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| Vetunitidula mandibulata Zhao, Engel, Huang & Cai, 2025 |
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.
Keywords: taxonomy, palaeoentomology, sexual dimorphism, pollination
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| Photomicrographs of Vetunitidula mandibulata gen. et sp. nov. (NIGP203942) and a stenurothripid thrips from mid-Cretaceous Kachin amber; under normal reflected light. (a) Dorsal view. (b) Ventral view. (c) Dorsal view of thrips (cf. Didymothrips abdominalis Guo et al. 2024). Scale bars: 1 mm in (a, b) and 0.2 mm in (c). |
Systematic palaeontology
Order: Coleoptera Linnaeus, 1758
Superfamily: Nitiduloidea Latreille, 1802
Family: Nitidulidae Latreille, 1802
Genus: Vetunitidula gen. nov.
Type species: Vetunitidula mandibulata sp. nov.
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.
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. Meso- and meta-tibiae armed with two longitudinal rows of spines dorsally; two tibial spurs present.
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.
Qian Zhao, Michael S. Engel, Diying Huang and Chenyang Cai. 2025. A Cretaceous Sap Beetle with Specialized Mandibles (Coleoptera : Nitidulidae). R. Soc. Open Sci. 12; 241761. DOI: doi.org/10.1098/rsos.241761 [26 February 2025]
