Reinterpretation of Yunnanozoon as the earliest known hemichordate

摘要: THE Chengjiang fossil Lagerstatte is one of the earliest and most important palaeontological sites from Phanerozoic era1,2, about 530 million years ago3. It yields extremely abundant remarkably preserved soft-bodied fossils shells with soft parts various kinds, including bradoriids4–6, trilobites7,8, crustaceans9, brachiopods, worms, sponges, algae many unknown forms10–13. One these Yunnanozoon14, which we reinterpret here as known hemichordate. Possessing half characteristic chordate features providing an anatomical link between invertebrates chordates15, Hemichor-data a minor but phylum in evolutionary biology. Hemichordates comprise two main groups: enteropneusts, or 'acorn worms', pterobranchs. Apart presumable inclusion graptolites pterobranchs16–19, there are very few hemichordate fossils2,17,20. Although Yunnanozoon superficially similar to chordates21, its typical tripartite body plan broadly consistent that living balanoglossid hemichor-dates (enteropneusts).