Around 540 million years ago, life on the earth underwent a profound growth spurt: during the Cambrian explosion, the planet¿s multicellular life diversified rapidly. Scientists writing in the journal Science say that they have identified in rocks from China what may be the beginnings of this revolution. According to the report, the fossils are the earliest evidence of animals with a two-sided body plan (as opposed to a radial one) and date to around 55 million years before the Cambrian explosion.

Jun-Yuan Chen of the Nanjing Institute of Geology and Paleontology and an international team of researchers identified 10 fossils in the Doushantuo Formation in southwest China, which is between 580 and 600 million years old. The remains, which the researchers christened Vernanimalcula guizhouena, or "small spring animal," measure just 200 micrometers across and are oval in shape (see image). The team identified a number of organs inside the specimens, including mouths, guts, possible sense organs and body cavities called coeloms.

The new finds indicate that the "genetic toolkit" required for two-sided development evolved long before the Cambrian, the authors argue. Vernanimalcula guizhouena implies that very early life-forms did not have to be large to be complex.