The Ediacaran critters were an odd bunch—from ringed discs and patterned blobs to lumpy ropes and wavy fronds. Taking to the warm shallow seas as early as 570 million years ago, these soft and squishy misfits were Earth's earliest complex life.

One of the most famous of the lot is Dickinsonia. This flattened, ribbed oval can grow over four feet across and sports a distinct ridge down its center. However, the question of what exactly Dickinsonia is has long puzzled scientists. At various points in history, they’ve assigned these curious forms to almost every kingdom of life. In recent decades, the debate has swirled around three groups: some researchers proposed fungi, others said protists, still others say animals.

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