The rarefaction graphs and trophic nuclei of dead molluscan shell cumulates and their associated live molluscan fauna from seven ‘ecological’ habitats in the Essex Chenier Plain facies are examined and compared. The results show that while the trophic nuclei of the live and dead faunas tend to be dissimilar, the rarefaction graphs indicate that the dead fauna will be more diverse than the live, though changes in the diversity of the live fauna tend to be mirrored in the dead fauna.

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.

Silurian crinoids reached maximum abundance on shallow shelf bottoms of skeletal-rich carbonate. In-place crinoid preservation in the Wenlock Limestone of Dudley, England, provides a community model for these occurrences, showing a pattern among crinoids of high taxonomic diversity, conspecific clustering, relatively robust morphology, and numerical dominance of other invertebrates. Densities of about 40 crinoid individuals per m2 occupied a feeding level between 10 cm and 1 m above the bottom and may have effected trophic control over other fauna. Beneath the crinoids lived a second level of bryozoa, a third level of tabulates, and a sparse fauna of brachiopods and other solitary organisms. Crinoids also exercised significant biologic control of substrate. In contrast to the Dudley assemblage, Silurian communities of terrigenous, soft-bottom environments contained crinoids of low abundance, low taxonomic diversity, and small size. In the terrigenous communities, crinoids appear to have had no major effect on either trophic structure or substrate. High sedimentation rates limited the role of crinoids in such communities, and the dominant organisms were deposit feeders and solitary, low-level suspension feeders.

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.

The paleoecologist has been hampered in his studies of ancient communities by an inability to obtain reasonable estimates of standing crops and diversities. Finding the diversity of an ancient community is no simple matter, because a fossil assemblage is a mixture of living and recently dead individuals from that community. Considerable numbers of each group may be missing. The relationship of the elements in a fossil population for an individual species can be expressed as follows: F = Fl + Fd, where F is the average number of fossil individuals collected per unit area, Fl is the part of the sample produced by the burial of live individuals, and Fd is the part produced by the individuals already dead at the time of burial. Fl is a product of the standing crop S (number of individuals per unit area), multiplied by the probability of failure P (proportion of the standing crop which can be expected to fail to escape anastrophic burial), or Fl = (S) (P). Fd is the product of the death rate D (number of individuals which die per age-class time unit) multiplied by the residence time R (average length of time expressed in age-class time units that the remains of an individual will persist after death), or Fd = (D) (R). The probability of failure, residence time, and death rate can all be estimated from modern communities; the death rate can also be estimated from the fossils. Thus, the standing crop of an individual species can be expressed as follows:

This equation can be modified to eliminate the need to estimate D, as follows where i is the subscript indicating the number of the specific age class where the youngest is 1 and oldest is n. Once the standing crop for each species in the community has been estimated, a meaningful diversity can be calculated. Study of the model reveals that in populations where high-early mortality is the rule the likelihood of error in estimating population parameters is lower than for constant and low-early mortality populations.

A major aim of the analysis of faunal remains from archaeological sites is the reconstruction of the palaeoecology of early man. Since taphonomic work must precede palaeoecological work, theories concerning the palaeoecology of early man would benefit from firmly based taphonomic studies of the archaeological deposits. One of the numerous taphonomic factors to be considered is the bone fragmentation produced by early man.

The degree of bone fragmentation in a deposit uninfluenced by human factors is an expression of the resistance of the various bones to mechanical and chemical decomposition before and during burial. Thus, the degree of fragmentation where human factors are predominant should provide an illustration of man as a taphonomic factor. In both cases the degree of fragmentation may be used as an indicator of the degree of taphonomic overprint.

Examination of bone material from four West European Mesolithic sites (all bog deposits), Star Carr 7200 ± 120 B.C., Kongemosen 6600 ± 100 B.C., Præstelyngen 3200 ± 100 B.C., and Muldbjerg I 2900 ± 80 B.C., reveals differences in marrow fracturing techniques. Furthermore, the different techniques result in different numbers of fragments for the same type of bone. Comparison of faunas from different sites based on the number of bone fragments must therefore be preceded by analysis of the marrow fracturing techniques used at the various sites. The number of fragments per estimated minimum number of individuals should indicate the degree of taphonomic loss.

The various types of marrow fracturing found seem to belong to cultures at different levels of technical development. Thus, it may be possible within a limited area such as northern Europe to establish a chronology using marrow fracturing type as one of the ecostratigraphic tools.

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.

The hypothesis is proposed that mean level of heterozygosity is functionally related to rate of speciation in evolutionary phylads. Under this hypothesis, phylads which speciate more rapidly do so because of increased level of within-species genetic variability which is then available to conversion to species differences under appropriate ecological or environmental conditions. An important corollary is that rate of speciation could be limited in phylads with low genetic variability, irrespective of environmental considerations.

This hypothesis has been tested with respect to electrophoretically detectable variation in products of structural genes in two families of North American fishes characterized by grossly different rates of speciation. Totals of 69 species of the highly speciose Cyprinidae, and 19 species of the relatively depauperate Centrarchidae, were assayed for mean level of heterozygosity at 11–24 genetic loci. Since Cyprinidae and Centrarchidae exhibit on the average nearly identical levels of genic variation (Ĥ = 0.052 ± 0.004, and Ĥ = 0.049 ± 0.009, respectively), the hypothesis that level of heterozygosity affects rate of speciation in these fishes is not supported.

Nonetheless, the amount of genic variability in both Cyprinidae and Centrarchidae is large, comparable to mean levels in previously studied vertebrates. The great wealth of genome variability, reflected in the electrophoretic variation present in virtually all outcrossing organisms, apparently can accommodate considerable flexibility in rate and pattern of evolutionary response to the various environmental regimes challenging organisms.

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.