Tymkivia primitiva gen. nov. sp. nov., a new type of fossils from the late Ediacaran (Vendian) Kanylivka Group in Podolia, Ukraine

A thick sequence of Ediacaran (Vendian) deposits is exposed in the southwestern part of Ukraine along the valley of the Dniester River and its left tributaries. The stratigraphy and lithology of these deposits have been studied in some detail, but information on the fossil record is still very scarce. The Kanilovka Group sedimentary sequence has the lowest level of exploration. Tymkivia primitiva gen. nov. sp. nov. is described from Late Ediacaran shallow-water marine rocks of the Podolia region. The fossils are casts of the inner surface and imprints on the surface of bacterial mats (“death masks”) of small, sedentary sac-like organisms. Numerous imprints on the surface of mudstone and siltstone slabs testify to the existence of mass settlements of these organisms in the Volyn-Podilsky sedimentary basin in the Late Ediacaran. Morphological details that could be interpreted as a mouth, anus, and internal organs are not found in the fossils. Tymkivia was found in association with bacterial mat remains and the carbonaceous compressions of Vendotaenia, Kanilovia, and the problematic rod-shaped Harlaniella. Tymkivia is interpreted as possible remains of benthic plants; it is morphologically similar to some modern green algae. The option of interpretation as a fossilized record of the polyp stage of Medusozoa (Cnidaria) cannot be ruled out either. The appearance and disappearance of these organisms are the benchmarks of the stage of sedimentation of the Kanylivka Group.