Half-billion-year-old fossil rewrites starfish evolutionary origin
Researchers discovered fossilised animals named Yujingia glutenotunica in southwestern China, dated to the Cambrian explosion, that are thought to be close to the last common ancestor of ambulacrarians—a group including starfish, sea urchins, and acorn worms. The fossils, measuring 8–22 millimetres, preserve soft body parts including a tentacle-based feeding system and appendages for anchoring to the seabed. Phylogenetic analysis of 505 morphological characters across 100 living and extinct taxa places Yujingia closer to the last common ancestor of living ambulacrarians than previously described fossils. The findings challenge the longstanding hypothesis that the ambulacrarian ancestor was a tentacle-free, pharyngeal-filtering worm, instead suggesting the ancestor possessed sophisticated tentacle-based feeding structures, with later echinoderm specialisations and other features evolving afterward.