In recent articles in this journal Hansen (1980) and Jablonski (1980) discussed the planktonic larval stages of fossil benthic invertebrates and the relation of type of larval development to geographic ranges, nearshore-offshore position, speciation, and extinction. The fossil record provides a view of long term consequences of types of larval development, and the emphasis of these, and other, paleobiological studies was on selection among species which are characterized by different developmental adaptations.

The prices of scientific books are much talked about, but data to serve as points of reference on the subject are hard to come by. Table 1 shows the results of some attempts to find such data. The first row of data given is taken from the most frequently cited set of statistics on book prices, the average per-volume prices of hardcover books (U.S. domestic and imported) published annually by the R. R. Bowker Company. The Bowker tabulation attempts to be exhaustive but includes under “science” (i.e., Dewey Decimal 500–599) books intended for general audiences and therefore can be expected to underestimate the prices of books needed by working scientists.

The Field Museum of Natural History, Chicago, held a conference on Macroevolution, October 16–18; it was organized by J. Cracraft, J. Levinton, N. Eldredge and D. M. Raup. The nature of the meeting called to mind the 1946 Princeton conference on Genetics, Paleontology and Evolution (which resulted in the book of the same name1), and indeed 3 members of that conference spoke again, 34 years later, in 1980—Sewall Wright, G. Ledyard Stebbins, and Bobb Schaeffer. However, no book is planned this time.

The presumed geometry of clam and brachiopod clades (brachiopod declines matched closely by clam increases) has long served as primary data for the classic case of gradual replacement by competition in geological time. Agassiz invoked the geometric argument to assert the general superiority of clams, and it remains the standard textbook illustration today. Yet, like so many classic stories, it is not true. The supposed replacement of brachiopods by clams is not gradual and sequential. It is a product of one event: the Permian extinction (which affected brachiopods profoundly and clams relatively little). When Paleozoic and post-Paleozoic times are plotted separately, numbers of clam and brachiopod genera are positively correlated in each phase. Each group pursues its characteristic and different history in each phase—clams increasing, brachiopods holding their own. The Permian extinction simply reset the initial diversities. The two groups seem to track each other in each phase and a plot of brachiopod vs. clam residuals (each from their own within-phase regressions against time) yields significantly positive association. Some of this tracking may be an artifact of available rock volumes; we could, however, detect no effect of stage lengths. Passive extrapolation of microevolutionary theory into the vastness of geological time has often led paleontologists astray. Competitive interaction may rule in local populations, but differential response to mass extinctions (surely not a matter of conventional competition) may set the relative histories of large groups through geological time. Similarly, adaptive superiority in design cannot, in the usual sense of optimal engineering, have much to do with the macroevolutionary success of clams. The interesting question lies one step further back: what in the inherited Bauplan of a clam permits flexibility in design and why are other groups, however successful in their own domain, unable to alter their basic design.

In evaluating the biotic effects of transgressions and regression, care must be taken to ensure that observed patterns are not simply an artifact of the location of available stratigraphic sections along an ancient onshore-offshore gradient of adaptive types. Analysis of Recent bivalves suggests that very nearshore benthic assemblages are dominated by species that are geographically more widespread, are more eurytopic, and more often have planktotrophic larvae than species in offshore assemblages (Jackson 1974; Jablonski and Valentine 1980); this pattern may serve as a null hypothesis for paleobiogeographic analysis. Late Cretaceous bivalve and gastropod faunas of the Gulf and Atlantic Coastal Plain exhibit decreasing levels of endemism and increasing mean geographic range over the course of regression and return to high levels of endemism and low mean geographic range with the succeeding transgression. In addition, species with longer durations are more frequent at peak regression, while geologically shorter-lived species are more prevalent at peak transgression. As seen in Recent examples, the molluscan assemblages from nearshore facies have a higher proportion of species with broad environmental tolerances and planktotrophic larvae, and thus more extensive geographic and stratigraphic ranges, than do the more offshore shelf assemblages. Because late regressive phases are represented only by very nearshore facies, these directional changes in biogeographic and evolutionary characteristics are most parsimoniously interpreted as a reflection of the nature of the facies available for sampling rather than biotic effects of transgression and regression.

Rates of modern sedimentation in various depositional settings have been compiled and adjusted for compaction for the purpose of estimating the spans of time represented in thin stratigraphic samples. Owing to discontinuous or low rates of sedimentation, it is either impossible or impractical to recover a continuous series of discrete life assemblages of fossil populations by collecting microstratigraphic samples from continuously fossiliferous intervals. Assemblages that are less time-averaged may be recovered from discontinuous records formed in depositional environments with higher rates of intermittent sedimentation, but these are isolated in time and cannot be used to observe the dynamics of local faunal history. Patterns of fossil distribution may appear similar to patterns of living populations explained by neontologic processes, but the longer time scale of even the best fossil sequences suggests the action of uniquely paleontologic processes that may be driven by environmental changes.

A general model of taxonomic diversity, incorporating diversity-dependent rates of origination and extinction, is constructed to examine the dynamic responses of diversity to perturbation. The model predicts that the trajectories of diversification increase and decrease are substantially different. The trajectories of diversity during disequilibrium conditions are displayed in phase diagrams to permit a simple graphical analysis of stability. A positive displacement of diversity from equilibrium results in a rapid decline in diversity and may involve an initial overshoot of the equilibrium condition. A negative displacement of equal magnitude results in a gradual increase in diversity. The model is expressed as a nonlinear difference equation to incorporate intrinsically a delay time due to the characteristic noninstantaneous response of origination and extinction. The model initially assumes a parabolic curve expressing total taxon origination rate as a function of diversity. A second model, constructed assuming a sigmoidal total taxon origination rate derived from considerations of allopatric speciation, enhances the asymmetry of the diversity response. The delayed recovery of the Triassic fauna is shown to be characteristic of return to equilibrium from an undersaturated condition, whereas the more rapid “catastrophic” decline in the Late Permian fauna is shown to be characteristic of return to equilibrium from the oversaturated condition. It is proposed, although not assumed, that perturbation may include a degree of selectivity related to the dispersal abilities of organisms, thereby enhancing the observed asymmetry.

It is often assumed that, if a few species are introduced into a relatively empty environment, the subsequent diversification will take the form of a logistic growth curve, rising to an equilibrium level of species richness. The diversifications of taxa in higher categories commonly resemble logistic curves, although there are no well-defined theoretical bases for such a resemblance.

A model of diversification of taxa in higher categories is based on the notion that many taxa originate rapidly. Relatively small changes leading to new species occur at a high frequency, while larger changes leading to progressively higher taxa occur with progressive rarity. During diversification in an empty environment, few large changes will occur before the environment is filled. The rate of filling, relative to the rate of production of higher taxa, determines the richness of taxa in higher categories and gives the diversification curves a logistic appearance although the maximum level achieved is not an equilibrium. Subsequently, opportunities for diversification will generally lead only to the appearance of taxa in progressively lower categories.

Many apparent homeomorphs have been recognized among genera assigned to the Paleozoic stenolaemate bryozoan orders Trepostomata and Cryptostomata. Morphologies are evaluated to determine whether such homeomorphy should be expected, or is likely to have resulted from incomplete taxonomic analysis. Historical and constructional constraints prevalent in the phylum appear to provide ample opportunity for adaptive convergence, a conclusion supported by the occurrence of similar morphologies in distantly related post-Paleozoic bryozoans.

Cryptostomes are distinguished in part by the presence of restricted budding loci. Loci pattern is hypothesized to be the key innovation in the establishment of the clade and the pattern also is considered critical to the evolution of the relatively slender branches and short zooecia typical of cryptostomes.

Loci development does not provide a taxonomic panacea. This is because the hypothesis does not preclude convergent evolution of broadly similar restricted loci in Paleozoic non-cryptostome groups, although presumably the cryptostomes in general would have been best equipped to succeed under conditions favoring restricted loci.

Environmental conditions for the cryptostomes in general and changing life history strategies for rhabdomesoids in particular provide possible controlling factors for the evolution of these bryozoans.

Stick-like bryozoans from 1 to 5 cm tall, and of varying degrees of colony robustness, are common in deposits from Ordovician through Cenozoic in age; their occurrence has been used to infer strength of bottom currents. Three species which are modern analogues of this mode of growth occur abundantly at subtidal depths near Friday Harbor, Washington; we studied one of these forms, the calcitic cyclostome Heteropora pacifica. Branch diameter was used as an indication of colony robustness because it can be measured in both living and fossil material. Branch diameter decreases significantly with depth (in collections from approximately 9, 15 and 30 m depth) at each of 4 transect localities.

At each locality, currents 6 to 10 cm above the bottom were measured continuously in water depth of ≃ 15 m, for several hours at a time. Under these conditions, the maximum sustained current through the several hour tidal cycle was 70 to 90 cm/sec at one locality, and 20 cm/sec or less at each of the other 3 localities. Suspended matter was determined at heights of 0.2, 0.5 and 1.0 m above the bottom. The amount of suspended matter 0.2 m above the bottom was 40 to 45 mg/cm2/day at the locality with the high current (depth of 15 and 30 m), and usually 5 to 10 mg/cm2/day at the localities with the low current (depth 15 and 30 m). Despite these several fold differences in current strength and suspended matter between localities, for any given depth bryozoan branch diameter does not vary. Branch breaking strength (23 MN/m2) and elastic modulus (30 GN/m2) were measured using small (.16 mm) strain gauges affixed to dry branches of Heteropora. These values are typical of carbonate skeletons of corals. Although Heteropora branch diameter (and colony robustness) decreases significantly with depth, this trend probably is unrelated to current strength.

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.

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.