Geologists have discovered the first ancestor on the family tree that contains most animals today, including humans. The wormlike creature, Ikaria wariootia, is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut. It was found in Ediacaran Period deposits in Australia and was 2-7 millimeters long, with the largest the size of a grain of rice.