EARLIEST RECORD OF SHELTERING STRATEGY FOR PREDATOR AVOIDANCE FROM THE EARLY CAMBRIAN OF THE MARBLE MOUNTAINS, CALIFORNIA

The use of discarded shells as shelters (conchicolous habit), after the original builder has died, is a common predator avoidance strategy in many groups of benthic invertebrates. Following the Cambrian Explosion, life during the Early Cambrian underwent a spectacular diversification. In the near absence of predators, sessile and mobile benthic species experimented with wide variety of grazing, deposit and suspension feeding strategies. With the rise of predatory species during the latter part of the Early Cambrian, epifaunal species were forced to develop new strategies for protection or avoidance of the new and more efficient predators. The occupation of discarded hyolith shells by conchioles in the Early Cambrian Chambless Limestone and Cadiz formation of the Marble Mountains in southeastern California as shelters represents the earliest record of sheltering strategy for predator evasion in the Phanerozoic.

The presence of continuous uninterrupted passageways extending from the apertural region of hyolith shells through the enclosing oncolitic (bacterial) encrustation suggests that some conchicole organisms utilized the discarded hyolith shells as shelters. The unobstructed nature of opening, smooth wall surface of the passageway through the oncoid indicate that the conchicole organism took up residency in the shell shortly after the death of the hyolith and occupied the shell as the oncoid encrustation enveloped and thickened around the shell. Hyolith shells, used for shelters, are frequently visible on weathered surfaces of the Chambless Limestone. Individual oncoids from the Cadiz Formation display remarkably well preserved examples of this conchicolous habit. We have interpreted the occupation and habitation of oncoid encrusted hyolith shells from the Marble Mountains as the earliest example of sheltering as a predatory avoidance strategy. The recognition of the appearance of predatory avoidance strategies during the Early Cambrian provides new insight into early history evolutionary history of benthic communities.