Swimming trace of a coelacanth fish from the Lower Keuper of south-west Germany

Abstract

Parundichna schoelli igen. nov., isp. nov. from the Middle Triassic (Ladinian) Lower Keuper of Rot am See (Baden-Württemberg, Germany) consists of clusters of sigmoidal scratches symmetrically arranged in a plaited pattern. It is here interpreted as the swimming trace of a large coelacanth fish. In contrast to ichnospecies of Undichna there is no unpaired groove left by the tail fin. Instead, the sets of parallel scratches resulted from the pendulum motion of two pairs of appendages, the pectoral and pelvic fins, which acted in alternation, as in tetrapods. This strange mode of swimming is compared to films of modern Latimeria and to computer simulations; it probably corresponds to a particular foraging behaviour. The presence of fittingly-sized coelacanths is documented in coeval carbonates (Alberti-Bank) by disarticulated skeletal elements. Since the Lower Keuper represents a fluvial and estuarine facies of the receding Muschelkalk sea, we cannot be sure whether this trace was made in a marine or freshwater environment.