A Late Triassic aquatic community: Undichna-like and related swimming traces from a freshwater pond in the lower Elliot Formation of South Africa

• Published in: Journal of African earth sciences (1994) 2020-12, Vol.172, p.104026, Article 104026
• Main Authors: Sciscio, Lara, Bordy, Emese M., Head, Howard V.
• Format: Article
• Language: English
• Subjects: Amphibian; Fish; Karoo Basin; Late Triassic; Semionotus; Stormberg Group; Swim traces; Tracks; Undichna
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2020.104026

Swimming and subaqueous traces and trails are reported, for the first time, from a freshwater pond community in the middle Norian lower Elliot Formation (lEF) in the main Karoo Basin of South Africa. These ichnofossils, associated abiotic tool marks, and sedimentary structures are preserved on the upper bedding plane of a fine- to medium-grained sandstone that is overlain by laminated mudstones. The assessment of the relationship between the sedimentology and ichnology of this ichnosite reveals a unique perspective into a Late Triassic ecosystem. Here, a brief time window showcases events ranging from the abandonment of a river channel, to the initiation of a floodplain pond, and its subsequent infilling by silty sediments. The trace fossil assemblages, their cross-cutting relationships and the sedimentological evidence suggest that several generations of traces formed during the silting up of this floodplain pond, a palaeoenvironment infrequently documented in the lEF. Some trails are described as similar to Undichna Anderson 1976, and can be attributed to small, swimming freshwater fish. Didactyl tracks with Grallator/Anchisauripus-like affinities are associated with both sickle-shaped digit drag marks and 3–8 cm long disorderly striations showing variable morphology (e.g., narrowly incised, straight to slightly sinuous, V-shaped grooves). Their preservation indicates wading and subaqueous behaviour of tetrapods. Other traces range from semi-circular impressions of unknown affinity to unique, yet indistinct, < 2-cm-long, partially preserved ichnofossils with three (or possibly four) slender digit impressions. Together these ichnofossils provide evidence for animals currently unrecorded in the osteological record of the lEF. [Display omitted] •A rare, overbank pond setting is reconstructed from the middle Norian of South Africa.•Ichnofossils indicate occupation of the freshwater pond prior to it being silted up.•Vertebrates (fish, tetrapods) swam and wadded across the bottom of the pond.•Ichnofossils reveal biota unrecorded by body fossils in the lower Elliot Formation.