By Anne Oatman ’20
For 15 years, scientists agreed that fossilized burrows found in 555 million-year-old Ediacaran Period deposits in Nilpena, South Australia, were made by bilaterians (an animal who has a left and a right side that are mirror images of each other). Until now there was no sign of the creature that made the burrows, leaving scientists with nothing but speculation.
With funding from a NASA exobiology grant, Scott Evans, a recent doctoral graduate from UC Riverside; and Mary Droser, a professor of geology at UC Riverside, traveled to Southern Australia to study these burrows. What they found was remarkable. They used a three-dimensional laser scanner that revealed the regular, consistent shape of a cylindrical body with a distinct head and tail and faintly grooved musculature. This laser helped them to discover that the animal ranged between 2-7 millimeters long and about 1-2.5 millimeters wide (largest being a grain of rice) just the right size to have made the burrows. What they found was the fossils of the Ikaria Wariootia, the earliest bilaterian and one of the earliest human ancestors.
These tiny wormlike creatures were one of the first animals that evolved to move purposefully and have a successful way of organizing their bodies and the structures inside of it. They burrow in thin layers of well-oxygenated sand on the ocean floor in search of organic matter using their extremely impressive sensory skills. The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows. The fossils that the researchers found had V shaped ridges, which supports the hypothesis that the Ikaria Wariootia moved by contracting its muscles across its body like a worm. This finding is extremely important as it proves the hypotheses of several evolutionary researchers.