Overview
- Researchers published their findings in Nature on Wednesday, July 29, reporting 32 phosphatized microfossils named Eoceras shaanxiense from the ~520-million-year-old Shuijingtuo Formation in South China.
- Scanning electron microscopy and micro-CT reconstructions show an orthoconic shell with multiple septa and a ventrally placed, segmented tube that links chambers through tiny canals, which the team interprets as a primitive siphuncle.
- The authors propose a three-step pathway for early cephalopod buoyancy: chambered straight shells, a sealed segmented siphuncle as seen in Eoceras, and later evolution of a true siphuncle with septal necks and connecting rings.
- Because the siphuncle in Eoceras appears simple, the team infers a mainly benthic life on the seafloor, but they stress that soft-body anatomy is not preserved and ecological claims remain provisional.
- If confirmed by more early Cambrian finds, the discovery narrows a long-standing discrepancy between molecular-clock estimates and fossil evidence and will prompt more targeted searches of phosphatized 'small shelly fossils' worldwide.