Serial amber fossils unveiling the innovation process of mouthparts in water boatmen (Hemiptera: orixoidea) in the phylogenetic context of total evidence

Insects are the most species-rich group of animals, and the high morphological complexity and spectacular diversification of mouthparts among insects are crucial to their prosperity. Currently, the knowledge on insect mouthpart types remains largely stationary, yet little evidence has been documented to illustrate the transitional forms. In this study, we report for the first time a series of fossil specimens which reveal the successive process between two types of insect mouthparts. Correspondingly, three new families including six new species are established based on such mid-Cretaceous Kachin amber to place these new fossil records. Starting from the morphological differences in the mouthparts of the newly defined families and the extant water boatmen families, we further deduce the structural homology between different mouthpart types and find the coevolution between the mouthparts and the forelegs in the phylogenetic context of total evidence. Our discovery provides direct evidence of the transformation process of the water boatmen’s mouthparts from a sucking to a triangular type. This study provides new evidence and perspectives for in-depth understanding of the evolutionary process of insect mouthparts.

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