Benthic ecologists have successfully applied rarefaction techniques to the problem of compensating for the effect of sample size on apparent species diversity (= species richness). The same method can be used in studies of diversity at higher taxonomic levels (families and orders) in the fossil record where samples represent world-wide distributions of species or genera over long periods of geologic time.

Application of rarefaction to several large samples of post-Paleozoic echinoids (totaling 7,911 species) confirms the utility of the method. Rarefaction shows that the observed increase in the number of echinoid families since the Paleozoic is real in the sense that it cannot be explained solely by the increase in numbers of preserved species. There has been no statistically significant increase in the number of families since mid-Cretaceous, however. At the order level, echinoid diversity may have been nearly constant since late Triassic or early Jurassic.

Facets of the Silurian receptaculitid Ischadites barrandei are arranged in circlets about a nucleus. They form a set of spirals, originally eight in number, but increasing by the intercalation of new facets (initiating new spirals) in later circlets. We have simulated the surficial geometry of this alga by assuming, as much evidence indicates, that facets are limited in final size and that new spirals must therefore be intercalated in order to cover the surface with a fully tesselated pattern. We use only five parameters in our simulation: nature of the surface (radius of a sphere), tightness of the spirals (assumed to be logarithmic) and rate of increase in facet width (three parameters of an equation fitted to actual data). The program draws facets in circlets and intercalates new ones whenever the sum of facet diameters is at least a facet less than the circumference of the circlet. By holding all but one parameter constant, we can test the influence of single factors upon the pattern of intercalation. We compare these figures with actual patterns of intercalation for eight specimens. Variation in tightness of the spiral seems to affect the pattern most radically—tight spirals intercalate fewer facets because new circlets stay near the pole of the sphere. The morphology of intercalation supports the interpretation of Rietschel (1969, contra Nitecki, 1972 and Byrnes, 1968) that the nuclear circlets are the oldest part of the plant and that new circlets are generated at the opposite pole. Our simulation represents a basic pattern in nature, not a specific feature of receptaculitids. All structures that fill space with spirals and impose limits upon the size of individual units must add new spirals. Bryozoans subject to similar constraints but growing in a completely different way (peripheral growth in radial rows) display the same final pattern.

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.

Analysis of stratigraphically separated collections of Late Ordovician fossilized marine invertebrates suggests that our understanding of faunal changes through time may be enhanced by considering them in terms of a successional framework. The faunal succession in the Nicolet River Valley, St. Lawrence Lowlands, Quebec, began with the initial colonization of an offshore barren mud by two or three presumably opportunistic deposit-feeding species. Diversity, both of species and of trophic types, increased gradually, peaked, and then decreased slightly with some faunal shifts, especially in the numerical predominance of the epifaunal element. A three-fold repetition of this quiet-water succession seems in each case to have been terminated by an external physical perturbation. There also appears to be a second, separate successional sequence which became localized on a somewhat coarser-grained and perhaps less stable substratum as the paleoshoreline was approached, due to sediment filling of the basin.

Succession involves changes in a community through time, whether internally or externally controlled. As succession progresses, niche specialization, species diversity (variety and equitability), complexity of food chains, and pattern diversity increase; net production and species growth rate decrease. We apply the succession concept to three types of ancient community sequences: 1) fossil reefs (Ordovician—Cretaceous in age), 2) short-term successions occurring through thin stratigraphic intervals, and 3) long-term successions occurring through thicker stratigraphic intervals. Ancient reefs show four vertical zones: (1) a basal stabilization zone (autogenic), 2) the overlying colonization zone (autogenic, pioneer stage), 3) the diversification zone, the bulk of most reefs (diversification culminating in climax), and 4) the uppermost domination zone. The first three zones represent autogenic succession but the final stage may involve allogenic succession. Short-term succession usually occurs where periodic allogenic catastrophes wipe out the community which is rebuilt through autogenic succession. Opportunistic pioneer species are important and in our examples (Ordovician, Silurian, and Cretaceous) are species which pave soft substrata. Paleozoic strophomenid brachiopods filled this role, and inoceramid pelecypods served the function in the Mesozoic. The succession which begins with opportunists progresses to a climax community of equilibrists. Repetition of catastrophe-succession couplets produces a cyclic stratigraphic record. Long-term successions are recorded in thicker stratigraphic sequences, and are of two types: 1) autogenic succession in unchanging physical environments and 2) allogenic succession in changing physical environments. Our examples of these are from the Devonian Haragan-Bois D'Arc formations of Oklahoma and the Lime Creek Formation of Iowa. This type of succession represents a temporal-spatial mosaic. The Haragan data (unchanging environments) indicate characteristic, intergrading, and ubiquitous species in the brachiopod communities. Most ubiquitous species in the pioneer community were eurytopic opportunists. The Lime Creek data allows testing of the prediction that environmental changes cause regression to an earlier succession stage. The brachiopod communities after environmental changes have more ubiquitous and intergrading eurytopic species. These represent an earlier stage in the succession.

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.

Taxonomic survivorship curves may reflect stratigraphic as well as biologic factors. The approximately lognormal distribution of lengths of Phanerozoic time intervals produces an error in the estimation of taxonomic durations that is also lognormally distributed. As demonstrated by several simulated examples, this error may cause concave taxonomic survivorship curves to appear linear, especially if the maximum durations involved are relatively short. The error of estimation also makes highly concave taxonomic survivorship curves virtually unrecognizable. Incomplete sampling of the fossil record, on the other hand, may not be a serious problem in survivorship analysis. Simulated paleontological sampling employing a simple model suggests that survivorship curves tend to retain their original shapes even when as few as 20% of the taxa have been discovered. However, concave taxonomic survivorship curves tend to lose their concavity as efficiency of sampling declines.

A theory is presented that cranial crests of hadrosaurs were visual and acoustical display organs. Facial morphology and phylogeny of the Hadrosauridae and earlier theories of crest function are reviewed. The following hypothesis is presented: cranial crests, whether hollow or solid, served as visual signal structures, and hollow lambeosaur crests were also vocal resonators; all crests promoted successful matings within species, i.e., they served as premating genetic isolating mechanisms. The following predictions are tested and found to support the hypothesis: (1) hadrosaurs had well-developed eyes and ears; (2) external features of crests varied independently of internal structure; (3) crest variations were species-specific and sexually-dimorphic; (4) crest distinctiveness correlates with species diversity; (5) crest size tended to increase through time. The circumnarial depression on the side of the face in hadrosaurines housed an inflatable diverticulum of the nasal passage which served as a visual display organ. Primitive hadrosaurs (kritosaurs) possessed a small nasal horn used as a butting weapon in intraspecific combat. Because the weapon was also used in intimidative displays, narial diverticula evolved to draw attention to it. In the kritosaur Brachylophosaurus fighting was modified to ritualized head-pushing using the flat nasal “shield”. Saurolophines expanded the diverticula on to the elongated nasal horn, converting the weapon to a dominance rank symbol. In non-crested edmontosaurs, enlarged diverticula assumed a vocalization function. Lambeosaurs created resonators by enclosing the diverticula in bone; they further enhanced the resonator function of the nose by forming elongated “organ pipes” in the premaxillae. This “pushed” the olfactory region above the eyes as a conspicuous dome which then was modified to form species-specific visual display organs.

Experiments show that diductor muscles of articulate brachiopods are normally relaxed, contracting only when the valves gape. Consequently, dead brachiopods rarely gape.

The linear survivorship curve of Van Valen's Law can be generated from stochastic loss of lineages, given a decreasing sample size within an adaptive zone. No special biological explanation is required or called for in order to explain “linearity” in taxonomic survivorship curves.

Quantitative systems for describing naticid borehole position in bivalve and gastropod prey are presented. Pleistocene nassariid prey were bored at 53% of the distance up the shell and 8° to the right of the columella. A similar stereotyped position was found for Recent prey. The longitudinal shell axis and the aperture of the gastropod shell are proposed as primary cues in orienting prey for boring.

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.

While the importance of allopatric speciation in the fossil record has long been underestimated, phyletic change within single unbranching lineages also occurs. The 50% increase in thoracic width observed in the radiolarian species Pseudocubus vema from an Antarctic deep-sea core is a clear example of a long-term phyletic trend in a continuous fossil sequence. Phyletic change in P. vema occurred at varying rates, but changes in the morphologic rate of evolution do not correspond to any obvious breaks in the fossil record such as would be indicated by missing segments of the core's magnetic stratigraphy. Variation in thoracic width, as measured by the coefficient of variation, does not depend on the morphologic rate of evolution, proportional rate of evolution, nor the amount of time required for the width to change by one standard deviation, so much as it depends on whether change was accomplished by addition or removal of extreme phenotypes to or from the population.

Studies of the internal anatomy of Mississippian camerate crinoids have revealed the presence and plan of groove and ridge networks here interpreted as evidence of former nervous systems in these animals. The inner thecal surfaces of hollow specimens and surfaces of internal chert molds possess radiating networks of grooves and ridges in both the dorsal cup and tegmen that resemble the plan of the aboral and hyponeural nervous systems, respectively, of modern crinoids. The aboral network of camerates radiates from the basal region of the dorsal cup at the point of stem attachment and provides one radially positioned nerve trunk per arm. In addition to the radial trunks, branches are present in each of the five interrays; the pattern in the CD (i.e., posterior) interray is different from the others. Two ring commissures interconnect the radial and interradial nerve trunks. The hyponeural nerve network in the tegmen originates from a ring commissure located near the upper part of the tegmen. From the ring commissure radiate radial and interradial nerve trunks that divide to produce two nerve trunks per arm as in modern crinoids. Raised ridges that define the hyponeural nerve network on the inner tegminal surface are separate from impressions representing the water vascular network.

By analogy to living crinoids, the aboral nerve center in camerates was located in the base of the dorsal cup. The radial portion of the aboral nervous system is judged to have functioned as the main motor network in camerates, innervating arm flexor muscles, pinnules, and arm epidermis, thus controlling the “display” of arms to form an effective filtration baffle. The interradial aboral nerves may have been sensory nerves which were part of an active balance system in these stalked echinoderms. The hyponeural system in camerates, as in living forms, probably acted as a sensory system by innervation of the lateral walls of the tube feet and arms. A third system, the ectoneural system, which lines the ciliated food grooves and gut of living crinoids has not been detected in fossil camerates; however, due to its functional significance, its presence in camerates was very probable.

The prosogyrous shape and flattened lunule of a typical clam shell form a blunt anterior, the function of which is related to the forward-and-back rocking motion of the shell in burrowing. Analysis of movies has revealed that each rocking motion of a morphologically typical clam, Mercenaria mercenaria (Linné), involves purely rotational movement, with no translational component. The clam is able to burrow by “walking” its way downward only because the axis of backward rotation lies to the anterior of the axis of forward rotation. Experiments with burrowing robots show that the blunt anterior serves to shift the axis of backward rotation anteriorly, thus aiding in downward progress. The prosogyrous condition and the rotational mechanism of burrowing are fundamental adaptations of burrowing clams and were apparently present in the ancestral bivalves of the Cambrian.

Geological data show that high Andean habitats have been available for plant colonization only since the end of the Tertiary. The manner in which plant species moved into these habitats, the times during which, and the methods by which they differentiated during the Pleistocene varied altitudinally and latitudinally along the tropical Andes. The process of speciation in all areas, however, was the same as that in temperate environments, namely, geographic isolation and subsequent divergence. Except on the Altiplano, most plant species expanded their ranges during glacial periods when vegetation zones were lowered. In the northern paramos at elevations above treeline, colonization was greatest during glacial periods but has always occurred in a manner similar to that of oceanic islands. At lower elevations in the northern Andes, and along the Eastern Cordillera, direct migration was possible in glacial times because of increased contiguity of upper montane forest habitats. On the upper slopes of the west coast of Perú, glacial-age plant migrations were fostered more by changes in precipitation than by the lowering of vegetation belts. In all of these areas, interglacial periods were, and are, times of isolation and differentiation. Across the Altiplano in contrast, glacial periods were times of population fragmentation accompanied by differentiation and/or speciation.

Muscular articulations on the brachials and pinnules of Paleozoic crinoids have traditionally been inferred by the presence of a transverse ridge. We here provide evidence that the microstructure of the stereom, fine meshed where muscles once inserted and coarse meshed where ligaments were emplaced, provides a reliable microstructural criterion for muscular articulation on well-preserved arm ossicles. Partially pyritized ossicles of Aesiocrinus magnificus Miller & Gurley from the Lane Shale of Pennsylvanian age at Kansas City, Missouri exhibit well-preserved stereom in three dimensions under the scanning electron microscope. These brachial and pinnular plates show clearly the distinctiveness of stereom at sites of muscule and ligament attachment. This criterion should be useful in tracing the evolutionary development of flexible arm articulations in several lineages of Paleozoic crinoids.

Open-ended tubes were found extending inward from the inner surfaces of brachial valves of three different species of Emsian spiriferid brachiopods. It is believed that these tubes were formed by the outer epithelium of the brachiopods, precipitating shell material around a small commensal filter feeding organism living in the outer mantle cavity. The position of the open ends of these tubes, the business end of the filter feeding organism, in every case discovered is between the bases of the two spiralia. This lends support to the suggestion of Ager (1961) and Wallace and Ager (1966) that spiriferid brachiopods had median inhalant and lateral exhalant feeding currents. These structures are named Burrinjuckia spiriferidophilia n.gen. n.sp. They are trace fossils of indeterminate taxonomic position.

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.