A subaerial arthropod trackway from the Upper Silurian Clam Bank Formation of Newfoundland

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Abstract
Trackways are reported for the first time from Silurian rocks in Newfoundland. They occur in the Clam Bank Formation of the Port au Port Peninsula. At least one of the trackways represents one of the earliest known occurrences of a large subaerial arthropod trace fossil. It is preserved in hyporelief in a red fine-grained sandstone. The trackway, Diplichnites Dawson, 1873, consists of two parallel series of clearly defined imprints. It is attributed to a myriapod similar to the Lower Devonian Eoarthropleura. The sandstone contains halite pseudomorphs that indicate that the sediment horizon had been subject to desiccation immediately prior to the formation of the trackway. The arthropod walked on a red siltstone deposited in an alluvial flats environment. Analysis of the trackway suggests that the arthropod was approximately 23 cm long and had 17 pairs of walking appendages. It appears that a high-geared gait with a ratio of forestroke:backstroke of 8:2 was used in walking across the substrate, that is, approximately 20% of walking appendages were in contact with the substrate at any one time. This rapid gait, and the lack of a body drag mark, indicates that the arthropod was well adapted to subaerial locomotion. Knowledge of modern myriapod gaits has been used to extrapolate a theoretical trail, which compares well with the fossil trackway. Smaller, less well preserved trackways occur elsewhere in the Clam Bank Formation and may have been made by a similar arthropod.