrichophora lobata and †Eosciadocera pauciseta Grimaldi) and two living species (Archiphora patagonica and Sciadocera rufomaculata) also show characters fitting the early model. These four species are assigned to the subfamily Sciadocerinae. However, the re-evaluation of †U. labata shows a Sc vein that does not fused in RA, unlike all the other species. This feature is also found in the wing pattern of the family Ironomyiidae, but with the difference that distally, in †U. lobata, the Sc does not separate from the RA before merging with C. All other Cenozoic and living species have reduced veins that fit with the recent model.

Outgroup comparison

For the four families Lonchopteridae (Additional file 1: Fig. S7a), Opetiidae (Additional file 1: Fig. S7b), Platypezidae (Additional file 1: Fig. S7c), and Ironomyiidae (Additional file 1: Fig. S7d): the costal vein stops at the tip of wing; Sc vein and all the radial veins fuse to C. The Lonchopteridae and Opetiidae are closed, the medial veins system is similar with a long fork of M1 and M2 and absence of d cell and m-m crossvein. The wing patterns of Platypezidae and Ironomyiidae are closer than those of Phoridae, the medial vein system is similar with a large d-cell and the presence of a long m-m crossvein.

Systematic palaeontology

Order Diptera Linnaeus, 1758.

  • Family Phoridae Curtis, 1833

  • Genus †Euliphora Arillo and Mostovski, 1999

  • Type species: †Euliphora grimaldii Arillo and Mostoski, 1999: 252–254, figs. 1–4.

  • Monogeneric.

†Euliphora grimaldii Arillo and Mostoski, 1999 (Fig. 5a–e)

Material examined: Holotype, ♂, SPAIN: Álava, Albian, Lower Cretaceous, Álava amber (or Peñacerrada I, Spanish amber), amber piece MCNA 8648 housed at MCNA (Museo de Ciencias Naturales de Álava).

Other specimens examined, not described in this study: Holotype, unknown, SPAIN: Álava, Albian, Lower Cretaceous, Álava amber (Peñacerrada I, Spanish amber) (MCNA 12734). Holotype, isolate wing, SPAIN: Álava, Albian, Lower Cretaceous, Álava amber (Peñacerrada I, Spanish amber) (MCNA 15469).

Revision and additional characters of holotype

Matching the early model. C covered with two rows of strong, short, spine-like setae. Sc long, runs slightly along the anterior margin of RA before fusing to RA. RA and RP1+2 fused to C, while RP3+4 not; RP4 continues spectrally parallel to the wing margin. MA runs along the posterior margin of R and ends at the level of R fork, and seems to run into CuA + CuP. Crossvein r-m present, broad at the level of RP fork. M present, M fork absent; M1 proximal vanishing before reaching M1+2; M2 proximal connected to M1+2; M1 and M2 mostly straight, and reach margin of wing; crossvein m-m narrow, tiny, and tubular; M3+4 short and strongly broad, proximal not connected to M; M3 present but as a short peduncle; M4 tubular; m-cu long. CuA + CuP short, broad, bulla-shaped; CuA ends just after m-cu connexion, with a seta posterior distally; CuP runs under CuA, and ends slightly after the end of CuA; cup cell absent. Intercalary vein, fiv, runs along the posterior margin of CuP, below CuA + CuP and slightly along MA before reaching the proximal cell of the wing; fiv proximally spectral and distally tubular. Crossvein cu-pcu present, long. PCu with two short branches. A1 proximally fused with the posterior branch of PCu. A2 long, runs along the axillary margin and extends into the anal part of wing. Eight setae on axillary ridge (instead of five setae mentioned in the original description).

Remarks

The characters “CuP runs under the CuA, and ends slightly beyond the CuA”, and “crossvein cu-pcu present, long” are not observed in other Cretaceous genera but observed in other specimens of Álava amber identified as belonging to the †Euliphora genus (†Euliphora n. sp. 1, Fig. 5d; and †Euliphora n. sp. 2, Fig. 5e), these specimens will be described in a future study. The crossvein cu-pcu connects the proximal part of the CuA + CuP vein to the proximal part of the PCu vein, and run under the fiv. These two morphological characters are considered diagnostic of the genus †Euliphora. No female of the genus †Euliphora has yet been found.

  • Genus †Prioriphora McAlpine and Martin, 1966.

  • Type species: †Prioriphora canadambra McAlpine and Martin, 1966: 532, figs. 2, 9–12, 21.

  • Other included species: †Prioriphora canadambra, †P. casei Grimaldi and Cumming, †P. cheburashka Mostovski, †P. longicostalis Brown and Pike, †P. luzzii Grimaldi and Cumming, †P. polyankae Mostovski, †P. schroederhohenwarthi, †P. setifemoralis Brown and Pike.

†Prioriphora schroederhohenwarthi Solórzano-Kraemer and Perrichot, 2011 (Fig. 6a–d)

Fig. 6
figure 6

Wings of †Prioriphora schroederhohenwarthi Solórzano-Kraemer and Perrichot, holotype IGR-ARC-382. a Three-dimensional virtual extraction of the right wing ventrally. b Three-dimensional virtual extraction of the right wing dorsally. c Right wing drawing of the holotype. d Wing drawing of the paratype IGR-ARC-04

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Material examined: Holotype, ♂, FRANCE: Charente-Maritime, Archingeay, Cenomanian, mid-Cretaceous, Archingeay amber (Charentese amber), amber piece IGR-ARC-382.1b housed at IGR (Geological Institute of Rennes). Paratype, isolate wing, FRANCE: Charente-Maritime, Archingeay, Cenomanian, mid-Cretaceous, Archingeay amber (Charentese amber) (IGR-ARC-04).

Revision and additional characters of holotype

Matching the early model. C with two rows of strong short, spine-like setae (instead of “covered with minute setae” mentioned in the original description); Cratio: 4.3; 1.5; 1. Sc runs along RA and fused to RA just before RA fused to C (Fig. 6). RA and RP1+2 fused with C, while RP3+4 not; RP fork long; RP4 continues spectrally parallel to the anterior margin of wing. Cossvein r-m broad, at level of RP fork. MA long, runs along R and before R fork level plunges towards in proximal CuA + CuP, distally seems to fused with proximal tip of CuA + CuP and M. M and M1+2 present; M seems to originates from MA and CuA + CuP; M1+2 divides into M1 and M2; M1 and M2 slightly straight, and reach margin of wing; crossvein m-m tiny and tubular; M3+4 vanishing, but short and wide, not connected to M; M3+4 divided in M3 and M4; M3 present, short proximal growth, then by an absence-of-setae line in the paratype (e.g. observation in paratype photograph in [34]: fig. 4c), and observable by a long remnant vein in the holotype (Fig. 6b). Cells br, bm and d, present; br cell elongates and narrow, proximal part close by MA and M; proximal part of bm cell close by M and CuA + CuP; d cell tiny, and slightly open to bm cell, distally close by crossvein m-m. CuA + CuP present; CuA ends quickly after crossvein m-cu; CuP short, vanishing before connection of CuA with m-cu; cup cell absent (instead of cup cell present and “anterior margin of cell cup fused to Rs, A1 + CuA2 runs into posterior margin of cup” mentioned in the original description). Proximal section of fiv seems to vanish at proximal tip of CuA + CuP, then runs along posterior margin of CuP, and reaches posterior wing margin. PCu with two short branches. Proximal part of A1 fused with posterior branch of PCu; A1 long, and ends quickly in the anal part of wing. A2 long, runs along axillary margin and extends into the anal part of wing. Seven setae on axillary margin.

†Prioriphora n. sp. (Fig. 7a–d)

Fig. 7
figure 7

Wing of †Prioriphora n. sp., collection number IGR-FRS-7. a and c Infrared reflected photographs of the left wing: a zoom of the base of the wing, c complete wing, b drawing of the left wing, d a photograph of the left wing. Scale 0.5 mm

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Material examined: Holotype, isolate wing, FRANCE: Charente-Maritime, Fouras, Cenomanian, mid-Cretaceous Fouras-Bois-Vert amber (Charentese amber) (IGR-FRS-7). The amber piece IGR-FRS-7 contain several inclusions, 53 arthropods and 3 conifers fragments, the list of syninclusions detailed in [35].

Diagnosis

Sc runs slightly along RA before fused with RA; distal RP with one seta; RP3+4 slightly longer than C. RP4 projection and MA absent. M3 present, long, and proximally tubular before vanishing in three-quarters of M4 length. A2 long and separated to axillary ridge.

Description of wing

Matching the early model. Wing length 1.14 mm and width 0.70 mm. Wing covered with minute setae. C long; CI: 0.64; Cratio: 4.1; 2.8; 1; C covered by two rows of dense, medium, spine-like setae. Sc fused to RA in the mid-length. RA and RP1+2 fused with C, while RP3+4 not; RP fork long. Cossvein r-m broad, at level of RP fork. M and M1+2 present; M seems to connect with CuA + CuP; M1+2 extends to M2, fork absent; proximal M1 vanishes well before reaching M; M1 straight and distally posteriorly curved while M2 sigmoid; M1 and M2 reach margin of wing; crossvein m-m tiny and tubular; proximal M3+4 vanishing, not connected to M; M3+4 short, strong, and wide, divided in M3 and M4. Cells br, bm and d, present; br cell elongates and narrow, proximal cell open in the proximal cell; proximal bm cell close by M and CuA + CuP; d cell small, and slightly open to bm cell, distally closed by crossvein m-m. CuA + CuP present; CuA ends at level of crossvein m-cu; CuP short, transparent, vanishing quickly; cup cell absent. Proximal tip of fiv starts from the middle of the proximal cell, then runs along the posterior margin of CuA + CuP and CuP; fiv reaches the posterior wing margin. PCu with one branch. A1 short, runs along posterior PCu, and ends before the anal part of wing; A2 extends into the anal part of wing. Seven setae on axillary margin.

Remarks

As this is an isolated wing and no phorid body has been observed in the Fouras-Bois Vert amber, it is not possible to describe a new species. The wing veins are very similar to †P. casei, differing in that the fiv does not join the wing margin and no seem seta on RP are present (i.e. not mentioned in [36]: fig. 59); however, this wing differs from all other †Prioriphora. This wing is also very similar to the genus †Gemmaphora Mostovski, showing a similar CI and Cratio, but differing in the absence of the M1+2 fork (e.g. fork present is mentioned as a diagnostic character of †Gemmaphora). The genus †Prioriphora is rather problematic because of the five diagnostic characters of this genus, four are based on wing vein characters [37] that can also be found in other Cretaceous genera. Therefore, we have classified this specimen in the †Prioriphora genus. We decided to describe this wing for two reasons: (1) the particularity of the M3 which is long and whose proximal part is tubular, indicates that it is a new species of †Prioriphora; (2) the presence of Phoridae in a new locality reinforces the knowledge of the biodiversity of phorids in the Cretaceous and the possibility of finding new remains of phorids in the Fouras-Bois Vert amber in the future.

  • Genus †Ulrichophora Brown, 2007.

  • Type species: †Ulrichophora lobata Brown, 2007: 1–2, figs. 1–5.

  • Monogeneric.

†Ulrichophora lobata Brown, 2007 (Fig. 4a–c)

Material examined: Holotype, ♂, RUSSIA: Kaliningrad, Baltic amber, amber piece LACM ENT 159890 housed at LACM (Natural History Museum of Los Angeles County).

Revision and additional characters of holotype

Matching the early model. Wing length 2.6 mm and width 1.22 mm. C long; CI: 0.95, and Cratio: 2.72; 1.63; 1 (i.e. paratype, [2]: figs. 4 and 5); C covered by two rows of tiny, dense, spine-like setae. Sc speedy runs along RA, but not fused to RA (black arrows in Fig. 4a), fused to C without separating from RA (instead of Sc fused to RA mentioned in the original description by “wing similar to that of extant sciadocerines”). RA, RP1+2, and RP3+4 fused with C not; RP long, and fork long. Crossvein r-m broad, between R fork and RP fork. M and M1+2 present; M seems to originate to proximal part of CuA + CuP; M1+2 fork present; M1 and M2 straight; M1 and M2 reach margin of wing; crossvein m-m longer than other Cretaceous species and tubular; proximal M3+4 vanishing, not connected to M; M3+4 short, as wide as other medial veins, divided in M3 and M4; M3 present, long, and proximally tubular before vanishing at mid M4 length. Cells br, bm and d, present; br cell elongates and large, proximal part close by MA and M; proximal part of bm cell close by M and CuA + CuP; d cell small, and slightly open to bm cell (in paratype, d cell close, [2]: figs. 4 and 5), distally close by crossvein m-m. Proximal section of fiv not close to CuA + CuP, then runs close along posterior margin of CuP, and reaches posterior wing margin. A2 long, runs along axillary margin and extends into the anal part of wing; holotype A2 reaches posterior wing margin while paratype A2 vanishes before reaching the wing margin. Seven setae on axillary margin.

Family Ironomyiidae McAlpine and Martin, 1966.

†n. gen. n. sp. (Fig. 8a–d)

Fig. 8
figure 8

Wing of Ironomyiidae †n. gen. n. sp., collection number SJNB2012-12–10. a and c Wing photograph: a complete wing, c zoom of the base of the wing, b wing drawing, d infrared reflected photographs. Scale 0.5 mm

Full size image

Material examined: Holotype, isolate wing, SPAIN: Teruel, San Just, Utrillas municipality, Albian, Lower Cretaceous, San Just amber (Spanish amber) (SJNB2012-12–10). Proximal and postero-proximal wing part absent, the distal part is present but broken, in amber piece SJNB2012-12–10, with several inclusions, 36 arthropods, the list of syninclusions detailed in [38] and in “Additional file 2”.

Diagnosis

Wing hyaline except in the wing tip with a short microtrichia line between RP3+4 and M4 and a large microtrichia line after M4. C end between RP1+2 and RP3+4. Distal M1+2 part between m-m level and fork long; proximal M1 not in the continuity of distal M1+2; m-m slightly oblique.

Description of wing

Matching the early model. C setae minute and few dense. Sc fused to RA over most of their lengths. Cell d (length d/length wing) long 0.33.

Remarks

Wing is similar to †Palaeopetia Zhang, and †Macalpinomyia Li and Yeates in having a short microtrichia line between RP3+4 and M4 and a large microtrichia line after M4, and to Ironomyia White and †Proironia Grimaldi in being fully hyaline. In all other genera C end at or after RP3+4. †Proironia and †Palaeopetia also have minute setae along C, but in †Palaeopetia the setae are more dense. †Palaeopetia has Sc fused to RA over most of its length; however, in †Macalpinomyia Sc is not fused but is close to RA. †Macalpinomyia and †Palaeopetia are similar in having a long M1+2 between the crossvein m-m and the fork, however, in †Proironia this part is short and in Ironomyia and †Cretonomyia Li and Yeates absent. †Macalpinomyia, †Palaeopetia, †Proironia are similar in that the proximal M1 is not in continuity with the distal M1+2, but Ironomyia has it in continuity; †Proironia and †Macalpinomyia are similar in that m-m is slightly oblique; however, in Ironomyia m-m is strongly oblique, and perpendicular in †Palaeopetia. †Macalpinomyia and †Eridomyia Mostovsky are similar in having cell d long 0.33 (length d/length wing), in †Palaeopetia and †Hermaeomyia Mostovsky d is short [39]. Until now, no Ironomyiidae species were known from Spanish amber. The discovery of an Ironomyiidae in another Cretaceous deposit confirms their important biodiversity during this period while no Cenozoic fossils have yet been found during the Cenozoic (Fig. 1). The wing discovered differs from all currently described species in that it displays a new combination of characteristics not present in †Macalpinomyia, †Palaeopetia, and †Proironia. Together, all these features are an indication that this specimen would correspond to a new genus. Preservation of the wing is incomplete and in the absence of the rest of the body, we do not formally describe this specimen.

Discussion

Describing fossil species in amber has been challenging across the centuries. Insects in amber are often in sub-optimal positions, the quality of preservation is sometimes poor, and together with the not-always-transparent nature of fossil resins limits our current knowledge of fossil insects, including phorids. Furthermore, the lack of morphological data from the fossil record is due to limitations such as inadequate microscopes or insufficient light intensity for detailed vein examination (i.e. the proximal part of the wing which is often obscured by the body, or impurities surrounding the specimen could hide the connections of veins). The scarcity of new descriptions is not due to the absence of fossil remains—thousands of phorid fossils have been discovered in various amber deposits, copal, and Defaunation resin, housed in worldwide museums and institutional collections—but several factors contribute to the relative unpopularity of the family. These include decentralised data, their small size, and the lack of extraordinary features that might captivate researchers, or else the unresolved family phylogeny which further discourages some new investigations. Additionally, many descriptions provide only minimal details [31, 40,41,42,43,44,45,46,47,48], sometimes with imprecise diagnostic characters, combined with the absence of an image or drawing making the use of these data for other studies complicated. In contrast, closely related families such as Lonchopteridae, Opetiidae, Platypezidae, and Ironomyiidae contain many more species described relative to the number of specimens found in various fossiliferous deposits. All these families have living representatives but interestingly, no specimens of the Ironomyiidae have been discovered in the Cenozoic (Fig. 1). The other families also have large gaps in their fossil records (Fig. 1), unlike the Phoridae, which are present in many deposits throughout the geological periods, with only two gaps in the Palaeocene and Pleistocene epochs (Fig. 1). However, this is to be expected as we have gaps in amber bioinclusions at these times [49].

The fact that wing variability is also a feature of sexual dimorphism in some living species, but not in the Cretaceous fossils, is another aspect to highlight. In some females, the wings are absent, atrophied or vestigial (extremely reduced) as in some Chonocephalus or Cyphophorina Borgmeier and Prado species, while males have well-developed wings [31]. However, to date, no fossil female phorid of the Cretaceous with a significant reduction of the wings has been reported. To investigate this further, we need to study additional Cretaceous specimens, focusing on finding males and females with similar morphologies preserved together in the same resin layer in single pieces.

The evolution of wings shows a significant modification in the morphology of Phoridae before (early model) and after (recent model) the K-Pg (Cretaceous–Paleogene) extinction event. This morphological change is reflected in the biodiversity of the major groups. The Sciadocerinae is a group that was highly diversified during the Cretaceous and had little biodiversity in the post-Cretaceous. This decline in biodiversity may be due to (1) changes in forest diversity that occurred during the Angiosperm Terrestrial Revolution (ATR, 100–50 Ma, [50]), which has impacted many groups of insects (e.g. [51]) such as ants (e.g. [52, 53]); (2) the survival of some populations in endemic places and the extinction of groups elsewhere; (3) a significant competition of territory or food resources between other groups of insects or other Phoridae. The absence of records for the group “†Prioriphorinae” Mostovski during the Cenozoic suggests a pair of alternative hypotheses: (1) the whole group disappeared during the ATR, and therefore the records are strictly Cretaceous, or (2) the group has been heavily impacted by its biodiversity as for Sciadocerinae, but their presence has not yet been discovered. The genus †Agaphora is strictly Cretaceous, but, as already mentioned, the wing shows characters of both models with radial veins (early model) and medial veins (recent model) that suggest it could be a “transitional” taxon and therefore belongs to the here-named “†Agaphorine-group.” The Euphorida were not present during the Cretaceous (except †Metopina goeleti) and had explosive radiation in the post-Cretaceous which suggests that the reduction of veins has favoured the explosion of the family. The evolution of the Phoridae favoured reduction, especially at the level of the wings with (1) shortening the radial veins and the proximal medial vein sector, and/or (2) the disappearance of the proximal medial vein sector leading to the disappearance of cells br, bm, and d, the cubital and anal sector veins (Additional file 1: Fig. S6). Moreover, some reductions observed on other structures such as femoral bristles are lost, or in males in abdominal segment 6 and terminalia, tergites are reduced and lost [25].

For the reduction of morphological structures in modern Phoridae, we propose two main hypotheses. The first is that a change in the environment with a predominance of Angiosperms after the ATR which has significantly altered the dynamics of the forests causing evolutionary pressures on insects [51]. The second is that co-evolution with other insect groups, e.g. with ants or termites, affected extinction-survival dynamics. It is well known that many Phoridae have a close relationship with ants or termites (e.g. [54,55,56,57,58]), thus the origin of complex sociality in ants and termites may have altered the food resources and reproduction opportunities for these flies (e.g. [59, 60]), potentially impacting their behaviour and morphology. Phorids that parasitise ants spend most of their time walking or flying short distances above the ground. Therefore, their wings do not require much strength or ventilation for flying. Phoridae that have changed to parasitic behaviour could result in a reduction in the number of veins. Hunting and predation behaviour during the Cretaceous that requires strength in the wings for a long flight would explain the need for a large number of veins to support its flights.

The interpretation of the phorid wing venation, and closely related families, has changed over time (Table 1), and accordingly, has an impact on the interpretation of the phylogenetic relationships (e.g. a re-described species can move into another genus as †Maksika Mostovski or can lead to the creation of a new genus as †Hennigophora Brown) [3, 4, 25, 31, 33, 61]. By redefining the wing vein terminology and creating two stable and unambiguous wing vein models, we propose a solution to this problem (Figs. 2 and 3). Our wing observations suggest that the Ironomyiidae are more similar to the Platypezidae than to the Phoridae (e.g. [39]), although Ironomyiidae is often considered to be an early family of Phoridae [25, 62,63,64,65]. The Opetiidae is more similar to the Lonchopteridae than to the other families, and the Lonchopteridae specimens have more plesiomorphic wing vein characters than other families.

The choice to develop two models is supported by the difference between the taxa mostly discovered in the Cretaceous (i.e. Sciadocerinae and “†Prioriphorinae”) and the rest of the Phoridae (i.e. clade Euphorida). The first model corresponds to phorids with a more complex wing vein pattern and little variability. Almost all Cretaceous species show this pattern, except for the genus †Agaphora and †Metopina goeleti. However, †Agaphora is probably a “transitional” genus between the Mesozoic and the Cenozoic, i.e. it possesses both characters identified as early and characters identified as recent, and †Metopina goeleti more probably comes from the Kinkora locality from the Magothy Formation, post-Cretaceous in age and containing modern fauna [63,64,65]. In contrast, few post-Cretaceous species show this pattern, namely only three species in Baltic amber and two living species, four of which belong to Sciadocerinae and †Ulrichophora lobata, sometimes included in the subfamily Sciadocerinae [2, 33]. Our results suggest the exclusion of †Ulrichophora from Sciadocerinae because of the lack of fusion of Sc to C, with the Sc running along RA until directly fused distally to C. This character is more similar to the Ironomyiidae with the Sc vein direction, except that it is not separated distally from RA before being fused to C. The majority of the Cretaceous species shows an early pattern, which is why we named this model the early model. The second model corresponds to the rest of the phorids, which show a venation pattern with important reductions. This model includes almost all post-Cretaceous species (i.e. Euphorida) with recent morphological characters (i.e. morphological characters found in the Cenozoic fossils and the living fauna), which gives the name recent model. In particular, many Baltic amber species in the genera Hypocera Lioy, Gymnophora Macquart, and Megaselia have these recent morphological characters. In contrast to the early model, the variability between species is very high, ranging from a slight reduction in all veins to the disappearance of all posterior veins (i.e. medial, post-cubital, and anal veins). For the few species that show a very significant vein reduction, we propose an example, as a support for labelling the veins, which should facilitate future research (Fig. 3c,d). In conclusion, the reduction of wing veins in Phoridae seems to occur first in the posterior part (i.e. anal veins then cubital veins) and then in the anterior part (i.e. medial vein then radial veins). Conversely, no tendency was observed for the distal part to have reduced veins before the proximal part, or vice versa.

We could not re-examine all the holotypes. Nevertheless, during the re-examination of certain holotypes, we noted errors of observation or interpretation of the wing veins, as for †Prioriphora schroederhohenwarthi, mainly due to the difficulty of observing the base of the wings, which requires strong luminosity or even more powerful tools (i.e. infrared microscopes or μ-CT scans). However, it will therefore be important, in future studies, to re-evaluate the fossil holotypes using new methods and applying new knowledge to verify the characters described, particularly the diagnostic characters to complement the descriptions and to have enough morphological characters for, for example, phylogenetic studies.

Conclusions

The venation of insect wings has been studied and discussed with a foundation of constancy for 120 years, with revisions based on a variety of homology hypotheses. In recent years, new technologies have made it possible to develop new methods of observing things that were difficult to observe in the past, such as the base of the wings. Wing structures have evolutionary significance and are an important character pool for the study of new fossils. Our study provides a supporting tool for the description of morphological characters around the wings, and the clarification of the phorid wing venation, which may help the future descriptions of unknown fossil fauna as well as facilitate the identification of early fauna, in which the wing venation is a robust character for the identification. Thus, the homogenisation of wing vein terminology plays a pivotal role in advancing our understanding of the phylogenetic relationships of the Phoridae family, its relationships with outgroups, and the spatiotemporal evolution of the Phoridae as a whole. However, a future re-evaluation of the Cretaceous fauna is still necessary to clarify the diagnostic characters of each genus. In this respect, the numerous new phorids in amber from e.g. Myanmar and Spain will contribute to understanding this family’s early biodiversity.

Methods

Taxa examined

The three phorid holotypes re-evaluated in this study are: (1) †Euliphora grimaldii in Spanish amber in Álava locality (piece number is MCNA 8648, and information of piece in [66]), (2) †Prioriphora schroederhohenwarthi in Charentese amber in Archingeay-Les Nouillers locality (piece number is IGR-ARC-382.1b, and information of piece in [34]), and (3) †Ulrichophora lobata in Baltic amber (piece number is LACM ENT 159890, and information of piece in [2]). In Additional file 1, we show wing characters of fossil or living phorid specimens with different wing patterns, the figures are marked as “SX”, which have not yet been studied.

The isolate phorid wing found in Fouras-Bois Vert amber discovered by Dr Vincent Perrichot (University Rennes 1) is described here. This wing is preserved in the piece IGR-FRS-7, and it is housed in IGR. The Fouras-Bois Vert deposit is located in Charente-Maritime, western France, in the B2ms subunit belonging to the Upper Albian-Cenomanian [35, 67]. The locality Fouras-Bois Vert is also part of the set of ambers called “Charentese amber” [35, 68, 69]. The piece IGR-FRS-7 contain 53 arthropods and three conifer fragments as syninclusions (for a detailed list see [35]).

The first ironomyiid, in San Just amber (a wing), is described here. The wing is the first Ironomyiidae from the Albian period (113.0 to 100.5 Ma) and in Spanish amber. San Just is a locality of Urillas Municipality, in Teruel, Spain. The amber from San Just in northeastern Spain, within the Teruel Province, was first documented by Peñalver et al. [70] and was initially dated to the middle-upper Albian period [71]; however, recent comprehensive studies on palynomorphs suggest that it is more accurately placed in the upper Albian [72, 73]. The wing is preserved in the piece SJNB2012-12–10 (palaeontological excavation in 2012), housed in the Dinópolis collection (Teruel, Spain).

Most of the amber pieces in this work are prepared and embedded in epoxy resin for preservation, following [74] and [75]. We use the wing orientation provided by the Cumming and Wood [13]: proximal to distal and anterior to posterior (Fig. 9). The Costal Index (CI) and Costal ratio (Cratio), represented in Fig. 9, are calculated by:

Fig. 9
figure 9

Wing orientation and vein distances. In black, the orientation of the wing. Blue line, length of costal (B) and wing (A) for calculating the CI. Orange line (a, b, c), the distance between crossvein h and radial veins for calculating the Cratio. The formula No. 1 with the CI and the formula No. 2 with the Cratio

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$$\text{CI}=\frac{\text{Costal length}\;(B)}{\text{Wing length}\;(A)}$$
(1)
$$\begin{aligned} {\mathrm C}_{\mathrm{ratio}} &=\frac{\mathrm{distance}\;\mathrm h-\mathrm{RA}\;\mathrm (a)}{\mathrm{distance}\;{\mathrm{RP}}_{1+2}-{\mathrm{RP}}_{3+4}\;\mathrm (c)}; \frac{\mathrm{distance}\;\mathrm{RA}-{\mathrm{RP}}_{1+2\;}\mathrm (b)}{\mathrm{distance}\;{\mathrm{RP}}_{1+2}-{\mathrm{RP}}_{3+4\;}\mathrm (c)};\;1 \end{aligned}$$
(2)

The wing terminology of the two new models follows the schematic representation of forks and veins diagram in Fig. 10.

Fig. 10
figure 10

Schematic representation of forks and veins diagram of new combined terminology of Phoridae wings. Veins follow the colour code, the forks of radial, medial, cubital, and post-cubital veins are shown by the number. Crossveins are represented by a black trait. The cell by a coloured zone

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Imaging and drawing

The photographs and Z-stacks images of the amber specimens were performed under a Nikon SMZ25 microscope, using Nikon SHR Plan Apo × 0.5 and SHR Plan Apo × 2 objectives with a microscope camera Nikon DS-Ri2 and the NIS-Element software (version 4.51.00 www.microscope.healthcare.nikon.com) at the SMF (Senckenberg Research Institute, Frankfurt am Main, Germany). Infrared-reflected photographs were taken with a Nikon Eclipse ME600D at the SMF (for precise technical information, see [76]). The living and fossil specimen pictures were photographed with a Nikon Z7II camera with a Nikon SHR Plan App WD:60 × 1 lens, both attached to the Nikon SMZ 25 stereomicroscope at the MNHN, and with a Keyence V-5000 imaging system at the Natural History Museum of Los Angeles County (LACM). The pictures were taken with the NControlPro 2 software and then processed on NX Studio; Helicon Focus software (version 7.6.1) was finally used to merge the pictures. Figures were performed using Adobe Photoshop software (version 25.4 www.adobe.com), and the Procreate software (version 5.3.7) on a tablet iPad Pro 10 (model A1876) was used for all digital drawings. The models were created from a combination of observations and do not correspond to any described species.

The original scan of †Prioriphora schroederhohenwarthi (see [34] for scan method) has been used for the re-evaluation of the wing, and it has been modified using VGStudioMax (version 3.3.1 www.volumegraphics.com/de, Volume Graphics, Heidelberg, Germany).

Abbreviations (with colour codes)

Veins: A1: first anal vein (in black); A2: second anal vein (in black); A3: third anal vein (in black); C: costa vein (in cyan); Cu: cubitus vein; CuA: anterior branch of cubitus vein (in yellow); CuA1: anterior branch of first cubitus vein; CuA2: anterior branch of first cubitus vein; CuA+CuP: fusion of anterior branch and posterior branch of cubitus vein; CuP: posterior branch of cubitus vein (in shadow yellow); fiv: forewing intercalary vein (in shadow grey); MA: anterior branch of medial vein (in shadow blue); MA1: anterior branch of first medial vein; MA2: anterior branch of second medial vein; M1: first medial vein (in blue); M2: second medial vein (in blue); M3: third medial vein (in blue); M4: forth medial vein (in blue); MP: posterior branch of medial vein; MP1: posterior branch of first medial vein; MP2: posterior branch of second medial vein; MP3: posterior branch of third medial vein; MP4: posterior branch of fourth medial vein; PCu: postcubitus vein (in clear grey); R: radius vein; R1: first radius vein; R2+3: second and third radius vein; R4+5: fourth and fifth radius vein; RA: anterior branch of radius vein (in magenta); RP: posterior branch of radius vein (in purple); RP1+2: posterior branch of first and second radius vein (in purple); RP3+4: posterior branch of third and fourth radius vein (in purple); Rs: radius sector vein; Rs1+2: first and second radius sector vein; Rs3+4: third and fourth radius sector vein; Sc: subcostal vein (in red); ScP: posterior branch of subcostal vein.

Cells: bm: proximal medial cell; br: proximal radial cell; cup: posterior cubital cell; d: discal cell.

Crossveins: h: humeral crossvein (in beige); cu-pcu: cubital-postcubital crossvein (in black); m-cu: medial-cubital crossvein (in black); m-m: medial-medial crossvein (in black); r-m: radial-medial crossvein (in black).

Data availability

All data generated or analysed during this study are included in this published article and its Additional files 1 and 2.

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Acknowledgements

Dany Azar (State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China, and Natural Sciences Department, Faculty of Sciences II, Lebanese University, Fanar-El-Matn P.O. Box, Lebanon) for taking the time to look for potential new Phoridae in Lebanese amber, and Vincent Perrichot (Géosciences Rennes, Université de Rennes, CNRS, Rennes, France) for providing the new wing in French amber. We are grateful to Thomas Schubnel (Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, Université des Antilles, Paris, France) for his advice on hypotheses concerning the evolution of wing veins in Phoridae, and Dalton de Souza Amorim (Departamento de Biologia, Universidade de São Paulo, Ribeirão Preto, Brazil) for the helpful discussions. We would like to thank Christophe Daugeron (Muséum National d’Histoire Naturelle, Centre National de la Recherche Scientifique, Mécanismes Adaptatifs et Évolution Paris, France) for providing extant Lonchopteridae, Platypezidae and Phoridae specimens. Appreciation is extended to Robin Kunz (Senckenberg Research Institute, Frankfurt am Main, Germany) for the efforts in sorting, preparing, and cataloguing the amber collection deposited at SMF.

Funding

Open Access funding enabled and organized by Projekt DEAL. This work part of the first author's PhD was supported by the grant of the German Research Foundation (DFG-project 457837041 (SO 894/6–1)). Mónica M. Solórzano-Kraemer was supported by the same grant of the German Research Foundation. Antonio Arillo was supported by the Spanish Ministry of Economy, Industry, and Competitiveness (projects CGL2014-52163, CGL2017-84419/AEI/FEDER, UE, and PID2022-137316NB/AEI/10.13039/501100011033/FEDER, UE).

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Authors and Affiliations

  1. 1Paläontologie und Historische Geologie, Senckenberg Forschunginstitut und Naturmuseum, Senckenberganlage 25, Frankfurt-Am-Main, 60325, Germany

    Mélanie C. M. Herbert & Mónica M. Solórzano-Kraemer

  2. Institut Systématique Evolution Biodiversité (ISYEB), Muséum National d’Histoire Naturelle, CNRS, Sorbonne Université, EPHE, Université Des Antilles, Paris, France

    André Nel

  3. Department of Entomology, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA, 90007, USA

    Brian V. Brown

  4. Departamento de Biodiversidad, Facultad de Biología, Universidad Complutense, Ecología y Evolucíon, Madrid, Spain

    Antonio Arillo

  5. Entomology II, Abteilung Terrestrische Zoologie, Senckenberg Forschungsinstitut und Naturmuseum, Senckenberganlage 25, Frankfurt-Am-Main, 60325, Germany

    Brendon E. Boudinot

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  1. Mélanie C. M. Herbert
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  2. André Nel
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  4. Antonio Arillo
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Contributions

Study conception and design: M.C.M.H., A.N. and M.M.S-K; Data collection: M.C.M.H., B.V.B and M.M.S-K; Conducted the fieldwork and the preparation, identification, and analysis of the field samples: M.C.M.H., B.V.B, A.A. and M.M.S-K; Analysis and interpretation of results: M.C.M.H., A.N., B.V.B, and M.M.S-K; Manuscript draft: M.C.M.H. and M.M.S-K. Wrote the manuscript: M.C.M.H., A.N, B.V.B, A.A, B.E.B. and M.M.S.-K; Imaging and figure preparation: M.C.M.H. Funding acquisition and project administration: M.M.S.-K. All authors contributed to the discussion, reviewed the results, and approved the final version of the manuscript.

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Correspondence to Mélanie C. M. Herbert.

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Supplementary Information

12915_2025_2376_MOESM1_ESM.pdf

Additional file 1: Complementary Figures of Phoroidea wings, Figures S1–S7. Fig. S1 – Photographs of wings of living specimens with an early model. Fig. S2 – Photographs of wings of living specimens with a recent model. Fig. S3 – Wing of †Agaphora iunior. Fig. S4 – Photographs of wings of fossil specimens with an early model. Fig. S5 – Photographs of wings of fossil and extant specimens with a recent model. Fig. S6 – Hypothesis of reduction of Phoridae medial veins. Fig. S7 – Wing patterns of Lonchopteridae, Opetiidae, Platypezidae and Ironomyiidae.

Additional file 2. Additional of information on piece SJNB2012-12–10.

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Herbert, M.C.M., Nel, A., Brown, B.V. et al. Review of wing morphology in fossil and modern species of humpbacked flies (Diptera: Phoridae). BMC Biol 23, 298 (2025). https://doi.org/10.1186/s12915-025-02376-8

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