Pagodocerus, a new beetle genus of Mastigocoleidae from mid-Cretaceous Kachin amber (Coleoptera: Dryopoidea)Abstract
Mastigocoleidae are an extinct beetle family known from only a few Cretaceous deposits. Here, we describe Pagodocerus volkovitshi gen. et sp. nov., a new mastigocoleid species preserved in mid-Cretaceous Kachin amber. Pagodocerus is primarily distinguished from all other beetles by its asymmetrically perfoliate antennae, with flagellomeres pronouncedly tapering apically. This discovery expands the known diversity of Mastigocoleidae and enhances our understanding of this rare beetle lineage.
Keywords:
Mastigocoleidae; Fossil; Cretaceous; Kachin amber
INTRODUCTION
The mid-Cretaceous Kachin amber represents an exceptional window into Cretaceous terrestrial ecosystems and has yielded several newly recognized beetle families (e.g., Boucher et al., 2016; Alekseev & Ellenberger, 2019; Clarke et al., 2019; Li et al., 2021; summarized by Ross, 2024). Among them are Mastigocoleidae, a rare lineage considered to occupy a basal position within the recently redefined superfamily Dryopoidea, potentially closely related to Lutrochidae and Dryopidae (Cai et al., 2022; Tihelka et al., 2022). To date, representatives of Mastigocoleidae have been recorded only from a few Cretaceous deposits, including Kachin amber in northern Myanmar, the Yixian Formation in northeastern China, and the Crato Formation in northeastern Brazil. The most distinctive feature of this family is the morphology of the antennae, in which elongate antennomeres 3-11 gradually taper apically. Such an antennal structure is not only highly unusual within Dryopoidea, but also possibly unique across the whole Coleoptera.
Due to the scarcity of specimens and the limited literature available, the morphological diversity and evolutionary relationships of Mastigocoleidae remain poorly understood. Currently, only two genera have been recognized within the family: Mastigocoleus Tihelka & Cai and Cretaceocoleus Tihelka et al. Here, we describe a new genus of Mastigocoleidae from Kachin amber. This new taxon expands the morphological and taxonomic diversity of Mastigocoleidae and provides new insight into the evolutionary history of this Cretaceous beetle family.
MATERIAL AND METHODS
The Kachin amber specimens studied herein (Figs. 1-5) originated from amber mines near Noije Bum (26°20′N, 96°36′E), Hukawng Valley, Kachin State, northern Myanmar. The amber specimens are deposited in the Nanjing Institute of Geology and Palaeontology (NIGP), Chinese Academy of Sciences, Nanjing, China. The amber piece containing the new species was trimmed with a saw mounted on a handheld rotary tool, ground with emery paper of different grit sizes, and finally polished with polishing powder.
General habitus of Pagodocerus volkovitshi, holotype, NIGP208696, under reflected light. (A) Dorsal view. (B) Ventral view. Scale bars: 2 mm.
Brightfield images were obtained with a Zeiss Discovery V20 stereo microscope, under reflected illumination. Widefield fluorescence images were obtained with a Zeiss Axio Imager 2 light microscope combined with a fluorescence imaging system. Confocal images were obtained with a Zeiss LSM710 confocal laser scanning microscope, using the 488 nm (Argon) laser excitation line (Fu et al., 2021). Images were stacked with Helicon Focus 7.0.2, Zerene Stacker 1.04 and Adobe Photoshop CC, and were further processed in Adobe Photoshop CC to adjust brightness and contrast.
RESULTS
Systematic Paleontology
Order Coleoptera Linnaeus, 1758
Superfamily Dryopoidea Billberg, 1820
Family Mastigocoleidae Tihelka, Jäch, Kundrata & Cai, 2022
Genus Pagodocerus gen. nov.
Type species:Pagodocerus volkovitshisp. nov., here designated.
Diagnosis: Antennae appearing somewhat perfoliate, with flagellomeres (antennomeres 3-11) pronouncedly tapering apically (Fig. 2A). Anterior pronotal angles more or less orthogonal (Fig. 1). Prosternum anteriorly subtruncate (Figs. 2E, 3B); prosternal process with glabrous longitudinal median carina (Fig. 3C). Mesocoxae comparatively broadly separated (Fig. 3D). Metacoxae moderately separated (Fig. 1B). Tarsi moderately long (tarsomeres 1-4 longer than wide) (Figs. 2D, 3G, H).
Details of Pagodocerus volkovitshi, holotype, NIGP208696, under widefield fluorescence. (A) Head, dorsal view. (B) Elytral base, dorsal view. (C) Elytral apex, dorsal view. (D) Hind leg. (E) Prothorax, ventral view. (F) Abdominal apex, ventral view. Scale bars: 500 μm.
Details of Pagodocerus volkovitshi, holotype, NIGP208696, under confocal microscopy. (A) Mouthparts, ventral view. (B) Posterior part of head, ventral view. (C) Prothorax, ventral view. (D) Mesothorax, ventral view. (E) Abdominal apex, ventral view. (F) Prothorax, dorsal view, with arrow indicating pronotal sulcus. (G) Fore leg, with arrow indicating protibial spur. (H) Mid leg. Abbreviations: gl = gula; lbp = labial palp; md = mandible; mtv = metaventrite; mxp = maxillary palp; msts = mesotarsus; pn = pronotum; ps = prosternum; pts = protarsus; v5 = abdominal ventrite 5. Scale bars: 300 μm.
Etymology: The generic name is derived from pagoda (a tiered tower with multiple eaves, common in East and Southeast Asia) and the Greek κέρας (keras), meaning “horn”. It refers to the distinctive shape of the antennae, which resemble the layered, tapering form of a pagoda. The name is masculine in gender.
Pagodocerus volkovitshi sp. nov.
(Figs. 1-3)
Material: Holotype, NIGP208696 (NIGP), sex unknown.
Locality and horizon: Amber mine located near Noije Bum Village, Tanai Township, Myitkyina District, Kachin State, Myanmar; unnamed horizon, mid-Cretaceous, Upper Albian to Lower Cenomanian.
Diagnosis: As for the genus.
Description: Body elongate, about 9.5 mm long, 2.7 mm wide; surface with dense hairs.
Head hypognathous, without constricted neck. Eyes moderately large and protuberant. Antennal insertion exposed from above, separated approximately by width of scape. Subantennal grooves absent. Antennae appearing somewhat perfoliate, with dense long setae on outer face; antennomeres 2-10 asymmetrical, expanded more on inner side than on outer side; antennomere 3 narrower at base and wider at apex, slightly wider than long and wider than antennomere 2; antennomere 4 about as wide as antennomere 3, transverse; antennomeres 4 to 11 gradually narrowing with increasing length-to-width ratio. Mandibles small, apically possibly tridentate. Maxillary palp 4-segmented; galeae with numerous stout setae apically; laciniae with numerous stout setae mesally. Mentum subtrapezoidal; sides converging anteriad; submentum transverse; articulations of labial palps located on ventral surface of prementum and visible from below.
Pronotum slight wider than long, with sides arcuate; anterior pronotal angles slightly produced, more or less orthogonal; disc basally with one pair of sulci. Prosternum more than twice as long as longitudinal diameter of procoxa; anteriorly subtruncate; prosternal process extending well beyond procoxae, with glabrous longitudinal median carina. Procoxal cavities narrowly separated, open externally. Scutellar shield slightly longer than wide; anterior margin medially broadly angulate. Elytra long, subparallel-sided in anterior ⅔, apically conjointly rounded. Mesoventral cavity well-developed, extending along entire length of mesoventrite, posteriorly bordered by metaventrite. Mesocoxae comparatively broadly separated. Metacoxae moderately separated, mesally moderately extended anteroposteriorly, abruptly reduced in length laterally.
Pro- and mesotibial spurs small; only one spur doubtlessly observed, second spur not clearly discernible (not necessarily present). Metatibial spurs long and stout, unequal. Tarsi 5-5-5, moderately long (tarsomeres 1-4 longer than wide); tarsomeres 1 and 2 ventrally weakly projected, tarsomere 5 ventrally distinctly projected. Pretarsal claws well-developed, equal on fore and hind legs, seemingly slightly unequal on middle legs.
Abdomen with five ventrites. Intercoxal process of ventrite 1 moderately broad, anteriorly acute. Ventrite 5 apically emarginate.
Etymology: The species is named after the coleopterist Dr. Mark G. Volkovitsh.
DISCUSSION
The newly described Pagodocerus can be assigned to the family Mastigocoleidae, primarily due to its unique antennal morphology, with flagellomeres gradually tapering apically (Fig. 2A). This antennal morphology represents an apomorphy for the family and is likely unique among all Coleoptera. Additional diagnostic features, including the paired pronotal sulci (Fig. 3F), the leg morphology (Figs. 2D, F, 3G, H), and the overall body habitus, are also consistent with its placement within Mastigocoleidae. However, apart from the more symmetrical and less compact antennae, the family Mastigocoleidae itself shows considerable similarity to Dryopidae, suggesting that the relationship between the two families may warrant further investigation.
Pagodocerus could be easily differentiated from the two other known genera of Mastigocoleidae, Mastigocoleus and Cretaceocoleus. In Pagodocerus, the antennae appear somewhat perfoliate, with antennomeres 2-10 asymmetrically expanded on each side of the articulation and either wider than long or approximately as long as wide (Fig. 2A). In contrast, Mastigocoleus and Cretaceocoleus have antennae that are more filiform (Fig. 5A; Tihelka et al., 2022: fig. 2G), with Cretaceocoleus showing less pronounced tapering than the other two genera. The anterior pronotal angles of Pagodocerus are orthogonal, aligning with Cretaceocoleus but differing from the acutely produced angles of Mastigocoleus. The prosternum of Pagodocerus is subtruncate anteriorly (Figs. 2E, 3B), lacking the strongly projecting chin-piece seen in both Mastigocoleus and Cretaceocoleus (Figs. 4B, 5D). The prosternal process of Pagodocerus bears a glabrous longitudinal median carina (Fig. 3C), which is absent in Mastigocoleus and Cretaceocoleus (Figs. 4B, 5D). The spacing of the mesocoxae and metacoxae further distinguishes these genera. Mastigocoleus features narrowly separated mesocoxae and metacoxae (distance between mesocoxal cavities approximately 0.1× longitudinal diameter of mesocoxal cavities; Fig. 4C), while Cretaceocoleus has moderately separated mesocoxae but narrowly separated metacoxae (distance between mesocoxal cavities slightly less than half longitudinal diameter of mesocoxal cavities; Fig. 5E). In Pagodocerus, the separation of mesocoxae is broader even than those in Cretaceocoleus (distance between mesocoxal cavities slightly greater than half longitudinal diameter of mesocoxal cavities; Fig. 3D), and the separation of metacoxae is moderate (Fig. 1B), broader than those in Mastigocoleus and Cretaceocoleus. The tarsi of Pagodocerus are moderately long, with tarsomeres 1-4 longer than wide (Figs. 2D, 3G, H). This contrasts with the short tarsi of Mastigocoleus, where tarsomeres 1-4 are not longer than wide (Tihelka et al., 2022: fig. 2G).
Details of Mastigocoleus resinicola Tihelka & Cai, holotype, NIGP174708, under widefield fluorescence. (A) Prothorax, dorsal view. (B) Prothorax, ventral view. (C) Pterothorax, ventral view. (D) Abdomen, ventral view. Scale bars: 500 μm.
Details of Cretaceocoleus saetosus Tihelka, Kundrata & Cai, holotype, NIGP174709, under widefield fluorescence. (A) Head and prothorax, dorsal view. (B, C) Elytra, dorsal view. (D) Head and prothorax, ventral view. (E) Pterothorax, ventral view. (F) Abdomen, ventral view. Scale bars: 500 μm.
These morphological distinctions justify the erection of Pagodocerus as a new genus within Mastigocoleidae. They also expand the known morphological diversity within this Cretaceous family and provide new data for understanding the evolutionary trajectory and ecological adaptations of these extinct beetles. Ultimately, Pagodocerus sheds light on the hidden complexity of mid-Cretaceous beetle assemblages and highlights the importance of amber fossils in revealing unexpected evolutionary novelties. Given the exceptional preservation and taxonomic richness of this deposit, continued systematic investigation is essential to fully uncover the evolutionary and ecological complexity of the ancient insect fauna.
DATA AVAILABILITY:
The original confocal data are available in the Zenodo repository (https://doi.org/10.5281/zenodo.17635557).
ACKNOWLEDGMENTS:
Yan Fang assisted with confocal microscopy. Jing-Jing Tang assisted with widefield microscopy. Two reviewers provided helpful comments on the manuscript.
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AI USE:
AI tools were used to improve the readability of the manuscript.
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FUNDING:
Financial support was provided by the National Key Research and Development Program of China (2024YFF0807601). Y.-D.L. is supported by a scholarship granted by the China Scholarship Council (202108320010) and the Bob Savage Memorial Fund of the University of Bristol.
