THE ORIGINS OF FOSSIL ASSEMBLAGES: TESTING THE FOUNDATIONS OF PALEOBIOLOGY

Most fossil assemblages are formed by the accumulation of post-mortem remains and the winnowing of material through taphonomic processes over a period of time-averaging. A perfect (or iso-taphonomic) fossil assemblage should record the biological productivity of a community. If all of the taxa in the living community have the same survivorship curve (i.e., lifespan), then the living and the dead assemblages should be correlated. If taxa have different preservation probabilities and/or life-spans, then death assemblages should not be expected to mirror the living communities that produced them.

Rather than test "the fidelity of the fossil record", I propose a simple mechanistic model of the origin of fossil deposits that enables us to test the null (and really useful) hypothesis: "the censused live-community cannot be distinguished from the biological communities that created the dead assemblage." In well-mixed lagoon molluscan assemblages (central Great Barrier Reef, Australia) taxon-specific probabilities of preservation typically differ by 2x and can differ by up to 4x, whereas taxon-specific differences in annualised production typically differ by 8x and can differ by up to 32x. These results indicate that uncertainties associated with our understanding of life-history exceed those associated with taphonomic processes. This test suggests that differences in life-history are more important than taphonomic differences when comparing living molluscan communities to their fossil records, and that the assumption of similar survivorship amongst the formerly living may be more important to paleontological comparisons than assumptions of similar taphonomy.