A population of shells of the Cretaceous oyster Agerostrea mesenterica was obtained from a single locality. The age at death for each shell could be determined, and the population was deemed to be essentially undisturbed and capable of providing a mortality record of the local population averaged over a span of time. We measured four morphometric characters which, on the basis of a functional morphologic model, could be expected to have adaptive value. The frequency distribution of each character was analyzed separately for the three year old and for the six year and older specimens in order to determine which individuals died young and which survived to old age. Ontogenetic effects were separated from those of differential mortality by independent means. The results indicated that there was (1) directed selection for maximum curvature, (2) centripetal selection for a plica number of about 8, and (3) a net centripetal effect on both arc length and plica height, composed of selection against largest values coupled with a possible selection against smaller values that cannot be separated from ontogenetic effects. Only the selection for maximum curvature and optimal plica number can be reconciled with the predictions of the model.

The fossil record of Phanerozoic brachiopod genera and Late Cenozoic New World mammal genera is examined for evidence of evolutionary equilibria. One necessary (but insufficient) condition is met: within temporal intervals, numbers of originations correlate with numbers of extinctions. Eliminating temporally short-ranging brachiopods, however, reduces the correlation so that it explains only 16% of the variation. More decisive tests of the equilibrium hypothesis appear impossible with available data. Difficulties of temporal and geographic scale, taxonomic level, and ecological consistency must be resolved before equilibrium models can be applied in paleontology for other than inspiration.

The history of life is replete with apparent order. Much of this order may reflect the deterministic causes conventionally invoked, but we cannot be sure until we measure and subtract the order that arises in simple random systems. Consequently, we have constructed a random model that builds evolutionary trees by allowing lineages to branch and become extinct at equal probabilities. We proceed by dividing our simulated tree into clades and by comparing their sizes and shapes with the patterns exhibited by “real” clades as recorded by fossils.

We regard the similarity of real and random clades as the outstanding result of this comparison. In both real and random systems, extinct clades arising after an “ecological barrel” had been filled have their maximum diversity at the midpoint of their duration; clades arising during the initial “filling” reach an earlier climax during this preequilibrial period of rapid diversification. However, some potential differences also emerge. Clades still living are much larger than extinct clades. We may attribute this to the morphological superiority of survivors, but we can also simulate it in a model that chooses the originators of clades at random. Real clades undergo greater fluctuations in diversity than do random clades, but the effect is not marked.

Diversity data from stochastic phylogenies and from uniformly spaced Gaussian curves were subjected to Q-mode factor analysis in order to determine whether a few factors would account for a large percentage of the original variance. In both analyses, a small number of factors show systematic variations in time and account for more than 90% of original data variance. To further study the question of evolutionary pulsations, turnover rates were calculated between successive samples. These turnover rates indicate that stochastic phylogenies have pulses similar to those recorded in the fossil record. Large scale environmental changes are not required to explain such pulses. Therefore the observed existence in the real world of biologic diversity associations and evolutionary pulsations can as equally well be accounted for in a stochastic world (in which each species is an independent variable) as in a deterministic world. This supports the notion that there may be stochastic laws in paleontology akin to the gas laws of chemistry.

In the fossil record, biogeographic data at the species level are normally not adequately preserved to be utilized in the reconstruction of marine paleoprovinces; consequently, higher taxa are employed. Thus it is cogent to question whether modern marine provinces, which are generally recognized by their species content, are still distinctive at higher taxonomic levels. Similarity coefficients computed from the bivalve and gastropod faunas of six contiguous and five spatially separated modern provinces indicate that the present-day marine provinces are in fact recognizable at the generic and in most cases at the familial level. The deficiencies and biases of the fossil record obscure the distinctiveness and reduce the precision with which ancient provinces can be delimited. Nevertheless, paleoprovinces that are recognized from the distribution patterns of genera and families are clearly comparable to modern provinces that are determined by species distributions.

An analysis of the geographic and stratigraphic distribution of nearly 200 Jurassic bivalve genera leads to a number of new discoveries. Similarities between regions reached a maximum in the middle of the period, while the percentage of endemism correspondingly decreased. Diversity increased through the Lower Jurassic to a level which remained more or less stable from Middle Jurassic times onwards, while the origination rate shows the opposite trend. Extinction rate increased early in the period to a maximum in the Pliensbachian and fell thereafter to a low value until the Tithonian, which is marked by a sharp rise. The overall taxonomic composition of the fauna in terms of orders remained substantially stable throughout the period. The relationship with facies is discussed and three major ecological groups distinguished: marginal marine (euryhaline), shallow neritic and deep neritic. Certain pterioids have a very wide distribution and the order as a whole has a significantly higher proportion of cosmopolitan to endemic genera than any other order; the hippuritoids and trigonioids have the highest proportion of endemics. Five faunal provinces are distinguished, and the dominant control on distribution considered to be sea level. Times of high sea level were marked by widespread distribution of taxa and low endemism. High extinction rates were provoked both by regression (in the Tithonian) and by a sharp rise of sea level in the Toarcian, marked by the widespread onset of anaerobic or near-anaerobic conditions in many epicontinental seas. Some latitudinal control is recognised, notably for the hippuritoids and other stenotopic thick-shelled genera, which are confined to low latitudes.

Modern crinoids are dominated by the comatulids (unstalked forms) which range from the intertidal to abyssal depths. Modern stalked crinoids are restricted to depths greater than about 100 m. In the geologic past some stalked crinoids lived at depths of a few tens of meters or less in reef and bank environments. The primary vehicles postulated for the post-Triassic radiation of comatulids are lack of permanent fixation to the substratum and the capacity for mobility. Development of complex muscular articulations has enabled crawling or swimming which serve in habitat selection and avoidance of stress and predators. These and other adaptations may have bestowed on comatulids a higher survival capacity in shallow-water environments compared to stalked crinoids. Modern stalked crinoids lack mobility and complex behavioral adaptations seen in comatulids. Possibly, stalked crinoids in shallow water were unable to cope with the radiation of abundant, predaceous bony fishes in the late Mesozoic and became restricted to greater depths while the more adaptable comatulids gained ascendancy in shallow water.

Implosion of 47 epoxy-sealed shells of Nautilus pompilius indicates that very young shells (20-30 mm diameter at last septum) can withstand 136 atm pressure (= 1360 m equivalent depth), but intermediate and mature shells (30-145 mm diameter) implode at approximately 30–70 atm (= 300–700 m). Strain gages attached to the shells during implosion tests show that the flank and venter are compressed by external pressure, but the septum undergoes tension and structurally should be the most vulnerable to hydrostatic pressure. Overall shell strength is substantially less than reported values of tensile strength (approximately 364 atm) and compressive strength (approximately 1561 atm) of the constituent shell material, nacre. Shell strength as a depth limiting factor appears to be controlled by shell and septal architecture and by stress concentrators such as flaws and microstructural inhomogeneity. The wide range in implosion values and lack of strong correlation between such parameters as septal thickness and implosion pressure indicate that determination of depth ranges for fossil cephalopods may be difficult.

Colonies of Late Paleozoic lyre-shaped fenestrate bryozoans began growth on rigid substrates which were on the sea floor. After production of a basal disc, a fenestrate network developed in the shape of an erect bowed fan. The fenestrate fan was initially concave on the apertural side, but the curvature reversed a few millimeters above the base. Colonies were then separated along or just above the basal disc, and rested directly on the sea floor. The zooecial apertures were directed upward. The lateral margin of the fan grew to form the supporting struts of the soon-to-be lyre-shaped colony. An open vault formed below the upwardly bowed fan.

Lyre-shaped colonies are interpreted to have lain on the sea floor so that each had the proximal end on the upcurrent side. Feeding zooids were on the upper surface and pulled water through their expanded tentacles. The filtered water passed through the fenestrules, into the vault, and out the open end of the vault, which was on the downcurrent side.

An intertidal sample of 118 to 155 Terebratalia transversa on Saltspring Island, B.C., was censused in 1974, 1975, and 1976. Growth in length was a maximum of 7.8 mm per year and declined with size (age). As in fossil articulates, mortality rate was independent of age (size). Recruitment was patchy in time and space, was multi-annual or continuous, and was concentrated near conspecific adults. There were as many as 800 individuals/m2. None moved or changed orientation. Morphologic variation of Terebratalia valves is not directly controlled by the intensity of waves or currents.

Paleontological survivorship curves based on size-frequency data are subject to ambiguous interpretation because two critical assumptions (direct relationship of size and age, constant population structure) are difficult to justify.