Many species of scleractinian reef corals deposit aragonite skeletons with cyclic bands of higher and lower density whose periodicity is annual. As these growth bands are frequently preserved in fossil corals, attention has been focused on their possible use as environmental indicators in as much as density variations may reflect changes in water temperature and/or light intensity. Relationships between skeletal growth banding and environmental parameters have been investigated by X-radiographic examination of 1488 specimens of modern reef corals representing 31 reef localities widely distributed over the Indo-Pacific and Caribbean regions. Average monthly seawater temperature and solar radiation data are available for each locality, and the date of collection is known for each sample. Of the 47 genera and subgenera included in the study, density variations were most pronounced in skeletons of Astreopora, Coscinarea, Cyphastrea, Favia (especially species with small corallites such as F. stelligera), Goniastrea, Hydnophora (massive forms only, e.g. M. microconos), Leptoria, Montastrea (especially M. annularis, with small corallites), Pavona, Polyastra, and Plesiastrea. Less useful are Diploastrea, Diploria, and Favites (which tend to have large corallite diameters), and Goniopora, Alveopora, Porites, Siderastrea, and Stephanaria (which frequently exhibit numerous secondary density variations within the annual cycle). Despite considerable variability among different individual corals from the same population, the average thickness of the skeletal growth bands is positively correlated with mean annual water temperature. By comparing characteristics of the outermost growth increment and the date of collection with monthly records of water temperature and solar radiation, it appears that maximum skeletal density is associated with those periods of the year when seawater temperature is above average.

In this paper, we present detailed quantitative studies of evolutionary changes over all or part of the stratigraphic ranges of five fossil radiolarian species from Pacific deep-sea sediment cores. Each of these species shows some variation of a distinctive evolutionary pattern: increase in size of measured morphologic characters, preceded and/or followed by an interval during which little or no significant change occurred.

One of the species studied (Eucyrtidium matuyamai) was allopatrically differentiated from another (Eucyrtidium calvertense). The others (Calocycletta caepa, Pterocanium prismatium and Pseudocubus vema) underwent phyletic change within a single lineage. Those species undergoing phyletic change towards larger size maintained almost constant variability of shell size over long periods of time, including periods of both rapid and extremely slow evolution. This constancy of variability suggests that diminution of selection against larger size may have acted as a stimulus to size increase. In contrast, E. calvertense decreased in variability during evolution towards smaller shell size. We believe this decrease may be interpreted as the result of two factors: (1) strong selection against larger size apparently exerted on this species by its direct descendant, E. matuyamai, during the neosympatric phase of speciation and (2) continuation of previous selection against very much smaller size.

The “niche-variation” model predicts that increase in environmental stability should be accompanied by increase in homozygosity and reduction in morphological variability. All Late Cambrian trilobite biomeres show an increase in regional species diversity from low in the biomere toward the top. This change in diversity is believed to reflect increasing environmental stability and consequently affords the opportunity to indirectly test the “niche-variation” hypothesis in a paleontological context. Measurements were made of eight cranidial features of samples of 17 species populations from the Pterocephaliid Biomere of the Great Basin. Coefficients of variation and a multivariate analog of them failed to reveal a relationship between morphological variability and species diversity. Consideration of these data together with contradictory, but limited, informaton for other organisms suggests that the predicted decrease in genetic variability may either be absent or be readily masked in naturally occurring populations, which typically retain a high degree of genetic polymorphism. If heterozygosity is common, it would appear that accidents of geography, rather than the genetic consequences of stable or unstable environments, are among the primary factors controlling the probability of speciation.

Evidence is presented that primitive artiodactyls had a diploid number of 14. The higher diploid numbers of most living artiodactyls are interpreted as resulting from karyotypic fissioning at the times of past adaptive radiations. The fossil record appears to support this contention.

An evolutionary sequence of unusual X chromosome transformations has been deduced from the differences that exist among extant species. From these, and from interrelationships of karyotypes, certain phylogenetic revisions are suggested.

Mammalian generic, familial, and ordinal diversities correlate significantly with continental area. The area effect is similar in form to that shown for true islands: S = kAz, where S is the diversity, A is the area, and k and z are fitted constants. For mammalian genera and continental area, z equals 0.33, for families, z equals 0.23, and for orders, z equals 0.13.

The area effect permits quantitative modeling of extinction due to biotic competition between previously isolated faunas. The Late Cenozoic extinction of North and South American mammalian faunas following the rise of the Panamanian land bridge is overestimated by seven families. The overestimate may result from assumptions of complete biotic interchange and universal competition. The role of plate tectonics in regulating diversity may be extensively modified by regional environmental conditions.

Analysis of several thousand mammalian fossils from late Pleistocene sediments in California provide data on sampling in mammalian paleoecology. Recovery of bones and teeth from the screenwashed bulk sediment sample residue is considered nearly total. Neither surface collecting alone, nor small bulk samples provide satisfactory quantitative data on original community structure or postmortem alterations in community organization. Minimum sample size for the analysis of diversity is discussed. Diversity and size-trophic ratios of the total identifiable mammalian component of this fauna (N = 1222) are similar to those expected in living communities, and therefore suggest adequate sampling, and minimally biased samples.

The extinction of endemic brachiopods in North America at the end of the Ordovician and recolonization by European species has been related to glacio-eustatic lowering of sea level which disrupted conditions in epicontinental seas. North American species may have been narrowly adapted to relatively stable conditions of broad, tropical shallow seas. European invaders may have been less specialized because they were adapted to conditions in both the open ocean and in narrow European epicontinental seas. Being less narrowly adapted, European species probably were better able to cope with changing environmental conditions than were North American species.

During the Lower and Middle Llandovery, shallow water, low diversity communities of Pentamerus Community depth were unstable and characterized by repeated extinctions and invasions. Following the crisis at the Ordovician-Silurian boundary 3 to 5 million years were needed to reestablish communities that were persistent in geologic time.