Abstract: The preservation potential of a brachiopod shell is in part determined by the post-mortem loss in its mechanical resilience to physical destruction. The loss of mechanical resistance, whether due to the decay of the shell's organic matrix, or other processes, can be observed using engineering testing techniques. Tests at various post-mortem intervals on evacuated shells of a population of the extant eastern Pacific terebratulid brachiopod from the San Juan Islands, Terebratalia transversa revealed that a measurable decrease in preservation potential had occurred. This decrease was demonstrated by the loss of structural integrity of both the hinge mechanism in articulated specimens, and of shell walls of the individual valves. For the hinging mechanism, this loss in preservation potential was evidenced by an increase in the gape angle at failure at greater post-mortem intervals when the hinge was disarticulated by forcing the valves open. The loss of structural integrity of the disarticulated valves was demonstrated by a tendency to fracture under compressive forces into a greater number of fragments for the same input of work at longer, but still brief, post-mortem intervals. The less massive, less convex brachial valves fractured into a greater number of fragments at a lower input of work than the more robust and convex pedicle valves, implying a natural preservational bias of pedicle valve over brachial valves for T. transversa in compression.