Australia: The Land Where Time Began

A biography of the Australian continent 

Comment on “Trace fossil evidence for Ediacaran bilaterian animals with complex behaviors”

Chen et al. have interpreted trace fossils from the Shibantan Member of the Denying Formation (551-541 Ma), South China, as evidence of under mat feeding, epibenthic locomotion and temporary dwelling of a small worm-like animal (Metazoa, Bilateria), showing 4 features that are not compatible with that interpretation: bulbous ends, interruptions, variable width, narrow ends and beaded levees. Retallack suggests these features are better explained as having been made by the formation of a sporocarp base, looping upwards, Changing shape, cell aggregation and slime nodules, respectively, of the slug (grex or pseudoplasmodium) phase of a cellular slime mould which are comparable to an extant Dictyostelium discoideum (Amoebozoa, Mycetozoa). There are a further 3 features that are observed in the trails of worms as well as slime moulds: transverse markings, central ridge and, small size. There are a number of other deposits in which similar observations can be made, and the consideration of affinities with mycetozoans for comparable trace fossils from the Ediacaran Member, South Australia (550 Ma), Ust Pinega Formation in Russia (558 Ma), Tacuari Formation, Uruguay (600-585 Ma), Chorhat Sandstone, India (1,100 Ma), and the Stirling Range Sandstone, western Australia (2,000-1,800 Ma). Slime moulds are terrestrial eukaryotic protists that Retallack suggests may have a fossil record that extends back as far as the likely 1,900 Ma age of aquatic metazoans.

Sources & Further reading

1. Retallack, G. J. (2013). "Comment on “Trace fossil evidence for Ediacaran bilaterian animals with complex behaviors” by Chen et al. [Precambrian Res. 224 (2013) 690–701]." Precambrian Research 231(0): 383-385.