The first known cephalopod was only a millimetre long and lived about 520 million years ago

Nature, Published online: 29 July 2026; doi:10.1038/d41586-026-02319-5
The locomotion of modern cephalopods, such as squid and cuttlefish, relies on buoyancy control achieved mainly by a specialized structure called a siphuncle. The discovery of fossils of Eoceras — a millimetre-sized cephalopod with a siphuncle — suggests that the group had already emerged in the early Cambrian, around 520 million years ago. ...