The remarkable antiquity, diversity and ecological significance of arthropods have inspired numerous attempts to resolve their deep phylogenetic history, but the results of two decades of intensive molecular phylogenetics have been mixed1,2,3,4,5,6,7. The discovery that terrestrial insects (Hexapoda) are more closely related to aquatic Crustacea than to the terrestrial centipedes and millipedes2,8 (Myriapoda) was an early, if exceptional, success. More typically, analyses based on limited samples of taxa and genes have generated results that are inconsistent, weakly supported and highly sensitive to analytical conditions7,9,10. Here we present strongly supported results from likelihood, Bayesian and parsimony analyses of over 41 kilobases of aligned DNA sequence from 62 single-copy nuclear protein-coding genes from 75 arthropod species. These species represent every major arthropod lineage, plus five species of tardigrades and onychophorans as outgroups. Our results strongly support Pancrustacea (Hexapoda plus Crustacea) but also strongly favour the traditional morphology-based Mandibulata11 (Myriapoda plus Pancrustacea) over the molecule-based Paradoxopoda (Myriapoda plus Chelicerata)2,5,12. In addition to Hexapoda, Pancrustacea includes three major extant lineages of ‘crustaceans’, each spanning a significant range of morphological disparity. These are Oligostraca (ostracods, mystacocarids, branchiurans and pentastomids), Vericrustacea (malacostracans, thecostracans, copepods and branchiopods) and Xenocarida (cephalocarids and remipedes). Finally, within Pancrustacea we identify Xenocarida as the long-sought sister group to the Hexapoda, a result confirming that ‘crustaceans’ are not monophyletic. These results provide a statistically well-supported phylogenetic framework for the largest animal phylum and represent a step towards ending the often-heated, century-long debate on arthropod relationships.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
C.W.C. thanks W. Hartman for early insight into questions of arthropod phylogeny and D. Percy for sequencing. J.W.M. and R.W. thank N. Tait, G. Hampson and R. Hessler for help collecting samples. J.C.R. and A.Z. thank M. Cummings and A. Bazinet for making available grid computing, and the DNA Sequencing Facility at the Center for Biosystems Research, University of Maryland Biotechnology Institute. J.W.S. was supported by the Maryland Agricultural Experiment Station. C.W.C. was supported by the Whiteley Center. This work was funded by two programmes at the US National Science Foundation, namely Biocomplexity in the Environment: Genome-Enabled Environmental Science and Engineering, and Assembling the Tree of Life.
Author Contributions C.W.C., J.C.R., J.W.S., A.Z. and J.W.M. designed the project. J.W.S., J.W.M., R.W. and J.C.R. designed and carried out taxon sampling and collection. J.C.R. and C.W.C. supervised DNA sequencing and editing, with PCR templates generated by J.C.R., B.B. and others. J.C.R., A.Z., C.W.C. and J.W.S. decided on the strategy for data analysis and its implementation, with the degen1 coding method developed and implemented by J.C.R., A.H. and A.Z. J.C.R. and A.Z. assembled the Supplementary Information and submitted sequences to GenBank. J.W.S. and J.W.M. proposed the names for the new, strongly supported clades in the Pancrustacea. C.W.C. wrote the first draft of the manuscript, with major additions by J.C.R. and J.W.S. and additional contributions by J.W.M. and A.Z. All authors commented on the manuscript.
This file contains the nucleotide data matrix, 80 taxa.
This file contains the degen1 data matrix, 80 taxa.
This file contains the amino acid data matrix, 85 taxa.
This file contains the perl script to generate degen1 data matrices.