A complete insect from the Late Devonian period

Abstract

After terrestrialization, the diversification of arthropods and vertebrates is thought to have occurred in two distinct phases, the first between the Silurian and the Frasnian stages (Late Devonian period) (425-385 million years (Myr) ago), and the second characterized by the emergence of numerous new major taxa, during the Late Carboniferous period (after 345 Myr ago). These two diversification periods bracket the depauperate vertebrate Romer's gap (360-345 Myr ago) and arthropod gap (385-325 Myr ago), which could be due to preservational artefact. Although a recent molecular dating has given an age of 390 Myr for the Holometabola, the record of hexapods during the Early-Middle Devonian (411.5-391 Myr ago, Pragian to Givetian stages) is exceptionally sparse and based on fragmentary remains, which hinders the timing of this diversification. Indeed, although Devonian Archaeognatha are problematic, the Pragian of Scotland has given some Collembola and the incomplete insect Rhyniognatha, with its diagnostic dicondylic, metapterygotan mandibles. The oldest, definitively winged insects are from the Serpukhovian stage (latest Early Carboniferous period). Here we report the first complete Late Devonian insect, which was probably a terrestrial species. Its 'orthopteroid' mandibles are of an omnivorous type, clearly not modified for a solely carnivorous diet. This discovery narrows the 45-Myr gap in the fossil record of Hexapoda, and demonstrates further a first Devonian phase of diversification for the Hexapoda, as in vertebrates, and suggests that the Pterygota diversified before and during Romer's gap.

Molecular phylogeny of the Notostraca

“…For comparison, a separate and more conservative (see Section S.3.2) analysis was performed that assumed a node age for the split into Notostraca and Spinicaudata of 358.9 Ma (±0.2 stdev). This assignment used the minimum age of the oldest known notostracan fossils, which were recovered from a late Devonian (Upper Famennian) deposit (Garrouste et al, 2012, see associated electronic supplement for a photographic documentation of the notostracan fossils referred to). The Famennian spans 358.9 (±0.4)-372.2 (±1.6) Ma (see Cohen et al, 2012).…”

“…The Notostraca (tadpole shrimp) represent a group of branchiopod crustaceans that has existed since at least the late Devonian (Garrouste et al, 2012). At least one of its genera, namely Triops Schrank, 1803, appears to have attained a morphology indistinguishable from that of modern forms by the Upper Triassic (Trusheim, 1938).…”

Placoderm Assemblage from the Tetrapod-Bearing Locality of Strud (Belgium, Upper Famennian) Provides Evidence for a Fish Nursery

“…The tetrapod remains were found in association with very abundant flora [2], a putative insect [3–5], continental crustaceans [6–9] as well as sarcopterygian [10–12] and as yet undescribed acanthodian and actinopterygian fishes. The placoderm assemblage has been recently described and includes the antiarch Grossilepis rikiki , the groenlandaspidid Turrisaspis strudensis and the phyllolepidid Phyllolepis undulata [13,14].…”

Fossil record of stem groups employed in evaluating the chronogram of insects (Arthropoda: Hexapoda)

“…Insects are ancient, with definitive evidence of their occurrence as far back as the earliest Devonian, and they were the first lineage to evolve powered flight, a key innovation leading to subsequent phases of radiation and ecological specialization1234. Understanding the factors that led to these episodes of diversification and extinction over the more than 400 million years of insect history is vital for any comprehensive perspective on their evolution.…”