中国科学院南京地质古生物研究所机构知识库

The early history of deuterostomes, the group composed of the chordates, echinoderms and hemichordates(1), is still controversial, not least because of a paucity of stem representatives of these clades(2-5). The early Cambrian microscopic animal Saccorhytus coronarius was interpreted as an early deuterostome on the basis of purported pharyngeal openings, providing evidence for a meiofaunal ancestry(6) and an explanation for the temporal mismatch between palaeontological and molecular clocktimescales of animal evolution(6-8). Here we report new material of S. coronarius, which is reconstructed as a millimetric and ellipsoidal meiobenthic animal with spinose armour and a terminal mouth but no anus. Purported pharyngeal openings in support of the deuterostome hypothesis(6) are shown to be taphonomic artefacts. Phylogenetic analyses indicate that S. coronarius belongs to total-group Ecdysozoa, expanding the morphological disparity and ecological diversity of early Cambrian ecdysozoans.