Caveasphaera, a multicellular organism found in 609-million-year-old rocks in South China’s Guizhou Province, defies easy definition as animal or non-animal.
But, researchers say, it offers the earliest evidence of a key step in the evolution of animals – the capacity to develop distinct tissue layers and organs – and suggests animal-like embryological traits developed long before animals themselves.
An international team led by the Chinese Academy of Sciences (NIGPAS) and the University of Bristol, UK, used x-ray microscopy to analyse the tiny fossils, which measure about a half-millimetre in diameter and were preserved down to their component cells.
Different fossils displayed different stages of Caveasphaera development – from a single cell to a multicellular organism.
“Our results show that Caveasphaera sorted its cells during embryo development in just the same way as living animals, including humans, says NIGPAS’s Yin Zongjun. There is, however, “no evidence that these embryos developed into more complex organisms”.
The findings are published in the journal Current Biology.
More on Caveasphaera (from Wikipedia): The organism is notable due to the study of related embryonic fossils (measuring about a half-millimeter in diameter) which display different stages of its development: from early single-cell stages to later multicellular stages. Such fossil studies present the earliest evidence of an essential step in animal evolution – the ability to develop distinct tissue layers and organs. According to researchers, fossil studies of Caveaspaera have suggested that animal-like embryonic development arose much earlier than the oldest clearly defined animal fossils and may be consistent with studies suggesting that animal evolution may have begun about 750 million years ago. Nonetheless, Caveasphaera fossils may look similar to starfish and coral embryos. Still, researchers have concluded, “Parental investment in the embryonic development of Caveasphaera and co-occurring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved.”
Related reading: How to hunt fossils responsibly