Taphonomy of the Ediacaran Podolimirus and associated dipleurozoans from the Vendian of Ukraine

Abstract

Fossiliferous strata of the late Ediacaran Lomoziv Member of the Mohyliv Formation, once known from now flooded outcrops along the Dniester River, have been recently exposed in a large quarry near the Novodnistrovs’k electric plant dam in Podolia, Ukraine. Finely bedded arkosic sandstone with claystone/siltstone intercalations is locally rich in ‘elephant skin’ surfaces indicating original presence of microbial mats. Imprints of soft-bodied organisms frequently occur on the sole surfaces of the sandstones. There are no signs of early diagenetic cementation with iron sulfides and the fossils are usually strongly compacted, with low relief. Specimens of bilaterally symmetrical latest Precambrian animals newly collected at the quarry offer additional evidence that their bodies had a complex internal anatomy. This relates especially to Podolimirus mirus, previously known from only fragmentary specimens representing only marginal parts of its chambered organ (‘quilt’). It appears that there is a large region of the body in front of the ‘quilt’, with a lobate organ resembling bifurcating anterior structures earlier thought to represent intestinal diverticula in other dickinsoniids. The ‘quilt’ (presumably a dorsal muscular organ) of Podolimirus has a deep medial sinus that may have hosted a cylindrical axial organ analogous to that reported in the dickinsoniids from northern Russia and Australia.