 |
| Rutrizoma donoghuei, Poinarinius aristovi and polyaspidoid mites Rutrizoma Li & Cai gen. nov. in Li, Leschen, Kolibáč, Engel, Zhang, Yu, Huang et Cai, 2025. Artwork by Ding-Hua Yang |
Abstract
Ecological interactions are fundamental to understanding species’ trophic relationships and the evolution of ecosystem functions. However, the fossil record seldom captures these intricate dynamics, as most fossils preserve individual organisms rather than the interactions that shaped ancient ecosystems. Here, we describe a new genus of bark-gnawing beetles (Trogossitidae), Rutrizoma gen. nov., from mid-Cretaceous amber in northern Myanmar. This fossil genus reveals a rare combination of predatory and antipredatory adaptations, shedding light on the ecological complexity of Mesozoic forest ecosystems. Rutrizoma has specialized morphological features, such as shortened elytra and unidentate mandibles, suggesting an active predatory lifestyle in narrow wood galleries. Interestingly, some morphological traits of Rutrizoma mirror those of its potential prey, particularly bostrichid beetles, from the same amber deposit. One such trait is its specialized abdominal declivity, which probably functioned as a protective shield against predators and competitors, representing marked convergence with the elytral declivity of other subcortical beetles, such as bark and ambrosia beetles (Scolytinae and Platypodinae) and Bostrichidae. The presence of phoretic mites associated with Rutrizoma, along with co-preserved bostrichid prey, underscores the complex community dynamics beneath Cretaceous tree bark. This finding reveals a subcortical ecosystem that parallels modern ecological interactions.
Keywords: Cretaceous, beetle, phragmosis, defence, ecological interaction
Order Coleoptera Linnaeus, 1758
Family Trogossitidae Latreille, 1802
Subfamily Trogossitinae Latreille, 1802
Genus Rutrizoma Li & Cai gen. nov.
Type species. Rutrizoma donoghuei sp. nov., here designated.
Etymology. The generic name is formed based on the Latin rutrum, shovel, referring to the bordered declivity at the abdominal apex, and part of the name Nemozoma Latreille, a closely related trogossitid genus. When Latreille [1804] established the genus name Nemozoma, he likely intended it to reference the elongate body (νῆμα [nema]: thread + σῶμα [soma]: body). Although Latreille improperly latinized the second component, since ζῶμα (zoma) is still a Greek neuter noun, according to ICZN Article 30.1.2, Nemozoma should be treated as neuter (S. Laplante & P. Bouchard 2025, personal communication; contrary to [Kippenhan, 2023]). The new name Rutrizoma should thus also be neuter.
Diagnosis. Body slender. Frons with weak longitudinal median groove, without paired horn-like processes. Antennae with 11 antennomeres; club weakly asymmetrical; antennomeres 9 and 10 without exposed sensorial field; antennomere 11 with exposed sensorial field. Mandibles with one prominent apical tooth. Galea with ciliate setae. Pronotal disc elongate, with longitudinal median groove. Procoxal cavities narrowly separated, closed externally. Elytra strongly shortened, apically truncate, leaving abdominal segments IV–VII fully exposed, each with five distinct longitudinal grooves. Mesocoxal cavities narrowly separated, open laterally. Metacoxae contiguous, medially projecting, laterally not reaching lateral margin of metathorax. Protibia with robust spine on mesal edge. Abdominal tergite VII specialized, forming bordered declivity; margins with dense ciliate setae. Abdominal ventrites strongly convex.
 |
| Rutrizoma donoghuei sp. nov., under brightfield (A–C) or confocal (D–F) microscopy. (A) NIGP205681, dorsal view. (B) NIGP166142, lateral view. (C) NIGP166143, ventral view. (D) NIGP205682-1, head, dorsal view, with arrow indicating median groove on frons. (E) NIGP166142, head, ventrolateral view, with arrow indicating ciliate setae of galea. (F) NIGP166142, abdominal declivity, dorsal view, with arrow indicating projected lobes. Abbreviations: an, antenna; md, mandible. Scale bars: 1 mm in (A–C); 200 μm in (D–F). |
Rutrizoma donoghuei Li & Cai sp. nov.
Etymology. The species is named after the evolutionary biologist Dr Philip C. J. Donoghue.
Differential diagnosis. Rutrizoma donoghuei differs from R. pisanii in the smaller body size (about 4.1 mm long in the holotype and similar in all the paratypes) and the edge of abdominal declivity with projected lobes at the base.
 |
| Rutrizoma pisanii sp. nov., NIGP205685-1, under brightfield (A,B) or confocal (C,D) microscopy. (A) Dorsolateral view. (B) Ventrolateral view. (C) Head, ventrolateral view. (D) Abdominal declivity, dorsolateral view. Abbreviations: an, antenna; md, mandible; t6−7, abdominal tergites VI–VII. Scale bars: 1 mm in (A,B); 300 μm in (C,D). |
Rutrizoma pisanii Li & Cai sp. nov.
Etymology. The species is named after the evolutionary biologist Dr Davide Pisani.
Differential diagnosis. Rutrizoma pisanii differs from R. donoghuei in the larger body size (about 5.4 mm long in the holotype) and the simple edge of abdominal declivity.
 |
| Woodboring beetles and mites associated with Rutrizoma, under brightfield (A–D) or confocal microscopy (E). (A) NIGP205682, syninclusion of Rutrizoma donoghuei, Poinarinius aristovi and polyaspidoid mites. (B,C) NIGP205686, syninclusion of Rutrizoma sp., Poinarinius sp., and mites. (D) NIGP205687-3, Poinarinius aladelicatus preserved along with two individuals of Rutrizoma. (E) Detail of NIGP205682, showing polyaspidoid mites associated with Rutrizoma. Scale bars: 2 mm in (A–C); 500 μm in (D); 200 μm in (E). |
 |
| Artistic reconstruction of Cretaceous Rutrizoma pursuing Poinarinius beneath bark. Artwork by Ding-Hua YANG |
Yan-Da Li, Richard A. B. Leschen, Jiří Kolibáč, Michael S. Engel, Zhi-Qiang Zhang, Yali Yu, Diying Huang and Chenyang Cai. 2025. Specialized Bark-gnawing Beetles reveal Phragmotic Defence and Subcortical Ecology in the Cretaceous. Proc. R. Soc. B. 292: 20251004. DOI: doi.org/10.1098/rspb.2025.1004 [11 June 2025]
