Earliest siphuncle-bearing cephalopod from the early Cambrian

Recent cephalopods are the most intelligent invertebrates and are unique among molluscs in possessing chambered, gas-filled shells penetrated lengthwise by a siphuncle that regulates buoyancy, enabling their nektonic and predatory lifestyle through jet propulsion. The origin of this key innovation remains enigmatic, as there is a major gap between the earliest known cephalopod, Plectronoceras cambria from the late Cambrian, and molecular clock estimates that place the lineage’s divergence from other molluscs in the early Cambrian. Here we report millimetre-scale, orthoconic shells tentatively assigned to Cupitheca sp. from the Shuijingtuo Formation (Cambrian Stage 3) of South China. Internally, the shells exhibit multiple septa and a peripherally situated segmented tube, indicating that the soft body migrated anteriorly to form successive chambers during growth while maintaining contact with earlier chambers via the tube. Collectively, these features identify the segmented tube of Cupitheca sp. as a primordial siphuncle. Our findings show that Cupitheca—previously regarded as a hyolith—was instead a mollusc with key cephalopod characters, extending the earliest cephalopod record by ~30 million years to the acme of the Cambrian Explosion (~520 Ma).