It looks like an animal, but…
Caveasphaera adds to a complex story.
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.