LIFE × EVOLUTION

Large Life, Soft and Unarmed

~575 to 539 million years ago

Proterozoic · Neoproterozoic · Ediacaran

Large, complex bodies, and none of them shaped like anything since: fronds anchored in the mud, flat quilted discs, ribbed ovals lying on the microbial mats they fed from. Fossil cholesterol extracted from Dickinsonia settles at least that one as an animal. They come in three successive communities, and between the second and the third, four fifths of the known forms disappear.

Why it matters

For thirty million years the sea held large bodies, most of which no living group accounts for. Then, halfway through, the community reorganises: animals that move, that compete for space, that reproduce in complex ways. The loss that follows runs as deep as those of the great extinctions to come. This is the world the Cambrian replaced, and it was already changing before the Cambrian arrived.

Dating & uncertainty

Soft-bodied fossils are rare and their affinities contested. Cholesterol biomarkers settle Dickinsonia and its close relatives as animals, but leave the rest of the assemblage open, and it has been read as everything from giant single-celled protists to terrestrial lichens.

Sources

1. Bobrovskiy et al. (2018), Science · Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals
2. Evans et al. (2022), PNAS · Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition
3. Droser et al. (2017), Annual Review of Earth and Planetary Sciences · The rise of animals in a changing environment: global ecological innovation in the late Ediacaran

Earth history as one day

20:57:373 h 2 min before midnight

if Earth’s 4.54 billion years were compressed into a single day