Specimen preparation and photography

Given that the amber piece IGR.FRS-7 contained many fossils embedded within different amber flows, it was cut into several smaller fragments using a scalpel blade to enable easier observation of the inclusions. Each fragment containing at least one organic inclusion was embedded into mineralogical-grade epoxy Epotek 301-2 using a vacuum chamber. The resulting blocks were polished for an optimal view of the fossils. A total of 34 fossiliferous fragments were prepared and numbered IGR.FRS-7.1–7.34. The melyrid specimen described herein is preserved in fragment IGR.FRS-7.2 deposited in the collection of the Geological Department and Museum of the University of Rennes, France.

A Zeiss Discovery V20 stereomicroscope was used for observation and photography. Green epifluorescence microphotographs were taken using the Zeiss Axio Imager 2 light microscope in eGFP mode.

X-ray microtomography

Due to the generally quite opaque nature of Charentese amber, high-resolution X-ray microtomography (micro-CT) was used to reveal fine morphological detail of the fossil. The specimen was scanned using Zeiss Xradia 520 versa at the micro-CT laboratory of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences in Nanjing, China. A CCD-based ×4 objective was used, which provides isotropic voxel sizes of 2.9478 μm with the help of geometric magnification. The acceleration voltage for the X-ray source was 50 kV. To improve signal-to-noise ratio, 3001 projections over 360° were collected, and the exposure time for each projection was 2 s. The tomographic data were analysed using AVIZO (v. 2019.01; gold-coloured reconstructions) and VG Studio (v. 3.0; Volume Graphics; silver-coloured reconstructions).

Systematic position of Protodasytes gen. nov.

The fossil can be unambiguously assigned to the melyrid subfamily Dasytinae on the basis of the presence of a distinct clypeus; procoxae prominent, nearly contiguous, open posteriorly; body lacking obvious eversible vesicles; tarsomere 1 not shorter than tarsomere 2 on all legs; confused elytral punctation that does not form striae; and first two ventrites not connate (Mayor 45; Lawrence et al. 32; Gimmel et al. 16). In its current sense, the subfamily Dasytinae includes the following four tribes: Danaceini, Chaetomalachiini, Listrini and Dasytini (Gimmel et al. 16). Protodasytes gen. nov. possesses an unusual combination of characters that precludes an unambiguous placement into either of the modern tribes. It is excluded from Danaceini by its transverse clypeus and labrum and symmetrical claws. Placement in the tribe Chaetomalachiini is ruled out by tarsomeres 2–3 not distinctly broadened and segment 4 not distinctly slenderer than segment 3. It does not belong to Listrini, because its tarsomeres are not subequal in length and claws lack free membranous appendages. Although dasytines often have appendiculate claws, Protodasytes gen. nov. has symmetrical claws that lack extensive modifications but possess a basal tooth.

Protodasytes cretaceus gen. et sp. nov. is mostly similar to the tribe Dasytini in its serrate to moniliform antennae; eyes not pubescent; tarsomere 4 slightly shorter than tarsomere 3 on all legs but not distinctly narrower; claws symmetrical, with a basal tooth (Majer 37, 41; Mayor 45). However, unlike all modern Dasytini, Protodasytes gen. nov. has a distinct lateral fringe on the pronotum and elytra. Moreover, the indistinct antennal club of the new genus is unique within crown Dasytini. Both characters, the presence of a pronotal and elytral fringe and a small antennal club, are present in the tribes Danaceini, Chaetomalachiini and Listrini (Majer 38, 39). Given that in Majer's (41) cladogram, Listrini + Dasytini formed a clade, with Chaetomalachiini sister to both and Danaceini as the earliest diverging clade within the subfamily, both characters can be regarded as plesiomorphic. Given that it shares characters present in both Dasytini and Listrini, we regard Protodasytes gen. nov. as a ‘fossil link’ between the two tribes (Fig. 4). Majer (41) provided a list of morphological characters supporting the sister relationship between Dasytini and Listrini, and this relationship has also been recovered by molecular analyses based on four genes (Gimmel et al. 16). However, the same analysis also recovered a non-monophyletic Danaceini and Chaetomalachiini, and further recovered the tribe Amauronioidini as closely related. Deeper relationships between melyrid tribes vary between molecular studies that are based on only a few genes (Bocáková et al. 5), given that they may be susceptible to phylogenetic artefacts due to insufficient phylogenetic signal and the limits of the phylogenetic inference software (e.g. Young & Gillung 70; Tihelka et al. 64). Given the unresolved higher classification of Dasytinae, we choose to provisionally treat Protodasytes gen. nov. as tribe incertae sedis.

Fossil record of Melyridae

The earliest fossil melyrid is the Middle Jurassic Sinomelyris praedecessor from Daohugou Beds in north-eastern China. The fossil has been assigned to the subfamily Melyrinae mostly based on its habitus characters, but a more precise systematic placement was not possible (Kolibáč & Huang 23). The only other Mesozoic melyrid known to date is the Albian Acanthocnemoides sukatshevae from Siberian Taimyr amber. The fossil, known from two fragmentary specimens, has been originally assigned to the family Acanthocnemidae (Zherikhin 1002), but a recent re-examination of the type material supported its inclusion in the dasytine tribe Danaceini (Kolibáč & Perkovsky 24). Two undescribed specimens from Lower Cretaceous Lebanese amber, apparently belonging to Malachiinae and Dasytinae, were mentioned by Kirejtshuk & Azar (21). Further undescribed specimens from Albian Spanish amber were mentioned by Peris et al. (51). A single Albian–Cenomanian melyrid has been mentioned from Burmese amber in the collections of the Natural History Museum in London (Rasnitsyn & Ross 60). This makes P. cretaceus gen. et sp. nov. the earliest described member of Melyridae from the Mesozoic of Europe.

Soft-winged flower beetles are more abundant in the Cenozoic fossil record. They are known from Eocene Baltic and Rovno ambers (Spahr 62; Hieke & Pietrzeniuk 20). Majer (42) reviewed the melyrid fauna of Baltic amber, and since then several new species have been described (Kubisz 26; Tshernyshev 66, 67). Two malachiine species are known from Eocene Oise amber (Kirejtshuk & Nel 22). The recent species Attalus lusitanicus Erichson, 1000 reported from Eocene–Oligocene Bembridge Marls is herein removed from the family and treated as Polyphaga incertae sedis, given that it is represented by a single poorly preserved specimen lacking the important diagnostic characters that would support its assignment to this particular species. Fossils described from the late Eocene Florissant Formation in Colorado are all in need of revision (Wickham 68, 69; Mawdsley 43), given that many are very fragmentary. Troglops punctatissima Théobald in Piton & Théobald, 1935 was described from the late Oligocene of Puy-de-Dôme, France, based on only a single elytron without any informative diagnostic characters (Piton & Théobald 59), and as such it is excluded from the family and treated as Polyphaga incertae sedis. Malachius vertummni Heer, 19 from the Miocene of Oeningen, Germany (Heer 19) is excluded from Melyridae due to the lack of diagnostic characters and is treated as Polyphaga incertae sedis. Subfossil soft-winged flower beetles are also known from Quaternary sediments (e.g. Elias 10; Elias et al. 11), these specimens are not included in the overview of the described fossil Melyridae species given in Table 1.

Soft-winged flower beetles: potential pollinators of early angiosperms?

The earliest unequivocal fossil angiosperms date back to the Early Cretaceous (Friis et al. 15). Their diversification during the mid-Cretaceous, when they replaced the previously dominant gymnosperms (Benton 4), is believed to have drastically altered food chains and led to the diversification of many terrestrial animal lineages in an event known as the Cretaceous Terrestrial Revolution (Lloyd et al. 36). Together with thrips, lacewings, flies, and scorpionflies (Labandeira et al. 27, 28), beetles were among the first pollinators of gymnosperms during the Mesozoic (Cai et al. 6; Liu et al. 35). Beetles associated with pollen are known from Cretaceous ambers (Bao et al. 3; Peris et al. 53; Peris & Jelínek 49), and it has been suggested that the diversification of angiosperms may have contributed to the radiation of phytophagous beetles (Farrell 13; Ahrens et al. 1).

Adult soft-winged flower beetles are believed to be exclusively pollinivorous and nectarivorous, although predation and scavenging has been reported as well (Mayor 45). In summer, they can be collected in large numbers on the inflorescences of diverse angiosperm groups such as daisies, legumes, and mustards. as well as on some gymnosperms such as pines. Mawdsley (44) listed 68 genera of plants belonging to 26 families from North America visited by dasytines. Large quantities of pollen that adhere to the beetle's setose elytra and abdomen are transported between flowers during the course of normal feeding (Hawkeswood 18). At least two Nearctic members of the phlox family Polemoniaceae depend primarily on pollination by soft-winged flower beetles (Grant & Grant 17), and dasytines have also been demonstrated to contribute to the pollination of sunflowers in South Africa (du Toit 65). The body of Protodasytes gen. nov. is densely setose and possesses deep grooves, which are frequently found in pollinating beetles (Cai et al. 6). The occurrence of diverse monocots and eudicots at Fouras (Peyrot et al. 58) suggests that like its modern relatives, P. cretaceus gen. et sp. nov. may have visited and pollinated early angiosperms in the Cenomanian of western Europe. Further specimens associated with pollen would be required to directly confirm this association. At the very least, P. cretaceus gen. et sp. nov. provides an important calibration point for the Mesozoic diversification of dasytines.