Ancient Chinese Fossil Reveals Earliest Cephalopod Siphuncle, Rewriting Buoyancy Evolution

Paleontologists describe Eoceras shaanxiense from China’s Early Cambrian (~520 million years ago) as the oldest siphuncle-bearing cephalopod, offering a crucial transitional step in buoyancy evolution between early chambered shells and later cephalopods. The study, based on 32 specimens from the Shuijingtuo Formation, suggests these ancient animals had a primitive buoyancy system and likely spent most of their lives on the seafloor; the findings are published in Nature.