Using a geometric model of shell morphology, it is demonstrated that biconvex brachiopods occupy only a small region of the potential geometric space available to organisms with planispiral exoskeletons composed of two articulated valves. Measurements taken for a sample of 324 genera of the articulate orders Pentamerida, Rhynchonellida, Spiriferida, and Terebratulida were analyzed using a simple geometric model of shell form and ontogeny. The frequency distribution of brachiopod shell morphologies exhibited by the four orders represents the biological optimization of the spatial relationships between area and volume. Biconvex brachiopods develop shells which are designed to minimize shell surface area while maximizing internal shell volume. The means by which optimization is achieved is related directly to the effects of increase in absolute size during ontogeny. The boundaries upon shell geometries utilizable by biconvex brachiopods are determined by (1) limitations of articulation, and (2) limitations of surface and volume.

Worn enamel surfaces of the cheek teeth in fossil and recent rhinoceroses are characterized by fine, parallel ridges aligned perpendicular to the enamel-dentin interface. We show that these ridges result from an unusual enamel ultrastructure in which a primitively horizontal layering of the prisms has become vertical. The new structure apparently appeared between early and middle Eocene, at the time when the superfamilies of perissodactyls were rapidly diverging. Similar modifications of the enamel structure occurred in certain parts of the cheek teeth in tapiroids, chalicotherioids and brontotherioids, but hardly at all in the equids. The modified enamel structure, where it occurs in groups other than rhinocerotoids, is associated with lophs but not cusps. Experimental evidence shows that the modified enamel is more resistant to wear than the unmodified enamel. The consistent association with thin lophs rather than cusps suggests that the modified enamel evolved to prolong the life of the lophs, where occlusal pressures are highest and attrition greatest. The dominance of modified enamel in rhinocerotoids correlates with the higher degree of compression of the cusps and extreme lophodonty in this group. The absence of modified enamel structure in the equids, even in the ectoloph, correlates with the lesser importance of the ectoloph in equids relative to brontotherioids, chalicotherioids and rhinocerotoids.

Bone-collecting behavior in the harvester ant, Messor barbarus, has been observed for the first time. Excavation to the depth of the packed substrate of a single ant hill yielded 1167 modern bones derived from nine or more species of small vertebrates. Since harvester ants of various species are well-known from the Americas, Africa, and Eurasia, ants may have served as important agents of concentration for micromammal assemblages in the fossil record. Analysis of the faunal and skeletal representation of the ant hill assemblages reveals characteristic patterns that might be used to distinguish such assemblages from those collected by avian or mammalian predators.

Models for the areal distribution of marine animals may be formulated in such a way that their validity can be tested statistically. Five such models are described here: in each case the distributions of the individual taxa are made functions of depth of water, oceanicity, and substrate type.

The simplest model proposes that benthic species are substrate-dependent: it can be verified by a series of χ2 tests. Benthic species can also be seriated along an environmental gradient: this second model can be tested by using a Monte Carlo simulation procedure. The third model proposes that planktic species are to some degree stratified in the water column, and hence that their remains are distributed additively in the underlying sediments: tests on modern and sub-fossil data sets indicate that realistic versions of this model are probably valueless for most geological work. The final models are extensions of the additive model: they are used here to demonstrate the importance of selecting an appropriate model and, in particular, of knowing the mode of life of each species before the model is selected.

During the past 20 years, paleobiology has established the foundations of a nomothetic science based upon evolutionary theory. This radical break with a past philosophy based on irreducible historical uniqueness is still impeded by (1) overreliance upon the inductivist methodology that embodied this previous philosophy, and (2) an unadventurous approach to biology that attempts passively to transfer the orthodoxies of microevolutionary theory across vast stretches of time and several levels of a hierarchy into the domain of macroevolution. I analyze the major trends of recent invertebrate paleobiology in the light of these two impediments. The formulation, by paleobiologists and with paleobiological data, of new macroevolutionary theories should end the subservience of passive transfer and contribute, in turn, to the formulation of a new, general theory of evolution that recognizes hierarchy and permits a set of unifying principles to work differently at various levels.

Growth increments in bivalve shells have been used in geophysics and paleoecology. However, little study has been given to the variability of increment patterns within and between shells. The variability of increment patterns is examined visually and quantitatively, with the help of a serial correlation computer program. Analyses of increment patterns of the bivalves Chione fluctifraga and Protothaca staminea (Veneridae) indicate that: 1) quantitative results complement the visual observations; 2) increments are not consistently detected during successive measurements; 3) a striking similarity exists between right and left valves of the same specimen; and 4) different specimens collected from the same natural environment do not show any one-to-one increment relationship—however, increment width trends may be present. The variation of increment patterns seen between specimens suggests caution in the use of bivalve increments in paleoecology.

The modern synthesis, as an exclusive proposition, has broken down on both of its fundamental claims: extrapolationism (gradual allelic substitution as a model for all evolutionary change) and nearly exclusive reliance on selection leading to adaptation. Evolution is a hierarchical process with complementary, but different, modes of change at its three major levels: variation within populations, speciation, and patterns of macroevolution. Speciation is not always an extension of gradual, adaptive allelic substitution to greater effect, but may represent, as Goldschmidt argued, a different style of genetic change—rapid reorganization of the genome, perhaps non-adaptive. Macroevolutionary trends do not arise from the gradual, adaptive transformation of populations, but usually from a higher-order selection operating upon groups of species, while the individual species themselves generally do not change following their geologically instantaneous origin. I refer to these two discontinuities in the evolutionary hierarchy as the Goldschmidt break (between change in populations and speciation) and the Wright break (between speciation and trends as differential success among species).

A new and general evolutionary theory will embody this notion of hierarchy and stress a variety of themes either ignored or explicitly rejected by the modern synthesis: punctuational change at all levels, important non-adaptive change at all levels, control of evolution not only by selection, but equally by constraints of history, development and architecture—thus restoring to evolutionary theory a concept of organism.