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Hallucigenia’s onychophoran-like claws and the case for Tactopoda

Smith, M.R.; Ortega-Hernández, J.

Hallucigenia’s onychophoran-like claws and the case for Tactopoda Thumbnail


J. Ortega-Hernández


The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ known from exceptional fossil deposits1, 2, 3, 4, 5, 6, 7, 8, 9. Although lobopodians occupy a deep phylogenetic position within Panarthropoda, a shortage of derived characters obscures their evolutionary relationships with extant phyla (Onychophora, Tardigrada and Euarthropoda)2, 3, 5, 10, 11, 12, 13, 14, 15. Here we describe a complex feature in the terminal claws of the mid-Cambrian lobopodian Hallucigenia sparsa—their construction from a stack of constituent elements—and demonstrate that equivalent elements make up the jaws and claws of extant Onychophora. A cladistic analysis, informed by developmental data on panarthropod head segmentation, indicates that the stacked sclerite components in these two taxa are homologous—resolving hallucigeniid lobopodians as stem-group onychophorans. The results indicate a sister-group relationship between Tardigrada and Euarthropoda, adding palaeontological support to the neurological16, 17 and musculoskeletal18, 19 evidence uniting these disparate clades. These findings elucidate the evolutionary transformations that gave rise to the panarthropod phyla, and expound the lobopodian-like morphology of the ancestral panarthropod.

Journal Article Type Article
Acceptance Date Jun 11, 2014
Online Publication Date Aug 17, 2014
Publication Date Aug 17, 2014
Deposit Date Oct 6, 2015
Publicly Available Date Jun 22, 2016
Journal Nature
Print ISSN 0028-0836
Electronic ISSN 1476-4687
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 514
Issue 7522
Pages 363-366
Public URL
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