Animal embryos evolved before animals: Study
Animal-like embryos developed from single-cell animals long before critters themselves, as shown by a study which assessed the fossilised remains of an organism located in 609-million-year-old rocks in South China’s Guizhou Province. The researchers, such as people from the Nanjing Institute of Geology and Palaeontology of the Australian Academy of Sciences (NIGPAS), analysed the tiny fossils of the multicellular organism of Caveasphaera, which measured about a half-millimetre in diameter, and were preserved down to their component cells.
The analysis, published in the journal Current Biology, used X-ray microscopy to assess the various fossils displaying different stages of Caveasphaera growth – from one cell to a multicellular organism. “X-Ray tomographic microscopy functions like a medical CT scanner, but enables us to see features that are under a thousandth of a millimetre in size. We could form the fossils into growth stages, reconstructing the embryology of Caveasphaera,” said study co-author Kelly Vargas in the University of Bristol in the united kingdom.
The researchers stated that before today, sufficient fossil records had not been accessible to know when and how animal ancestors created the transition from single-celled microbes to complex multicellular organisms. Thus far this query could be addressed by studying their loved ones and living animals.
In the present study, the investigators found evidence that a vital step in this evolutionary transition occurred long before complex animals arose in the fossil record. They said this evidence could be found at the fossilised embryos resembling multicellular stages in single-celled relatives of animals’ life cycle. “We were able to sort the fossils into expansion phases, adjusting the embryology of Caveasphaera,” Vargas said. According to the researchers, Caveasphaera needed a life cycle like their close living relatives which alternate between single-celled and multicellular stages.
The analysis noted that Caveasphaera piled its cells during embryo development in a similar way the process worked including people. “But we have no proof that these embryos developed into more complicated organisms,” said Yin Zongjun, study co-author in NIGPAS.
However, the researchers are uncertain whether Caveasphaera was a creature alone, or simply an important step in animal development. “Caveasphaera looks much as the embryos of a few starfish and corals – we don’t locate the adult stages only because they are harder to fossilize,” said Zhu Maoyan, co-author of this study from NIGPAS.