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Advanced Cambrian hydroid fossils (Cnidaria: Hydrozoa) extend the medusozoan evolutionary history

Citation

Song, Xikun et al. (2021), Advanced Cambrian hydroid fossils (Cnidaria: Hydrozoa) extend the medusozoan evolutionary history, Dryad, Dataset, https://doi.org/10.5061/dryad.rjdfn2z8s

Abstract

Primitive cnidarians are crucial for elucidating the early evolution of metazoan body plans and life histories in the late Neoproterozoic and Palaeozoic. The highest complexity of both evolutionary aspects within cnidarians is found in extant hydrozoans. Many colonial hydrozoans coated with chitinous exoskeletons have the potential to form fossils; however, only a few fossils possibly representing hydroids have been reported, which still require scrutiny. Here, we present an exceptionally well-preserved hydroid found in the Upper Cambrian Fengshan Formation in northern China. It was originally interpreted as a problematic graptolite with an uncertain systematic position. Based on three characteristic morphological traits shared with extant hydroids (with paired hydrothecae, regular hydrocaulus internodes and special intrathecal origin pattern of hydrocladium), we propose this fossil hydroid as a new genus, Palaeodiphasia gen. nov., affiliated with the advanced monophyletic hydrozoan clade Macrocolonia typically showing loss of the medusa stage. More Macrocolonia fossils reviewed here indicate that this life strategy of medusa loss has been achieved already as early as the Middle Devonian. The early stratigraphical appearance of such advanced hydroid contrasts with previous molecular hypotheses regarding the timing of medusozoan evolution, and may be indicative for understanding the Ediacaran cnidarian radiation.

Methods

Photomicrographs of the fossils and three extant Diphasia species were taken using cameras connected to stereomicroscopes with the software Leica Application Suite. All images have not been processed.

Usage Notes

See details in the research paper.

Funding

National Natural Science Foundation of China, Award: 41772010

Strategic Priority Research Program of Chinese Academy of Sciences, Award: XDB26000000

China Postdoctoral Science Foundation, Award: 2018T110647

Xiamen University, Award: MEL Postdoctoral Scholarship

China Geological Survey Project, Award: DD20190078

National Natural Science Foundation of China, Award: 41876180

China Postdoctoral Science Foundation, Award: 2018M632579

Strategic Priority Research Program of Chinese Academy of Sciences, Award: XDB26000000