On the basis of about 70,000 species citations in the Zoological Record, it is estimated that about 190,000 fossil invertebrate species were described and named through 1970. The true figure may be higher because of incompleteness of the Zoological Record or lower because the estimate does not account for synonymy.

About 70% of the species were described from USSR, Europe, and North America. About 42% are Paleozoic, 28% Mesozoic, and 30% Cenozoic. In the Cambrian part of the sample, 75% of the species are trilobites. In the Mesozoic and Cenozoic, about 70% are either molluscs or protozoans.

When the data are normalized for absolute time, diversity (species per million years) shows a Paleozoic high in the Devonian which is approximately four-tenths of the Cenozoic level.

Species diversity among fossil invertebrates of the Phanerozoic is highly correlated with volume and area of sedimentary rocks. The correlations are statistically significant at the 1% level. The relationship holds even in regions (such as Canada) where the area and volume of rock do not increase through time. These results are interpreted as indicating that the apparent number of species is strongly dependent on sampling and that many of the changes in diversity seen in the Phanerozoic are artifactual. Consequently, there is no compelling evidence for a general increase in the number of invertebrate species from Paleozoic to Recent. This conclusion applies primarily to marine organisms. Diversity may have been in dynamic equilibrium throughout much of this time.

A few intervals of the Phanerozoic have consistently fewer invertebrate species than would be predicted from the amount of sedimentary rock available for study. The Silurian, Permian, and Cretaceous stand out in this regard. This may result either from lower than normal diversity during these periods or from an unusual abundance of unfossiliferous rocks (evaporites, red beds, etc.).

Raup's (1976a) data on Phanerozoic species numbers are examined for species-area relationships, using published estimates of areas of continental seas. By means of multiple regression, species numbers are regressed on both estimated areas of seas and amounts of available rock for sampling, as measured by outcrop area and rock volume. Although the sampling effects apparently have the strongest influence on fossil species diversity, areas of seas substantially increase the total correlation, suggesting that Phanerozoic species numbers were in equilibrium with habitat area. This is further supported by the fact that estimated parameters in the regressions are fairly consistent with established island biogeographic theory. Much of the remaining residual variation can be explained by periods of disequilibrium.

The schizochroal eye of trilobites bears lenses of high optical quality. Cooperation between adjacent lenses, which must have had retinas rather than rhabdomeres, might have allowed the trilobite stereoscopic vision throughout its visual field. We propose a simple neurophysiological model for the schizochroal eye in which neural connections between lenses on vertical “visual strips” could have provided the integration necessary for stereoscopic vision. Simple neural signals could have coded information on the position, size, speed and nature of an object in the field of view. The model of stereoscopic vision is consistent with data on the shape of the eye, the arrangement of lenses on its surface, and with current views on the origin and early evolution of the schizochroal eye. It implies that the lens arrangement, neural network and shape of the eye surface were a coadapted morphological complex, and it is consistent with accepted ideas of the Phacopina as living in benthic habitats in the photic zone.

We investigated the hydrodynamic properties of cephalopod shell sculpture in two ways: 1) flow visualization experiments with sculptured shells; and 2) application of drag coefficient data for simple geometric bodies to cephalopod shells. Results of this work suggest:

1) the hydrodynamic effect of shell sculpture depends primarily on the size of the sculptural elements relative to the size of the shell and on the positions of sculpture elements on the shell and relative to each other.

2) sculpture is detrimental to swimming (reduces hydrodynamic efficiency) if it exceeds the height of the lower part of the shell's boundary layer.

3) sculpture is advantageous to swimming (increases efficiency) if it remains immersed in the boundary layer and induces premature conversion to turbulent boundary layer flow. To be hydrodynamically optimal, small shells (diam ≈ 10 cm) must have rough (sculptured) surfaces, whereas large shells (diam ≈ 100 cm) require smooth surfaces. Thus, in order to maintain maximum efficiency throughout life, the ontogeny of small individuals, or species, should be characterized by progressive roughening of the shell, while large forms should become increasingly smooth. Such allometries are observed among many ammonoids.

4) sculpture always has an effect on the flow around a cephalopod shell. In some species this effect was probably negligible, while in others, those with compressed shells especially, it was probably of major importance. In these species, sculpture appears to have functioned primarily to increase swimming ability.

The claw equipped forelimbs have been shown to be an important hunting weapon for modern felids. In light of its functional importance, the claw retractile mechanism for modern felids was compared with that of the saber-toothed felids. In this regard, the functional anatomy of claw retraction for saber-toothed felids was found to be the same as that of modern forms. Body proportions of modern felids were also compared with saber-toothed felids and the relationship of their morphology to habitat structure and habitat utilization were studied. It was found that the relative body proportions for Hoplophoneus and Smilodon were similar to modern forest felids (dwellers of high structured dense forest), while Dinictis and Machairodus could probably compete in more open terrain (open woodland, meadow). It is postulated that saber-toothed felids used their claw equipped forelimbs to grasp and hold their prey as do modern felids. In this fashion, the enlarged upper canines could then be used to kill the victim, and this was probably done by a stab to the nape of the neck. It is also thought that Smilodon, like the modern lion, adapted to open habitats by forming prides.

Small mammal species distribution, density, and composition of modern and Pleistocene faunas from the eastern United States provide information about environmental gradients. Higher summer temperatures and less effective moisture along a transect from the northeast to the southwest can be correlated with the distribution of small mammals as well as decreases in the total number of shrew and vole species. Relative frequencies of “boreal”, “deciduous”, and “steppe” species are more equal in late Wisconsin than modern faunas which are predominantly composed of only one group. A higher vole species density is prevalent in each late Wisconsin fauna and eleven of twelve of these faunas have a higher shrew species density than the corresponding modern fauna. Many shrew and vole species that are today endemic to the boreal provinces were cosmopolitan during the late Wisconsin. Moderate environmental gradients of the equable late Wisconsin climates allowed integration of boreal species with resident species in the south.

The beginnings of biospheric evolution had far-reaching biogeochemical consequences for the related evolutions of atmosphere, hydrosphere, and lithosphere. Feedback to the sedimentary record from these several simultaneously interacting aspects of crustal evolution provides the evidence from which historical biogeology is reconstructed. The interpretation of that evidence, however, is beset with pitfalls. Both biogenicity and a primary origin need to be demonstrated, or confidence limits established for each supposed morphological and biochemical fossil. Relevance to biospheric or related evolutions must be critically evaluated for every geochemical and sedimentological anomaly.

Indirect evidence suggests primitive, oxygen-generating autotrophy by ∼ 3.8 × 109 years ago (3.8 Gyr or gigayears), while free O2 first began to accumulate only ∼ 2 Gyr ago. Various reduced substances in the atmosphere and in solution functioned as oxygen sinks, keeping photolytic and biogenic O2 at levels tolerable by primitive anaerobic and microaerophilic procaryotes.

The oldest demonstrably biogenic and certainly primary microstructures are procaryotes from ∼ or > 2 Gyr old strata around Lake Superior. Improved biologic O2 mediation, continued carbon segregation, and filling of O2 sinks initiated atmospheric O2 buildup, leading to an ozone screen ∼ or < 2 Gyr ago. Consequences were essential termination of banded iron formation, onset of red beds, and O2 shielding of anaerobic intracellular processes, heralding the eucaryotic cell.

Probable eucaryotes appear in ∼ 1.3 Gyr old rocks in California as large unicells and large-diameter, branched, septate filaments. Likely consequences of eucaryotic evolution were increased atmospheric O2, increased carbonate and sulfate ion, and the rise of sexuality. Meiosis had definitely evolved > 0.7 Gyr ago and probably > 1.3 Gyr ago, perhaps simultaneously with the mitosing cell. Whatever the timing, it completed the evolution of the eucaryotic heredity mechanism and foreshadowed (given sufficient free O2) the differentiation of tissues, organs, and advanced forms of life—with all their potential for biogeochemical feedback to sedimentary, diagenetic, and metallogenic processes. The first Metazoa appeared ∼ 0.7 Gyr ago. Being dependent on simple diffusion for O2, they lacked exoskeletons. The latter appeared, perhaps 0.6 Gyr ago, when increasing O2 levels favored the emergence of more advanced respiratory systems.

For the past twenty years, Ralph Gordon Johnson contributed significantly in three areas of paleobiology: understanding the dynamics of benthic marine communities, exploring the mode of formation of fossil assemblages, and describing the remarkably preserved Mazon Creek fauna.