Abstract

Detailed study of the Khatyspyt Formation in arctic Siberia has shown that, contrary to common expectations, the earliest ichnofabric is of late Ediacaran age, records a food-seeking behavior, and is found in a distal carbonate ramp setting where it co-occurs with fossils of Avalon-type Ediacaran soft-bodied organisms. Preserved depth of bioturbation reaches 5 cm. The ichnofabric solely comprises Nenoxites, the oldest known meniscate trace fossil, which is interpreted as burrows with terminal backfill structure formed as a result of active displacement of sediment to form a tunnel within the substrate, followed by emplacement of the material behind the animal as it progressed through the sediment. In addition to being the most reliable paleontological evidence for the existence of bilaterians at ca. 555 Ma, the late Ediacaran bioturbation is regarded as a key step in the escalatory “engineering” of Phanerozoic ecospace leading to sudden diversification of macroscopic organisms and macrocommunities.

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