The biologist had just come from the first floor, where tanks held a colony of gelatinous comb jellies. The blob was bigger than others, and it looked as though two of the jellies had merged into one.

A 520-million-year-old fossil resembling a flower is the great ancestor of modern-day comb jellies, jellyfish-like sea creatures that cast a rainbow-like effect as they propel their way through ocean ...