AN ANALYSIS OF MULTIPLE TRACKWAYS OF PROTICHNITES OWEN, 1852, FROM THE POTSDAM SANDSTONE (LATE CAMBRIAN), ST. LAWRENCE VALLEY, NY
At least eight distinctive trackways of multi-legged telson-bearing individuals are present with a roughly bimodal size distribution (widths of 11.6 cm, 11.1 cm, 8.5 cm, 6.7 cm, and 6.5 cm). A disturbance at the intersection of trackways 1 and 2 has been interpreted to show the earliest evidence of invertebrate mating activity (Erickson, 2004). Trackway 1 (11.1 cm wide) consists of repeated series of six pairs of impressions (labeled A-F and A'-F') with a continuous medial telson drag. Impressions are arranged in a chevron pattern with track A being proximal to the medial line and E and F distal. The number of impressions present in a series has not yet been related to the number of legs on the track-maker, nor has direction of movement.
Stride distance in cm (distance between the same impressions in adjacent series) over seven iterations of tracks is as follows: A-10.0, B-9.7, C -10.1, D -10.1, E -10.3 and F -10.3. The mean stride for the tracks on the this side of the medial line (the outside of a shallow curve) is 10.1 cm. Stride distance on the opposite side of the medial line is: A' -9.4, B' -9.6, C' -9.5, D' -9.7, E' -10.0 and F' -9.7. The mean stride for tracks on the inside of the curve is 9.6 cm, and the overall mean stride for this trackway is 9.8 cm. The narrower trackway (2) (width 6.5 cm) does not preserve as complete a series of impressions and has a discontinuous medial telson drag.
The trackways are consistent in number of impressions per series (leg number?) and stride lengths with members of the original descriptions of ProtichnitesOwen, 1852, although a tridactyl condition can not be recognized on any digit. Variable preservation was probably a resulted from varying thickness of the microbial mat and/or varying water depth or wind and wave action in an intertidal pool.