The founders of North American vertebrate paleontology, F. V. Hayden, Joseph Leidy, E. D. Cope, O. C. Marsh, and their colleagues, collected and described the first suites of fossil mammals obtained from the rich Tertiary successions of the western United States. Among them were remains of fossil horses, and subsequent study of these resulted in an interpretation that supported the concept of Darwinian gradualism as the major mode of evolution. The fossil record of horses also contributed importantly to the demise of orthogenesis as an evolutionary pattern, and to the evaluation of evolutionary rates and long-term evolutionary trends in a major phyletic group of organisms.

Few would argue with the assertion that within the practice of comparative morphology, the comparison of shapes is fundamental to any line of synthesis in paleontology. Yet the common act of such a comparison involves a great range of judgments concerning the homology, correspondence and divergence of form of various parts of any two related shapes. Considerations of similarity must include the scalar effects of size and material, the conversion of proportions as descriptive geometric dimensions to those useful numerical values that will be represented as ratios of measured distance (relative or compared against a standard), and, by no means insignificant, the judgment about the design or functional geometry implicit in the static as well as dynamic systems being measured. This review is concerned with these considerations and with quantitative comparisons of biological shape wherein some parts of specimens obviously have changed and others parts have not.

Fine-scale sampling and analysis of fossiliferous sequences have been used in the debate over gradual vs. punctuated evolutionary transitions between species. The time scale and completeness of these studied sequences can be evaluated using criteria based on compilations of sedimentation rates over different time spans. A set of procedures, herein termed “resolution analysis,” provides the means for estimating the time scale and quality of sequences from which evolutionary patterns are distilled. Seven such published studies are evaluated with these procedures. In general, most fossil sequences are too incomplete on fine time scales to show changes operating within a standing population. Short segments of some sequences have the potential to document nearly complete morphological histories on time scales approaching generation-to-generation processes. Resolution analysis is a necessary step in inferences regarding fossil evidence of evolutionary tempo and mode.

Stratigraphic incompleteness necessarily results from the episodic nature of sedimentation. Many stratigraphic gaps result from minor, temporary shifts in sediment distribution, though other, more profound gaps result from changes in habitat conditions that must have had an effect on local biotic distribution. Analyzing paleontological patterns involves not only the positive evidence provided by fossiliferous strata, but also the negative evidence left as gaps by shifting habitat conditions. Thus, incomplete sequences may not be “flawed” records of continuous populations. Incomplete sequences may be a faithful, literal record of separate populations separated in time by local extinctions and re-invasions.

It is shown that the abundant Jurassic oyster Gryphaea provides material adequate to test biogeographic and evolutionary hypotheses involving speciation. Phyletic size increase is widespread if not characteristic and tends to be marked by a sharp initial increase followed by a longer period of stability. The larger size of phyletically younger forms is apparently because of greater age of individuals rather than a higher growth rate. Species durations fall within the range of the majority of Jurassic bivalve species. The detailed study of European Gryphaea indicates a pattern of punctuated equilibria allied with morphological trends, some of which are paedomorphic. Gradualistic, species selection and cladistic models of change are not supported. World-wide analysis of Gryphaea species supports centres of origin and migration rather than vicariance, and a relationship exists between migrational and evolutionary events and changes in the physical environment.

A survey was undertaken of the developmental types of the neogastropod families Volutidae, Fasciolariidae, Nassariidae, Mitridae, Buccinidae and Olividae in the Palaeocene and Eocene series of the Gulf of Mexico. Although the families were dominated by planktotrophic development in the Paleocene, most show a general increase in numbers of species with nonplanktotrophic development through the Eocene. Present day environmental correlations with larval development do not adequately explain the observed shift in developmental types in the Early Tertiary. It is proposed that higher speciation rates for nonplanktotrophs and a unidirectional trend in developmental change may account for the progressive increase of nonplanktotrophic development.

Shell form is not strictly linked to life habits in modern marine turritelliform gastropods. To test the usefulness of various morphological characters in determining life-mode, I present a set of predictions giving the expected distribution of characters occurring in turritelliform snails with three different life-modes. Burrowing species should lack sculpture, possess columellar folds and a flat whorl profile, and have an orthocline or prosocline aperture. Mobile epifaunal forms should have sculpture, a rounded whorl profile, a displaced tangential aperture and a smooth columella. Sedentary forms should resemble epifaunal forms but have non-tangential apertures. These predictions were tested with a sample of 105 Recent marine species. Each hypothesis was found to be a statistically valid generalization and in 92 of the species (88%) the life habits were correctly predicted. Accuracy may be further improved by considering additional features such as ratchet sculpture and disjunct or open coiling. These patterns of shell form can be used to interpret fossil species as burrowers, or as sedentary or active epifaunal forms. For example, the unusual Devonian murchisoniid gastropod Ptychocaulus verneuili is interpreted as an active burrower.

The relatively imperfect relationship between shell form and life-mode in turritelliform gastropods, as compared to the Bivalvia, apparently results in part from the behavioral complexity of the Gastropoda. Gastropods have a repertoire of activities which would place them in different life-modes at different times; snail morphology reflects this complexity.

Growth rhythms are described in the accretionary skeletons of Rafinesquina alternata, a Late Ordovician brachiopod from southeastern Indiana. Contiguous growth increments widen and narrow in repeating series, giving the appearance of adjacent clusters of increments. Fourier analyses of growth increment widths and counts of the number of increments within individual clusters yield similar periodicities. Increments vary in width over a period of approximately 19 increments, modulated with a lower amplitude oscillation of 27 increments. The number of increments per cluster falls into two groups; clusters having between 8 and 17 increments outnumber those having between 18 and 30 increments.

All specimens were obtained from a Maysvillian facies of the Dillsboro Formation, previously inferred to represent a shallow subtidal environmental setting. The growth periodicities described here are consistent with this interpretation. The intensity of tidal parameters such as emersion-immersion cycles, substrate shifts, changes in nutrient supply or in oxygen tension declines with depth as would the number of growth increments added each month in response to these factors. Thus, for these specimens, the maximum number of increments per cluster probably approximates the true number of “tidal” days in the Late Ordovician synodic month (period between full moons).

The paleoecological model derived from these analyses can be used in future studies to predict the rate of the earth's rotation and the motion of the moon in the Late Ordovician and, equally importantly, to evaluate the limits of uncertainty of such studies.

Associations of bathymetrically anomalous fossils, a phenomenon particularly common in shallow-water, marine, Neogene faunas of the northeastern Pacific, have yet to be explained adequately. No known physical transport processes can selectively move species upslope from deep water into diverse nearshore, shallow-water habitats. Previously proposed biological explanations are based on undocumented phenomena. We document bathymetric anomalies in Recent mollusc accumulations on Southeast Farallon Island, California, that are created by the activities of diving marine birds. Application of these observations to patterns in the Neogene fossil record is direct, involving the same genera and often the same species. We argue that the process has occurred since at least the Miocene when diving marine birds radiated rapidly, probably in response to trophic resources created by intensive upwelling (Lipps and Mitchell 1976) and that they could have transported specimens upslope in sufficient quantity to have contributed anomalous species to the Neogene fossil record. Specific examples from the literature are discussed.

The siphuncular tube is a key component of the buoyancy control and mechanical strength systems in both Nautilus and fossil cephalopods. We measured the rate of hydrostatically induced fluid flow across the tube wall and tube rupture strength of Nautilus pompilius at hydrostatic pressures in the range of 10–85 bars. We found that in fresh, undecayed tubes, rupture occurs at pressures of about 80–85 bars. This is equivalent to the strength of the shell proper and to the depth limit of the live animal. The siphuncular tube is neither markedly stronger, nor weaker, than the shell. Siphuncle rupture strength is constant in the last 20 chambers of the shell despite a strong decrease in the siphuncle strength index (ratio of tube thickness to radius). The notion that strength index gives an accurate indication of tube strength is therefore in error. This suggests that the geometry of the siphuncular tube can not be straightforwardly used as an index of living depth in fossil cephalopods. Rupture occurs at the siphuncle-septum contact. The junction of the tube to its mechanical supports is thus weaker than the tube itself. Measured flow rates are in the range of 1–20 ml/h/chamber. Flow rates increase linearly with applied pressure and in successively larger chambers as a result of size-related variation in surface area and thickness of the tube wall. Rates of osmotic pumping in live animals are up to three orders of magnitude lower than hydrostatically induced flow rates across the siphuncular tubes of empty shells. Pumping capacity of live animals is apparently limited by functional constraints of the osmotic pump rather than by the fluid conductance properties of the tube wall. Living depth in evolving cephalopod lineages may be limited ultimately by physiologic or chemical restrictions of the osmotic pumping mechanism rather than by mechanical strength of the shell or siphuncle.

Liquid removal rates in chambers of the living cephalopod Nautilus depend on two factors: the surface area of siphuncular epithelium exposed to liquid in the chambers and the buoyancy of the specimen. In Nautilus made artificially heavy, liquid removal rates are increased as much as five times above neutral buoyancy rates in surface aquaria. Although chamber volume increases faster than siphuncular surface area in successively larger chambers, the increase is small, especially in the last formed dozen chambers. Under conditions of constant liquid removal per unit area of siphuncular epithelium, this means that removal rates of liquid from any two or three successive chambers are nearly constant.

Nautilus shows ranges of chamber volume/siphuncular surface area ratios of .04 cc/mm2 (early, small chambers) to .12–.14 cc/mm2 in late, large chambers. These values are not characteristic of all chambered cephalopods. Comparison of extinct chambered cephalopod taxa with Nautilus indicate a variety of volume/area ratios for similarly sized chambers.

The degree to which the relative abundances of the species in a fossil assemblage represent those in the living community from which it came is an indication of the fidelity of the assemblage in preserving most of the aspects of community structure that we may hope to find in the fossil record. I have developed a model for the formation of attritional fossil mammal assemblages that shows that the logarithm of the number of individuals of each species in an ideal unbiased assemblage, when regressed on the logarithm of body mass, will exhibit a slope of approximately −1.05 ± 0.25 (approximate 95% confidence interval). This value is based upon ubiquitous scaling relationships of population density and turnover rate with body mass among extant mammals. These relationships are the results of widespread energetic and metabolic regularities in community structure and physiology and can be expected to have been essentially the same in the remote past. The slope of −1.05 provides for the first time a reference standard for community structure of sufficient generality for use in the analysis of this aspect of fossil assemblages. We can use this value as a sort of “null hypothesis” of no bias against which we can compare actual fossil assemblages.

Analysis of some promising assemblages reveals that they exhibit badly biased relative abundances. However, it is likely that in these cases we can explain this bias as almost entirely the result of pre-burial differential destruction of the carcasses of different-sized species.

The combination of this new, biological approach with the largely physical approaches of taphonomy and sedimentology will allow us to ask more specific questions about bias in fossil assemblages, avoiding circular arguments. We can now distinguish, in a large number of situations, assemblages that preserve reliable community-structure information from those that do not.

Diachronic variation in insectivore remains from a deeply stratified cave deposit in southeastern North America is described. The paleobotanical record for the region is congruent with variation in the soricid (shrew) and talpid (mole) faunal assemblages. Both faunal and floral records reflect considerable climatic change since the full Wisconsinan in this unglaciated portion of eastern North America. Variations in the insectivore assemblages indicate the presence of a more equable climate during the late Pleistocene. Continental climates ushered in at the end of the Pleistocene resulted in a marked decrease in insectivore diversity. Relative frequency changes in taxa throughout the Holocene reflect the mid-Holocene Climatic Optimum.