An addition to the Middle Triassic Monti Pisani Ichnoassemblage: Characichnos, a tetrapod swimming trace

The paleoichnological (trace fossil) record testifies to the ancient behaviours of the tracemaking organisms, which include walking, eating, resting and nesting among others. Trace fossil evidence for swimming is particularly rare, since the conditions for preservation of swimming-induced traces are extremely peculiar. Here, we describe new and previously collected traces from the Ladinian (Middle Triassic) Quarziti Viola Zonate Member of the Quarziti del Monte Serra Formation, (Monti Pisani massif, northern Appennines) as belonging to the ichnogenus Characichnos. The latter was originally described for groups of two to four, slightly sinuous, parallel hypichnial ridges (or epichnial grooves) that reflect the tracemaker’s underwater scratching of shallow floor while buoyant (White & Romano, 2001). The overall size and morphology of Characichnos isp. from the Monti Pisani trace fossil assemblage are comparable to those of the lepodosauromorph and archosauromorph ichnotaxa Rhynchosauroides, Rotodactylus, and Synaptichnium, all of which have been previously reported from the Quarziti del Monte Serra Formation, whose remarkable tetrapod ichnoassemblage has been recently revised (Marchetti et al.,2021). Our discovery of representatives of Characichnos in the Quarziti Viola Zonate strata is consistent with previous reconstruction of the palaeoenvironmental setting of this deposit as a coastal pond system, covered by very shallow water and periodically dried up (Rau & Tongiorgi, 1974).