LIFE × EVOLUTION

The First Predators

~780 to 740 million years ago

Proterozoic · Neoproterozoic · Tonian

The first predators were protists, single-celled organisms with a nucleus, which ate other cells and left round holes bored through the walls of Grand Canyon microfossils between 780 and 740 million years ago.

The first predators are known only from the holes they left in their prey. The evidence lies in shales, rocks made of hardened mud, laid down where the Grand Canyon now cuts. In these shales, seven species of microfossil, the fossils of microscopic organisms, have round perforations that pass right through the wall. The perforations are 0.1 to 3.4 microns across, a micron being a thousandth of a millimetre. Predatory protists drill holes of the same size and shape today to reach the contents of their prey. At least some of the prey are unambiguously complex cells, that is, cells with a nucleus. The predators themselves left no fossil, since a cell without a wall leaves none.

Why it matters

Predation was a new selective pressure, a cause of death that favours the cells able to resist it. It made defences worth their cost: a thicker wall, a larger body, spines. Rocks of this age contain many ornamented cysts, cells enclosed in a resistant wall. These ornaments therefore served for protection more than for decoration.

Dating & uncertainty

The Grand Canyon microfossils have circular perforations a few microns across, drilled through their walls. These perforations match the way present-day predatory protists open their prey. Researchers have since reported comparable perforations in Arctic Canada, in rocks about 1,150 to 900 million years old. They interpret them as probable traces of the same kind of predation. If so, predation by perforation would be 150 to 400 million years older than the Grand Canyon fossils.

Earth history as one day

19:52:354 h 7 min before midnight

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