An extraordinary cluster consisting of hundreds of Arthrophycus alleghaniensis, a well-known trace fossil guide to the Lower Silurian in the Valley and Ridge Province of eastern USA, provides evidence of behavioral ecology of the trace-producing animal. Although taxonomic affinity
of the trace producer remains unknown, patterns of resource exploitation (mobbing and concentrated mining of a thin subsurface mud layer) and interaction with conspecific animals (many instances of apparent avoidance reactions) are clearly preserved in our specimens. Based on depositional
setting, the spatial patterns of burrows and their morphologic variations, the trace producer was likely a powerful burrower capable of penetrating a thick tidal sand blanket, locating food-rich patches within a buried mud layer, of mining the patches (while simultaneously avoiding adjacent
burrowers in many cases), and backfilling its burrow system as it either shifted position for more mining activity or withdrew from the area. The pattern does not necessarily record the activities of hundreds of endobenthic animals in a small space, but instead could reflect a burst of activity
by a small population exploiting the food-rich mud before subsequent deposition put the resource out of reach.
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