The world's oldest animal, which dates back 558 million years, was unearthed in Russia on September 19. Our earliest known ancestor was identified after traces of cholesterol were found, confirming that the fossil is of an animal and not a plant. The bizarre marine creature grew to be almost 1.4 meters long. Hailed as "the Holy Grail of paleontology," the fossil looks like a cross between a leaf and a thumbprint.