The story
Cloudina is a tiny animal that lived in a tube of calcium carbonate made of stacked, funnel-shaped cones, each tube just a few millimetres wide and a few centimetres long. Its remains, found in rocks about 550 to 538 million years old, are among the oldest skeletons built by an animal. Geologists first described it from the Nama Group of Namibia in 1972 and named it for Preston Cloud, an American paleontologist. Later finds in China, Spain, Oman, Brazil and the United States show it was widespread.
Before Cloudina, almost all animals were soft-bodied. A hard tube protects against being eaten and also lets an animal stand up from the seafloor into the current. Some Cloudina tubes carry small, neat holes bored through the wall, reported from the Dengying Formation of China by Hua Hong and colleagues in 2003. They are the oldest known evidence of predation, probably by a small borer that chewed into the tube, and they show that prey and hunters were already evolving against each other. In Namibia Cloudina grew in clumps and helped build early reefs together with the goblet-shaped Namacalathus.
Cloudina's affinity is unclear, with proposals ranging from worms to cnidarians, and it vanishes near the base of the Cambrian. Its main significance is what it reveals: skeletons and predators had appeared before the Cambrian Explosion, providing an early push for armour, burrows and an arms race that drove the explosion.
Why it mattered
- Cloudina shows biomineralised skeletons evolving before the Cambrian, so the Explosion did not start from nothing.
- Boreholes in its tubes record the first known predator and prey dynamic, a driver of evolutionary arms races.
- Its tube reefs were the first animal-built reefs, an early example of animals engineering their habitat.
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