Cambrian fossils illuminate the ambulacrarian common ancestor.

Yujingia glutenotunica from the early Cambrian (518 Ma) reveals ambulacrarians evolved from semi-sessile suspension feeders with complex appendages.

• Why it matters: Understanding the origins of ambulacrarians, which include diverse echinoderms and hemichordates, is crucial for reconstructing early deuterostome evolution.
• What they did: Researchers described Yujingia, a fossil with a simple cylindrical body and specialized filter-feeding appendages, and used phylogenetic analyses to place it basal to all modern ambulacrarians.
• The result: Findings suggest ambulacrarians originated from complex suspension-feeding ancestors, challenging traditional worm-like models and indicating deep evolutionary roots for echinoderm and pterobranch body plans.