An exceptional find of a chiton preserved at the end of its locomotion trace comes from the Culm facies, that is, from a succession of turbidity-controlled dark shales, greywackes and sandstones. The chiton trace is a smooth, rather indistinct, 7-8 mm wide bilobate ridge (convex epirelief), forming an incompletely preserved loop of estimated extent 50 x 80 mm. At its end is preserved a completely articulated chiton .i.Proleptochiton./i. sp., 4.0 mm wide and 11.5 mm long, oriented congruently with the trace. The neighbouring strata provide relatively common ichnofossils, including .i.Chondrites./i. isp., .i.Planolites./i. isp., .i.Dictyodora liebeana./i. (Geinitz) and .i.Diplocraterion./i. isp. The chiton’s trace fossil corresponds to ichnotaxa that have historically been compared to modern gastropod trails. The gastropods are well-known for two different monotaxic locomotion techniques, one for hard substrates such as glass, and another for soft substrates, where the animals move through muscular waves of much higher amplitude than observed on glass. Thereby, adhesion useable for movement on the hard surface is functionally replaced with friction. Loosening of the sediment by rapid movements of foot muscles is the cause of the structure’s convexity, that is, increasing volume. Similar behaviour is documented for the first time in chitons. The studied specimen is the first locomotion trace fossil attributed to polyplacophorans. The find documents the burrowing technique of chitons in deep-marine, turbidity-influenced soft substrate during the Viséan (330 Ma). It demonstrates the similarity of chiton and some gastropod traces in soft substrates, and adds to the lengthening list of animals that were fossilized within their traces.
Mikuláš et al. (Sun,) studied this question.