The faunas of three fossil sites in Africa that contain time successive groups of fossil Hominoidea have been analyzed to determine their paleoenvironments. The basis for the analysis is an assessment of the ecological diversity of the fauna, which is expressed in terms of four categories: taxonomic composition, body size, feeding habits and locomotor zonal adaptation. This method has shown that the community structures of the three fossil faunas are significantly different, and comparisons with the community structure of modern habitats suggest that the environment of the early Miocene fauna of Songhor, and the primitive apes associated with it, was probably a type of lowland forest; the habitat of Ramapithecus and the Fort Ternan middle Miocene fauna compares best with modern woodland-bushland habitats; and the habitat of Homo habilis at Olduvai appears to have been intermediate between grassland and woodland-bushland. If man evolved from one of the early forest living apes, as seems likely on present evidence, an adaptive shift from forest to non-forest habitats must have occurred at some stage in his evolution. The evidence from Fort Ternan shows that in Africa Ramapithecus made this adaptive shift, and it is also now becoming clear that several genera of Eurasian apes, including Ramapithecus, made a similar environmental change at the same time.

Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.

Gastropod opercula are classified here on a new morphogenetic basis, which distinguishes three main types: (1) flexiclaudent spiral (mostly multispiral) operculum, the shape of which does not coincide with that of the aperture, (2) rigiclaudent spiral (usually paucispiral) operculum, the shape of which fits that of the aperture, and (3) rigiclaudent concentric operculum, also aperture-fitting. The first type fits by flexing into the aperture and is secreted when the soft parts are partly or wholly extended (i.e., when the operculum is not in a closed position). The other two types do not flex upon retraction (except at the very margin) and grow when the operculum closes over the aperture, with or without rotation. A study of opercular types at the family level confirms the systematic and evolutionary significance of opercula. Types 1 and 2 are the only ones present in archaeogastropods, Type 1 being predominant. Opercula (if present) in Neritopsina are always rigiclaudent. Within Caenogastropoda, Type 2 predominates; the only flexiclaudent spiral opercula are found in certain basal cerithioidean families. Concentric opercula are predominant in higher neotaenioglossans and exclusive in neogastropods. Except for one family, opercula in Heterostropha are always rigiclaudent spiral. Morphological, systematic, and histological criteria point to the flexiclaudent spiral operculum as the ancestral form. This leads us to propose the “periostracum shaving” model in prosobranchs to account for the origin of this kind of operculum. According to this model, in the earliest trochospiral gastropods the periostracum ceased to serve a shell-formation function at the band of overlap between whorls (the parietal band). The periostracal band was then extruded from the shell to constitute an incipient operculum, taking on the appearance of a spiral strip coiling opposite to the shell. The parietal segment of the periostracal groove migrated toward the epipodium and became independent from the rest of the mantle. The concomitant development of an opercular disc allowed the successive turns of periostracal strip to seal together. In this way, a spiral operculum emerged, coiling counterclockwise without matching the aperture shape. During the course of prosobranch evolution, rigiclaudent spiral opercula emerged several times from the ancestral flexiclaudent type, although they were always restricted to apertures with a spiral-shaped outer (labral) edge. Such opercula enlarged the range of shell morphologies for which the operculum constituted an efficient protective barrier to include those of neritoidean or naticoidean type. The onset of calcification in opercula took place with the rigiclaudent type. Concentric opercula also evolved independently from rigiclaudent spiral opercula in several gastropod groups, thus further broadening the spectrum of apertures and, hence, of shell morphologies using opercula for protection. From the standpoint of adaptation, the concentric type was probably the only one available to neogastropods having long and wide siphonal canals.

A physical, model-based approach to body temperatures in dinosaurs allows us to predict what ranges of body temperatures and what thermoregulatory strategies were available to those dinosaurs. We argue that

1. 1. The huge range of body sizes in the dinosaurs likely resulted in very different thermal problems and strategies for animals at either end of this size continuum.

2. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in the absence of insulation. The smallest animals in which metabolic heating resulted in predicted body temperatures ≥ 2°C above operative temperatures (Te) weigh 10 kg. Body temperature would respond rapidly enough to changes in Te to make behavioral thermoregulation possible.

3. 3. Body temperatures of large dinosaurs (>1000 kg) likely were sensitive to both metabolic rate and the delivery of heat to the body surface by blood flow. Our model suggests that they could adjust body temperature by adjusting metabolic rate and blood flow. Behavioral thermoregulation by changing microhabitat selection would likely have been of limited utility because body temperatures would have responded only slowly to changes in Te.

4. 4. Endothermic metabolic rates may have put large dinosaurs at risk for overheating unless they had adaptations to shed the heat as necessary. This would have been particularly true for dinosaurs with masses > 10,000 kg, but simulations suggest that for animals as small as 1000 kg in the Tropics and in temperate latitudes during the summer, steady-state body temperatures would have exceeded 40°C. Slow response of body temperatures to changes in Te suggests that use of day-night thermal differences would have buffered dinosaurs from diel warming but would not have lowered body temperatures sufficiently for animals experiencing high mean daily Te.

5. 5. Endothermic metabolism and metabolic heating might have been useful for intermediate and large-sized (100–3000 kg) dinosaurs but often in situations that demanded marked seasonal adjustment of metabolic rates and/or precise control of metabolism (and heat-loss mechanisms) as typically seen in endotherms.

Mammalian carnivores are rarely incorporated in paleoenvironmental reconstructions, largely because of their rarity within the fossil record. However, multivariate statistical modeling can be successfully used to quantify specific anatomical features as environmental predictors. Here we explore morphological variability of the humerus in a closely related group of predators (Felidae) to investigate the relationship between morphometric descriptors and habitat categories. We analyze linear measurements of the humerus in three different morphometric combinations (log-transformed, size-free, and ratio), and explore four distinct ways of categorizing habitat adaptations. Open, Mixed, and Closed categories are defined according to criteria based on traditional descriptions of species, distributions, and biome occupancy. Extensive exploratory work is presented using linear discriminant analyses and several fossils are included to provide paleoecological reconstructions.

We found no significant differences in the predictive power of distinct morphometric descriptors or habitat criteria, although sample splitting into small and large cat guilds greatly improves the stability of the models. Significant insights emerge for three long-canine cats: Smilodon populator, Paramachairodus orientalis, and Dinofelis sp. from Olduvai Gorge (East Africa). S. populator and P. orientalis are both predicted to have been closed-habitat adapted taxa. The false “sabertooth” Dinofelis sp. from Olduvai Gorge is predicted to be adapted to mixed habitat. The application of felid humerus ecomorphology to the carnivoran record of Olduvai Gorge shows that the older stratigraphic levels (Bed I, 1.99–1.79 Ma) included a broader range of environments than Beds II or V, where there is an abundance of cats adapted to open environments.

A hierarchical branching model is presented that tracks diversity of lineages and paraclades simultaneously. It is based on three parameters: (1) lineage origination within a paraclade, (2) lineage origination that founds new paraclades, and (3) lineage extinction. The model assumes stochastic constancy of evolutionary rates and, therefore, exponential growth of diversity is the null expectation. The probabilistic model can be used to generate confidence intervals for exponential growth through Monte Carlo simulation. These confidence intervals can be compared to empirical curves to test the null hypothesis of exponential growth. The analytic solution for paraclade diversity gives the statistical expectation for the probabilistic model. It can be applied to empirical diversity curves of supraspecific taxa to estimate total speciation rate, the intrinsic rate of increase, and the proportion of speciation events that found new paraclades. Two factors were identified with the model that may cause diversity curves for higher taxa (e.g., genera, families) to deviate from simple exponential growth during initial phases of diversification: (1) stochastic fluctuation at low diversity, and (2) taxonomic structure (i.e., species/genus ratio). These sources of variability should be evaluated before macroevolutionary explanations for specific diversity trends are invoked. Two kinds of evolutionary radiations were investigated with this model: (1) prolonged periods of low diversity (macroevolutionary lag) in cheilostome bryozoans and mammals prior to their main phases of diversification, and (2) rapid bursts in diversity of bivalves following the late Permian and end-Cretaceous mass extinctions. In all cases these patterns were found to deviate significantly from the null expectation of exponential growth lending support to previous macroevolutionary explanations. Finally, rates of speciation during radiations were compared to rates of speciation during background times for articulate brachiopods, cheilostome bryozoans, bivalves, and mammals. Speciation events that found new paraclades tend to make up a larger proportion of total speciation events during radiations compared to background times indicating that the opportunity for new adaptive zones to be filled at higher taxonomic levels is proportionately higher during these periods of increased evolutionary activity, and is not simply a result of an increased frequency of speciation.

Inferring the causes for change in the fossil record has been a persistent problem in evolutionary biology. Three independent lines of evidence indicate that a lineage of the fossil stickleback fish Gasterosteus doryssus experienced directional natural selection for reduction of armor. Nonetheless, application to this lineage of three methods to infer natural selection in the fossil record could not exclude random process as the cause for armor change. Excluding stabilizing selection and genetic drift as the mechanisms for biostratigraphic patterns in the fossil record when directional natural selection was the actual cause is very difficult. Biostratigraphic sequences with extremely fine temporal resolution among samples and other favorable properties must be used to infer directional selection in the fossil record.

One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within- and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within- and among-genus components. We find that size reduction following the end-Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within-lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within- and among-lineage processes rather than from large but offsetting effects of within- and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms.

Taxon discovery underlies many studies in evolutionary biology, including biodiversity and conservation biology. Synonymy has been recognized as an issue, and as many as 30–60% of named species later turn out to be invalid as a result of synonymy or other errors in taxonomic practice. This error level cannot be ignored, because users of taxon lists do not know whether their data sets are clean or riddled with erroneous taxa. A year-by-year study of a large clade, Dinosauria, comprising over 1000 taxa, reveals how systematists have worked. The group has been subject to heavy review and revision over the decades, and the error rate is about 40% at generic level and 50% at species level. The naming of new species and genera of dinosaurs is proportional to the number of people at work in the field. But the number of valid new dinosaurian taxa depends mainly on the discovery of new territory, particularly new sedimentary basins, as well as the number of paleontologists. Error rates are highest (>50%) for dinosaurs from Europe; less well studied continents show lower totals of taxa, exponential discovery curves, and lower synonymy rates. The most prolific author of new dinosaur names was Othniel Marsh, who named 80 species, closely followed by Friedrich von Huene (71) and Edward Cope (64), but the “success rate” (proportion of dinosaurs named that are still regarded as valid) was low (0.14–0.29) for these earlier authors, and it appears to improve through time, partly a reflection of reduction in revision time, but mainly because modern workers base their new taxa on more complete specimens. If only 50% of species are valid, evolutionary biologists and conservationists must exercise care in their use of unrevised taxon lists.

There is growing evidence that changes in deep-sea benthic ecosystems are modulated by climate changes, but most evidence to date comes from the North Atlantic Ocean. Here we analyze new ostracod and published foraminiferal records for the last 250,000 years on Shatsky Rise in the North Pacific Ocean. Using linear models, we evaluate statistically the ability of environmental drivers (temperature, productivity, and seasonality of productivity) to predict changes in faunal diversity, abundance, and composition. These microfossil data show glacial-interglacial shifts in overall abundances and species diversities that are low during glacial intervals and high during interglacials. These patterns replicate those previously documented in the North Atlantic Ocean, suggesting that the climatic forcing of the deep-sea ecosystem is widespread, and possibly global in nature. However, these results also reveal differences with prior studies that probably reflect the isolated nature of Shatsky Rise as a remote oceanic plateau. Ostracod assemblages on Shatsky Rise are highly endemic but of low diversity, consistent with the limited dispersal potential of these animals. Benthic foraminifera, by contrast, have much greater dispersal ability and their assemblages at Shatsky Rise show diversities typical for deep-sea faunas in other regions.

Statistical analyses also reveal ostracod-foraminferal differences in relationships between environmental drivers and biotic change. Rarefied diversity is best explained as a hump-shaped function of surface productivity in ostracods, but as having a weak and positive relationship with temperature in foraminifera. Abundance shows a positive relationship with both productivity and seasonality of productivity in foraminifera, and a hump-shaped relationship with productivity in ostracods. Finally, species composition in ostracods is influenced by both temperature and productivity, but only a temperature effect is evident in foraminifera. Though complex in detail, the global-scale link between deep-sea ecosystems and Quaternary climate changes underscores the importance of the interaction between the physical and biological components of paleoceanographical research for better understanding the history of the biosphere.

Model calculations predict that pathways of alpha- and beta-diversity in diversifying ecosystems notably differ depending on the relative role of competition, predation, positive effects of species' interactions, and environmental parameters. Four scenarios are discussed, in which alpha- and beta-diversity are modeled as a function of increasing gamma-diversity. The graphic illustration of this approach is herein called α-β-γ plot, in which the x-axis indicates increasing diversification rather than absolute time. In purely environmentally controlled systems, beta-diversity maintains near-maximum values throughout the diversification interval, whereas mean alpha-diversity increases linearly, with a slope being reciprocal to beta-diversity. A second scenario is based on the assumption that increasing richness will have predominantly positive effects on the addition of further species; here, alpha- and beta-diversity increase simultaneously (though not necessarily at the same rates) and without reaching a predictable upper limit. In ecosystems that are characterized by low competition between species, mean alpha-diversity asymptotically approaches a saturation level, whereas the increase in beta-diversity accelerates until alpha-diversity stagnates, and then continues to rise linearly. If competition is high, addition of species first increases beta-diversity until no further habitat contraction is possible, followed by a period in which alpha-diversity increase through adaptive divergence becomes the principal drive of diversification. Because there is a continuous transition between the late stage of the low-competition model and the early stage of the high-competition scenario, both can be combined in a single model of diversity partitioning under the premise of a diversity-dependent increase of competition. This summary model predicts three phases of diversity accumulation: (1) a niche overlap phase, (2) a habitat contraction phase, and (3) a niche differentiation phase. The models herein discussed provide a potential tool to assess the question which factors primary controlled the diversification of life over geological times.

In recent articles in this journal Hansen (1980) and Jablonski (1980) discussed the planktonic larval stages of fossil benthic invertebrates and the relation of type of larval development to geographic ranges, nearshore-offshore position, speciation, and extinction. The fossil record provides a view of long term consequences of types of larval development, and the emphasis of these, and other, paleobiological studies was on selection among species which are characterized by different developmental adaptations.

Studies of ecological structure and diversity over time in extinct groups have always been challenged by the inability to observe the behavior of fossil taxa directly. The only available evidence for function, behavior, and interactions between taxa is the morphological characteristics of the preserved fossils. Recent studies on modern groups have shown that morphological analyses may give misleading results in terms of ecological pattern and diversity. An alternative approach is to focus on functionally relevant aspects of morphology through a paleobiomechanical paradigm. The purpose of this research is to examine variation in the lower jaw morphology in Late Devonian arthrodire placoderms and develop biomechanical metrics that can be used to quantify functional diversity among this fossil group. Nine functionally relevant morphological characters were collected for 94 isolated arthrodire inferognathals from the Gogo Formation in Western Australia and the Cleveland Shale in Ohio. These data were used to address aspects of functional morphology, biomechanical disparity, and ecological structure in arthrodire placoderms from the Late Devonian. Results were compared with results from previous morphometric work on the same set of jaws.

Statistical tests show a significant difference in functional characters between the two faunas. The differences may be related to phylogenetic differences between faunas, as the two major clades of arthrodire taxa included in this study are almost completely segregated between faunas. Average pairwise disparity analyses of the mechanical characters indicate that there is no significant difference in overall functional diversity between the Cleveland Shale and Gogo Reef arthrodire faunas. This result is at odds with previous results that show overall morphological disparity to be much higher in the Cleveland Shale. Clustering patterns within a multivariate function-space show tightly constrained functional groups of taxa independent of phylogenetic or shape-based morphological similarity. These functional groups illustrate a level of ecological diversity in Late Devonian arthrodires that is comparable to that in certain modern faunas.

Further statistical analysis of the morphological and functional disparity of these Late Devonian taxa shows a disjoint between the two measures. Model I regression analysis of and Spearman rank-correlation analysis of average pairwise morphological and functional disparity measures indicate no significant relationship between morphological and functional disparity among the jaws used in this study. Although function is obviously derived from morphology, these results show that morphological shape analysis is not necessarily a good proxy for eco-functional diversity.

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.

Capture-mark-recapture of Nautilus belauensis in Palau shows that (a) immature animals added an average of 0.1 mm of shell per day at the ventral circumference (projected mean annual increment of 37 mm), but this rate decreases rapidly as maturity is approached; (b) rate of growth line secretion is irregular, ranging from 4 to 8 days per growth line in immature animals; (c) overall weight is an imprecise measure of size and growth in Nautilus due to fluctuations in crop content and chamber liquid; (d) this species is shown to live for at least 4 yr beyond maturity. Age estimates based on the highest growth rate obtained (0.12 mm/day = 43.8 mm/yr) range from 14.5 to 17 yr for seven animals recaptured 45–355 days after release. Combined, these data indicate that the life span of Nautilus may exceed 20 yr.

Concavo-convex brachiopods are generally assumed to have lived with their convex valves against the sediment. This orientation is based primarily on the a priori assumption that the upturned commissure would prevent fouling of the brachiopods' mantle cavity. Here, I present epibiontic and taphonomic evidence from orthids and nonproductid strophomenids that concavo-convex brachiopods lived in the reverse life orientation, with the convex valve on top.

Ten testable epibiontic and taphonomic criteria are proposed to establish the uppermost valve during encrustation and whether epibionts encrusted primarily live or dead hosts. The criteria are evaluated for 11 collections of Ordovician and Devonian nonproductid concavo-convex brachiopods that contain a total of over 500 brachiopods and 4000 epibionts. In all cases, the results support a convex-up orientation and the encrustation of live hosts. Five criteria concern epibiont growth patterns and show that (1) epibionts predominate on convex valves, (2) epibionts are not restricted to shell margins, (3) distinct exposed and cryptic faunas, as predicted theoretically and described in previous studies, exist on convex and concave valves respectively, (4) epibiont colonies were often truncated by the commissures and hinges of live hosts, and (5) growth patterns of some epibionts indicate live hosts. Five taphonomic criteria show that (1) concavo-convex shells have greater epibiont cover than other morphologies, (2) internal surfaces of disarticulated specimens are rarely encrusted, (3) interiors of articulated specimens are rarely mud-filled, (4) standard taphofacies indicators suggest little postmortem exposure, and (5) sedimentological reconstructions suggest rapid burial.

Convex-up brachiopods suggest that the Paleozoic mud bottoms they lived on were probably firmer than usually assumed and that a more complex functional interpretation of concavo-convexity is required. Hydrodynamic stability was important to many concavo-convex, plano-convex, and unequally bi-convex brachiopods. Brachiopods with these morphologies probably lived in the more stable orientation on their concave or flat valve. Productid brachiopods, although also concavo-convex, lived convex valve down and are ecologically distinct from earlier concavo-convex taxa. Productids were anchored, semi-infaunally, by spines and were more similar to Mesozoic oysters in orientation and shell function.

A diffusion model of the distribution of a phenotypic character in a group of species is developed and analyzed. The model incorporates the combined effects of phyletic evolution, speciation and extinction. Directed speciation is modeled by assuming there is some bias to phenotypic changes during speciation. Species selection is modeled by assuming there is some dependence of either speciation or extinction rates on the phenotypic character. Three examples are analyzed to illustrate the use of the model. A model of completely random changes due to both phyletic evolution and speciation shows how between-species differences are established. A model of directed speciation due to multiplicative changes during speciation shows how a simple assumption about the speciation process can produce macroevolutionary trends. A model of species selection due to differences in extinction rates shows how the efficacy of species selection depends on the between-species variance produced both by speciation and by phyletic evolution.

Applications of the species-area equation to studies of fluctuations in Phanerozoic diversity have great promise but can involve questionable assumptions. Sepkoski's (1976) analysis of marine diversity throughout the Phanerozoic record assumes that total rock volume is a sufficient measure of sampling efficiency and that an isomorphous equation is appropriate for all of Phanerozoic time. The area of marine sedimentary rock and the area of continental seas are not independent variables. Residual variation in diversity (that which remains after subtracting the effects of rock volume) might be explained by either the species-area relationship or by another component of sampling efficiency. A species-area equation in which the slope (z) and intercept (k) are assumed constant receives mixed support from arguments based on Recent terrestrial and aquatic organisms. Observed z-values cluster near a value of 0.30 despite a wide taxonomic range, but are generally below those found for the Phanerozoic record. Temporal fluctuations in k values, in response to changes in the area of continental seas, may produce elevated estimates of z.

Application of computed tomography to the most recently recognized specimen of Archaeopteryx demonstrates the potential of this technique for paleontological issues. Contrary to earlier interpretations of these specimens, the results of computed tomography appear to show the presence of an avian-like doubled-headed quadrate bone in this earliest true bird.

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.