Cheilostome bryozoans that grew as rigidly erect arborescent colonies dominate many bryozoan-rich assemblages of Tertiary age, in which they are found most commonly as small dissociated fragments. The regularity with which branching and branch thickening occur in intact colonies of living species provides a basis for quantitative reconstruction of these growth processes in fossils. We propose models to describe branch thickening, develop methods to extend both thickening and branching models to fossils, investigate the thickening and branching properties of four Paleocene and five Oligocene species and compare the properties of these fossils to those of nine living species.

The properties investigated are largely mutually independent and species specific irrespective of geologic age and have similar numerical ranges among different assemblages of coeval species. Species are evenly distributed across the range of possible morphologies between observed extremes, without obvious gaps. Statistically significant trends through time are identified in gradients of branch thickening, which have implications for the resistance of colonies to mechanical stress, and in angles of bifurcation, that are important in the way growing colonies occupy space.

Patterns of dental and cranial variation are analyzed in a unique sample of early Eocene equid Hyracotherium from one fossil quarry of late Wasatchian age in the Huerfano Basin of southern Colorado. The sample includes remains of two species differing principally in size: H. vasacciense and H. tapirinum. The larger species, H. tapirinum, is represented by 24 individual specimens that show marked bimodality in cranial size and robustness and in upper and lower canine size. These differences are attributed to sexual dimorphism. Males tend to be about 15% larger than females in cranial dimensions and 40% larger than females in canine dimensions suggesting, by comparison with modern ungulates, that early Eocene horses were probably polygynous. The appearance of Hyracotherium in North America and its rise to dominance in early Eocene mammalian communities coincides with development of an environmental mosaic including open park woodland and savanna habitats. The evolutionary success of Hyracotherium may reflect, in part, the adaptive superiority of a social structure in which females in open habitats are grouped for mutual protection from predators, for optimal foraging in patchy environments, or both.

Factor analysis of morphometric data from fossil and recent Archaeogastropoda reveals that there has been a progressive reduction in the variety of archaeogastropod shell shapes through time. High and low spired genera have slowly disappeared while equidimensional forms, which have always been the most common, have become even more abundant. The taxonomic manifestation of this trend has long been appreciated and involves: 1) the extinction of most of the Pleurotomariacea, the Euomphalacea, Trochonematacea, and several other superfamilies, which collectively comprise most of the variation in shape among early archaeogastropods, and 2) the proliferation of the primarily equidimensional Trochacea and Neritacea. I suggest that this macroevolutionary trend may be explained by the general process I refer to as “stabilizing species selection.” More specifically, I suggest that the mechanism of stabilizing species selection in the case presented here may have been differential rates of origination.

I believe that the innovative concept of species selection has been burdened by the adherence of its advocates to the idea that differential extinction is its primary mechanism. This preference for differential extinction is rooted in our emphasis upon differential mortality in microevolution and is not based upon data of macroevolutionary change. I argue that differential origination may be as important as differential extinction in directing macroevolutionary change and that demographical and autecological properties of species may be its agents. Recognition of the importance of differential origination will have an important impact upon our concept of the relationship between adaptation and the evolutionary process.

The history of diversity, origination and extinction of Cambro-Ordovician nautiloid cephalopods is explored to determine if differences in evolutionary rates between nautiloid orders are sufficient to document significantly high or low rates of evolutionary turnover (taxotely of Raup and Marshall 1980). The stratigraphic ranges of 425 nautiloid genera are analyzed for this purpose.

Evolutionary rates for five of the seven time intervals analyzed fall within frequency distributions of rates which are thought to be characteristic for a given time interval (horotelic distribution of Simpson 1944). Sufficient heterogeneity is present among extinction rates of Arenigian orders and origination rates of Caradocian orders to reject the null hypotheses of horotely in favor of taxotely. The orders Ellesmerocerida and Tarphycerida, each with a significantly high rate of extinction (P ≥ 0.99), and the Actinocerida, with a significantly low rate of extinction (P ≥ 0.99), were responsible for taxotely during the Arenigian. The Oncocerida and Discosorida, each with a significantly high rate of origination (P ≥ 0.99), were responsible for taxotely during the Caradocian. In each case, taxotely is attributable to the influence of North American endemics. This effect is believed to be more the result of real biological aspects of nautiloid evolution than an artifact of the fossil record.

Shape measurements have been made on planktonic foraminifera from a South Pacific Late Miocene to Recent temperate evolutionary lineage (Globorotalia conoidea through intermediate forms to G. inflata in DSDP Site 284). The sampling interval is about 0.1 Myr over nearly 8 Myr. Gradual evolution (phyletic gradualism) clearly occurs in all but one measured parameter. No clear evidence exists for abrupt evolutionary steps (punctuated equilibria) within the bioseries. If they occur, they are the exception rather than the rule. The number of chambers in the final whorl decreases almost linearly, despite known paleoceanographic oscillations within the temperate water mass. Mean size and apertural shape variations seem to correlate with paleoceanographic change. It is speculated that certain major morphological changes that took place within this evolutionary bioseries (i.e. loss of keel, rounding of periphery) developed in response to a major latest Miocene cooling, associated with instability in the water column and resulting adjustments of the test structure to water density changes. Changes exhibited in shape measurements may offer a precise method of stratigraphic correlation between temperate South Pacific Late Cenozoic sequences. Four species and two subspecies, long recognized to form the basis of this lineage, are redefined biometrically.

The pattern of arm branching and arm morphology in the camerate crinoid family Melocrinitidae became more complex during an evolutionary sequence which extended from Late Ordovician to Late Devonian. The fully evolved melocrinitid arm pattern bears an amazing resemblance to the theoretically ideal lay-out for harvesting roads on a banana plantation. This may not be coincidental since the problems faced by a banana plantation manager are much the same as those of a crinoid: the harvesting of an evenly distributed micro-particulate resource from an area and its delivery to a central point for processing. The analogy suggests a detailed explanation of the melocrinitid morphology and evolution. It also raises the question: why did the pattern not become dominant among crinoids if it was so efficient? It may have been unlikely to evolve; it may reflect an unusual food supply. I prefer an explanation in which the plantation pattern demands a rigidity of the crinoid crown which is characteristic of camerates but is uncommon among other crinoids: the latter have adopted a strategy of feeding which emphasizes flexibility in anatomy and behavior. The banana plantation pattern is equally rare among other organisms. Thus an “ideal” may not be common in a group of organisms for cost-benefit reasons. This does not mean that the adaptationist's approach is improper, or that random, historical, or constructional constraints routinely overwhelm adaptation. Rather, it means that cost-benefit analysis should take a larger part in functional studies, as it does in natural selection, and that theoretical ideals should be viewed with caution.

Systematics and paleontology have had a long conceptual relationship, united by the common goal of reconstructing the history of life. Yet, with few exceptions, paleontologists have had little input into formulating systematic theory and methodology. The reasons for this apparently relate to two conceptual-philosophical traditions of post-Darwinian paleontology: (1) the widespread adoption of a species concept in which taxa are viewed as nondiscrete, arbitrarily designated segments of evolutionary continua, and (2) the belief that phylogenetic reconstruction is primarily an empirical matter of tracing evolutionary change through the stratigraphic record.

Available systematic evidence supports the hypothesis that species are real, discrete units in space and time and that, unless they are postulated to be directly ancestral to another species, they can be defined by the possession of one or more evolutionary novelties (derived characters). Species beginnings are delineated by speciation (vicariance) events and their terminations by subsequent speciation events or by extinctions.

Natural groups are composed of taxa that have shared a common genealogical history. Cladistic analysis is a method to construct and test hypotheses of monophyly and thereby define natural groups. Cladistic hypotheses are necessary to investigate many of the major questions within contemporary paleobiology. Virtually no studies of evolutionary rates, patterns of taxonomic diversity, modes of taxic evolution, and patterns of morphological diversification can be undertaken without reference to cladistic hypotheses about the composition of natural groups.

Because paleobiology is historical in its content, paleontologists are greatly limited in their ability to use paleontological data to investigate questions about the evolutionary process. According to current evolutionary theory, the concepts of adaptation and natural selection relate to genetic and ecological processes that take place within local populations (microevolution). If so, then data relevant to examining these phenomena are likely to be lacking in paleontological samples. Consequently, explanations of paleontological pattern that include process-related concepts such as adaptation and natural selection are axiomatic in their logical structure and thus cannot be falsified or critically evaluated by that paleontological pattern.

The pedicle differentiates brachiopods from all other phyla. With its associated musculature, it is more variable than any other brachiopod system at or above the generic level and is considered to contribute to the versatility of behavior possessed by some species. Differences in pedicle type are reflected clearly in the beak.

Quantification of Paleozoic, Triassic, Jurassic, and Cretaceous ammonoid shell ornamentation shows that commonality and roughness of ornamentation increased throughout the geologic range of the ammonoids. The two major hypotheses concerning the function of ammonoid shell ornamentation are that 1) ornament served a protective (defensive) function against shell breakage by predators, and 2) it increased hydrodynamic efficiency of the shell during swimming. The heavily ribbed and spined ammonoid shells of the late Mesozoic have ornamentation too coarse to have served any hydrodynamic purpose. The increasing proportion of such shells during the Jurassic and Cretaceous may have been in response to increased numbers of late Mesozoic shell crushing predators and “better armed” ammonoid prey. This trend parallels adaptive trends of other invertebrate groups during the “Mesozoic marine revolution” as defined by Vermeij (1977).

Skull and tooth dimensions of Homo erectus fossils from Africa, Europe and Asia appear to fluctuate rather than to change progressively during an interval of 1.3 Myr prior to the start of the Upper Pleistocene. No significant trends can be observed. This suggests a period of stasis in human evolution, after which Homo sapiens may have evolved rapidly from archaic mid-Pleistocene ancestors.

Among the various forms developed by marine colonial filter feeders, erect colonial fans have evolved in representatives of several phyla. Branches are relatively narrow, evenly spaced from one another, proliferate by bifurcation, and in most colonies continue from their point of origin to the distal margin of the colony. Their narrowness and uniform placement is apparently related to filling an area with multiple tentacle bells of similar size. The major architectural problem for such a colonial suspension feeder seems to be construction of a sheet composed of narrow branches such that water may be filtered as it flows through the sheet, between branches.

The simplest form of the filtration sheets is a uniformly expanding wedge, in which new branches originate at regular intervals from the point of origin of the wedge. Variation in rate of addition of new branches results in more complex forms, such as paraboloids, flaring fans, spirals, and highly folded sheets.

The growth rate of Nautilus pompilius in its natural environment has been determined from radioactive disequilibrium between 210Pb (half-life 22.3 yr) and its granddaughter 210Po (half-life 138 d) in septa of two juvenile specimens. 210Pb and 210Po data from the most recently formed shell material of both specimens indicate that 210Pb from sea water is incorporated into septa during septal formation and 210Po is excluded. Therefore the 210Po/210Pb activity ratio serves as a chronometer to estimate the age of each septum and the time between formation of septa. In the specimens studied the average time between sucessive points in septal deposition is 75 d for the nine most recent septa of one specimen and 23 d for the six most recent septa of the other specimen. These different growth rates, if representative of the ontogeny of each animal, suggest that the timing of septal deposition probably is dependent on the rate of shell and tissue growth coupled with buoyancy requirements and is not a unique period for all Nautilus. The habitat and ontogeny of Nautilus may be inferred from the pattern of stable isotopes of oxygen and carbon in the septa. Both specimens show a pronounced break in δ18O from nearly uniform light values in the first seven septa to heavier values (∼1%) after the seventh septum. We interpret this break to correspond to the hatching of Nautilus. A temperature (i.e. water depth) interpretation of the δ18O data for septa after the eighth is complicated by a positive correlation between δ18O and δ13C. This may reflect horizontal migration of the animal or a kinetically controlled fractionation of carbon and oxygen isotopes during septal formation.

Fusion occurred between pairs of conspecific colonies of Permian fenestrate bryozoans that were of approximately equal radius at time of contact. In contrast, no fusion occurred in pairs of conspecific colonies that were of unequal radius at time of contact. It is suggested that histologically compatible colonies developed from larvae that settled essentially simultaneously and that the larvae were siblings, lecithotrophic with low mobility, and of the same genotype (i.e., polyembryonic). Thus polyembryony appears to have existed as a reproductive “strategy” for at least 275 Myr, and its scarcity in modern taxa cannot be due to recentness of evolution.

Size variation among several species of large mammals is examined both throughout a wide geographical range today and within the Late Pleistocene-Holocene archaeo-faunal sequence of Israel. A regression of log dental size on environmental temperature produces similar negative slopes for recent Palaearctic foxes, wolves and boars as well as for Nearctic foxes. These species, and others which also exhibit an inverse correlation between size and temperature today, became dwarfed at the end of the Pleistocene in Israel. Abundant fossil gazelle and fox mensural data indicate that this diminution coincided with the temperature elevation 12,000 yr ago. Both the similarity of regression slopes for the recent material and the temporal coincidence of dwarfing among fossil species, representing different ecologies, strongly implicate temperature as the main body-size determining factor. Changes evidenced in the fossil record for boar, wolf and fox approximate a 15°C temperature change (Δt) based on their respective present-day size-temperature regressions. This Δt, if taken as an estimate for the eastern Mediterranean, is considerably higher than generally accepted values.

An additional size reduction of aurochs, wolf and boar at the end of the Pleistocene or several millenia later is associated with their domestication. It may reflect man's preference for a large “head count” over individual large body size.

The chamber formation cycle in externally shelled, chambered cephalopods consists of mural ridge formation, secretion of the siphuncular connecting ring, septal calcification, and cameral liquid removal. Radiographic observation of the chamber formation cycle in specimens of Nautilus macromphalus allows direct observation of the various processes of the chamber formation cycle in a chambered cephalopod, and gives direct measures of rates. New chamber formation in N. macromphalus initiates when slightly more than half of the cameral liquid has been removed from the last formed chamber. At this volume, the liquid within the chamber drops from direct contact with the permeable connecting ring to a level where it is no longer in direct contact and must move onto the connecting ring due to wettable properties of the septal face and septal neck. This change from “coupled” to “decoupled” emptying coincides with the formation of a mural ridge at the rear of the body chamber, in front of the last formed septum. With completion of the mural ridge, the septal mantle moves forward from its position against the face of the last formed septum and attaches to the new mural ridge, where it begins calcifying a new septum in front of the newly created, liquid-filled space. Emptying of the new cameral liquid from this space commences when the calcifying septum has reached from one-third to two-thirds of its final thickness. The cessation of calcification of the septum coincides with a liquid volume in the new chamber of approximately 50%, at which point the cycle begins anew. During the chamber formation cycle apertural shell growth appears to be continuous. Since apertural shell growth is the prime factor leading to increased density in seawater, and hence decreased buoyancy, the period in the chamber formation cycle between the onset of septal calcification and the onset of emptying would be a time of greatly decreasing buoyancy. This is avoided by the removal of decoupled liquid from previously produced chambers. In this way constant neutral buoyancy is maintained. The time between chamber formation events in aquarium maintained N. macromphalus appears to be between 70 and 120 d.

In cheilostome bryozoans with rigidly arborescent growth habits, resistance to breakage under forces generated by flowing water or collision with moving objects depends on the strength and design of supporting skeletal parts. To investigate the abilities of modern and Tertiary cheilostomes to resist breakage, we measured bending strength in fresh, preserved, and fossil material; measured drag on actual and model colonies; and calculated stress within colonies and breaking values under concentrated and uniform loads. Among nine modern, five Oligocene, and four Paleocene species, inferred live bending strength (24–85 MNm−2) and stiffness (42–65 GNm−2) appear to be species-specific properties overlapping those of similar mineral-organic composite skeletons of Mollusca. Unlike those of Mollusca, cheilostome skeletons appear isotropic in bending, with strength not clearly related to microstructure or composition. Bending strength and morphologic disposition of skeletal material combine to produce a wide range of abilities to resist breaking. At early growth stages, almost all species appear highly resistant; at later ones, some break at velocities <0.2 m sec−1 or concentrated loads <2 g, whereas others remain unbroken at velocities >2 m sec−1 or concentrated loads >100 g. A negative correlation between strength and resistance indicates that design is the more important factor in the abilities of these bryozoans to withstand forces of these kinds. An apparent trend toward more resistant designs from Paleocene to modern species is related chiefly to increasing rates at which branches thicken toward the colony base. The consequent change in design may even have permitted modern species to use weaker skeletal material while increasing their overall resistance.

Analysis of post-mortem buoyancy loss in Nautilus shells suggests that extensive nekroplanktonic drifting occurs infrequently. Most shells do not reach the surface but settle to the sea floor, after a short period of ascent. This occurs because the rate of water influx into the phragmocone due to ambient hydrostatic pressure is sufficiently rapid in most cases to overcome positive buoyancy before the shell reaches the surface. The resulting geographic distribution of Nautilus shells would therefore mirror the distribution of the live animals. Thus, post-mortem drift in Nautilus cannot be used as a basis for questioning the validity of cephalopod paleobiogeography. Estimate of influx rates in ammonoid siphuncles indicates that many, if not most, ammonoid shells also would not become nekroplanktonic. This is especially true for small (<5 cm diameter) shells. Cephalopod paleobiogeographic investigation appears less subject to criticism stemming from the supposed obfuscating effects of post-mortem drift than previously thought.

Using computer simulations and analytic calculations, we have evaluated whether conspicuous expansions and contractions of natural clades may have represented chance fluctuations that occurred while probabilities of speciation and extinction remained equal and constant. Our results differ from those of previous workers, who have not scaled generating parameters empirically at the species level. We have found that the waxing and waning of many real clades have almost certainly resulted from changes in probabilities of speciation and extinction. For some of these changes, likely explanations are evident. The emplacement of adaptive innovations, for example, has at times elevated probability of speciation. We conclude that chance factors have not played a dominant role in producing dramatic changes in standing diversity within speciose higher taxa.

Lambeosaurine dinosaur crests are judged to have been conducive to resonation on the basis of an acoustic analysis of the structure of the nasal cavity. Size and shape of the nasal cavity suggest low vocal frequencies in adults, as does information on potential auditory acuity in these animals. Lateral diverticula (present in all but juvenile specimens) acted to suppress portions of the vocal spectrum. Juveniles vocalized at higher frequencies than adults and potential auditory sensitivity at high frequencies in adults suggests a high degree of parent-offspring vocal communication. Sexual variation and causes of selection for low frequency vocalization are also examined.

Two kinds of adaptation aid infaunal bivalve mollusks in sustaining their life positions against potentially disruptive water movements: (1) ability to retard scour of surrounding sediment and (2) ability to reburrow rapidly if exhumed.

The shell of the venerid Anomalocardia brasiliana is ornamented with concentric ridges that are asymmetrical in cross-section; experiments show that these ridges aid the animal in burrowing by gripping the sediment during backward rotation of the shell. The shell of the less deeply burrowing venerid Chione cancellata also bears concentric ridges, but these are symmetrical and experiments show that they hinder burrowing; other experiments demonstrate that these ridges reduce scour of sand from around a partly exposed animal. The single cardiid species Trachycardium egmontianum possesses adaptations comparable to those of the two venerid species, in the form of spines of two varieties; experiments show that the flared anterior spines facilitate burrowing and the cupped posterior spines reduce scour.

Conspicuous ornamentation of the kinds considered here was rare throughout the Paleozoic. Its evolutionary deployment occurred primarily during the post-Paleozoic adaptive diversification of infaunal bivalves, which was triggered by the evolution of efficient burrowing mechanisms. The general premium on maintaining infaunal life positions was accentuated for bivalves after the Paleozoic by the origins of important modern predatory taxa.