A stupid argument brings shame to any scholarly effort; but no dishonor attends an erroneous claim—especially in science, lest we all become psychological basket cases, because the vast majority of novel hypotheses turn out to be dead wrong. I would even grant substantial kudos to a class of claims that one of my colleagues, speaking of Emmanuel Velikovsky's neocatastrophic theories, called “gloriously wrong”—for this complex and radical argument enjoyed at least a glimmer of empirical plausibility, and would have annihilated most of our complacent beliefs about the nature of geologic change, had the evidence proved sound and the mechanism workable. But Venus turned out to be an old planet with a stable orbit, not a young comet, and the hypothesis of “worlds in collision” collapsed.

The shell size of 1236 ammonite species representing all known Early Jurassic faunas is analyzed. Size patterns are studied for the entire period and then at the biozone scale for the first four stages of the Jurassic (28 Myr), during which ammonites recovered from the crisis at the Triassic/Jurassic (T/J) boundary. Our analysis reveals that (1) a size continuum (normal distribution from “dwarfs” to “giants”) exists for all Early Jurassic ammonites; (2) although there are no sustained trends (e.g., no Cope's rule), the succession is not monotonous and patterns may differ conspicuously from one biozone to the next; and (3) increases and decreases in size range are the most frequent evolutionary styles of size change. The only pattern that can be connected with a particular episode of Early Jurassic ammonite history is the initial increase in size disparity during the first four biozones attributable to phyletic radiation after the T/J crisis. Subsequent correlations with environmental constraints (e.g., sea-level changes), although suspected, cannot be shown.

The Siwalik formations of northern Pakistan consist of deposits of ancient rivers that existed throughout the early Miocene through the late Pliocene. The formations are highly fossiliferous with a diverse array of terrestrial and freshwater vertebrates, which in combination with exceptional lateral exposure and good chronostratigraphic control allows a more detailed and temporally resolved study of the sediments and faunas than is typical in terrestrial deposits. Consequently the Siwaliks provide an opportunity to document temporal differences in species richness, turnover, and ecological structure in a terrestrial setting, and to investigate how such differences are related to changes in the fluvial system, vegetation, and climate. Here we focus on the interval between 10.7 and 5.7 Ma, a time of significant local tectonic and global climatic change. It is also the interval with the best temporal calibration of Siwalik faunas and most comprehensive data on species occurrences. A methodological focus of this paper is on controlling sampling biases that confound biological and ecological signals. Such biases include uneven sampling through time, differential preservation of larger animals and more durable skeletal elements, errors in age-dating imposed by uncertainties in correlation and paleomagnetic timescale calibrations, and uneven taxonomic treatment across groups. We attempt to control for them primarily by using a relative-abundance model to estimate limits for the first and last appearances from the occurrence data. This model also incorporates uncertainties in age estimates. Because of sampling limitations inherent in the terrestrial fossil record, our 100-Kyr temporal resolution may approach the finest possible level of resolution for studies of vertebrate faunal changes over periods of millions of years.

Approximately 40,000 specimens from surface and screenwash collections made at 555 localities form the basis of our study. Sixty percent of the localities have maximum and minimum age estimates differing by 100 Kyr or less, 82% by 200 Kyr or less. The fossils represent 115 mammalian species or lineages of ten orders: Insectivora, Scandentia, Primates, Tubulidentata, Proboscidea, Pholidota, Lagomorpha, Perissodactyla, Artiodactyla, and Rodentia. Important taxa omitted from this study include Carnivora, Elephantoidea, and Rhinocerotidae. Because different collecting methods were used for large and small species, they are treated separately in analyses. Small species include insectivores, tree shrews, rodents, lagomorphs, and small primates. They generally weigh less than 5 kg.

The sediments of the study interval were deposited by coexisting fluvial systems, with the larger emergent Nagri system being displaced between 10.1 and 9.0 Ma by an interfan Dhok Pathan system. In comparison to Nagri floodplains, Dhok Pathan floodplains were less well drained, with smaller rivers having more seasonally variable flow and more frequent avulsions. Paleosol sequences indicate reorganization of topography and drainage accompanying a transition to a more seasonal climate. A few paleosols may have formed under waterlogged, grassy woodlands, but most formed under drier conditions and more closed vegetation.

The oxygen isotopic record also indicates significant change in the patterns of precipitation beginning at 9.2 Ma, in what may have been a shift to a drier and more seasonal climate. The carbon isotope record demonstrates that after 8.1 Ma significant amounts of C4 grasses began to appear and that by 6.8 Ma floodplain habitats included extensive C4 grasslands. Plant communities with predominantly C3 plants were greatly diminished after 7.0 Ma, and those with predominantly C4 plants, which would have been open woodlands or grassy woodlands, appeared as early as 7.4 Ma.

Inferred first and last appearances show a constant, low level of faunal turnover throughout the interval 10.7–5.7-Ma, with three short periods of elevated turnover at 10.3, 7.8, and 7.3–7.0 Ma. The three pulses account for nearly 44% of all turnover. Throughout the late Miocene, species richness declined steadily, and diversity and richness indices together with data on body size imply that community ecological structure changed abruptly just after 10 Ma, and then again at 7.8 Ma. Between 10 and 7.8 Ma the large-mammal assemblages were strongly dominated by equids, with more balanced faunas before and after. The pattern of appearance and disappearance is selective with respect to inferred habits of the animals. Species appearing after 9.0 Ma are grazers or typical of more open habitats, whereas many species that disappear can be linked to more closed vegetation. We presume exceptions to this pattern were animals of the mixed C3/C4 communities or the wetter parts of the floodplain that did not persist into the latest Miocene. The pace of extinction accelerates once there is C4 vegetation on the floodplain.

The 10.3 Ma event primarily comprises disappearance of taxa that were both common and of long duration. The event does not correlate to any obvious local environmental or climatic event, and the pattern of species disappearance and appearance suggests that biotic interactions may have been more important than environmental change.

The 7.8 Ma event is characterized solely by appearances, and that at 7.3 Ma by a combination of appearances and disappearances. These two latest Miocene events include more taxa that were shorter ranging and less common, a difference of mode that developed between approximately 9.0 and 8.5 Ma when many short-ranging and rare species began to make appearances. Both events also show a close temporal correlation to changes in floodplain deposition and vegetation. The 7.8 Ma event follows the widespread appearance of C4 vegetation and is coincident with the shift from equid-dominated to more evenly balanced large-mammal assemblages. The 7.3 to 7.0 Ma event starts with the first occurrence of C4-dominated floras and ends with the last occurrence of C3-dominated vegetation. Absence of a consistent relationship between depositional facies and the composition of faunal assemblages leads us to reject fluvial system dynamics as a major cause of faunal change. The close correlation of latest Miocene species turnover and ecological change to expansion of C4 plants on the floodplain, in association with oxygen isotopic and sedimentological evidence for increasingly drier and more seasonal climates, causes us to favor explanations based on climatic change for both latest Miocene pulses.

The Siwalik record supports neither “coordinated stasis” nor “turnover pulse” evolutionary models. The brief, irregularly spaced pulses of high turnover are characteristic of both the stasis and pulse models, but the high level of background turnover that eliminates 65–70% of the initial species shows there is no stasis in the Siwalik record. In addition, the steadily declining species richness and abrupt, uncoordinated changes in diversity do not fit either model.

Human vanity always drives us to elevate the ordinary. “He put a feather in his cap and called it macaroni…. Yankee doodle dandy.” The Oxford English Dictionary gives the appropriate definition (not pasta in this case) as “an exquisite of a class which arose in England about 1760 and consisted of young men who had traveled and affected the tastes and fashions prevalent in continental society … a fop.” In a standard Renaissance version of this universal tendency, scholars translated their common names into the ancient tongues of a classical world that had, in their firm conviction, learned everything worth knowing. Thus, Georg Bauer (literally George the farmer), became Georgius Agricola (the same, but in Latin) and published, under this prettified name, the first great geological treatise (De natura fossilium plus four shorter works) in 1546. But Philipp Schwartzerd (Mr. black earth) tried to conquer his cultivator by reinventing himself in even classier Greek–becoming Philipp Melanchthon (the same Mr. black earth in Athenian splendor), the right-hand man of Martin Luther and the Reformation.

Previous studies have established a close relationship between the evolutionary origin of new clades of planktonic foraminifera and heterochrony. Studies of the Paleogene radiation of the genus Morozovella revealed, for example, a temporal pattern of variation consistent with paedomorphosis. Our study focused on the late Paleocene species of Acarinina, sister group of Morozovella. Shape variations related to evolution and ontogeny are appraised through a morphometric method based on outline analysis using the elliptic Fourier transform. Patterns of developmental and evolutionary changes are studied and compared within each species (Acarinina nitida, A. subsphaerica, and A. mckannai). As no congruence is found, we suggest that the evolutionary change observed within these species is not related to a heterochronic process. We also test for similarity of both evolutionary and ontogenetic changes among species. Although we observe no significant correlation between temporal patterns of shape change among species, the tight congruence of ontogenetic trajectories suggests that the developmental constraints affecting these trajectories have been preserved in spite of the evolutionary diversification of acarininids. Heterochrony is not clearly involved in the early Paleogene diversification of acarininids and therefore may not be as common as previously claimed. The role of developmental constraints in monitoring morphological evolution therefore needs to be reassessed.

Kepler famously remarked of his great Florentine friend that he could never keep sufficiently straight a man whose first name so resembled his last: Galileo Galilei. Others have labored under (or benefited from) this duality, and this third essay of my series tells a tale of the most obscure, yet highly significant, character that I have ever encountered from the early history of our science: the Neapolitan scholar (1461–1523) who called himself Alessandro ab Alessandro, or Alexander de Alexander, or Alessandro degli Alessandro—all meaning (roughly) Alexander from the family of Alexander.

We still have much to learn about the evolution of taxonomic diversity gradients through geologic time. For example, have latitudinal gradients always been as steep as they are now, or is this a phenomenon linked to some form of Cenozoic global climatic differentiation? The fossil record offers potential to address this sort of problem, and this study reconstructs latitudinal diversity gradients for the last (Tithonian) stage of the Jurassic period using marine bivalves. At this time of relative global warmth, bivalves were cosmopolitan in their distribution and the commonest element within macrobenthic assemblages.

Analysis of 31 regional bivalve faunas demonstrates that Tithonian latitudinal gradients were present in both hemispheres, though on a much smaller magnitude than today. The record of the Northern Hemisphere gradient is more complete and shows a steep fall in values at the tropical/temperate boundary; the Southern Hemisphere gradient exhibits a more regular decline in diversity with increasing latitude.

Tithonian latitudinal gradients were underpinned by a tropical bivalve fauna that comprises almost equal numbers of epifaunal and infaunal taxa. The epifaunal component was dominated by three pteriomorph families, the Pectinidae, Limidae and Ostreidae, that may be regarded as a long-term component of tropical bivalve diversity. Of the mixture of older and newer “heteroconch” families that formed the bulk of the infaunal component, the latter radiated spectacularly through the Late Cretaceous and Cenozoic to dominate tropical bivalve faunas at the present day. This pulse of heteroconch diversification, which was a major cause of the steepening of the bivalve latitudinal gradient, provides important evidence that rates of speciation may be negatively correlated with latitude.

Nevertheless, we cannot exclude the possibility that elevated extinction rates in the highest latitudes also contributed to the marked steepening of bivalve latitudinal gradients over the last 150 Myr. Rates of extinction within epifaunal bivalve taxa appear to have been higher in these regions through the Cretaceous period, but this was largely before any significant global climatic deterioration. Infaunal bivalve clades have had differential success over this time period in the polar regions. Whereas, in comparison with the Tropics, heteroconchs are very much reduced in numbers today, the anomalodesmatans are much better represented, and the protobranchs have positively thrived. We are beginning to appreciate that low temperature per se may not be a primary cause of elevated rates of extinction. Food supply may be an equally important control on both rates of speciation and extinction; those bivalves that have been able to adapt to the extreme seasonality of food supply have flourished in the polar regions.

Many fossil assemblages are time-averaged, with multiple generations of organisms mixed into a single stratigraphic horizon. A time-averaged sample of a taxon should be more variable than a single-generation sample if enough morphologic change occurred during the interval of time-averaging. Time-averaging may also alter correlations between morphologic variables and obscure allometric relationships in an evolving population. To investigate these issues, we estimated the variability of six modern, single-generation samples of the bivalve Mercenaria campechiensis using Procrustes analysis and compared them with several time-averaged Pleistocene samples of M. campechiensis and M. permagna. Both the modern and the fossil samples ranged in variability, but these ranges were virtually identical. Morphology was quite stable over the hundreds to many thousands of years that passed as the assemblages accumulated, and the variabilities of the fossil samples could be used to estimate single-generation variability. At one fossil locality, the environment and paleocommunity changed partway through the collection interval; the morphology of Mercenaria appears stable above and below the transition but changes across it. This change is similar in magnitude to the differences between geographically separated modern populations, whereas temporal variation within single environmental settings is distinctly less than geographic variation. Analytical time-averaging (the mixing of fossils from different horizons) between paleocommunities increased variability slightly (but not significantly) above that found in living populations. While its constituent populations appear stable on millennial timescales, M. campechiensis has been evolutionarily static since at least the early to middle Pleistocene.

Iterative evolutionary changes are of special interest because they imply that the recurring morphological changes had a cause that also repeated itself and might therefore be possible to uncover. We describe a set of iterative morphological changes in melanopsid gastropods from the ancient, long-lived Lake Pannon. First in the Pannonian Age, and again in the Pontian Age approximately three million years later, a smooth-shelled ancestor gave rise to a shouldered descendant. In both cases, the morphological change was probably coincident with a shift from habitats just outside the lake (e.g., rivers and streams) to habitats within the lake itself. Many other convergent examples exist in which a smooth-shelled river dweller is closely related to a shouldered and/or ribbed lacustrine snail. The frequency of this type of morphological change suggests that it has an adaptive basis; response to differing predators or hydrodynamic conditions seem the most plausible explanations, but the functional nature of these morphological changes remains unknown.

Spatial and temporal variations in biological diversity are critical in understanding the role of biogeographical regulation (if any) on mass extinctions. An analysis based on a latest database of the stratigraphic ranges of 89 Permian brachiopod families, 422 genera, and 2059 species within the Boreal, Paleoequatorial, and Gondwanan Realms in the Asian–western Pacific region suggests two discrete mass extinctions, each possibly with different causes. Using species/family rarefaction analysis, we constructed diversity curves for late Artinskian–Kungurian, Roadian–Wordian, Capitanian, and Wuchiapingian intervals for filtering out uneven sampling intensities. The end-Changhsingian (latest Permian) extinction eliminated 87–90% of genera and 94–96% of species of Brachiopoda. The timing of the end-Changhsingian extinction of brachiopods in the carbonate settings of South China and southern Tibet indicates that brachiopods suffered a rapid extinction within a short interval just below the Permian/Triassic boundary.

In comparison, the end-Guadalupian/late Guadalupian extinction is less profound and varies temporally in different realms. Brachiopods in the western Pacific sector of the Boreal Realm nearly disappeared by the end-Guadalupian but experienced a relatively long-term press extinction spanning the entire Guadalupian in the Gondwanan Realm. The end-Guadalupian brachiopod diversity fall is not well reflected at the timescale used here in the Paleoequatorial Realm because the life-depleted early Wuchiapingian was overlapped by a rapid radiation phase in the late Wuchiapingian. The Guadalupian fall appears to be related to the dramatic reduction of habitat area for the brachiopods, which itself is associated with the withdrawal of seawater from continental Pangea and the closure of the Sino-Mongolian seaway by the end-Guadalupian.

During the Ordovician Radiation, domination of benthic marine communities shifted away from trilobites, toward articulated brachiopods, and, to a lesser degree, toward bivalves and gastropods. Here, models are formulated that mathematically represent alternative hypothesized causes of this transition. These include models in which per-genus origination or extinction probabilities were constrained to be (1) constant, (2) diversity-dependent, (3) productivity-dependent, or (4) jointly dependent on productivity and diversity. Using a method adapted from capture-mark-recapture (CMR) population studies, we estimate origination, extinction, and sampling probabilities jointly in order to avoid confounding patterns in turnover probabilities with temporal variation in the quality of the fossil record. Using Akaike's Information Criterion (AIC), we assessed the fit of the alternative causal models relative to one another, and relative to a noncausal “phenomenological” alternative that placed no constraints on the pattern of temporal variation in origination or extinction. There were differences among taxa in the relative fit of these models, suggesting that the effects of productivity and diversity varied among higher taxa. In the aggregate, however, there was strong support for diversity-dependent origination. For extinction, poor fit of the alternative causal models suggests that we lack a good explanation for extinction patterns. These analyses support the hypothesis that diversity-dependent origination, particularly in trilobites, contributed to the Ordovician faunal transitions. By contrast, the effects of increased productivity, if indeed they were large enough to influence global diversification patterns, did not proceed in the hypothesized manner.

Colonial organisms vary in the degree to which they are individuated at the colony level, i.e., in the degree to which the colony constitutes a unified whole, as opposed to a group of independent lower-level entities. Various arguments have been offered suggesting that evolutionary change along this continuum may be biased, that increases may be more probable than decreases. However, counterarguments can be devised, and the existing evidence is meager and inconclusive. In this paper, we demonstrate how the question can be addressed empirically by conducting a test for bias in a group of stenolaemate bryozoans, the cyclostomes. More specifically, we suggest three criteria for colony individuation: degree of connectedness among lower-level entities (in this case, zooids), degree of differentiation among lower-level entities, and number of intermediate-level parts. And we show how these criteria can be used together with a phylogeny and ancestral-state reconstruction methods to test for bias. In this case, results do not unambiguously support any single interpretation but are somewhat supportive of a null hypothesis of no bias in favor of increase.

As part of the demonstration, we also show how results can be transformed into a quantitative estimate of an upper limit on bias. Finally, we place the question of bias in a larger context, arguing that the same criteria and methods we employ here can be used to test for bias in other colonial taxa, and also at other hierarchical levels, for example, in the transitions from free-living eukaryotic cells to multicellular organisms.

Living fossils are taxonomic groups surviving for a long time without any remarkable morphological change. Most of them retain low taxonomic diversities. Although some of them have survived in refuges to avoid predators and competitors, not all living fossils live in refuges. The survival of these groups, therefore, should be discussed in the context of biological interaction. I carried out computer simulations of a model food web system, in which each species feeds on others according to its feeding preference. The system evolves via evolution of species. In the simulation, some clades, like “living fossils,” survived for a long time with low species diversities. Such clades consisted of species with low evolutionary rates, which result in high predation pressure and intraclade competition for food. Nevertheless, the clades sustainably utilize prey clades and are consequently provided with sufficient food. In addition, because of the low species diversities of the clades, predators of the clades soon become extinct through lack of food. This study strongly suggests that in an evolving food web system, the low evolutionary rates of living fossils allow the long survival of those groups with low taxonomic diversities.

Accurate estimates of predation intensity, the frequency of mortality from predation, are critical to studies of the evolution of species in response to predation, and to studies of predator-prey systems in general. Most commonly used indirect proxies for predation intensity in the fossil record have logistical or theoretical problems. Direct proxies, using actual traces of predatory activity, such as drilling and repair scars, may hold more promise. However, these direct proxies often have been used in conjunction with optimal foraging models, and in this context, the underlying assumptions and predictions of optimal foraging are examined.

Results from theoretical models using optimal foraging suggest that (1) the ratio of internal shell volume to shell thickness of prey (benefit/cost ratio) may be a questionable measurement of prey “value” to the predator, as it fails to account adequately for energetic cost to the predator during pursuit and grappling; (2) drilling and repair frequency are invalid measures of prey preference, because optimal foraging predicts that specific prey types are either always taken or always ignored; (3) pooled drilling frequency will not be a useful metric of predation intensity in systems in which the predator need not always drill; and (4) an increase in repair frequency can be a consequence of either an increase or a decrease in predation intensity.

Although drilling frequency may not indicate prey preference, it is a valid proxy for selection due to predation. An approach using size classes, in which the minimum size at which a predation refuge is achieved, is suggested for use with repair frequency.

The late Paleocene-early Eocene transition was characterized by a long period of global warming that culminated with the highest temperatures of the Cenozoic. This interval is associated with a significant increase in plant diversity in temperate latitudes. However, data from tropical regions remain largely unknown. The record of pollen and spore diversity across the late Paleocene to the early middle Eocene of eight sections in central and eastern Colombia was analyzed. Several techniques, including range-through method, rarefaction, bootstrap, detrended correspondence analysis, and Shannon index, were used to assess the significance of the observed diversity pattern. The palynofloral record indicates that the lower to middle Eocene contains a significantly higher palynofloral diversity than the underlying upper Paleocene strata. This pattern is maintained after accounting for sample size, number of samples/time unit, lithofacies, and depositional systems. Eocene palynofloras have higher alpha and beta diversities and a higher equitability than Paleocene palynofloras. This increase in diversity is the product of a gradual increase in the rate of first appearances and a gradual decrease in the rate of last appearances. The early to middle Eocene increase in diversity, as well as the increase in spore abundance and diversity, suggests that tropical (equatorial) climate became wetter during the early to middle Eocene. This interpretation favors causes for early Eocene warming that do not involve significant increases in greenhouse gases. Samples from strata associated with the Paleocene/Eocene thermal maximum were barren for palynomorphs, and the effects of this climatic event on tropical vegetation remains uncertain.

The characters and body parts of organisms are shaped by mechanical forces at two temporal scales. At the ontogenetic scale, the relevant forces are those of every day, exerted by muscles, other metabolism-powered processes, and normal interactions between the body and the external environment. At the phylogenetic scale, forces are strong enough to kill some individuals or to cause reproductive failure. These forces act more intermittently.

I explore these ideas by examining the characters of molluscan shells, which grow by the addition of skeletal material along the rim of the open end of a hollow, conical tube that is closed at its narrow (apical) end. In the idealized case of a null shell, the skeleton is a right circular cone, in which the magnitude and direction of growth are the same at each point along the rim. The rate of expansion of the cone is determined by the shell-builder's metabolism. Real shell-builders are exposed to, and themselves exert, forces that affect shell shape. These forces are generated by contact between the shell-secreting mantle margin and the substratum, by local or temporary deformations of the mantle margin imposed by other parts of the body and previously formed parts of the shell, and by contraction of muscles that connect the soft tissues to the inner shell surface. Early mollusks whose shells more or less resemble the null shell were slow-moving, epifaunal animals that clamped the shell against the substratum. Evolutionary increases in metabolic rate, associated with greater mobility and faster growth, made some ontogenetically important forces stronger and introduced new forces. As a result, the range of available phenotypes expanded. Refinements in genetic regulation of form, perhaps including an increase in the number of semiautonomous regulatory regions, further added to the specification and range of variation of characters that were subject either to evolutionary conservation or to natural selection. For example, the mantle margin in plesiomorphic gastropods appears to comprise one such region, which produces a growing shell margin in the form of a logarithmic spiral; in more-derived gastropods, the mantle margin may comprise two or more regions, which together produce a growing shell margin that departs strikingly from the logarithmic form of the outer shell lip.

The morphospace occupied by accretionary shells can be described by (1) the number of semiautonomous developmental modules, (2) selective regimes observable as phenotypic adaptive evolution, and (3) metabolic rate. The perspective outlined here implies that shells initially occupied a limited morphospace encompassing one or two modules, adaptation as an epifaunal clamping animal, and slow growth (low expansion rates) and metabolism. Further compartmentalization, together with increased metabolic rates in ecologically dominant taxa, caused the morphospace to expand both in the number of independent descriptors and in the range of values that each parameter spans. These trends in morphospace may characterize all major multicellular clades.

The precise knowledge of the number and nature of the species belonging to a fossil assemblage as well as of the structure of each species (e.g., age, sex) is of great importance in paleontology. Mixture analysis based on the method of maximum likelihood is a modern statistical technique that concerns the problem of samples consisting of several components, the composition of which is not known. Nonparametric bootstrap and jackknife techniques are used to calculate a confidence interval for each estimated parameter (prior probability, mean, standard deviation) of each group. The bootstrap method is also used to evaluate mathematically how many groups are present in a sample. Experimental density smoothing using the kernel method appears to be a better solution than the use of histograms for the estimation of a distribution. This paper presents some basic concepts and procedures and discusses some preliminary results concerning sex ratios and mortality profile assessments using bones and tooth metric data of small (Ovis antiqua) and large (Bos primigenius) bovines from European Pleistocene sites.