Comment on “Trace fossil evidence for Ediacaran bilaterian animals with complex behaviors” by Chen et al. [Precambrian Res. 224 (2013) 690–701

Abstract

Trace fossils from the Shibantan Member of the Denying Formation (551–541Ma) of South China, interpreted by Chen and colleagues as evidence of undermat feeding, epibenthic locomotion and temporary dwelling of a small worm-like animal (Metazoa, Bilateria), show four features incompatible with that interpretation: (1) bulbous ends, (2) interruptions, (3) variable width, (4) narrow ends and (5) beaded levees. These features are better explained as due to formation of a sorocarp base, looping upward, shape changing, cell aggregation and slime nodules, respectively, of the slug (grex or pseudoplasmodium) phase of a cellular slime mold comparable with living Dictyostelium discoideum (Amoebozoa, Mycetozoa). Another three features are found in worm as well as slime mold trails: (6) transverse markings, (7) central ridge and (8) small size. Similar observations can be made, and mycetozoan affinities considered for comparable trace fossils from the 550Ma Ediacaran Member of South Australia, 558Ma Ust Pinega Formation of Russia, 585–600Ma Tacuari Formation of Uruguay, 1100Ma Chorhat Sandstone of India and 2000–1800Ma Stirling Range Sandstone of Western Australia. Slime molds are terrestrial eucaryotic protists, and may have a fossil record extending back as far as the likely 1900Ma age of aquatic metazoans.