The age (mortality) profiles of ungulate species in a fossil fauna are useful for reconstructing modes of death and of bone accumulation. Crown height measurements probably provide the most practical means of obtaining age profiles in most fossil samples. Reliable, interpretable profiles will result when individual age is estimated from crown height using a mathematical model first suggested by C. A. Spinage and when the individual ages are grouped into relatively broad age classes. One potential objection to the model is that it requires tedious calculation and there is a strong possibility of calculation error when many crown heights are involved. This problem may be circumvented by the use of an interactive BASIC program appended to this paper. The user supplies the raw crown heights in a fossil sample, together with estimates of initial unworn crown height, ages of dental shedding and eruption, and maximum possible individual age. The program then tabulates the number of individuals in successive 10%-of-potential-lifespan intervals.

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.

The thoughts and writings of Stephen Jay Gould have had an enormous impact on the shaping of macroevolutionary theory. The notion of punctuated equilibria (Eldredge and Gould 1972) remained prominent throughout his work. It also unleashed a storm of debate in paleontology and evolutionary theory. A second theme that recurs throughout Gould's opus is heterochrony (evolution by changes in the rates and timing of ontogenetic events, sensu Gould 1977a). His analyses of these two subjects have inspired many of us to explore further and add to them. My contribution discusses their expansion to encompass large numbers of lineages through long time, and the relationship of punctuated equilibria and heterochrony to physical environmental change, and to each other.

Terrestrial mass extinctions have been attributed to a wide range of causes. Some of them are external to Earth, such as bolide impacts (as widely discussed for the K/T boundary) and radiation events. Among radiation events, there are possible large solar flares, nearby supernovae, gamma-ray bursts (GRBs), and others. These have variable intensity, duration, and probability of occurrence, although some generalizations are possible in understanding their effects (Ejzak et al. 2007). Here we focus on gamma-ray bursts (Thorsett 1995; Scalo and Wheeler 2002), a proposed causal agent for the end-Ordovician extinction. These are the most remote and infrequent of events, but by virtue of their power, a threat approximately competitive with, for example, that of nearby supernovae. A GRB of the most powerful type (Woosley and Bloom 2006) is thought to result from a supernova at the end of stellar evolution for very massive stars with high rotational speed. Much of their energy is channeled into beams, or jets, which include very high energy electromagnetic energy, i.e., gamma-rays and X-rays. It is a testament to the power of these events, far across the observable universe, that they were first detected in the 1969–1970 results from monitoring satellites designed to detect nuclear explosions on Earth's surface. It was not until the 1990s, when the distance to the events became known, that their power became apparent. Several such events occur every day in the observable universe. Other kinds of events are also potentially damaging, such as so-called short bursts and solar flares, but rate information is only now beginning to clarify how much threat is likely from such sources.

Stratigraphic data are compared to morphologic data in terms of their fit to phylogenetic hypotheses for 29 data sets taken from the literature. Stratigraphic fit is measured using MacClade's stratigraphic character, which tracks the number of independent discrepancies between observed order and the order of occurrence that would be expected on the basis of a given phylogenetic hypothesis. Acceptance of a phylogenetic hypothesis despite such discrepancies requires ad hoc hypotheses concerning differential probabilities of preservation and recovery. These stratigraphic ad hoc hypotheses are treated as logically equivalent to morphologic ad hoc hypotheses of homoplasy. The retention index is used to compare the number of stratigraphic and morphologic ad hoc hypotheses required by given phylogenetic hypotheses. Each data set is subjected to five analyses, varying in the constraints imposed on the structure of the phylogenetic tree against which fit is measured. Analyses 1–4 compare the stratigraphic and morphologic retention indices using phylogenetic trees consistent with the morphologically most-parsimonious cladogram reported in the original study. Analysis 5 compares retention indices using the overall (stratigraphically and morphologically) most-parsimonious phylogenetic tree, which may be, but is not necessarily, consistent with the reported cladogram. Proceeding from Analysis 1 to Analysis 5, stratigraphic data are allowed greater influence in determining the structure of phylogenetic trees, with the trees in Analysis 1 derived without reference to the stratigraphic character and the trees in Analysis 5 derived from full interaction of stratigraphic and morphologic characters. Morphologic and stratigraphic retention indices for these 29 studies cannot be statistically distinguished in comparisons 3–5, suggesting very similar degrees of fit. The values of these retention indices are high, indicating a generally high level of congruence under these phylogenetic hypotheses. Significant gains (49%) in stratigraphic fit can be realized without significant loss (4%) in morphologic fit as the stratigraphic and morphologic evidence are both allowed to participate in constraining the structure of phylogenetic hypotheses. These results suggest that arguments based on alleged “noisiness” of stratigraphic data offer inadequate grounds for ignoring stratigraphic order in phylogenetic analysis. In terms of congruence, stratigraphic and morphologic data perform about equally well.

Analysis of the evolution of the Globorotalia (Fohsella) lineage of planktic foraminifera suggests that reproductive ecology and shell shape have evolved independently in this group. The silhouette of fohsellid shells displays a nearly unbroken anagenetic trend, yet isotopic data show that the fohsellids changed their depth of reproduction during the anagenetic evolution of their skeletons. Remarkably, there are no correlations between anagenesis in skeletal shape and the establishment of reproductive isolation. Apparently, anagenesis masks at least one speciation event that is apparent only in the isotopic evidence for a change in reproductive ecology. Although anagenetic trends have been widely cited as evidence for gradual speciation in planktic foraminifera and other microfossil groups, our data suggest that they should not always be considered to record either the tempo or mode of speciation.

Speciation was apparently uncoupled from morphological evolution in fohsellids because these evolutionary phenomena occurred in different phases of ontogeny. Gradual morphological changes were associated with the main phase of shell growth of both the ancestor and descendant species in the near-surface ocean. Reproductive isolation occurred when ancestral and descendant populations became established at different depths near the end of the life cycle. Morphological evolution may also be uncoupled from reproductive isolation in other organisms that experience very different selection pressures over the duration of their ontogenies, such as parasites with many hosts, species with multiple phases of metamorphosis, and organisms that broadcast their gametes.

A preliminary report is presented documenting the evolution of the Globorotalia crassaformis (Galloway and Wissler) lineage from the Early Pliocene G. cibaoensis (Bermudez) in Hydraulic Piston Core 72/516 on the Rio Grande Rise (western South Atlantic). A new technique, eigenshape analysis, is used to describe the gross changes in morphology, and the use of “Raupian” analysis of expansion rates, angular displacement, position relative to coiling axis, and translation rates of chambers is suggested as a useful vehicle for inferring the geometric causes of observed evolutionary changes. These changes include size increase, decrease in the number of chambers per whorl, inflation, reduction of relative height of aperture, and increase in the peripheral angle. The sequence is judged to be an example of phyletic gradualism.

The turnover-pulse hypothesis (TPH) makes explicit predictions concerning the potential responses of species to climate change, which is considered to be a major cause of faunal turnover (extinction, speciation, and migration). Previous studies have tested the TPH primarily by examining temporal correlations between turnover pulses and climatic events. It is rarely possible to dissect such correlations and observe turnover as it is occurring or to predict how different lineages will respond to climate change. Thus, whether climate change drives faunal turnover in the manner predicted by the TPH remains unclear. In this study, we test the underlying mechanics of the TPH using well-dated Quaternary ungulate records from southern Africa's Cape Floristic Region (CFR). Changes in sea level, vegetation, and topographic barriers across glacial-interglacial transitions in southern Africa caused shifts in habitat size and configuration, allowing us to generate specific predictions concerning the responses of ungulates characterized by different feeding habits and habitat preferences. Examples from the CFR show how climatically forced vegetation change and allopatry can drive turnover resulting from extinction and migration. Evidence for speciation is lacking, suggesting either that climate change does not cause speciation in these circumstances or that the evolutionary outcome of turnover is contingent on the nature and rate of climate change. Migrations and extinctions are observed in the CFR fossil record over geologically short time intervals, on the order of Milankovitch-scale climate oscillations. We propose that such climate oscillations could drive a steady and moderate level of faunal turnover over 104-year time scales, which would not be resolved in paleontological records spanning 105 years and longer. A turnover pulse, which is a marked increase in turnover relative to previous and subsequent time periods, requires additional, temporally constrained climatic forcing or other processes that could accelerate evolutionary change, perhaps mediated through biotic interactions.

Short-term fluctuations in the diversification rate of Paleozoic marine animal genera are more strongly correlated with extinction-rate variation than with origination-rate variation. Diversity dynamics are strikingly different in the Mesozoic and Cenozoic, when variation in origination is more important than extinction. Data on the lithologic context of taxonomic occurrences in the Paleobiology Database are used to assess the substrate affinities of Paleozoic genera. The greater role of extinction-rate variation in the Paleozoic is found to characterize genera with an affinity for carbonate substrates but not those that prefer terrigenous clastic substrates. It is therefore plausible that the Paleozoic to post-Paleozoic shift in diversity dynamics is underlain in part by the secular decline in the relative areal extent of carbonate environments, and the concomitant decline in the relative diversity of carbonate-versus clastic-loving taxa.

A simple principle predicts a tendency, or vector, toward increasing organismal complexity in the history of life: As the parts of an organism accumulate variations in evolution, they should tend to become more different from each other. In other words, the variance among the parts, or what I call the “internal variance” of the organism, will tend to increase spontaneously. Internal variance is complexity, I argue, albeit complexity in a purely structural sense, divorced from any notion of function. If the principle is correct, this tendency should exist in all lineages, and the resulting trend (if there is one) will be driven, or more precisely, driven by constraint (as opposed to selection). The existence of a trend is uncertain, because the internal-variance principle predicts only that the range of options offered up to selection will be increasingly complex, on average. And it is unclear whether selection will enhance this vector, act neutrally, or oppose it, perhaps negating it. The vector might also be negated if variations producing certain kinds of developmental truncations are especially common in evolution.

Constraint-driven trends—or what I call large-scale trends of the fourth kind—have been in bad odor in evolutionary studies since the Modern Synthesis. Indeed, one such trend, orthogenesis, is famous for having been discredited. In Stephen Jay Gould's last book, The Structure of Evolutionary Thought, he tried to rehabilitate this category (although not orthogenesis), showing how constraint-driven trends could be produced by processes well within the mainstream of contemporary evolutionary theory. The internal-variance principle contributes to Gould's project by adding another candidate trend to this category.

The fossil record is incomplete in the sense that taxa for which there are no preserved finds are unrepresented. Because the probability that there is at least one preserved find is greater for long-lived taxa, failure to account for this effect will bias estimation of mean taxonomic duration. This paper describes maximum likelihood estimation of mean taxonomic duration, fossil preservation rate, and completeness of the local fossil record under a model in which duration has an exponential distribution and the locations of preserved finds follow a Poisson process. The estimates under this model have simple closed forms. It is also straightforward to construct confidence regions for the model parameters. The method is applied to data on 110 trilobite species from the Upper Cambrian—Lower Ordovician in Oklahoma.

The three dimensional structure of vegetation is an important component of ecosystems, yet it is difficult to reconstruct from the fossil record. Forests or woodlands prevailed at mid-latitudes in North America during the early Eocene but tree spacing and canopy structure are uncertain. Here we use stable carbon isotope values (δ13C) in early Eocene mammalian faunas to infer canopy structure. We compare δ13C values in two diverse fossil assemblages from the central Bighorn Basin to values predicted for mammals in a variety of open and closed habitats, based on modern floras and faunas. We conclude that these early Eocene faunas occupied an open canopy forest. We also use carbon and oxygen isotopes to infer diet and microhabitat. Three higher level taxa have significantly different mean δ13C values, and values are negatively correlated with body mass. The pattern suggests diets high in leaves for larger mammals, and fruit or other non-foliar plant organs for small ones. A preference in the larger mammals for wetter habitats with high water availability to plants may also have contributed to the pattern.

We investigate whether musculoskeletal anatomy and three-dimensional (3-D) body proportions were modified during the evolution of large (>6000 kg) body size in Allosauroidea (Dinosauria: Theropoda). Three adaptations for maintaining locomotor performance at large body size, related to muscle leverage, mass, and body proportions, are tested and all are unsupported in this analysis. Predictions from 3-D musculoskeletal models of medium-sized (Allosaurus) and large-bodied (Acrocanthosaurus) allosauroids suggest that muscle leverage scaled close to isometry, well below the positive allometry required to compensate for declining muscle cross-sectional area with increasing body size. Regression analyses on a larger allosauroid data set finds slight positive allometry in the moment arms of major hip extensors, but isometry is included within confidence limits. Contrary to other recent studies of large-bodied theropod clades, we found no compelling evidence for significant positive allometry in muscle mass between exemplar medium- and large-bodied allosauroids. Indeed, despite the uncertainty in quantitative soft tissue reconstruction, we find strong evidence for negative allometry in the caudofemoralis longus muscle, the single largest hip extensor in non-avian theropods. Finally, we found significant inter-study variability in center-of-mass predictions for allosauroids, but overall observe that consistently proportioned soft tissue reconstructions produced similar predictions across the group, providing no support for a caudal shift in the center of mass in larger taxa that might otherwise reduce demands on hip extensor muscles during stance. Our data set provides further quantitative support to studies that argue for a significant decline in locomotor performance with increasing body size in non-avian theropods. However, although key pelvic limb synapomorphies of derived allosauroids (e.g., dorsomedially inclined femoral head) evolved at intermediate body sizes, they may nonetheless have improved mass support.

Phytogeographic analysis of three Early Carboniferous intervals (Tournaisian–early Visean, Visean, and late Visean–early Namurian A) indicates a high level of phytogeographic differentiation in the beginning of the Early Carboniferous that decreases toward the end of this period. Climatic amelioration (warmer or wetter conditions) in the north middle and high latitudes, caused by the collision of Laurussia and Gondwana at the end of the Early Carboniferous, may be responsible for this decrease in phytogeographic provinciality. Toward the end of the Early Carboniferous, a large number of equatorial genera expand their ranges northward, and the average generic diversity of assemblages in the north high latitudes (Siberia) also rises. Both support the hypothesis of climatic amelioration. Northward migration of equatorial forms and the appearance of new genera endemic to Siberia both contributed to the rise in Siberian diversity. Although this trend is not statistically significant, additional evidence of diversity increase in northern high latitudes tied to climatic amelioration comes from the northernmost limit of diverse (≥ 10 genera) assemblages, which rises from 20°N at the beginning to 55°N at the end of the Early Carboniferous. Global plant diversity assessed at the generic level remained constant during the Early Carboniferous. The increase in Siberian diversity was offset by a decrease in equatorial diversity, perhaps due to the loss of pronounced latitudinal climatic gradients between north-middle and equatorial latitudes.

Most studies of extinction selectivity have focused on mass extinctions. Here we analyze the patterns of susceptibility to extinction during the late Pliocene and Pleistocene of California in the family Pectinidae. The Pectinidae declined in diversity from a high of 32 species in the late Pliocene to the current level of 11 species living in the California region, indicating that the composition of the living fauna has been shaped primarily by extinction in the last several million years. Extinction appears to have occurred in one large pulse, but because of uneven sampling we were unable to resolve the timing further and have analyzed the patterns of extinction treating the late Pliocene through middle Pleistocene as a single period of elevated extinction. Extinctions were not random with regard to taxonomic relationships. Species-level extinctions were higher in more speciose genera, but these genera were buffered against genus-level extinctions. This resulted in a disproportionately large number of monospecific genera in the living fauna. In addition, extinctions were not random with regard to body size, with large species preferentially surviving. This selectivity pattern is evident only when clade membership is taken into account; when analyzed across the entire family, no pattern of size selectivity was apparent. Our results suggest that (1) patterns of extinction selectivity at the genus level may be a poor proxy for species-level patterns, and (2) whole-fauna analyses may not uncover strong selectivity within lineages.

Despite exhaustive investigation of present-day Nautilus, the phylogenetic relationships of the five or six recognized species within this genus remain unclear. Mitochondrial and nuclear DNA sequence data plus a suite of morphological characters are used to investigate phylogenetic relationships. Systematic analysis of the morphological variation fails to characterize described species as independent lineages. However, DNA sequence analysis indicates that there are three geographically distinct clades consisting of western Pacific, eastern Australian/Papua-New Guinean, and western Australian/Indonesian forms. The morphologically and genetically distinct species Nautilus scrobiculatus falls outside the three geographically recognized assemblages. Members of the genus Nautilus also exhibit low levels of sequence divergence. All these data suggest that Nautilus is currently undergoing diversification, which may have begun only several million years ago. These data also suggest that some of the morphological features used to define Nautilus species may simply represent fixed variations in isolated populations within the same species.

The recurring debate over the causes of the massive extinctions of such groups as the dinosaurs, ammonites, and calcareous nannoplankton, and the crash of the distinctive Aquilapollenites pollen province, used by biostratigraphers to mark the close of the Cretaceous, has been considerably enlivened with the resurgence of hypotheses suggesting catastrophic events. The impact of an asteroid, explosion of a supernova, sudden changes in oceanic circulation and composition, or atmospheric perturbations, to mention a few, have been put forward as malefactors. But, just how sound is the evidence of a biotic catastrophe?

The mass, wingspan, and wing area of pterosaurs were reconstructed. Mass was estimated by determining volume and multiplying by avian density. This method was considered appropriate only for smaller pterosaur species because there is evidence for lower density in larger species. These reconstructions were used to compare the wing shapes of Triassic and Jurassic pterosaurs with those of birds. Pterosaurs had wings of below-average loading and above-average aspect compared to the avian mean. This wing design was compatible with relatively slow and highly efficient flight, with high maneuverability. Wing area depends on the reconstruction model adopted; wings attached to the hindlimb principally reduced aspect, and secondarily reduced loading, which would improve take-off performance at the expense of efficiency. The wing shape and cranial feeding adaptations of pterosaurs were most compatible with a marine or aerial predatory adaptive zone. The reconstructed pterosaurs show a limited range of wing shape compared to birds. This may partly reflect preservational bias favoring species living in marine or lagoonal environments, but this is not a complete explanation because there is a lack of pterosaurs with wings of high loading like the marine ducks and auks. Structural, physiological, or adaptive factors may have limited pterosaur wing shape.

Tectonic deformation is an important part of the taphonomic histories of many fossils. Although the effects of deformation, and methods to remove those effects, have been a subject of inquiry for over a century, systematic testing under known parameters has never been used to determine how the effects of deformation and the performance of retrodeformation techniques might vary. Comparative studies of morphology depend on the accurate estimation of variance-covariance structure, so an understanding of the effects of retrodeformation on covariance structure is important in assessing the utility of these methods. Here we address these issues by using geometric morphometric simulations. Nondeformed data sets were generated from specimens of the extant turtle Emys marmorata, which were known by definition to be nondeformed, and which possess a known ontogenetic signal. Deformation was simulated by applying a combination of uniform shear and uniform compression/dilation to the data. Data were retrodeformed by reflection and averaging of bilaterally symmetric landmarks, use of a principal components analysis to identify a deformation component of shape variation, and removal of the affine component of shape variation among specimens. Deformation increased the amount of variance in the data, as well as altering the variance structure. However, low to moderate levels of deformation did not prevent the confident recovery of the known ontogenetic signal in some cases. The tested retrodeformation techniques did not work well. They either removed too little or too much variance from the data, and provided little improvement in variance structure. Retrodeformation often did not improve our ability to extract the ontogenetic signal from the data, and in some cases introduced an arti-factual relationship between size and shape. All of the scrutinized methods showed some properties, such as reducing variance or producing visually appealing images of specimens, that could make them appear to be working in cases where the correct biological signal is not known. This emphasizes the need for simulation testing in the development and evaluation of retrodeformation techniques.

Analysis of a global elevation database to measure changes in shallow-marine habitat area as a function of sea level reveals an unexpectedly complicated relationship. In contrast to prevailing views, sea level rise does not consistently generate an increase in shelf area, nor does sea level fall consistently reduce shelf area. Different depth-defined habitats on the same margin will experience different changes in area for the same sea level change, and different margins will likewise experience different changes in area for the same sea level change. Simple forward models incorporating a species-area relationship suggest that the diversity response to sea level change will be largely idiosyncratic. The change in habitat area is highly dependent on the starting position of sea level, the amount and direction of sea level change, and the habitat and region in question. Such an idiosyncratic relationship between diversity and sea level reconciles the widespread evidence from the fossil record for a link between diversity and sea level change with the lack of quantitative support for such a relationship throughout the Phanerozoic.