The Nature of the Fossil Record: A Biological Perspective

Paleontology can be a rich source of theory and data on evolutionary and ecological processes at more inclusive hierarchical levels and greater time scales than those available to the neontologist. Although the generation-by-generation record of ancient populations and communities is obscured by inconstancy of sedimentation and bioturbation, the record of lager-scale patterns of intra- and interspecific morphological change (and stasis) can be analyzed with confidence when sampling schemes — and the questions being asked — allow for the discontinuous nature of the rock record and the difficulty of precise time correlation among localities. These considerations permit the analysis of such diverse problems as the evolutionary consequences of different genetic population structures (e.g., fragmented vs. panmictic) or genetical systems (e.g., sexual vs. asexual); the intrinsic and extrinsic factors giving rise to a bias towards stasis or gradualism within the species of a given group; and the origin, persistence, and cohesiveness of different ecological communities and community types. The rich morphological data of paleontology (generally only hardparts, although some extraordinary localities provide a far more complete record) yield insights into the pattern of occupation of morphospace through geological time and into the ways in which differential speciation and extinction generate evolutionary trends in groups dominated by morphological stasis. The smooth extrapolation of microevolutionary processes evidently also fails to explain the evolutionary consequences of mass extinction events, which are more frequent, more disruptive, and more important as agents of faunal replacement than previously thought. In its direct study of inclusive levels and long time intervals and of large and rare events that only repeat sufficiently often in the fulness of geological time, paleontology yields a wealth of phenomena not accessible to neontology and promises a fruitful union with microevolution and ecology for a more comprehensive theory of organic change and stability.