Ovipositor and mouthparts in a fossil insect support a novel ecological role for early orthopterans in 300 million years old forests.

Lu Chen,Olivier Béthoux,Alexander Blanke,Dong Ren,Jun-Jie Gu,Qiang Yang

doi:10.7554/elife.71006

Abstract

A high portion of the earliest known insect fauna is composed of the so-called 'lobeattid insects', whose systematic affinities and role as foliage feeders remain debated. We investigated hundreds of samples of a new lobeattid species from the Xiaheyan locality using a combination of photographic techniques, including reflectance transforming imaging, geometric morphometrics, and biomechanics to document its morphology, and infer its phylogenetic position and ecological role. Ctenoptilus frequens sp. nov. possessed a sword-shaped ovipositor with valves interlocked by two ball-and-socket mechanisms, lacked jumping hind-legs, and certain wing venation features. This combination of characters unambiguously supports lobeattids as stem relatives of all living Orthoptera (crickets, grasshoppers, katydids). Given the herein presented and other remains, it follows that this group experienced an early diversification and, additionally, occurred in high individual numbers. The ovipositor shape indicates that ground was the preferred substrate for eggs. Visible mouthparts made it possible to assess the efficiency of the mandibular food uptake system in comparison to a wide array of extant species. The new species was likely omnivorous which explains the paucity of external damage on contemporaneous plant foliage.

Highlights

The earliest known insect fauna in the Pennsylvanian, ca. 307 million years ago, was composed by species displaying mixtures of inherited and derived conditions, such as the griffenflies, and by highly specialized groups, such as the gracile and sap-feeding megasecopterans, belonging to the extinct taxon Rostropalaeoptera
Our analysis of material of Ct. frequens provides unequivocal evidence that olis2 occurs in this species
The ovipositor configuration in Ct. elongatus conforms that observed in extant cave crickets (Raphidophoridae) in which olis2 occurs in addition to olis1 and interlocks gs9 and gp9 (Figure 3A–C; Appendix 1, Section 2.2). This structure is present in ensiferan (‘sword-bearing’) Orthoptera possessing a developed ovipositor and is absent in caeliferan (‘chisel-bearing’) Orthoptera (Cappe de Baillon, 1920; Cappe de Baillon, 1922; Kluge, 2016; and see below). It follows that the new species is either more closely related to Ensifera than to Caelifera, or it is a stem-o rthopteran and olis2 was secondarily lost in Caelifera

Summary

Introduction

The earliest known insect fauna in the Pennsylvanian, ca. 307 million years ago, was composed by species displaying mixtures of inherited (plesiomorphic) and derived (apomorphic) conditions, such as the griffenflies (stem relatives of dragon- and damselflies), and by highly specialized groups, such as the gracile and sap-feeding megasecopterans, belonging to the extinct taxon Rostropalaeoptera. A prominent portion of this fauna were the so-c alled ‘lobeattid insects’. They have been recovered from all major Pennsylvanian outcrops, where some species can abound (Béthoux, 2005c; Béthoux, 2008; Béthoux and Nel, 2005a). At the Xiaheyan locality, China, for which quantitative data are available, they collectively account for more than half of all insect occurrences (Trümper et al, 2020). Another extinct group, the Cnemidolestodea, composed of derived relatives of

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Conclusion