TRIASSIC FISH TALE: QUANTIFYING THE GEOMETRY OF UNDICHNA TRACES (LOCATONG FORMATION, CARNIAN, SE PENNSYVANIA)

Bedding planes of black argillitic mudtsones of Lockatong Formation (Upper Triassic) represent lacustrine environments, which at times contain abundant skeletal remains or impressions of fish. Traces produced by fish should be common, however have been described to much lesser extent. This study focuses on a rippled bedding surface that, among numerous tetrapod traces, contains six segments of unpaired sinuous epichnial grooves that extent beyond the edges of the available surface. These marks are interpreted as piscine Undichna uniscula traces produced by anal or caudal fins of similar-sized fish, likely a palaeonisciform. The trails span 35-70 cm in length, range in wavelength between 25-50 mm, and exhibit average wave amplitude of ~8 mm. Several ichnites exhibit sets of three sub-millimeter-wide in-phase striations on the convex part of the wave, possibly related to fin spines. All trails have relatively constant depth (~1 mm) and lack breaks, thereby indicating consistent buoyancy and ability to maintain their height over the bottom and some degree of orientation with respect to the current, punctuated by several slight turns. Whereas there is no macro-morphological indication of swim direction, further micro-scale analysis of along-trace asymmetry of Undichna oriented near normal to ripple crests may support rheotactic behavior.