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Protomelission is an early dasyclad alga and not a Cambrian bryozoan

Nature volume 615, pages 468–471 (2023)Cite this article

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Abstract

The animal phyla and their associated body plans originate from a singular burst of evolution occurring during the Cambrian period, over 500 million years ago1. The phylum Bryozoa, the colonial ‘moss animals’, have been the exception: convincing skeletons of this biomineralizing clade have been absent from Cambrian strata, in part because potential bryozoan fossils are difficult to distinguish from the modular skeletons of other animal and algal groups2,3. At present, the strongest candidate4 is the phosphatic microfossil Protomelission5. Here we describe exceptionally preserved non-mineralized anatomy in Protomelission-like macrofossils from the Xiaoshiba Lagerstätte6. Taken alongside the detailed skeletal construction and the potential taphonomic origin of ‘zooid apertures’, we consider that Protomelission is better interpreted as the earliest dasycladalean green alga—emphasizing the ecological role of benthic photosynthesizers in early Cambrian communities. Under this interpretation, Protomelission cannot inform the origins of the bryozoan body plan; despite a growing number of promising candidates7,8,9, there remain no unequivocal bryozoans of Cambrian age.

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Fig. 1: Protomelission-like dasyclad algae from Xiaoshiba.
Fig. 2: Preservation of Protomelission? sp.
Fig. 3: Comparison of the Xiaoshiba Protomelission? sp. with Wirrealpa P. gatehousei and the Cambroclavid Deltaclavus graneus.

Data availability

Specimens are accessioned at the Institute of Palaeontology, Yunnan University (YKLP 12436–42).

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Acknowledgements

We thank J.-B. Hou, K.-S. Du, J.-F. He and K.-R. Li for assistance in fossil collection; X.-Y. Yang, Y. Wang and L.-J. Zou for performing the elemental map analysis; S. Conway Morris for images of Deltaclavus; and P. Taylor and Z.-F. Zhang for comments on earlier versions of the manuscript. This study was supported by the National Natural Science Foundation of China (41730318 to X.-g.Z. and 42162002 to J.Y.).

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Author notes

  1. These authors contributed equally: Jie Yang, Tian Lan

Authors and Affiliations

  1. Institute of Palaeontology, Yunnan University, Chenggong, Kunming, China

    Jie Yang & Xi-guang Zhang

  2. College of Resources and Environmental Engineering, Guizhou University, Guiyang, China

    Tian Lan

  3. Department of Earth Sciences, Durham University, Durham, UK

    Martin R. Smith

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Contributions

X.-g.Z., M.R.S. and T.L. designed the project. X.-g.Z., M.R.S. and T.L. carried out the morphological and anatomical analyses and contributed to the final version of the manuscript. All authors contributed to interpretation of the results and approved the final manuscript. M.R.S. and X.-g.Z. wrote the manuscript with input from other authors. J.Y., with help from T.L., organized the fieldwork and prepared fossils for photography. X.-g.Z. and M.R.S. produced the figures.

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Correspondence to Xi-guang Zhang or Martin R. Smith.

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Extended data figures and tables

Extended Data Fig. 1 Elemental abundances in Protomelission? sp.

Reflected light, backscatter electron, and energy-dispersive X-ray spectroscopy images of a, central thallus of YKLP 12451, corresponding to region 3i in Fig. 2a; b–c, flanges at thallus margin in b, YKLP 12451, corresponding to region b of Fig. 2a; c, YKLP 12446, corresponding to region of Fig. 1b.

Extended Data Table 1 Anatomical comparison between Protomelission and possible relatives
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Yang, J., Lan, T., Zhang, Xg. et al. Protomelission is an early dasyclad alga and not a Cambrian bryozoan. Nature 615, 468–471 (2023). https://doi.org/10.1038/s41586-023-05775-5

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