610-m-yr-old embryo fossils found in China

NANJING -- A class of Ediacaran fossils dating back 610 million years was found in Weng'an Biota in Southwest China's Guizhou province, which foreshadows the evolutionary origin of animal-like embryology.

The findings, which are believed to be the earliest embryo fossils ever discovered, were achieved by scientists at the Nanjing Institute of Geology and Palaeontology under the Chinese Academy of Sciences, in collaboration with British, Swedish and Swiss scholars.

Weng'an Biota is a rich microfossil assemblage that preserves its biological structure at a subcellular level of fidelity and encompasses a range of developmental stages.

Simple sponges, as well as complex vertebrates including humans, all fall into the category of multicellular animals. Studies have shown that the ancestors of multicellular animals evolved from even more ancient unicellular organisms.

However, there has been no definitive answer as to how this pivotal change occurred. The scientific community generally believes that the study of early embryos of animals may be the key to solving the mystery.

The newly-discovered embryo fossil, or "Caveasphaera," is ball-shaped and has a diameter of less than 1 mm. The fossils as a whole retain an exquisite multicellular structure.

Researchers used 3D imaging technology to reconstruct the structure of hundreds of fossil specimens. The results show that their development process is similar to that of unicellular relatives of animals, and more complicated as well, showing regular cell migration, reorganization and other specific developmental mechanisms that are unique to animal embryos.

"The fossils record a key stage in the evolution of animals from single-cells to multi-cells. The stage lays the biological foundation for the emergence of animals with truly differentiated cells and tissues," said Yin Zongjun, associate researcher at the Nanjing institute.

The research results were published in Current Biology on Nov 28.