A Cretaceous sap beetle with specialized mandibles (Coleoptera : Nitidulidae)

Abstract

Sap beetles (Nitidulidae) are species-rich, highly diverse, widely distributed and exhibit varied food habits. However, studies on nitidulids in Kachin amber are scarce, particularly those involving nitidulids with specialized mandibles. Here, we report a new genus and species of Nitidulidae, Vetunitidula mandibulata gen. et sp. nov., from mid-Cretaceous Kachin amber (approx. 99 Ma). This species is characterized by distinctly enlarged mandibles and a loose three-article antennal club, suggesting it as a stem-group nitidulid. The enlarged mandibles may be a manifestation of sexual dimorphism, as in some extant species. Together with previous studies of fossil nitidulids, our discovery highlights the remarkable diversity and morphological disparity of sap beetles during the late Mesozoic.

Headnote

Sap beetles (Nitidulidae) are species-rich, highly diverse, widely distributed and exhibit varied food habits. However, studies on nitidulids in Kachin amber are scarce, particularly those involving nitidulids with specialized mandibles. Here, we report a new genus and species of Nitidulidae, Vetunitidula mandibulata gen. et sp. nov., from mid-Cretaceous Kachin amber (approx. 99 Ma). This species is characterized by distinctly enlarged mandibles and a loose three-article antennal club, suggesting it as a stem-group nitidulid. The enlarged mandibles may be a manifestation of sexual dimorphism, as in some extant species. Together with previous studies of fossil nitidulids, our discovery highlights the remarkable diversity and morphological disparity of sap beetles during the late Mesozoic.

Keywords:

taxonomy, palaeoentomology, sexual dimorphism, pollination

1. Introduction

Nitidulidae, commonly known as sap beetles, are the most diverse family within the superfamily Nitiduloidea, comprising over 350 extant genera and nearly 4500 species [1]. Extant Nitidulidae are divided into 11 subfamilies: Calonecrinae Kirejtshuk, Carpophilinae Erichson, Amphicrossinae Kirejtshuk, Meligethinae Thomson, Epuraeinae Kirejtshuk, Nitidulinae Latreille, Cillaeinae Kirejtshuk and Audisio, Maynipeplinae Kirejtshuk, Cryptarchinae Thomson, Cybocephalinae Jacquelin duVal, and Prometopinae Böving and Craighead [1-3]. Nitidulid beetles are globally distributed, with higher abundance in tropical and Holarctic regions [1]. Their feeding habits are diverse, including mycophagy, predation, saprophagy, necrophagy, anthophagy, frugivory and tree fluid-feeding [1,4]. While most nitidulids feed on fungi or sap, Meligethinae and some species within Epuraeinae, Carpophilinae and Nitidulinae are primarily anthophagous [4].

Kachin amber is a crucial palaeontological resource, renowned for its exceptional preservation of mid-Cretaceous biodiversity [3,5-7]. This amber encapsulates a wide array of organisms, including bryophytes, flowering plants, gastropods, arachnids, vertebrates and a diverse range of insects, offering invaluable insights into an ancient ecosystem and the history of terrestrial life on Earth during the mid-Cretaceous [7]. To date, approximately 40 genera and over 65 species of Nitidulidae have been reported as fossils [8-11], although only 14 species are known from the Mesozoic. Among these fossils, five genera and nine species are known as impression fossils, including five species from the Jurassic: Nitidulites argoviensis Heer, 1865, Petrorophus truncatus Heer in Heer and Escher, 1852, Strongylites lavigatus Heer, 1865, Strongylites morio Heer, 1865 and Strongylites stygicus Heer, 1865, and four species from the Cretaceous: Crepuraea archaica Kirejtshuk, 1990, Crepuraea explanata Kirejtshuk, 1990, Crepuraea zherichini Kirejtshuk and Ponomarenko, 1990 and Cyllolithus mirandus Kirejtshuk, 1990 [12-14]. The remaining five species are preserved in Kachin amber: Sorodites angustipes Kirejtshuk, 2018, Protonitidula neli Zhao et al., 2022, Phenolia (Palaeoronia) haoranae Kirejtshuk and Jenkins Shaw, 2023, Spinanitidula nigroflavo and Cretabaltoraea volsella Peris, Jelínek & Audisio, 2024 [8,10,11,15,16]. In addition to the fossil species mentioned above, previous species in Kachin amber that were initially attributed to the Kateretidae have been reclassified as belonging to the extinct subfamily Apophisandrinae within Nitidulidae based on morphological analysis [17]. However, as precise phylogenetic relationships between Kateretidae and Nitidulidae remain unresolved, we remain cautious about fully endorsing this reclassification at the family level for the previously reported kateretids. Nonetheless, we acknowledge that the newly described genera and species assigned to this subfamily, such as Diopsiretes corniger Peris, Jelínek & Audisio, 2024 and Cornuturetes elaphus Peris, Jelínek & Audisio, 2024, are correctly placed within Nitidulidae [17]. Here, we report a new genus and species of Nitidulidae in Kachin amber, exhibiting robust and enlarged mandibles, representing the first fossil record of Mesozoic nitidulid with carinae on specialized mandibles. Moreover, the close proximity of the sap beetle to a stenurothripid thrips, often considered gymnosperm pollinators in the Mesozoic, within the same piece of amber enhances the likelihood of shared floral associations and potential ecological interactions between these insects and gymnosperms.

2. Material and methods

The unique specimen (accession number, NIGP203942) is permanently housed in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China. The amber piece was ground with sandpapers of different grit sizes and ultimately polished with diatomite mud for photography [18]. Photographs were taken using a Zeiss Stereo Discovery V16 microscope system with incident and transmitted light, and a Zeiss LSM 710 confocal laser scanning microscope (CLSM) with an attached digital camera [19,20]. Helicon Focus 7.0.2, Adobe Photoshop CC 2019 and Adobe Illustrator 2020 were used for image and figure plate composition.

The Kachin amber specimen was sourced from an amber mine near the Noije Bum Hill summit site, 20 km southwest of Tanai, in the Hukawng Valley, Kachin Province, northern Myanmar [21,22]. Zircon dating of wall rocks and palaeontological evidence suggests that the age of Kachin amber is mid-Cretaceous, from the latest Albian to the earliest Cenomanian (approx. 98.79 ± 0.62 Ma) [23]. The nomenclatural acts established herein are registered under LSIDurn:lsid:zoobank.org:pub:8C88BB0E- B1B2-4BCA-8DAF-EDE381AEAE56.

3. Results

3.1. Systematic palaeontology

Order: Coleoptera Linnaeus, 1758

Family: Nitidulidae Latreille, 1802

Genus: Vetunitidula gen. nov. (LSIDurn:lsid:zoobank.org:act:6BA19326-E441-439C-BA1F- DFF19312A36B)

(i) Type species

Vetunitidula mandibulata sp. nov.

(ii) Etymology

The generic name is a combination of the Latin adjective vetus, meaning, 'old', and the generic name Nitidula Fabricius; the name is feminine in gender.

(iii) Diagnosis

Body elongate, dorsally glabrous. Head rectangular, with distinct occipital ridge. Clypeus transverse, labrum distinct. Mandibles large, straight, with distinct medial (mediolongitudinal) carina (complete on left mandible, incomplete on right mandible), with at least two distinct teeth on the mesal edge of each mandible. Antenna concealed, with a loose club composed of three articles. Pronotal and elytral sides explanate horizontally, discs punctured. Prosternal process prolongate, with small lateral projection, procoxal cavities closed incompletely. Elytra truncate, with over two abdominal segments exposed. Mesoand meta-tibiae armed with two longitudinal rows of spines dorsally; two tibial spurs present.

(iv) Description

Body elongated and moderately flattened dorsoventrally (figure 1a,b). Surface dorsally glabrous but punctured (figure 1a).

Head prognathous, rectangular, with distinct occipital ridge (figures 1a and 2a). Mandibles large, straight, punctured, with acute apex; medial (mediolongitudinal) carina distinct and complete dorsally on left mandible, but incomplete on right mandible, and single mandible with at least two distinct teeth on mesal edge (figure 2a). Antenna is concealed by anterolateral margins of frons, with loose club composed of three articles (figure 2a-d). Clypeus transverse, rectangular; labrum distinct, transverse (figure 2a).

Pronotum transverse, with prominent and round anterior angles; lateral margin explanate horizontally; pronotal disc punctured, glabrous (figure 1a). Prosternum transverse, length slightly shorter than prosternal process; prosternal process prolongate behind procoxae, with lateral projection, apex sparsely setose; procoxal cavities closed incompletely (figures 1b and 2e).

Elytra truncate, quadrate, with over two abdominal segments exposed; anterolateral angles acute horizontally; disc surface seriate-punctate, glabrous; elytral sides explanate horizontally (figures 1a, 3a,b).

Mesoand meta-tibiae with a longitudinal row of sparse, stout spines and a separate row of dense, long spines on dorsal edge; two tibial spurs present (figure 3c,d).

Vetunitidula mandibulata sp. nov. (LSIDurn:lsid:zoobank.org:act:AFD94918-7761-4FB5-BD41- EF19684F3C38; figures 1-3)

(v) Etymology

The specific epithet refers to the distinctively large mandibles.

(vi) Diagnosis

As for the genus with the following additional characters: frontoclypeal region is distinctly present. Antennomere 11 is cylindrical. At least one large and blunter tooth and another acute tooth are distinct on the mesal edge of a single mandible. Prosternal process is relatively wide. Triangular mesoscutellar shield is small. Ventrite V with broad, transverse, apical extension with three apical teeth and dense setae.

(vii) Holotype

NIGP203942, tentatively male; the specimen is co-preserved with a Stenurothripidae thrips in close proximity (figure 1)

(?) Type locality and horizon

Amber mine in the Hukawng Valley, Myitkyina District, Kachin State, Myanmar; earliest Cenomanian (mid-Cretaceous) [24].

(ix) Description

Body length approximately 4.0 mm (measured from apex of mandibles to terminus of pygidium), with greatest width 1.7 mm (measured across midlength of pronotum); colour brownish yellow (diagenetically altered, though, by acidic clearing of integument, may not entirely reflect coloration in life) (figure 1a).

Head length 0.6 mm (measured from apex of clypeus to anterior margin of pronotum), width 1.3 mm across compound eyes (figure 1a). The anterior edge of the head protruded medially to form a distinct frontoclypeal region (figure 2a). Compound eyes protuberant, round, situated at the sides of the head, with short temples (figure 2a). Antenna with 11 antennomeres, densely setose; scape twice the length of pedicel; antennomeres II-VIII subequal in length and width, 0.7 × antennomere IX; antennomeres IX and X trapezoidal, subequal in length and width; antennomere XI cylindrical (figure 2b?d). Single mandible width 0.2 mm, length 0.8 mm, with one complete mediolongitudinal carina distinct dorsally on the left mandible (incomplete on the right mandible, effaced in the proximal quarter); at least two distinct teeth on the inner edge of each mandible, the first tooth largest, blunter and situated near the base and one acute tooth situated at mid-length (figure 2a).

Pronotum widest near the midline, with pronotal length/head length ratio 3 : 2; lateral margin widely explanate (figure 1a). Prosternal process is relatively wide, subequal with distance between metacoxae (figure 1b). Mesoscutellar shield small, triangular, with rounded apex (figure 1a). Mesoand meta-coxae are moderately separated, no wider than the width of the prosternal process (figure 1b).

Elytra medial length is equal to combined widths, approximately 1.5 mm; sides moderately explanate (figure 1a). Combined exposed abdominal segments are approximately 0.8 mm long (figure 3a,b). Abdomen with five ventrites, sides wrapped by long, dense setae; ventrite V longest, with broad, transverse, apical extension with three apical teeth and dense setae (figures 2b and 3a,b).

Femora canaliculate for reception of tibiae (figure 1b). Tibiae gradually widened distally, densely setose (figure 3c,d). Tarsal formula 5-5-5; three basal tarsomeres subequal, shapes simple; tarsomere IV smallest, tarsomeres I-III densely setose ventrally; tarsomere V longest, as long as combined lengths of basal three tarsomeres; pretarsal claws simple (figure 3e,f).

4. Discussion

4.1. Systematic position of Vetunitidula

The Nitidulidae group in Nitiduloidea is composed of Nitidulidae, Smicripidae and Kateretidae, with Nitidulidae and Kateretidae as the closest sister clades in phylogenetic analysis [3]. Vetunitidula is classified within the Nitidulidae group and differs from the closely related Smicripidae by features such as truncate elytra exposing three abdominal segments, 11 antennomeres with a trimerous club, a distinct labrum and a 5-5-5 tarsal formula with tarsomere IV smallest [1,3]. Kateretidae differ from Nitidulidae primarily in the presence of a galea [1,25]. Though the key feature is difficult to observe in this specimen, Vetunitidula can be distinguished from Kateretidae by its relatively wide and prolongate prosternal process with lateral projections and long setae on the lateral sides of the pygidium. In contrast, Kateretidae have a short, narrow prosternal process, not dilated posterior to the procoxae and lack long setae on the pygidium [1,25].

The antennal club is a common but important diagnostic trait in all nitiduloid families, regardless of the number of antennomeres or whether the club is loose or compact [3]. While both extant Kateretidae and Smicripidae have a loose trimerous club, the club is compact in extant Nitidulidae [1,25,26]. The trimerous club of Vetunitidula is loose and slightly larger than the preceding antennomeres, resembling that of Kateretidae, which is a significant feature to distinguish the genus from extant nitidulids [1,25,26].

Apart from the antennal club, Vetunitidula can be distinguished from most subfamilies in Nitidulidae, except Carpophilinae and Cillaeinae, by the following features: transverse head without a distinct neck, truncate elytra exposing over two abdominal segments, explanate and glabrous pronotal and elytral sides, subequal tarsomeres II-IV in length and width, distinct transverse labrum, incompletely closed procoxal cavities, metasternum without a medial sulcus, non-flattened tibiae, a 5-5-5 tarsal formula and simple pretarsal claws [1,2,27].

Carpophilinae and Cillaeinae are the two subfamilies most similar to Vetunitidula, as both have truncate elytra exposing at least two abdominal segments [1]. Carpophilinae and Cillaeinae are distinguished by the following character states: Carpophilinae generally lack seriate setae or have them partially, whereas Cillaeinae exhibit prominent seriate-punctate and seriate-setose patterns on the elytra or have glabrous seriate-punctate elytra; the combined length of the exposed abdominal segments is shorter than or subequal to the pronotum in Carpophilinae, whereas it is usually the opposite in Cillaeinae [1,27]. In Vetunitidula mandibulata, the combined length of exposed abdominal segments is subequal to pronotal length, which corresponds to species in Carpophilinae, and the elytral disc is glabrous and seriate-punctate in new species, which is consistent with elytra in some Cillaeinae [1,27]. Vetunitidula mandibulata seems to be related to the initial transitional species between extant Carpophilinae and Cillaeinae. Based on the above comparison, V. mandibulata is a Mesozoic extinct genus, different from all extant subfamilies in Nitidulidae, but the features in this new species could be observed in extant Nitidulidae, except the Kateretidae-like antennal club. The new species is a special species belonging to the Nitidulidae with Kateretidae-like club, given the differentiated manifestation of these features of two families in V. mandibulata.

The subfamilial relationships of Nitidulidae remain unclear, but it is relatively certain that Cryptarchinae is the earliest diverging subfamily [4]. Cryptarchinae is relatively primitive in having an incompletely closed procoxal cavity and a simple apical margin of the prosternal process, which is similar to that of V. mandibulata [1]. However, the absence of a subantennal groove and a loosely three-segmented antennal club in V. mandibulata are ancestral characters and are close to those of Kateretidae [2]. There are mid-Cretaceous nitidulids with compact antennal clubs found in Kachin amber, such as Sorodites angustipes, Phenolia (Palaeoronia) haoranae and Spinanitidula nigroflavo [8,10,11]. As such, Nitidulidae probably consisted of two major groups: one group shared features similar to Kateretidae, including V. mandibulata, Protonitidula neli, Cretabaltoraea volsella, Diopsiretes corniger and Cornuturetes elaphus [15-17]; and the other group possessed characters closely resembling those of extant sap beetles, distinctly different from Kateretidae. The latter group may have evolved into the present-day extant Nitidulidae, while the former lineage probably became extinct during subsequent evolution. Accordingly, Vetunitidula probably represents a stem-group lineage of Nitidulidae, retaining some symplesiomorphic characters with Kateretidae.

There are 16 Mesozoic species of Nitidulidae, including nine compression fossil species and seven in Kachin amber [8,10-17]. Due to poor preservation, comparing Vetunitidula with compression fossils is challenging. However, the enlarged mandibles of Vetunitidula make it easily distinguishable [12-14]. Among the amber fossils from northern Myanmar, Vetunitidula resembles Protonitidula and Cretabaltoraea, and differs from the other five species by its prognathous head, specialized mandibles, loose antennal club, absence of horns on the head, truncate elytra exposing three abdominal segments and mesoand meta-tibiae armed with two rows of spines [8,10,11,15-17]. Vetunitidula is characterized by over two exposed abdominal segments, absence of jugular projections, nearly parallel lateral sides of the prosternal process with small lateral projections posteriorly, subequal tibial spurs and a pygidium formed of an apical extension with three teeth and dense, long setae. In contrast, Protonitidula displays only a partially exposed pygidium, several small teeth on the last sternite, jugular projections, unequal tibial spurs and distinctly curved lateral sides of the prosternal process with prominent lateral projections [15]. Additionally, the differences between the newly described genus and Cretabaltoraea primarily involve the number of exposed abdominal segments, the morphology of the labrum and the specialized mandibles, which currently distinguish these two fossil genera [16].

4.2. Specialized mandibles

The most striking feature of Vetunitidula is its enlarged, straight mandibles. These mandibles are strong, with a medial carina on the dorsal side of each mandible (complete on the left mandible, incomplete on the right mandible), and their mesal margins are asymmetrical, with at least two distinct teeth. Nitidulids with such specialized mandibles are rare in the fossil record, especially in the Mesozoic period, probably due to the incompleteness of fossil preservation and imperfect fossil record. Cretabaltoraea is the only Mesozoic fossil record reported by other researchers. Nevertheless, the mandibles in Cretabaltoraea are simple, without carinae and tooth [16]. Mandibles in Vetunitidula are significantly different from those in Cretabaltoraea. Vetunitidula represents the first fossil record of nitidulids with carinae on enlarged mandibles.

Despite the diverse feeding habits of extant Nitidulidae, the morphology of the mandibles of Vetunitidula provides valuable clues for exploring their function. In Nitidulidae, mandible specialization does not seem directly related to feeding habits. Extant species with enlarged mandibles occur in Nitidulinae, Cryptarchinae and Cillaeinae, and their feeding habits are diverse and complex [1,4]. Among reported nitidulids with specialized mandibles, Glischrochilus parvipustulatus (Kolbe, 1886), Glischrochilus japonius (Motschulsky, 1858) (Cryptarchinae), Prometopia sexmaculata (Say, 1825) (Prometopinae) and some species of Platychora Erichson (Prometopinae) have been found under bark or on tree sap, suggesting they probably feed subcortically on tree sap [28-30]. These species have relatively simple but stout mandibles with one pair of teeth near the apex (or medially in some species) [28- 30]. In contrast, some species in Psilotus Fischer von Waldheim (Nitidulinae) possess elongate and slender mandibles with at least four preapical teeth, and these species are likely to feed on fungi under palm sheaths [31]. The mandibles of Vetunitidula are straighter than those of male Glischrochilus, Prometopia and Platychora [28-30]. Additionally, the mandibles are stouter, with a mediolongitudinal carina dorsally, and have more obtuse teeth compared with those of Psilotus [31]. Consequently, it is challenging to infer the feeding habits of Vetunitidula.

The scaling of body parts is crucial to morphological evolution. Typically, traits scale proportionally with body size, making larger adults magnified versions of smaller ones. Departures from this pattern, where traits scale disproportionately, can create dramatically exaggerated features. Such extreme morphologies are often hypothesized to result from sexual selection when asymmetrical between the sexes [32,33]. The possibility that the specialized mandibles in Vetunitidula are a form of sexual dimorphism cannot be ignored. Sexual dimorphism usually results from selective pressures acting on one sex, leading to a prominent phenotype in that sex relative to the other [34]. In insects, sexual dimorphism often manifests in variations in body size and shape, highly modified antennae and legs, and strong weapons [1,35-37]. Mandibles lacking sexual dimorphism typically exhibit small, simply curved characteristics [30, fig. 1]. Specialized mandibles are common in male beetles as a form of sexual dimorphism, and such traits are observed in extant Nitidulidae, especially in Nitidulinae, Cryptarchinae and Cillaeinae [1]. For example, males of these species typically possess specialized mandibles, whereas females generally do not. Librodor japonicus serves as a representative. In L. japonicus, 'The mandibles of males were larger and were straighter and thicker compared with the smaller, smoothly curved mandible of females' [38, fig. 1]. Similarly, the mandibles of the Vetunitidula specimen described herein are extremely enlarged, straight and thick, resembling those of male L. japonicus. It suggests a possible speculation that Vetunitidula probably exhibits sexual dimorphism, with its enlarged mandibles a manifestation of such asymmetrical exaggeration between the sexes, even though no female has yet been discovered (in living species, females never have such exaggerated mandibles). The specialized mandibles in these extant beetle species usually indicate that the males are stronger and more resistant to diseases and parasites, and play important roles in male-male competition and attracting females to assert resource ownership [34,38,39].

In Nitidulidae, the specialized mandibles are often allometric, and the mandibles of Vetunitidula are probably no exception [38]. For example, in the extant nitidulid L. japonicus, the outcome of malemale competition depends on the resources possessed by the male. This ownership status-dependent strategy may maintain intra-sexual dimorphism in smaller males of L. japonicus [38,40]. Although there is only one specimen of Vetunitidula, such a specialized mandible is rare in fossil specimens. Therefore, the possibility cannot be discarded, that it may be a sexual dimorphic trait and serve as the function described above.

4.3. Associated thrips and palaeoecological implications

The holotype of V. mandibulata represents the first fossil occurrence of a nitidulid preserved alongside a thrips in the same amber specimen. The presence of a thrips of the family Stenurothripidae (cf. Didymothrips abdominalis Guo, Engel, Shih, & Ren) close to the nitidulid (figure 1c) suggests possible habits of V. mandibulata. Some extant species of thrips play crucial roles as pollinators of angiosperms and gymnosperms [41]. Thrips were reported to pollinate lauralean flowers in the Early Cretaceous [42], but also most thrips are considered gymnosperm pollinators during the Mesozoic, evidenced by co-preserved cycad pollen in Early Cretaceous Spanish amber and mid-Cretaceous Kachin amber [41,43]. The co-preservation of V. mandibulata and a stenurothripid thrips in the same amber suggests that these insects probably shared the same microenvironment and perhaps similar ecological associations, such as with cycads, some 99 Ma. This raises the intriguing possibility that V. mandibulata might have been a pollen feeder of gymnosperms during the mid-Cretaceous. No pollen was found around the thrips or within this sample of amber, and so such pollinivory for Vetunitidula requires further testing as new material is discovered. Nonetheless, given the association, beetle pollinivory as a good hypothesis is worth further exploring.

5. Conclusion

Nitidulidae are a diverse family of beetles with high biodiversity, yet reports of nitidulids in Kachin amber are rare. We describe a new genus and species of Nitidulidae characterized by distinctly enlarged mandibles, representing the first fossil record of Mesozoic nitidulids with carinae on specialized mandibles. And, we briefly discuss the possibility of the specialized mandibles being sexual dimorphism, as inferred from comparisons with extant male nitidulids with large mandibles. Additionally, we tentatively propose the hypothesis that co-preservation of thrips in the same amber piece may provide insights into the habitat and ecological function of V. mandibulata during the mid-Cretaceous.

Ethics. This work did not require ethical approval from a human subject or animal welfare committee.

Data accessibility. We declare that there is no data in the paper, and the specimen referred in the paper (accession number, NIGP203942) is permanently housed in the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China, and we declare that the measurement of specimen is operated by Adobe Photoshop CC 2019.

Supplementary material is available online [44].

Declaration of AI use. We have not used AI-assisted technologies in creating this article.

Authors' contributions. Q.Z.: data curation, formal analysis, investigation, methodology, software, validation, visualization, writing-original draft, writing-review and editing; M.S.E.: investigation, visualization, writingreview and editing; D.H.: conceptualization, funding acquisition, resources; C.C.: conceptualization, data curation, formal analysis, funding acquisition, project administration, resources, supervision, writing-review and editing.

All authors gave final approval for publication and agreed to be held accountable for the work performed therein.

Conflict of interest declaration. We declare we have no competing interests.

Funding. This research was supported by the National Natural Science Foundation of China (grants 41925008, 42222201, 42288201). M.S.E. was supported by CONCYTEC through the PROCIENCIA program, under the 'Interinstitutional Alliances for Doctorate Programs' call, contract PE501084299-2023 PROCIENCIA-BM.

Acknowledgement. We are grateful to Yan Fang for technical assistance with confocal imaging and to two reviewers for their valuable comments on the manuscript. We thank editor and reviewers again for considering and reviewing our manuscript.

Sidebar

Cite this article: Zhao Q, Engel MS, Huang D, Cai C. 2025 A Cretaceous sap beetle with specialized mandibles (Coleoptera : Nitidulidae). R. Soc. Open Sci. 12: 241761.

Received: 14 October 2024

Accepted: 27 January 2025

Subject Category:

Organismal and evolutionary biology

Subject Areas:

evolution, palaeontology, taxonomy and systematics

Author for correspondence:

Chenyang Cai

e-mail: [email protected]

Electronic supplementary material is available online at https://doi.org/10.6084/ m9.figshare.c.7667238.

Footnote

royalsocietypublishing.org/journal/rsos R.Soc.OpenSci. 12: 241761

References

References

1. Jelínek J, Carlton C, Cline AR, Leschen RAB. 2011 Chapter 10.26 Nitidulidae Latreille, 1802. In Coleoptera, beetles, volume 2, morphology and systematics (elateroidea, bostrichiformia cucujiformia partim) (eds W Kükenthal, RAB Leschen, RG Beutel, JF Lawrence), pp. 390-407. Berlin, Germany: De Gruyter. (doi:10.1515/9783110911213.390)

2. Cline AR, Smith TR, Miller K, Moulton M, Whiting M, Audisio P. 2014 Molecular phylogeny of Nitidulidae: assessment of subfamilial and tribal classification and formalization of the family Cybocephalidae (Coleoptera: Cucujoidea). Syst. Entomol. 39, 758-772. (doi:10.1111/syen.12084)

3. Cai C. 2022 Integrated phylogenomics and fossil data illuminate the evolution of beetles. R. Soc. Open Sci. 9, 211771. (doi:10.1101/2021.09.22. 461358)

4. Lee MH, Lee S, Leschen RAB, Lee S. 2020 Evolution of feeding habits of sap beetles (Coleoptera: Nitidulidae) and placement of Calonecrinae. Syst. Entomol. 45, 911-923. (doi:10.1111/syen.12441)

5. Grimaldi DA, Engel MS, Nascimbene PC. 2002 Fossiliferous Cretaceous amber from Myanmar (Burma): its rediscovery, biotic diversity, and paleontologicalsignificance.Am.Mus.Novit.3361,1-71.(doi:10.1206/0003-0082(2002)3612.0.co;2)

6. Grimaldi DA, Ross AJ. 2017 Extraordinary lagerstätten in amber, with particular reference to the Cretaceous of Burma. In Terrestrial conservation lagerstatten: windows into the evolution of life on land (eds NC Fraser, HD Sues), pp. 287-342. Edinburgh, Scotland: Dunedin Academic Press Ltd: Liverpool University Press. (doi:10.2307/jj.12638994.12)

7. Ross AJ. 2024 Complete checklist of Burmese (Myanmar) amber taxa 2023. Mesozoic 1, 21-57. (doi:10.11646/mesozoic.1.1.4)

8. Kirejtshuk AG, Chetverikov PE. 2018 Discovery of a Nitidulidae in Cretaceous Burmese amber (Coleoptera, Cucujoidea) with description of a new genus and taxonomic notes. Cretac. Res. 89, 174-182. (doi:10.1016/j.cretres.2018.03.021)

9. Kirejtshuk AG, Nel A. 2018 Nitidulidae (Coleoptera) from the Paleocene of Menat (France). Zootaxa 4402, 141. (doi:10.11646/zootaxa.4402.1.1)

10. Zhao Q, Peris D, Huang D, Cai C. 2024 A new genus of sap beetles in Cretaceous amber from northern Myanmar (Coleoptera: Nitiduloidea: Nitidulidae). Palaeontogr. Abt. 327, 165-177. (doi:10.1127/pala/2024/0144)

11. Kirejtshuk A, Shaw J, Smirnov I. 2023 A new subgenus of the genus Phenolia (Coleoptera, Nitidulidae) from Myanmar Cretaceous amber with taxonomic, phylogenetic and bionomic notes on the 'Nitidulid' group of families. Insects 14, 647. (doi:10.3390/insects14070647)

12. Heer O. 1865 Die urwelt der schweiz. Zürich, Switzerland: F. Schulthess.

13. Kirejtshuk A, Ponomarenko A. 1990 Fossil beetles of the Peltidae and Nitidulidae families (Coleoptera). Paleontol. J. 2, 78-88.

14. Heer O. 1852 Ueber die Lias-Insel im Aargau. In Zwei geologische vorträge gehalten im märz 1852 (eds O Heer, AE Von der Linth), pp. 1-15. Zürich, Switzerland: E. Kiesling.

15. Zhao Q, Huang D, Cai C. 2022 A new genus of sap beetles (Coleoptera: Nitidulidae) from Mid-Cretaceous amber of northern Myanmar. Insects 13, 884. (doi:10.3390/insects13100884)

16. Peris D, Jelínek J, Sabatelli S, Liu MK, Zhao Q, Cai C, Mähler B, Kairišs K, Audisio P. 2024 Cretabaltoraea volsella gen. et sp. nov. (Coleoptera: Nitidulidae) from Cretaceous Kachin amber and its relationship with Eocene Baltoraea (Coleoptera: Nitidulidae). Mesozoic 1, 298-308. (doi:10. 11646/mesozoic.1.3.10)

17. Peris D et al. 2024 Archaic sap beetles (Coleoptera: Nitidulidae) as Cretaceous pollinators. Palaeoentomology 7.5, 594-610. (doi:10.11646/ palaeoentomology.7.5.4)

18. Sidorchuk E, Vorontsov D. 2018 Preparation of small-sized 3D amber samples: state of the technique. Palaeoentomology 1, 80-90. (doi:10. 11646/palaeoentomology.1.1.10)

19. Cai C, Huang D. 2014 The oldest micropepline beetle from Cretaceous Burmese amber and its phylogenetic implications (Coleoptera: Staphylinidae).Sci.Nat.101,813-817.(doi:10.1007/s00114-014-1221-z)

20. Fu Y, Li Y, Su Y, Cai C, Huang D. 2021 Application of confocal laser scanning microscopy to the study of amber bioinclusions. Palaeoentomology 4 266-278. . (doi:10.11646/palaeoentomology.4.3.14)

21. Cruickshank RD, Ko K. 2003 Geology of an amber locality in the Hukawng Valley, northern Myanmar. J. Asian Earth Sci. 21, 441-455. (doi:10. 1016/s1367-9120(02)00044-5)

22. Yin Z, Cai C, Huang D. 2018 Last major gap in scydmaenine evolution filled (Coleoptera: Staphylinidae). Cretac. Res. 84, 62-68. (doi:10.1016/j. cretres.2017.10.026)

23. Shi G, Grimaldi DA, Harlow GE, Wang J, Wang J, Yang M, Lei W, Li Q, Li X. 2012 Age constraint on Burmese amber based on U-Pb dating of zircons. Cretac. Res. 37, 155-163. (doi:10.1016/j.cretres.2012.03.014)

24. Mao Y. 2018 Various amberground marine animals on Burmese amber with discussions on its age. Palaeoentomology 1, 91-103. (doi:10.11646/ palaeoentomology.1.1.11)

25. Jelínek J, Cline A. 2010 Chapter 10.25 Kateretidae Erichson in Agassiz, 1846. In Handbook of zoology, Arthropoda: Insecta, Coleoptera, beetles morphology and systematics (eds E Leschen, R Beutel, J Lawrence), pp. 386-390. Berlin, Germany: De Gruyter. (doi:10.1515/9783110911213. 386)

26. Cline A. 2010 Chapter 10.27. Smicripidae Horn, 1879. In Volume 2 morphology and systematics (Elateroidea, Bostrichiformia, Cucujiformia partim) (eds W Kükenthal, R Leschen, R Beutel, J Lawrence), pp. 407-411. Berlin, Germany: De Gruyter. (doi:10.1515/9783110911213.407)

27. Kirejtshuk AG. 1998 Nitidulidae (Coleoptera) of the Himalayas and northern Indochina. Part 1: Subfamily Epuraeinae. Theses Zool. 28, 1-489.

28. Price M, Young D. 2006 An annotated checklist of Wisconsin sap and short-winged flower beetles (Coleoptera: Nitidulidae, Kateretidae). Insecta Mundi. 69-84.

29. Bigger M. 2012 A geographical distribution list of insects and mites associated with cocoa. See https://incocoa.org/docs/MBiggercocoa_insects_ Mdly.pdf.

30. Lee MH, Lee S, Lee S. 2020 Review of the subfamily Cryptarchinae Thomson, 1859 (Coleoptera: Nitidulidae) in Korea (Part I: genus Glischrochilus Reitter, 1873 and Pityophagus Shuckard, 1839). J. Asia Pac. Biodivers. 13, 349-357. (doi:10.1016/j.japb.2020.06.005)

31. Cline AR. 2004 A new species of Psilotus Fischer vonWaldheim (Coleoptera: Nitidulidae) from Peru, with new distribution records for other Psilotus species. Proc. Entomol. Soc. Wash. 106, 890-898.

32. Shingleton AW, Frankino WA. 2013 New perspectives on the evolution of exaggerated traits. BioEssays 35, 100-107. (doi:10.1002/bies. 201200139)

33. Lavine L, Gotoh H, Brent CS, Dworkin I, Emlen DJ. 2015 Exaggerated trait growth in insects. Annu. Rev. Entomol. 60, 453-472. (doi:10.1146/ annurev-ento-010814-021045)

34. Demuth JP, Naidu A, Mydlarz LD. 2012 Sex, war, and disease: the role of parasite infection on weapon development and mating success in a horned beetle (Gnatocerus cornutus). PLoS One 7, e28690. (doi:10.1371/journal.pone.0028690)

35. Honěk A. 1993 Intraspecific variation in body size and fecundity in insects: a general relationship. Oikos 66, 483. (doi:10.2307/3544943)

36. Emlen DJ. 2008 The evolution of animal weapons. Annu. Rev. Ecol. Evol. Syst. 39, 387-413. (doi:10.1146/annurev.ecolsys.39.110707.173502

37. Thomas MC. 2009 A review of the genus Dysmerus Casey (Coleoptera: Laemophloeidae). Insecta Mundi 74, 1-30. (doi:10.5281/zenodo. 5405025)

38. Okada K, Miyatake T. 2004 Sexual dimorphism in mandibles and male aggressive behavior in the presence and absence of females in the beetle Librodor japonicus (Coleoptera: Nitidulidae). Ann. Entomol. Soc. Am. 97, 1342-1346. (doi:10.1603/0013-8746(2004)097[1342:sdimam]2.0.co;2)

39. Mills M, Nemri R, Caelson E, Wilde W, Gotoh H, Lavine L, Swanson B. 2016 Functional mechanics of beetle mandibles: honest signaling in a sexually selected system. J. Exp. Zool. 325A, 3-12. (doi:10.1002/jez.1961)

40. Okada K, Miyatake T. 2007 Ownership-dependent mating tactics of minor males of the beetle Librodor japonicus (Nitidulidae) with intra-sexual dimorphism of mandibles. J. Ethol. 25, 255-261. (doi:10.1007/s10164-006-0021-0)

41. Peñalver E, Labandeira C, Barrón E, Delclòs X, Nel P, Nel A, Tafforeau P, Soriano C. 2012 Thrips pollination of Mesozoic gymnosperms. Proc. Natl Acad. Sci. USA 109, 8623-8628. (doi:10.1073/pnas.1120499109)

42. Crepet WL, Nixon KC, Grimaldi D, Riccio M. 2016 A mosaic lauralean flower from the Early Cretaceous of Myanmar. Am. J. Bot. 103, 179-364. 290-297. (doi:10.3732/ajb.1500393)

43. Guo D, Engel MS, Shih C, Ren D. 2024 New stenurothripid thrips from mid-Cretaceous Kachin amber (Thysanoptera, Stenurothripidae). ZooKeys 1192, 197-212. (doi:10.3897/zookeys.1192.117754)

44. Zhao Q, Engel M, Huang D, Cai C. 2025 Supplementary material from: A Cretaceous sap beetle with specialized mandibles (Coleoptera: Nitidulidae).FigShare(doi:10.6084/m9.figshare.c.7667238)