Swimming trails of fishes from the Permian playa-lake ecosystem of the Salagou Formation (Lodève Basin, southern France)

Abstract

The Col de Dio palaeontological site yields the first swimming trails of fishes from the continental Permian deposits of the Lodève Basin (southern France). Several morphologies of trails were distinguished, each of them including one, two or four thin, horizontal and sinusoidal grooves/ridges. Trails are ascribed to Undichna bina, Undichna britannica and Undichna unisulca. They co-occur with arthropod body remains (e.g. “conchostracans”, triopsids), invertebrate traces (cf. Cochlichnus, Diplichnites, and Diplopodichnus) and swimming tracks of tetrapods (Characichnos). The sedimentological analysis conducted at the Col de Dio tracksite indicates the presence of two orders of stratigraphic sequences that rule the alternation of humid and arid cycles in an endorheic terminal mud-dominated floodplain and playa-lake environment. Although body fossils of fishes remain unknown in the Salagou Formation, the presence of Undichna shows that ichthyofauna was an abundant component of the palaeoecosystem related to this formation. The diverse shapes of Undichna suggest a great diversity of fish morphologies and/or behaviours. This new discovery of fish trails co-occurring with tetrapod and arthropod tracks complements other coeval French tracksites, suggesting that such ichnofaunas were common in Permian terrestrial ecosystems from the Eastern Pangean intertropical zone.