Palaeontological and Molecular Evidence Linking Arthropods, Onychophorans, and other Ecdysozoa |
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Authors: | Gregory D Edgecombe |
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Institution: | (1) Department of Palaeontology, Natural History Museum, Cromwell Road, London, SW7 5BD, UK |
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Abstract: | Membership of Arthropoda in a clade of molting animals, the Ecdysozoa, has received a growing body of support over the past
10 years from analyses of DNA sequences from many genes together with morphological characters involving the cuticle and its
molting. Recent analyses based on broad phylogenomic sampling strengthen the grouping of cycloneuralian worms and arthropods
as Ecdysozoa, identify the velvet worms (Phylum Onychophora) as the closest living relatives of arthropods, and interpret
segmentation as having separate evolutionary origins in arthropods and annelid worms. Determining whether the water bears
(Phylum Tardigrada) are more closely related to onychophorans and arthropods or to unsegmented cycloneuralians such as roundworms
(Nematoda) is an open question. Fossil taxa such as the Cambrian anomalocaridids provide a combination of arthropod and cycloneuralian
characters that is not observed in any living ecdysozoan. Fossils break up long branches and help to resolve the sequence
of character acquisition at several critical nodes in the arthropod tree, notably in a suite of Cambrian lobopodians that
may include the stem groups of each of the major panarthropod lineages. |
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Keywords: | Cambrian Expressed sequence tags Fossils Lobopodians Phylogenomics |
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