The growth rates of ammonites and extinct nautiloids have been estimated in two ways: through analyses of shell growth lines and by analyzing the patterns of oxygen isotopic values from successive septa. In both types of studies, it has been assumed that the amount of time between successive chamber formation events is approximately constant. This assumption has never been tested with living cephalopods, however. To examine this, 10 immature Nautilus pompilius and two immature N. macromphalus were maintained in a surface aquarium for a period of 1 yr and periodically radiographed. The radiographs allowed direct observation of chamber formation events and apertural shell growth. During this observational period 61 separate chamber formation events were observed in the nautiluses. The time between separate chamber formation events increased in successively produced chambers, and varied from a minimum of 2–3 wk in a specimen of 45-mm shell diameter to a maximum of 13–15 wk in a specimen of 132-mm shell diameter. Unlike interval of chamber formation, which increased during ontogeny, rate of apertural shell growth showed no observable rate increase or decrease during ontogeny prior to maturity. With the onset of maturity, as marked by the shell characteristics defined by Collins et al. (1980), apertural shell growth rates dropped markedly, and ceased coincident with the removal of the last volumes of cameral liquid in the last formed, approximated chamber. Both rate of apertural shell growth and septal spacing were affected by degree of shell breakage.

The internal structures of the third metacarpals of Merychippus and Mesohippus are assessed from thin sections and from radiographs, and systems of trabeculae differing in orientation and density are described. The principal forces transmitted to the articular surfaces of these bones are reconstructed and are used to estimate the pressure of contact on each surface. The major correlations made between the structure and the function of the third metacarpal of Equus (Thomason, 1985a) are also observed in this bone in Merychippus and Mesohippus. More important, the differences in trabecular structure among the recent and fossil bones may be interpreted in terms of the differences in inferred function. Thus the functional interpretation of the internal structure of fossil bones may reasonably be attempted.

Gaps in the fossil record can be identified in compilations of stratigraphic ranges of lower taxa classified within higher taxa. Statistical properties of such gaps suggest the following conclusions. First, the random sampling model most commonly used to correct for incompleteness in the record is inconsistent with the data. Second, the decline in taxonomic extinction rate during the Phanerozoic is not just an artifact of an increase in the completeness of the record.

Problems of taphonomy and sampling adequacy hinder direct evolutionary interpretations of pattern in the Precambrian paleontological record; however, molecular studies of microbial phylogeny and comparative physiological and ecological investigations of living microorganisms can be combined with geological research to establish patterns of early evolution. The Late Proterozoic record of planktonic algae resembles those of Phanerozoic plants, animals, and microplankton in its patterns of diversification and turnover, as well as in the importance of major extinction events in shaping the course of evolution. Late Proterozoic eukaryotes thus appear to be discussable in terms of the macroevolutionary issues that have become central to Phanerozoic paleobiology. In contrast, evolutionary patterns in Precambrian prokaryotes appear to be different from those of plants and animals, a possible consequence of their differing systems of genetic organization and recombination.

Systematics, ostensibly the “old” paleontology, actually plays a central and crucial role in modern paleobiology. We argue that a revised ontology has recently clarified the nature of species and has expressly added monophyletic groups to the roster of spatiotemporally bounded entities—“individuals”—that are now seen as participants in the evolutionary process. Systematics is the study of species and monophyletic taxa, and fossils alone provide the data on the temporal boundedness of such taxa.

Cladistics (phylogenetic systematics) is explicitly geared to the recognition of monophyletic taxa. We review aspects of the core problem of character analysis in systematics, particularly addressing the still contended issue of the seemingly competitive claims of three methodologies: out-group comparison, comparative ontogeny, and the “paleontological method.” We find that these methods overlap in their basic assumptions to a significant extent, yet each retains a characteristic and distinctive flavor. They are not all “the same,” nor are they always “complementary”—and no one method is superior to the others in all circumstances.

Far from being the Victorian symbol of a moribund science, systematics lies at the very heart of modern paleobiological research, providing the central data for paleobiology's truly unique contribution, both real and potential, to evolutionary biology in general.

The late Precambrian genus Rangea Gürich, 1929, a frond-like fossil composed of repeated foliate elements, is one of the first discovered forms belonging to the now widely known soft-bodied assemblages characterizing the Ediacaran Period. Rangea occurs together with the genera Pteridinium Gürich, 1933, and Ernietta Pflug, 1966, in the lower parts of the Nama Group, Namibia (South West Africa).

Investigation of the preservation and structure of Rangea, utilizing a methodology similar to that established by Wade (1968, 1971), indicates that it was probably a colonial octocoral consisting of a large tapering primary polyp, or oozoid, and a number of leaf-shaped, conjoined fronds which bore the feeding polyps; it is suggested to belong to a group of early Ediacaran anthozoans which provide a fossil link between the still living Telestacea and Pennatulacea. Similar investigations of Pteridinium and Ernietta disclose that their structure is different from Rangea and does not support ideas that they are related to it.

A nonparametric analysis of the extinction patterns of 10 major marine invertebrate groups at the five most profound mass extinction events leads to five observations: (1) At each event some taxonomic groups were affected much more than others. (2) There is little consistency among events in terms of which taxonomic groups were most or least affected; however, adaptive groupings do exhibit consistency: benthic, mobile organisms suffered significantly fewer extinctions than sessile suspension feeders, while the pelagic organisms apparently suffered the most. (3) There are no convincing patterns of interrelated extinctions among taxonomic groups. (4) No group exhibits a persistent tendency through time for a relative increase or decrease in their extinction rate at the events. (5) Some relationships are seen between the extinction patterns of three pairs of events; the Late Ordovician and Late Devonian events exhibit a significantly similar pattern (the same taxonomic groups suffered the most extinction in both cases) as do the Late Triassic and Late Cretaceous events. The Late Permian and Late Cretaceous events show a significantly inverse pattern (the most affected groups in the former were among the least affected in the latter). Upon examination, these observations, notably 1, 2, and 5, are consonant with current scenarios of the effects of catastrophic bolide impacts on marine fauna.

In the past decade paleobiologists have applied the techniques of both ecological and historical biogeography, although vicariance/cladistic approaches have as yet had minimal impact. The traditional focus of paleobiogeographic study has been the province, a statistical entity defined by clusters of range endpoints of individual taxa. The study of such provinces has been useful in inferring past continental positions (although ambiguities remain that must be resolved using independent geological criteria) and in understanding the role of past global geographies in regulating biotic diversity through changes in the numbers and extent of provinces. This approach can be complemented by the treatment of geographic ranges of taxa as irreducible or emergent traits with far-reaching evolutionary effects upward and downward within a genealogical hierarchy. Temperature tolerances in benthic marine organisms appear to be by-products of selection for enzyme structures imparting favorable activity levels within the normal temperature range rather than direct products of selection for resistance to temperature extremes. Thus geographic range endpoints, which are also influenced by dispersal capability and the resulting scale of gene flow among disjunct populations, are not direct products of selection. However, the magnitudes of geographic ranges of species and clades behave as emergent properties and significantly influence taxonomic survivorship during background and mass extinctions in ways that are not extrapolations of effects at lower hierarchical levels. Biogeography shapes macroevolutionary patterns of origination and extinction during times of normal, background extinction and mass extinction. Preferential extinction among regions or among endemic rather than widespread clades can result in strong biases in the nature of the survivors of mass extinctions, with taxa being lost not because of selection against attributes of individual organisms but because of higher-order patterns of geographic selectivity.

Four main potential contributions of fossils to phylogenetic systematics and historical biogeography are (1) to provide additional taxa which (when sufficiently well preserved) can give new morphological and ontogenetic data in addition to those provided by Recent species; (2) to provide additional taxa which can increase the known biogeographic range of a taxon; (3) to help establish a minimum age for a taxon; and (4) to present fossil biotas that can be examined for biogeographic patterns not recognizable in younger (including the Recent) or older biotas.

The first three points have been expressed or at least implied by other workers and are only briefly reviewed. The fourth point is proposed as a method of using fossil biotas to provide time controls to cladistic studies of historical biogeography. Previously, cladistic vicariance biogeographers have used fossil plus Recent biotas, or the Recent biota alone, for the geographic areas of study. Such investigations that lack any time control in the data base cannot effectively deal with areas that have complex histories as, for example, an earlier area of endemism in which area relationships are later complicated through the addition of exotic taxa by dispersal. By using time controls provided by fossil biotas, we may learn more about the relationships of areas with complex histories and may reveal biogeographical information that is sometimes unavailable through examination of the Recent biota.

In the past decade, evolutionary paleoecology has shifted away from corroborative research of the “me-too-ecology” type toward its proper domain—the evolutionary consequences of ecological properties, roles, and strategies at the individual, population, community, and species levels. The science of evolutionary paleoecology tests for linkage between a species' ecology and its macroevolutionary history. Do the ecological characters of species within clades influence differential rate dynamics, particularly rates of faunal turnover and diversification? Intellectual coequality, once hampered by the misunderstanding that the role of paleoecology is to find examples of past ecology imperfectly entombed in the fossil record, is strengthened by the increasing number of evolutionary ecologists who have called for explicit paleontological contributions to resolve theoretical issues. The fossil record provides a necessary perspective to an understanding of process.

Taphonomy established itself in paleontology primarily as a subdiscipline of paleoecology, but it has evolved into a much broader study of the ways in which preservation affects the fossil record. The past decade has seen a change in emphasis from descriptive taphonomic studies of fossil assemblages to more experimental, process-oriented investigations of necrolysis, stratification, and diagenesis of organic remains in modern environments. These actualistic studies are increasing the sophistication of taphonomic analysis in the fossil record by sharpening the diagnosis of bias in paleontological data and by providing a baseline for quantitative modeling of preservational patterns. The analysis of bias is also expanding into the evaluation of temporal resolution in the fossil record (sample acuity, stratigraphic completeness), and taphonomic research is thus contributing to broad-scale problems in evolution, biogeography, and biostratigraphy. In addition, taphonomic studies are providing new insights into paleoenvironmental reconstruction and into the direct paleobiological significance of post mortem processes such as the behavior of scavengers and the role of dead hardparts in structuring benthic communities. One of taphonomy's most promising new frontiers is comparative analysis applied to different taxonomic groups within assemblages and across environments, tectonic settings, and climatic regimes. All of this currently active research is contributing to a better understanding of the fossil record as the result of a dynamic, evolving, integrated system of biological and sedimentological processes that have both limited and enhanced knowledge of Earth history.

Many questions have emerged recently regarding the importance and methodology of analysis of adaptation. Divergent views reflect both problems of definition and more substantive issues of interpretation. Defining the state of adaptation in terms of its contribution to current fitness, rather than origin by natural selection, is essential if natural selection is to be considered an explanation of adaptation. The context dependency and relativity of fitness apply also to adaptation. Design criteria are essential components of adaptation, but only to the extent that they are subsumed as elements of the causal interactions determining relative reproductive potential. The local, relational, contingent character of adaptation supports only limited reference to improvement. Most long-term patterns of change can be better described as diffusion within a structured design-space than as progressive improvement of design. The analysis of adaptation is part of a broader inquiry into the processes and constraints that control form and the history of changing form. It offers one perspective on how organisms operate on ecological time scales and how their configurations might be maintained or transformed over evolutionary time. Hypotheses concerning adaptation are sometimes tested by reference to predictions concerning the central tendency or trend of some aspect of an anatomical-behavioral system. These can be interpreted with minimal reference to assumptions of optimality if the analysis is viewed in terms of Bayesian inference. However, an alternative and frequently preferable approach to testing relies on limit-oriented predictions. Analysis of adaptation can be visualized as inferring the pattern and nature of interactions comprising the causal plexus that determines fitness. A comprehensive understanding of form and form-change requires that this be integrated with the perspective offered by studies of development, genetics, phylogenetic history, and external perturbations acting on the system.