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Published online: 9 May 2007 | doi:10.1038/nchina.2007.70

Primitive animals: No hurry to grow

Tim Reid

Introduction

© (2007) Nature

The Doushantuo Formation in Southern China contains fossils of the earliest complex organisms of the Ediacaran geological period, 635 to 542 million years ago. Leiming Yin and co-workers¹ at the Chinese Academy of Sciences in Nanjing found fossilized embryos of these animals encased in hard shells that may have protected them during a dormant phase in their life cycle.

Many small round fossils were unearthed in an Ediacaran layer of sedimentary rocks. The researchers initially thought the fossils might be giant bacteria, because they showed evidence of repeated cell division. However, many of the fossils were encased in thick, elaborate walls similar to some modern-day animal embryos. Such walls are called 'diapause egg cysts', and protect the embryos during a period of dormancy.

In the opinion of Leiming Yin and co-workers, the animals that produced the embryos were invertebrates inhabiting shallow seas, less than three million years after the 'Snowball Earth' ice age and before the Cambrian explosion of life. In such a harsh environment, the diapause egg cysts served the purpose of safely postponing development of the embryo until the animals reached a time and place of good growing conditions.

The authors in this work are from:
State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China; Botanical Museum, Harvard University, Cambridge, Massachusetts, USA.

References

1. Yin, L. et al. Doushantuo embryos preserved inside diapause egg cysts. Nature 446, 661–663 (2007). | Article | PubMed | ChemPort |