Possible Ediacaran Ancestry of the Halkieriids  

About sixty million years separate the early Cambrian Meishucun-type deposits from the preceding, taphonomically similar Doushantuo phosphorites, with no comparable taphonomic windows in between.  The lineages of modern animals can be traced back to near the base of the Cambrian, but not into the Ediacaran.  However, body plans of the Spiralia, and other main animal phyla, undoubtedly originated in the Ediacaran without leaving a convincing fossil record.  The Ediacaran biotas, although both taphonomically and ecologically rather bizarre, remain virtually the only source of fossil evidence on these events.  Unfortunately, metazoan affinities of the Ediacarans are still weakly supported.  Trace fossils are the earliest evidence of the Ecdysozoa, and indirectly imply that the priapulid body plan emerged near the end of the Ediacaran.  The possible relationship between the Ediacaran petalonamean ‘sea pens’ and the ctenophores is consistent with molecular expectations, but awaits convincing connecting links before it can be  accepted.  Some putative anatomical homologies between the dickinsoniid dipleurozoans and chordates (Deuterostomia) were also suggested.  Kimberella is believed to represent an Ediacaran proto-mollusc, even though it does not closely resemble Cambrian molluscs.  This introduces some uncertainty regarding affinities of this widely accepted pre-Cambrian member of the Spiralia.  It is suggested here that the gap in the stratigraphic succession may be filled with the Namibian Ausia. The distribution of proposed dorsal cuticular protuberances in an undescribed Ausia specimen resembles the distribution in the halkieriids.  Although limited, the new evidence also suggests a close relationship between the halkieriids and chancelloriids, supporting the concept of the Coeloscleritophora.  The affinity of halkieriids to the molluscs is another question.  Their jaw apparatuses rather remotely resemble the molluscan radula, but also show some similarity to underived polychaete jaws, e.g., of the Ordovician Archaeoprion.