An arthropoda-dominated trace fossil assemblage from the Upper Triassic of the Madygen Geopark, Kyrgyzstan

The Middle Triassic Madygen Formation of southwestern Kyrgyzstan has yielded a remarkably diverse non-marine flora and fauna, but few ichnia. The overlying Rhaetian to Lower Jurassic alluvial-fluvial sediments contain a moderately diverse ichnofossil record in an ephemeral pond that is characterized by the dominance of two types of traces assigned to different arthropod groups. The first type is assigned to Kouphichnium pterodactyli (Winkler) Malz 1964 and linked to xiphosuran tracemakers. This type is well-documented in marine and freshwater environments from the Pennsylvanian onwards. The second type represents a new ichnospecies in the ichnogenus Heteropodichnus Walter 1983 which so far is only known from the Lower Permian of central Germany and northern Italy. Twelve recovered traces of this type show signficant along-track changes in morphology that reflect the transition from swimming to walking locomotion and the dragging or rhythmic beating of the telson. Morphological comparisons indicate Kazachartra as likely tracemakers, in this case specifically Almatium gusevi Chernyshev 1940 which is preserved as fragmentary exuviae in the same horizon and more completely and abundantly in the lacustrine sediments of the underlying Madygen Formation. This find represents the first walking traces of Kazachartra, an order so far only known from the Middle Triassic to Lower Jurassic of China and Central Asia. For the Permian Heteropodichnus a notostracan tracemaker can be suggested.

The trace fossil assemblage is completed by three further types of invertebrate traces, the fish swimming trace Undichna unisulcata Gibert 1999 and rare swimming traces of small tetrapods, Lunichnium rotterodium Walter 1983.