A Fossil View of Insect Evolution: Integrating Paleontological Evidence to Explore the Origins of Insect Biodiversity

An enigmatic cucujiform beetle, Alloterocucus atratus Li, Leschen, Liu, and Cai gen. et sp. nov., is reported from mid-Cretaceous Burmese amber. The character combination of the new fossil is not completely consistent with any of the known cucujoid or erotyloid families. Based on our phylogenetic analyses, Alloterocucus is assigned to Cucujoidea and may be allied to Lamingtoniidae, which contains a single Australasian genus in the extant fauna. Alloterocucus shares with Lamingtoniidae a similar habitus and a series of characters, including the absence of postocular constriction, 3-segmented antennal club, externally open procoxal cavities, laterally open mesocoxal cavities, exposed pro- and mesotrochantins, and the absence of epipleural fovea and pronotal setose cavities, but differs from extant Lamingtoniidae in its apically truncate terminal maxillary palpomeres, 5-5-4 tarsi in male and absence of distinct dorsal punctation.

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Burrowing bugs are distinctive, beetle-like insects of the pentatomoid family Cydnidae, noteworthy for their morphological specializations for digging and a hemiedaphic life history. However, less is known about their biological significance and the early origin of soil dwelling. Direct fossil evidence illuminating the evolutionary history of soil dwelling in cydnids is extremely rare. In this study, we report four new species of the burrowing bug subfamily Amnestinae from mid-Cretaceous Burmese amber, including two exhibiting specialized bulldozing and digging morphological traits on the anterior of the head and forelegs. Associated morphological features and phylogenetic placement indicate that Acanthamnestus represents the earliest unequivocal soil-dwelling cydnids and pushes back the geological record of hemiedaphic true bugs to 99 Ma. Environmental evidence, the distribution of host plants, and the fossils provide a new window for understanding the early origin of soil habits in Amnestinae and may be linked to the appearance of Moraceae.