Researchers have discovered the fossilized remains of the oldest known ancestor of almost every animal in existence today. The creature, named Ikaria wariootia, is a wormlike animal about the size of a grain of rice, and it appears to be the earliest example of the bilaterian body shape that’s common to the overwhelming majority of animals ever since.
It’s an animal whose body has two symmetrical sides, with a mouth at one end and an anus at the other. This basic structure has proven so successful that it’s been conserved across hundreds of millions of years of evolution and countless incarnations, from ducks to dogs to dinosaurs. In fact, only a fraction of animals, like sponges and jellyfish, aren’t bilaterian.
And now, researchers have found the oldest known ancestor of this widespread group, dating back 555 million years. Ikaria looked a little like a slug, measuring between 2 and 7 mm (0.08 and 0.29 in) long and 1 and 2.5 mm (0.04 and 0.1 in) wide. It was very clearly symmetrical, and evidence points to it having a mouth, a gut and an anus – all features of bilaterians.
The burrows also showed signs of V-shaped ridges, which suggest that Ikaria moved like a worm, contracting muscles and dragging itself along. While simple by today’s standards, the researchers say that Ikaria would have been complex for its time.
“Burrows of Ikaria occur lower (in the rock record) than anything else,” says Mary Droser, co-author of the study. “It’s the oldest fossil we get with this type of complexity. Dickinsonia and other big things were probably evolutionary dead ends. This is what evolutionary biologists predicted. It’s really exciting that what we have found lines up so neatly with their prediction.”
https://newatlas.com/science/oldest-animal-ancestor-fossils-ikaria-warioota/