A re-assessment of the taxonomy, palaeobiology and taphonomy of the rangeomorph organism Hapsidophyllas flexibilis from the Ediacaran of Newfoundland, Canada

Newfoundland’s Mistaken Point is home to some of the world’s oldest known complex body fossils. Detailed observation of newly discovered specimens has led to a reconsideration of Hapsidophyllas flexibilis, which is diagnosed as being a complex epifaunal multifoliate rangeomorph with a basal stolon. This study has revealed that published material of H. flexibilis includes a cryptic epifaunal recliner that grew on, and slightly into, the seafloor in a manner similar to the common Ediacaran epifaunal organisms Fractofusus and Beothukis. The new genus and species erected herein to accommodate these epifaunal organisms is Gigarimaneta samsoni, an organism that is broadly round in outline and composed of rows of allantoid units that are further sub-divided into smaller spherocylindrical units. There is no evidence of rangeomorph branching, instead the divisions seen in Gigarimaneta are considered to represent invaginations of the lower epithelium that increased the surface-area-to-volume ratio of these organisms without the creation of true branches. The resulting ‘pneu’-like divisions may have allowed this quasi-infaunal taxon to have gained nutriment from the substrate via the culturing of sulfur-oxidizing bacteria, either as endo- or epi-symbionts, perhaps coupled with the absorption of dissolved organic material from pore/seawater.