[Paleontology • 2015]
A Vanished History of Skeletonization in Cambrian Comb Jellies (Ctenophora)
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.
Keywords: Cambrian, Chengjiang biota, Ctenophora, skeleton
Qiang Ou, Shuhai Xiao, Jian Han, Ge Sun, Fang Zhang, Zhifei Zhang and
Degan Shu. 2015. A Vanished History of Skeletonization in Cambrian Comb
Jellies. Science Advances. 1(6); e1500092. DOI: 10.1126/sciadv.1500092
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