The recent discovery of a tiny fossil, Eoceras shaanxiense, has the potential to revolutionize our understanding of squid and octopus evolution. This minuscule shell, measuring just 0.04 inches (1 millimeter) long, is the earliest known cephalopod fossil with evidence of buoyancy control. The fossil, found in 520-million-year-old rocks in South China, reveals a slender tube, the siphuncle, that ran the length of the shell, allowing cephalopods to control their buoyancy and hunt. This finding challenges the existing fossil record, which has a gap during the early Cambrian period, and aligns with molecular clock estimates of the cephalopod split in the early Cambrian. The study's authors propose a three-stage development of the cephalopod shell, from a straight, chambered shell to a sealed, segmented tube and finally to a true siphuncle. This discovery highlights the importance of searching for small shelly fossils in early Cambrian rock, as they may contain the ancestors of cephalopods. The findings are significant because they suggest that cephalopods were part of the burst of animal diversification during the Cambrian explosion, rather than a late arrival. This discovery also raises questions about the evolutionary path of cephalopods and the development of their buoyancy control system, which may have enabled their transition to a more predatory lifestyle.
