A Tube-Dwelling Early Cambrian Lobopodian
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2020-02-27
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2019-07-21
Subject Terms
Facivermis yunnanicus
luolishaniid
lobopodian
panarthropod
Cambrian
Chengjiang Biota
phylogenetic analyses
secondary loss
tube-dwelling lifestyle
luolishaniid
lobopodian
panarthropod
Cambrian
Chengjiang Biota
phylogenetic analyses
secondary loss
tube-dwelling lifestyle
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Abstract
Facivermis yunnanicus [1, 2] is an enigmatic worm-like animal from the early Cambrian Chengjiang Biota of Yunnan Province, China. It is a small (<10 cm) bilaterian with five pairs of spiny anterior arms, an elongated body, and a swollen posterior end. The unusual morphology of Facivermis has prompted a history of diverse taxonomic interpretations, including among annelids [1, 3], lophophorates [4], and pentastomids [5]. However, in other studies, Facivermis is considered to be more similar to lobopodians [2, 6-8]-the fossil grade from which modern panarthropods (arthropods, onychophorans, and tardigrades) are derived. In these studies, Facivermis is thought to be intermediate between cycloneuralian worms and lobopodians. Facivermis has therefore been suggested to represent an early endobenthic-epibenthic panarthropod transition [6] and to provide crucial insights into the origin of paired appendages [2]. However, the systematic affinity of Facivermis was poorly supported in a previous phylogeny [6], partially due to incomplete understanding of its morphology. Therefore, the evolutionary significance of Facivermis remains unresolved. In this study, we re-examine Facivermis from new material and the holotype, leading to the discovery of several new morphological features, such as paired eyes on the head and a dwelling tube. Comprehensive phylogenetic analyses using parsimony, Bayesian inference, and maximum likelihood all support Facivermis as a luolishaniid in a derived position within the onychophoran stem group rather than as a basal panarthropod. In contrast to previous studies, we therefore conclude that Facivermis provides a rare early Cambrian example of secondary loss to accommodate a highly specialized tube-dwelling lifestyle.
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Howard et al., 2020, Current Biology 30, 1529–1536 April 20, 2020 ª 2020 The Authors. Published by Elsevier Ltd. https://doi.org/10.1016/j.cub.2020.01.075
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Copyright © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). The linked file is the published version of the article.
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0960-9822
EISSN
1879-0445