title: A vanished history of skeletonization in Cambrian comb jellies.
abstract: Ctenophores are traditionally regarded as "lower" metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for example, an octamerous symmetry, oral-aboral axis, aboral sense organ, and octaradially arranged ctene rows). Unlike most modern counterparts, however, they lack tentacles, have a sclerotized framework, and have eight pairs of ctene rows. They are resolved as a monophyletic group (Scleroctenophora new class) within the ctenophores. This clade reveals a cryptic history and sheds new light on the early evolution of this basal animal phylum. Skeletonization also occurs in some other Cambrian animal groups whose extant members are exclusively soft-bodied, suggesting the ecological importance of skeletonization in the Cambrian explosion.
authors.affiliation: Early Life Evolution Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China. ; Early Life Institute, Collaborative Innovation Center of Continental Tectonics, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Ou
authors.affiliation: Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Shuhai
authors.initials: S
authors.lastname: Xiao
authors.affiliation: Early Life Institute, Collaborative Innovation Center of Continental Tectonics, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Han
authors.affiliation: Early Life Evolution Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China.
authors.forename: Ge
authors.initials: G
authors.lastname: Sun
authors.affiliation: Tsinghua University, Beijing 100084, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Early Life Institute, Collaborative Innovation Center of Continental Tectonics, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China.
authors.forename: Zhifei
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Early Life Evolution Laboratory, State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China. ; Early Life Institute, Collaborative Innovation Center of Continental Tectonics, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China.
authors.forename: Degan
authors.initials: D
authors.lastname: Shu
keywords: Cambrian; Chengjiang biota; Ctenophora; skeleton