Fossil Of Earliest Known Bilaterian: Ikaria wariootia

A fossil the size of a grain of rice appears to be the earliest known bilaterian, the group of animals with two-sided symmetry, two openings and a through-gut. The group includes all vertebrates — including us — and many invertebrate groups. More than 100 Ikaria wariootia and their burrowing tracks were found in South Australia and were dated to more than 555 million years ago.