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Fossil Record of Stem Groups Employed in Evaluating the Chronogram of Insects (Arthropoda: Hexapoda)


Fossil Record of Stem Groups Employed in Evaluating the Chronogram of Insects (Arthropoda: Hexapoda)

Yan-Hui Wang et al. Sci Rep.


Insecta s. str. (=Ectognatha), comprise the largest and most diversified group of living organisms, accounting for roughly half of the biodiversity on Earth. Understanding insect relationships and the specific time intervals for their episodes of radiation and extinction are critical to any comprehensive perspective on evolutionary events. Although some deeper nodes have been resolved congruently, the complete evolution of insects has remained obscure due to the lack of direct fossil evidence. Besides, various evolutionary phases of insects and the corresponding driving forces of diversification remain to be recognized. In this study, a comprehensive sample of all insect orders was used to reconstruct their phylogenetic relationships and estimate deep divergences. The phylogenetic relationships of insect orders were congruently recovered by Bayesian inference and maximum likelihood analyses. A complete timescale of divergences based on an uncorrelated log-normal relaxed clock model was established among all lineages of winged insects. The inferred timescale for various nodes are congruent with major historical events including the increase of atmospheric oxygen in the Late Silurian and earliest Devonian, the radiation of vascular plants in the Devonian, and with the available fossil record of the stem groups to various insect lineages in the Devonian and Carboniferous.


Figure 1
Figure 1. Possible positions for the fossil record in a defined clade.
A crisscross “†” stands for the fossil record of the corresponding group.
Figure 2
Figure 2. Phylograms inferred from the nuclear genes.
The left tree is based on the five nuclear genes with DNA model applied to the paired sites of rDNAs, while the right tree is based on the five nuclear genes with Doublet model applied to the paired sites of rRNAs. Numbers associated with each node indicate Bayesian posterior probabilities values and maximum-likelihood (ML) bootstrap values. An asterisk denotes that the clade is also present in the maximum parsimony analysis (only values ≥60% are shown). A dash is shown if the topology is not shown in the maximum likelihood analysis. The lengths of the branches follow the phylograms of the BI trees.
Figure 3
Figure 3. The maximum clade credibility chronogram from BEAST analysis.
The blue bars illustrate the extent of the 95% highest posterior density credibility intervals for each divergence time. The detailed estimated time for the deep divergences of winged insects were provided. The numbers on yellow solid circle background indicates the first appearances of the stem groups for certain clades, while the nodes with orange 95% HPD bars indicated the calibrated points. Numbers from one to eight are stand for species Delitzschala bitterfeldensis, Archaeorthoptera, Qilianiblatta namurensis, Sinonamuropteris ningxiaensis, Westphalothripides oudardi, Avioxyela gallica, Stephanastus polinae, and Westphalomerope maryvonneae respectively.

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