A palaeontological solution to the arthropod head problem


The composition of the arthropod head has been one of the most controversial topics in zoology, with a large number of theories being proposed to account for it over the last century1. Although fossils have been recognized as being of potential importance in resolving the issue2,3, a lack of consensus over their systematics4,5 has obscured their contribution. Here, I show that a group of previously problematic Cambrian arthropods from the Burgess Shale and Chengjiang faunas form a clade close to crown-group euarthropods, the group containing myriapods, chelicerates, insects and crustaceans6. They are characterized by modified or even absent endopods, and two pre-oral appendages. Comparison with reconstructions of the crown-group euarthropod ground plan6 and recent investigations into onychophorans7,8 demonstrates that these two appendages are the first antenna (of extant crustaceans) and a more anterior appendage associated with an ocular segment. The latter appendage has been reduced in all crown-group euarthropods. Its most likely relic is as a component of the labrum9. These fossils thus tie together results from disparate living groups (onychophorans and euarthropods).

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Figure 1: Cladistic analysis (see Supplementary Information for details) of upper stem-group euarthropods, with schematic drawings of the pre-oral region of selected taxa.
Figure 2: Scheme for arthropod head segmentation implied by this analysis.


  1. 1

    Rempel, J. G. The evolution of the insect head: the endless dispute. Q. Entomol. 11, 7–25 (1975)

    Google Scholar 

  2. 2

    Dewel, R. A. & Dewel, W. C. The place of tardigrades in arthropod evolution. Syst. Assoc. Sp. Vol. 55 109–123 (1997)

  3. 3

    Chen, J. Y., Edgecombe, G. D., Ramsköld, L. & Zhou, G. Head segmentation in Early Cambrian Fuxianhuia: implications for arthropod evolution. Science 268, 1339–1343 (1995)

    CAS  Article  ADS  PubMed  Google Scholar 

  4. 4

    Wills, M. A., Briggs, D. E. G., Fortey, R. A. & Wilkinson, M. The significance of fossils in understanding arthropod evolution. Verh. Deut. Zool. Gessell. 88, 203–215 (1995)

    Google Scholar 

  5. 5

    Simonetta, A. M. & Della Cave, L. in The Early Evolution of Metazoa and the Significance of Problematic Taxa (eds Simonetta, A. M. & Conway Morris, S.) 189–244 (Cambridge Univ. Press, Cambridge, 1991)

    Google Scholar 

  6. 6

    Walossek, D. in Proc. 4th Int. Crustacean Congr. (eds Schram, F. R. & von Vaupel Klein, J. C.) 3–27(Brill Academic, Leiden, 1999)

    Google Scholar 

  7. 7

    Eriksson, B. J. & Budd, G. E. The cephalic nerves of the Onychophora and their bearing on our understanding of head segmentation of stem-group evolution of Arthropoda. Arth. Struct. Dev. 29, 197–209 (2001)

    Article  Google Scholar 

  8. 8

    Eriksson, B. J., Tait, N. N. & Budd, G. E. Head development in the onychophoran Euperipatoides kanangrensis with particular reference to the central nervous system. J. Morphol. (in the press)

  9. 9

    Haas, M. S., Brown, S. J. & Beeman, R. W. Pondering the procephalon: the segmental origin of the labrum. Dev. Genes. Evol. 211, 89–95 (2001)

    CAS  Article  PubMed  Google Scholar 

  10. 10

    Whittington, H. B. Early arthropods, their appendages and relationships. Syst. Ass. Spec. 12, 253–268 (1979)

    Google Scholar 

  11. 11

    Walossek, D. & Müller, K. J. Upper Cambrian stem-lineage crustaceans and their bearing upon the monophyletic origin of Crustacea and the position of Agnostus. Lethaia 23, 409–427 (1990)

    Article  Google Scholar 

  12. 12

    Edgecombe, G. D. & Ramsköld, L. Relationships of Cambrian Arachnata and the systematic position of Trilobita. J. Paleontol. 73, 263–287 (1999)

    Article  Google Scholar 

  13. 13

    Budd, G. E. The morphology and evolutionary significance of Kerygmachela kierkegaardi Budd (Buen Formation, Lower Cambrian, North Greenland). Trans. R. Soc. Edinb. Earth Sci. 89, 249–290 (1999)

    Article  Google Scholar 

  14. 14

    Whittington, H. B. The lobopodian animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia. Phil. Trans. R. Soc. Lond. B 284, 165–197 (1978)

    Article  ADS  Google Scholar 

  15. 15

    Richter, S. & Scholtz, G. Phylogenetic analysis of the Malacostraca (Crustacea). J. Zool. Syst. Evol. Res. 39, 113–136 (2001)

    Article  Google Scholar 

  16. 16

    Bruton, D. L. & Whittington, H. B. Emeraldella and Leanchoilia, two arthropods from the Burgess Shale, Middle Cambrian, British Columbia. Phil. Trans. R. Soc. Lond. B 300, 553–585 (1983)

    Article  ADS  Google Scholar 

  17. 17

    Walossek, D. The Upper Cambrian Rehbachiella and the phylogeny of Branchiopoda and Crustacea. Fossils Strata 32, 1–202 (1993)

    Google Scholar 

  18. 18

    Giribet, G., Edgecombe, G. D. & Wheeler, W. C. Arthropod phylogeny based on eight molecular loci and morphology. Nature 413, 157–161 (2001)

    CAS  Article  ADS  PubMed  PubMed Central  Google Scholar 

  19. 19

    Hou, X.-G. & Bergström, J. Arthropods of the Lower Cambrian Chengjiang fauna, southwest China. Fossils Strata 45, 1–116 (1997)

    Google Scholar 

  20. 20

    Briggs, D. E. G. The morphology, mode of life and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), Middle Cambrian, Burgess Shale, British Columbia. Phil. Trans. R. Soc. Lond. B 281, 439–487 (1978)

    Article  ADS  Google Scholar 

  21. 21

    Briggs, D. E. G. & Collins, D. A Middle Cambrian chelicerate from Mount Stephen, British Columbia (Canada). Palaeontology 31, 779–798 (1988)

    Google Scholar 

  22. 22

    Hou, X.-G., Bergström, J. & Ahlberg, P. Anomalocaris and other large animals in the Lower Cambrian Chengjiang fauna of southwest China. GFF 117, 3–183 (1995)

    Google Scholar 

  23. 23

    Budd, G. E. Stem-group arthropods from the Lower Cambrian Sirius Passet fauna of North Greenland. Syst. Assoc. Sp. Vol. 55, 125–138 (1997)

  24. 24

    Dewel, R. A., Budd, G. E., Castano, D. F. & Dewel, W. C. The organization of the subesophageal nervous system in tardigrades: insights into the evolution of the arthropod hypostome and tritocerebrum. Zoologischer Anzeiger 238, 191–203 (1999)

    Google Scholar 

  25. 25

    Hou, X.-G. New rare bivalved arthropods from the Lower Cambrian Chengjiang fauna, Yunnan, China. J. Palaeontol. 73, 102–116 (1999)

    Article  Google Scholar 

  26. 26

    Bousfield, E. L. A contribution to the natural classification of Lower and Middle Cambrian arthropods: food-gathering and feeling mechanisms. Amphipacifica 2, 3–33 (1995)

    Google Scholar 

  27. 27

    Scholtz, G. Evolution of developmental patterns in arthropods—the analysis of gene expression and its bearing on morphology and phylogenetics. Zoology 103, 99–111 (2001)

    CAS  Google Scholar 

  28. 28

    Aguinaldo, A. M. A. et al. Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387, 489–493 (1997)

    CAS  Article  Google Scholar 

  29. 29

    Telford, M. J. & Thomas, R. A. Expression of homeobox genes shows chelicerate arthropods retain their deutocerebral segment. Proc. Natl Acad. Sci. USA 95, 10671–10675 (1998)

    CAS  Article  ADS  PubMed  Google Scholar 

  30. 30

    Winter, G. Beiträge zur Morphologie und embryologie des vorderen Körperabschnitts (Cephalosoma) der Pantopoda Gerstaecker, 1863. Z. Zool. Syst. Evol. 18, 27–61 (1980)

    Article  Google Scholar 

  31. 31

    Swofford, D. L. PAUP: Phylogenetic Analysis Using Parsimony, Version 3.1.1 (Illinois Natural History Survey, Champaign, Illinois, 1993)

    Google Scholar 

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This work grew out of a collaboration with R. A. Dewel, whom I thank for discussions that helped shape many of the ideas contained herein. D. Waloszek and J. Eriksson have also provided much help and insight. I also thank J. Bergström, H. Xianguang, D. Collins and D. Erwin for allowing access to material. The comments of G. Edgecombe substantially improved the paper. This work was funded by the Swedish Research Council (VR).

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Budd, G. A palaeontological solution to the arthropod head problem. Nature 417, 271–275 (2002). https://doi.org/10.1038/417271a

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