Under Cover at Pre-Angiosperm Times: A Cloaked Phasmatodean Insect from the Early Cretaceous Jehol Biota

Maomin Wang,Olivier Béthoux,Sven Bradler,Dong Ren,Frédéric M. B. Jacques,Yingying Cui

doi:10.1371/journal.pone.0091290

Abstract

BackgroundFossil species that can be conclusively identified as stem-relatives of stick- and leaf-insects (Phasmatodea) are extremely rare, especially for the Mesozoic era. This dearth in the paleontological record makes assessments on the origin and age of the group problematic and impedes investigations of evolutionary key aspects, such as wing development, sexual size dimorphism and plant mimicry.Methodology/Principal FindingsA new fossil insect species, Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov., is described on the basis of one female and two male specimens recovered from the Yixian Formation (Early Cretaceous, ca. 126±4 mya; Inner Mongolia, NE China; known as ‘Jehol biota’). The occurrence of a female abdominal operculum and of a characteristic ‘shoulder pad’ in the forewing allows for the interpretation of a true stem-Phasmatodea. In contrast to the situation in extant forms, sexual size dimorphism is only weakly female-biased in this species. The peculiar wing coloration, viz. dark longitudinal veins, suggests that the leaf-shaped plant organ from the contemporaneous ‘gymnosperm’ Membranifolia admirabilis was used as model for crypsis.Conclusions/SignificanceAs early as in the Early Cretaceous, some stem-Phasmatodea achieved effective leaf mimicry, although additional refinements characteristic of recent forms, such as curved fore femora, were still lacking. The diversification of small-sized arboreal insectivore birds and mammals might have triggered the acquisition of such primary defenses.

Highlights

Plant-insect interactions such as herbivory and crypsis are well documented and understood during the rise of angiosperms, but there is a severe gap of knowledge for pre-angiospermous times, when ‘gymnosperms’ were the dominant form of vegetation [1]
It is assumed that the mid-Mesozoic patterns of plant-insect interactions may be ecologically very similar to the Cenozoic ones, demonstrating an almost complete turnover of major plant and insect lineages
This applies for stick and leaf insects (Phasmatodea) whose extant forms supposedly underwent a rather recent radiation, in co-evolution with angiosperm plants [2,3]

Summary

Introduction

Plant-insect interactions such as herbivory and crypsis are well documented and understood during the rise of angiosperms, but there is a severe gap of knowledge for pre-angiospermous times, when ‘gymnosperms’ were the dominant form of vegetation [1]. It is assumed that the mid-Mesozoic patterns of plant-insect interactions may be ecologically very similar to the Cenozoic ones, demonstrating an almost complete turnover of major plant and insect lineages This applies for stick and leaf insects (Phasmatodea) whose extant forms supposedly underwent a rather recent radiation, in co-evolution with angiosperm plants [2,3]. Fossil species that can be conclusively identified as stem-relatives of stick- and leaf-insects (Phasmatodea) are extremely rare, especially for the Mesozoic era. This dearth in the paleontological record makes assessments on the origin and age of the group problematic and impedes investigations of evolutionary key aspects, such as wing development, sexual size dimorphism and plant mimicry

Methods

Discussion

Conclusion