LIFE × EVOLUTION

The First Animals

~800 million years ago (claims 890 to 635 Ma)

Proterozoic · Neoproterozoic · Tonian

Sponges sit at the base of the animal tree, so the search for the first animal is mostly a search for a sponge. Two candidates, three hundred and fifty million years apart, show how hard the search is. In 890-million-year-old Canadian reefs, a mesh of worm-like tubes threads through the rock exactly as the decayed tissue of living horny sponges does, or, others answer, exactly as certain mineral growths do. At 539 million years, a goblet-shaped fossil from South China, more than forty centimetres tall, is a crown-group sponge nobody disputes; its skeleton is organic rather than mineral, which is precisely why sponges are so hard to find before it.

Why it matters

If the older reading holds, animals were present before oxygen rose and lived through the snowball glaciations. The undisputed fossil makes the point on its own: an animal with no mineral parts leaves almost nothing behind, so the Cambrian explosion is in part an explosion in what fossilises.

Dating & uncertaintyDisputed

Molecular clocks place the origin of animals well before the Cambrian, but the fossils are contested: sponge-like structures in 890 Ma reefs are read by some as the oldest animal bodies and by others as mineral artefacts. The first crown-group sponge accepted without argument is late Ediacaran.

Sources

1. Turner (2021), Nature · Possible poriferan body fossils in early Neoproterozoic microbial reefs
2. Wang et al. (2024), Nature · A late-Ediacaran crown-group sponge animal
3. Cunningham et al. (2017), BioEssays · The origin of animals: can molecular clocks and the fossil record be reconciled?

Earth history as one day

19:46:154 h 14 min before midnight

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