THE FISH SWIMMING TRACE UNDICHNA FROM THE DEVONIAN CATSKILL FORMATION, EASTERN PENNSYLVANIA
The Undichna specimens are preserved in concave hyporelief (part and counterpart were recovered) on a fine-grained mudstone. This record of Undichna from the fluvial deposits of the Catskill Formation occurs on the crests of mud-draped ripple bedforms, in association with a diverse assemblage of other lithologic features, including fossil fish remains (bones, scales), invertebrate ichnotraces (e.g., Diplichinites, Planolites), sedimentary exposure features (raindrop impressions, mudcracks), and frequent examples of fluvial ripples. The Undichna traces consist of isolated, solitary, well-defined, narrowly incised, sinusoidal wave lines that have a wave length of 28 mm, wave amplitude of 0.5 mm, and a wave line width of approximately 0.1 mm.
The ichnogenus Undichna is the swimming trace of a fish that usually consists of a series of sinusoidal waves made on soft sediment at the bottom of standing water by the fins of a fish swimming by anguilliform locomotion. The single sinusoidal waves of the Catskill Formation specimens justify assignment to the ichnospecies U. unisulca Gilbert et al. 1999.
The Catskill Formation record of Undichna indicates the presence of a small fish with a caudal fin that touched the sediment during periods when subaerial surfaces were subaqueous. The length of the fish is estimated at 11.2 cm (4 times the wave length of the trail).