TUBULAR MACROFOSSILS FROM THE EDIACARAN NAMA GROUP, NAMIBIA

Paleontologists usually discuss Ediacaran life in terms of acritarchs and the distinctive macrofossils from which the period's name derives. Several deposits, however – notably the Doushantuo Formation in southern China – indicate that a broader diversity of macroscopic organisms inhabited Ediacaran oceans. This circumstance led Droser and others (2006) to propose that many structures reported as Ediacaran trace fossils are actually the casts and molds of tubular bodies. Abundant tubular macrofossils in shales of the 548-542 Ma Kuibis and Schwarzrand subgroups of the Nama Group, Namibia, exemplify the kind of tubular organisms that may have been widespread in Ediacaran platform and shelf environments. The Nama tubes occur on surfaces of parallel-laminated shales in both the Kliphoek and Feldschuhorn members, commonly in dense populations. The tubes are preserved as compressed three-dimensional structures that range in diameter from 0.5 to 2 mm and reach lengths of up to 20 cm. Individuals show sinuous bending and occasional brittle fracture, but rarely preserve evidence of morphological differentiation at their terminal ends. Walls originally consisted of strong but flexible organic matter. Little or no original organic material remains and fossils are commonly preserved by a surficial coating of iron or manganese oxides. Faint annulations on a few specimens suggest growth along an open apical margin. If correct, this would support the interpretation of Nama tubes as external protective sheaths of animals rather than as the compressed walls of algae such as Vendotaenia. The tubes are, by a wide margin, the most abundant fossils in Nama rocks. Similar populations occur in Ediacaran successions of Russia, China, and elsewhere. Thus, beyond their local abundance, such tubes may turn out to be among the most abundant records of Ediacaran life.