Pteridinium Research Articles

Ediacaran developmental biology.

ABSTRACTRocks of the Ediacaran System (635–541 Ma) preserve fossil evidence of some of the earliest complex macroscopic organisms, many of which have been interpreted as animals. However, the unusual morphologies of some of these organisms have made it difficult to resolve their biological relationships to modern metazoan groups. Alternative competing phylogenetic interpretations have been proposed for Ediacaran taxa, including algae, fungi, lichens, rhizoid protists, and even an extinct higher‐order group (Vendobionta). If a metazoan affinity can be demonstrated for these organisms, as advocated by many researchers, they could prove informative in debates concerning the evolution of the metazoan body axis, the making and breaking of axial symmetries, and the appearance of a metameric body plan. Attempts to decipher members of the enigmatic Ediacaran macrobiota have largely involved study of morphology: comparative analysis of their developmental phases has received little attention. Here we present what is known of ontogeny across the three iconic Ediacaran taxa Charnia masoni, Dickinsonia costata and Pteridinium simplex, together with new ontogenetic data and insights. We use these data and interpretations to re‐evaluate the phylogenetic position of the broader Ediacaran morphogroups to which these taxa are considered to belong (rangeomorphs, dickinsoniomorphs and erniettomorphs). We conclude, based on the available evidence, that the affinities of the rangeomorphs and the dickinsoniomorphs lie within Metazoa.

Three-dimensional microCT analysis of the Ediacara fossil Pteridinium simplex sheds new light on its ecology and phylogenetic affinity

Ediacara fossils often exhibit enigmatic taphonomy that complicates morphological characterization and ecological and phylogenetic interpretation; such is the case with Pteridinium simplex from the late Ediacaran Aar Member in southern Namibia. P. simplex is often preserved as three-dimensional (3D) casts and molds in coarse-grained quartzites, making detailed morphological characterization difficult. In addition, P. simplex is often transported, distorted, and embedded in gutter fills or channel deposits, further obscuring its morphologies. By utilizing microfocus X-ray computed tomography (microCT) techniques, we are able to trace individual specimens and their vanes in order to digitally restore the 3D morphology of this enigmatic fossil. Our analysis shows that P. simplex has a very flexible integument that can be bent, folded, twisted, stretched, and torn, indicating a certain degree of elasticity. In the analyzed specimens, we find no evidence for vane identity change or penetrative growth that were previously used as evidence to support a fully endobenthic lifestyle of P. simplex; instead, evidence is consistent with the traditional interpretation of a semi-endobenthic or epibenthic lifestyle. This interpretation needs to be further tested through microCT analysis of P. simplex specimens preserved in situ rather than transported ones. The elastic integument of P. simplex is inconsistent with a phylogenetic affinity with xenophyophore protists; instead, its physical property is consistent with the presence of collagen, chitin, and cellulose, an inference that would provide constraints on the phylogenetic affinity of P. simplex.

Taphonomy of the Ediacaran Fossil Pteridinium Simplex Preserved Three-Dimensionally in Mass Flow Deposits, Nama Group, Namibia

Ediacara-type fossils are found in a diverse array of preservational styles, implying that multiple taphonomic mechanisms might have been responsible for their preservational expression. For many Ediacara fossils, the “death mask” model has been invoked as the primary taphonomic pathway. The key to this preservational regime is the replication or sealing of sediments around the degrading organisms by microbially induced precipitation of authigenic pyrite, leading toward fossil preservation along bedding planes. Nama-style preservation, on the other hand, captures Ediacaran organisms as molds and three-dimensional casts within coarse-grained mass flow beds, and has been previously regarded as showing little or no evidence of a microbial preservational influence. To further understand these two seemingly distinct taphonomic pathways, we investigated the three-dimensionally preserved Ediacaran fossil Pteridinium simplex from mass flow deposits of the upper Kliphoek Member, Dabis Formation, Kuibis Subgroup, southern Namibia. Our analysis, using a combination of petrographic and micro-analytical methods, shows that Pteridinium simplex vanes are replicated with minor pyrite, but are most often represented by open voids that can be filled with secondary carbonate material; clay minerals are also found in association with the vanes, but their origin remains unresolved. The scarcity of pyrite and the development of voids are likely related to oxidative weathering and it is possible that microbial activities and authigenic pyrite may have contributed to the preservation of Pteridinium simplex; however, any microbes growing on P. simplex vanes within mass flow deposits were unlikely to have formed thick mats as envisioned in the death mask model. Differential weathering of replicating minerals and precipitation of secondary minerals greatly facilitate fossil collection and morphological characterization by allowing Pteridinium simplex vanes to be parted from the massive hosting sandstone.

New organic fossil finds in the Precambrian Valday series along the Syuz'ma River

New species of organic fossils are described from the Precambrian Valday series on the Onega peninsula. This ancient Precambrian faunal locality was discovered in 1973; the first fossils described from it were pteridinians, assigned somewhat tentatively to the species Pteridinium simplex Gürich (AN SSSR, Izvestiya ser. geol., no. 12, 1974). The present article describes scyphomedusas assigned to a new genus and species (Albumares brunsae Fedonkin), typical Pteridinium simplex Gürich, Dickinsonia costata Sprigg, and new arthropod genera and species — Onega stepanovi Fedonkin and Vendomia menneri Keller. The species assemblage found shows that the Valday series on the Onega peninsula is of the same age as the Pound sandstones of Ediacara province in Australia. —Authors.

A reinterpretation of Rangea schneiderhoehni and the discovery of a related new fossil from the Nama Group, South West Africa

Two new specimens of Rangea schneiderhoehni Gurich 1930 and a new fossil are here described from the Nama Group of South West Africa. A careful study of the two Rangea specimens and a reexamination of the holotype shows that R. schneiderhoehni forma plana and R. schneiderhoehni forma turgida are the same species as already suggested by Gurich, Richter, and Pflug, that the puzzling outer flange of forma plana is part of an underlying second leaf-like body, and that the Ediacara ‘Rangea’ does not belong to the genus Rangea. Here, therefore, it is introduced as the genus Glaessnerina. The new fossil, Nasepia altae, is related to Pteridinium simplex Gurich 1930 and Rangea schneiderhoehni Gurich 1930, and also to the problematic fossil Namalia villiersiensis Germs 1968.