The modern gorgonocephalid ophiuroid Astrophyton, a basketstar, has feeding habits which may be analogous to those of some Paleozoic crinoids that lack pinnulate arms (Meyer and Lane 1975). Field study has demonstrated the very quick response of Astrophyton when plankton impinge upon its arms. Study of the skeletal microstructure by scanning electron microscopy has shown that the quick response is facilitated by the development of relatively large ventral muscle fossae and articular surfaces whose shape follows a catenary curve. Prey are impaled by spines which articulate with the ventral surface of vertebral ossicles. Stereomic microstructure of vertebral ossicles is galleried where ligaments are present and labyrinthic where muscular tissue is present. The same microstructures are found in muscular articulations of modern crinoids. Future work on the arm structure of Paleozoic taxocrinids and cyathocrinids may demonstrate structural analogies and suggest similarities in food capture between such crinoids and modern baskets tars.

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.

The number of diatom valves and fragments per gram of surface sediment in the Atlantic Ocean accurately reflects diatom abundance in the overlying waters, without any evidence of significant lateral drift during settling to the sea bottom. The distribution pattern of the number of resting spores per gram is similar to that for the whole and fragmented diatom valves. Fresh water diatoms and opal phytoliths are abundant in the sediments off the west coast of Africa where they have been deposited by the Trade Winds.

Despite the relatively small number of core tops analyzed, the abundance and distribution patterns of diatoms in the sediments exhibit striking similarities to the patterns of primary productivity, phosphates, and annual production of silica in suspension in surface waters. Areas with high phosphate values and primary productivity and, therefore, areas of upwelling can be inferred from the quantitative distribution of diatoms in the sediments. Q-mode factor analysis, based on the abundance of forty-two species in thirty-seven core tops, produced six diatom species assemblages whose distributions provide additional information on the positions of certain water masses and major currents.

Since the data on the quantitative distribution of diatom valves as well as on the diatom assemblages in the sediments of the Atlantic Ocean today allow prediction of certain water mass characteristics and circulation patterns of the overlying waters, they therefore, permit the reconstruction of paleoceanographic circulation patterns in ancient Atlantic Oceans, using the diatom distribution in sediments from dated horizons.

The typical pelecypod form, long thought to be primitively adaptive to burrowing, is likely to have been originally adaptive to a suspension feeding, epifaunal, possibly crawling mode of life. At small body size (< 1 cm), pelecypods possessing typical burrowing features can function as epifaunal crawlers. Pelecypods arose at small body sizes and are part of a molluscan evolutionary sequence in which relative size of the mantle cavity increased to accommodate a few large gills specialized for suspension feeding.

Acquisition of a bivalved shell by ancestral epifaunal suspension feeders may have offered protection from sediment clogging on soft bottoms, additional control over the direction, volume, and rate of water flow through the mantle cavity, more effective protection from predators, and better short-term control of the internal environment. Consideration of invertebrate groups analogous to the pelecypods (Branchiopoda, Cladocera, Ostracoda, Phyllocarida) support the view that the bivalve condition is primarily an adaptation for suspension feeding and predator avoidance in benthic environments.

The earliest known pelecypod, Fordilla troyensis Barrande, was not necessarily infaunal just because it had features similar to much larger, Recent burrowers. The size, shell morphology and environment of preservation of F. troyensis all suggest that it is reasonable to envision Cambrian pelecypods as epifaunal suspension feeders, possibly crawling on sedimentary bottoms. Moreover, the sudden Ordovician expansion of pelecypods and increase in individual size may be explained as a result of invasion of the infaunal adaptive zone.

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.).

Consideration of the physics of sinking of hollow, rigid bodies leads to equations of motion for sinking cephalopod shells. We have derived equations of motion for three post-mortem sinking situations: sinking with a fixed amount of water in the phragmocone; rapid phragmocone filling (no siphuncular tube); and slow phragmocone filling (siphuncular tube intact). In all three cases sinking speed can be closely approximated by the terminal velocity calculated from the total weight, buoyancy, and drag parameters of the shell.

Experiments on modern Nautilus shells yield sinking velocities in agreement with calculated values. The experiments also show that orientation of a sinking Nautilus shell varies as the phragmocone fills with water. With small negative buoyancy the shell sinks with its plane of symmetry upright, but as it fills, it begins to rock from side to side and leans over and sinks with its plane of symmetry horizontal when the camerae are about 55% full.

The maximum sinking speed of upright adult Nautilus shells is approximately 30 cm/sec, which appears to be too small for embedding in the bottom upon impact. The maximum depth to which Nautilus sinks in the upright position ranges from about 7 m for rapidly filling shells to as much as 600 m for slowly filling shells. In the latter case, the shell will continue to fill after coming to rest on the bottom, and the stability of the vertical orientation will be removed within 1 or 2 days. Thus, primary vertical preservation of cephalopod shells indicates water depths less than about 10 m.

Marine shelf lagoon deposits of Middle Ordovician age in Tennessee contain the record of repeated ecological successions which began on soft, azoic, terrigenous muds and progressed to a complex bryozoan-brachiopod community. The stages of succession formed a skeletal limestone bed. The process led to an interbedded shale-limestone stratigraphic sequence. The pioneer was the brachiopod Strophomena basilica which paved the soft mud with accumulated shells. Encrusting bryozoans colonized this shell pavement and were followed by ramose bryozoans. The final stages of succession included bryozoans, gastropods, pelecypods, and pelmatozoans but were dominated by the brachiopod Rostricellula rostrata.

Measurements of total length, width, length to growth lines (Strophomena only), and thickness (Rostricellula only) were used to generate growth-rate, and survivorship curves for these two species. Strophomena shows low juvenile mortality, a moderate, linear growth-rate, and increased mortality in later ages. Rostricellula shows relatively higher juvenile mortality, a rapid non-linear growth rate, and nearly constant mortality. These attributes are contrary to expectations derived from theory, but can be understood in the light of autecological factors for each species. Adaptation to soft substrata was the primary factor controlling population dynamics in Strophomena, and crowding was the main factor in Rostricellula.

A scanning electron microscope survey of the regular echinoid test reveals that the outer surface of its component coronal plates may be sculptured with a fine-relief ornament that is species-characteristic for those species presently surveyed. Structural resemblances in surface ornamentation are more marked in species living in similar habitats than in those species that are apparently phyletically related. Plate ornament is related to skeletal magnesium levels. It is tentatively suggested that low growth rate echinoids that inhabit “low-energy” environments (and exhibit low total skeletal magnesium levels) and “high-energy” habitat-exploiting species with high growth rates (and relatively high skeletal magnesium levels) may have differential patterns of plate growth that can be distinguished by the degree of ornamentation of the plate surface.

True muscular articulations, as opposed to ligamentary ones, are reported here for the first time in the biserial arms of advanced inadunate crinoids (Poteriocrinina). The topography of biserial articular surfaces indicates clearly derivation from a uniserial muscular articulation with two muscle scars, a transverse ridge, and other structures considered typical of this articular mode. Biserial muscular articulations extend from the arm base to within a few brachials of the arm tip, although the articulations are more pronounced and better developed proximally. The inadunate facets are compared with those of the biserial arms of camerates, which are shown to be non-muscular and probably were capable of only limited movement. The arm movements of inadunate biserial arms are interpreted to have been ones where alternating muscle bundles on either side of the arm induced twisting motions of the arms so that a planar filtration fan mode of feeding was possible, in contrast to the parabolic feeding fan or other modes of feeding that were probably performed by other Paleozoic crinoids.

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.

Subcolony boundaries within Paleozoic bryozoan colonies, not otherwise easily observable, can be located precisely by computer mapping of variables derived from Fourier series. The monticule-centered subcolonies were maintained by morphogenetic gradients that controlled zooecial size and form, zooidal degeneration (producing brown bodies), and the spacing of monticules with respect to each other. These gradients were probably determined by the release of a budding inhibitor from polymorphic zooids within the monticule. In colonies with active monticular budding the morphogenetic gradients represent ontogenetic series, as the zooids that arose in the monticule gradually migrated outward along modified spiral pathways. Polymorphism, including reproductive functions, is probably reflected in the spatial order of zooids away from a monticule. In subcolonies with monticular budding, polymorphs represent different stages in the life history of a single zooid, with gradual transitions in zooecial form between castes.

The structural similarity between monticules and oghurd dunes supports the idea that they also functioned as excurrent water outlets, possibly with reproductive polymorphs clustered near the outflow. The variability of monticular size and spacing in some colonies indicates that hydrodynamic efficiency was compromised by the need for developmental plasticity. The development of active budding within monticules is considered an ecophenotypic response to the external environment, suggesting that all monticules within the Stenolaemata were potential budding sites. Monticules were successful adaptations in bryozoans because they performed a multiplicity of functions. While regulating the morphogenesis of the colony, they simultaneously served the metabolic functions of waste removal, feeding and reproduction.

A new account of the mechanical action of the heterocercal tail in fishes is given, developed from study of the swimming of sharks. The heterocercal tail is capable of delivering a thrust that can be oriented in a wide range of angles in the vertical plane. The orientation results from a balance of forces acting in the tail. Normally the heterocercal tail delivers neither an epibatic nor a hypobatic thrust, but rather one directly through the center of gravity of the fish. On the basis of the new account, predictions concerning the shape and proportions of the heterocercal tail are made and tested.

Ecological investigations were conducted on rodent faunas in the Sonoran Desert of the southwestern United States and the Monte Desert of northwestern Argentina. Both study areas are physiognomically quite similar and the rodents are only distantly related. Such conditions are ideal for an assessment of possible evolutionary convergence. Multivariate analyses of morphoecological characters support the subjective interpretation that ecological equivalents between the deserts differ in their degree of similarity. The data indicate that the Monte rodent fauna is composed of two distinct groups: a) the caviomorph rodents, which are highly desert adapted; and b) the murids, which range widely beyond the desert's boundaries and are probably not as highly desert adapted, as a group, as are the caviomorphs. When the Monte and Sonoran faunas are compared with a North American coniferous forest rodent fauna, data show that both desert groups have converged toward one another. The different degrees of desert adaptation and different distributional patterns indicate that the Monte Desert was colonized in two different periods (one in the early Tertiary and one in the late Pliocene or early Pleistocene) and can be interpreted as supporting theories regarding South America's colonization by mammals which were first proposed by Simpson (1951).

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.

Fossil data suggest that the great majority of metazoan classes that existed in the Early Cambrian arose after about 700 my ago. The rectangular model of evolution, which views most evolutionary change as being concentrated in speciation events, can easily accommodate the implied rate of divergence.

If, as some authors believe, the eukaryotic cell arose long before the start of the Cambrian, an explanation is required for the delay of large-scale metazoan divergence. The advent of sexuality may have triggered diversification, not by accelerating phyletic evolution, as traditionally believed, but by making possible speciation and, hence, adaptive radiation. Another important delaying factor may have been the near-saturation of Precambrian algal systems in the absence of cropping by herbivores. Uncropped Precambrian systems should have been self-limiting in terms of diversification. When advanced heterotrophy finally arose, self-propagating feedback systems of diversification should have been set in motion. Even if the eukaryotic cell arose later than commonly envisioned and triggered the radiation of the Metazoa about 700 my ago, the earlier absence of sexuality and cropping may have delayed the transition from the prokaryotic condition to the eukaryotic condition.

Pelagic marine mammals (cetaceans and pinnipeds) generally invaded the seas rapidly in response to new ecologic opportunities. After cetaceans initially appeared and radiated in the Eocene, they declined in the Oligocene, but radiated into many new adaptive types in the Miocene. Pinnipeds apparently evolved in the earliest Miocene, rapidly radiating into many adaptive types. We propose that the radiations, and declines, of species were responses to the availability of trophic resources in oceanic environments. These trophic resources are closely related to upwelling processes in the oceans. We suggest that increased upwelling intensity, due to climatic or tectonic events, permitted the initial invasions and radiations and that decreased intensity caused cetacean extinctions in the Oligocene.

Growth processes and patterns set functional limits on the adaptive range of organisms that have evolved a particular “Bauplan.” The design of the elastic ligament has played a large part in determining the scope of the evolutionary radiation of the Arcoida. Tensional lamellar and compressional fibrous materials of this ligament, which appear to be similar in their elastic properties to those of other bivalves, are not segregated in positions where they could best perform their different mechanical functions. The growth of this unspecialized ligament exhibits strong positive allometry, with respect to shell size, in many fossil and living arcoids. A simple mechanical model shows that this allometry is essential if the strength of the ligament is to keep up with the weight of the animal, during ontogeny. Inherent disadvantages of the allometry include increasing dorsal breakage of the ligament itself, interference with the function of the hinge teeth and reduction of the closing moment exerted by the adductor muscles. Direct measurements of living arcoids show that allometric growth just maintains a linear relationship between ligament strength and animal volume. Major differences in ligament strength are related to shell growth patterns and substantially different environmental adaptations. Ligament strength is highly variable within individual populations; between populations, it is correlated with shell thickness and local environmental conditions. Most arcoids are adapted for shallow-burrowing or epifaunal modes of life in physically unstable environments, where they are frequently disturbed. The large, muscular foot enables these mobile animals to regain suitable living positions after such disturbances. The weak ligament has limited the potential specialization of the arcoids for either deeper burrowing or permanent epibyssal attachment, also requiring the retention of the foot in epifaunal forms. This ligament has made diverse adaptations possible, while preventing extreme specialization, except in isolated taxa. As such, it is largely responsible for the evolutionary reversals documented by Stanley (1972). This is konstrukionsmorphologie No. 46.

Bryozoans are colonial animals and this permits the partitioning of their morphologic variability into components of within colony (i.e. within a single genotype) and between colony (i.e. between genotype) variance. These data have been obtained for four species of the endemic deep-sea genus Euginoma for a series of characters. In 8 comparisons, one component of the total variance dominated at the 5% level. Population (between colony) variance contributed significantly to the total variance in 63% of the comparisons (5 of 8); individual (within colony) variance contributed significantly to the total variance in 37% of the comparisons (3 of 8).

Compared to shallow water species, the surprising feature of the deep-sea data is that the between colony component of variance is as high as it is. Possibly in the more stable, deep-sea environment, the genotypic contribution to the variance of each individual colony is expressed to a greater degree than in the more variable, shallow water regime. If so, then analyses of variability in colonial animals may be an independent means of ascertaining stability gradients in the fossil record.

The American interchange of land mammals reached its acme during the late Blancan and early Irvingtonian in North America and during the Chapadmalalan and Uquian in South America. It lasted about two million years and included taxa adapted to diverse habitats. It was preceded in the early Hemphillian in North America and the Huayquerian in South America by the interchange of a few heralding genera. The MacArthur-Wilson faunal equilibrium hypothesis correctly predicts a marked increase in originations, number of genera, and turnover rate for the South American fauna during the peak of the interchange. Subsequent further increases were not so predicted but closely resemble patterns also observed in late Pleistocene land mammals of Europe and North America. The continued increase in South American land mammal genera after the interchange had largely ceased resulted principally from autochthonous evolution of northern immigrant stocks. A marked decrease in South American ungulate genera (from thirteen to three) coincided with the appearance of fourteen northern ungulate genera and therefore appears to be a replacement phenomenon. The area/diversity relationship predicts no important change in generic diversity if a maximum of only nine percent of North America is occupied by the interamerican mingled fauna. At the family level, however, diversity is seriously overestimated due to the nomenclatural artifact of increased relative diversity by filtering.

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.