Our Oldest Ancestor

摘要

VIEWED THROUGH AN ELECTRON MICROSCOPE, the newly discovered Saccorhytus coronarius is the oldest and most primitive deuterostome, a major branch of the animal kingdom that includes all vertebrates. At about 540 million years old, the millimeter-long specimen from China (top), described in January in Nature, pushes back the deuterostome record by tens of millions of years. Co-author and Cambridge University paleobiologist Simon Conway Morris believes an unusual chemical environment in its seabed home preserved the saclike animal in "jaw-dropping" detail. Structures around its large mouth may look like eyes and nostrils, but the researchers believe these "body cones" (better seen in the illustration) may have been early precursors to gills, flushing out water that Saccorhytus swallowed.