Tiny fossil has oldest known rear-end

Artist's rendering of Ikaria wariootia. (Sohail Wasif/UCR)

Tiny fossil has oldest known rear-end

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. “One major difference with a grain of rice is that Ikaria had a large and small end,” says palaeobiologist Scott Evans. “This may seem trivial but that means it had a distinct front and back end, which is the kind of organisation that leads to the variety of things with heads and tails that are around today.”

The Guardian | 5 min readReference: PNAS paper