New-found fossils of strange, tiny ball-like creatures from around 600 million years ago are reported in the research journal Nature this week.
Understanding creatures from this early time has been difficult as they are very different from anything alive today. The newfound fossils are no exception. They seem to represent a lineage that became an evolutionary dead end—they are not ancestors of living animals, according to the authors of the new study.
The fossils, from an area in southern China called the Ediacaran Doushantuo Formation, date back to just before a burst of animal diversity known as the Cambrian explosion, according to the researchers. Life had not yet emerged from the oceans. Yet this “pre-Cambrian era,” with hard-to-find fossils, represents almost 90 percent of the history of life on Earth.
The new specimens, slightly under a millimeter wide, are thought to offer a window onto the early evolution of complex multiple-celled organisms.
Many fossils from the region in China seem defy attempts to categorize them. For example, Megasphaera—another ball-like microfossil made up of one or more cells in a thick envelope—has been thought to represent various groups, including bacteria, algae or early animal embryos.
The new “microfossils” from the Doushantuo Formation show clear signs of traits characteristic of animals, said the authors, Shuhai Xiao of Virginia Tech university and colleagues. These characteristics include cell differentiation; separation of reproductive cells; and “programmed” cell death, a system used to clear out no-longer-useful cells.
The evidence indicates the fossils, dubbed Megaclonophycus, probably aren’t bacteria, the authors said, calling for further investigation into where the minuscule creatures sit on the “family tree” of life.
Source : world-science.net