Accretionary outlines of many brachiopods are closely matched by one or more episodes of logarithmic spiral growth where each episode has a constant growth gradient. An episodic model supports the observations of abrupt change, but not that of gradual change in accretionary growth. A reliable guide to the number of growth episodes is given by the pattern of residuals after fitting a single spiral to an outline. An episodic model exposes subtle variations in growth that are not easily described by visual examination. A three-episode model clarifies a shape difference between two species of the endemic New Zealand genus Neothyris. Direct observation, along with linear measurements and their ratios, was unable to pinpoint that the well-documented dorsoventral compression in one species arises from a growth episode in the ventral valve. Logarithmic spirals about a single coiling axis are not suited for large, disjunct changes in outline for which the moving-frame methods or aperture-deposition models are applicable.

Lipids found associated with skeletons represent an important avenue of study in molecular paleontology, because the chemical nature of these compounds means they are often biogenically specific and can survive in the geologic record over millions of years. Though it is clear that these skeletal compounds originate from the mineralizing organism, our understanding of the distributions and nutritional sources of lipids among invertebrates is still limited, requiring that baseline studies of modern taxa be completed to evaluate the potential of skeletal lipids in paleoecological studies.

In this study, skeletal lipids from nine modern invertebrate taxa (five mollusks, a brachiopod, an echinoid, a coral, and a barnacle) were extracted and analyzed. Though the major classes of lipids found in the skeletons are remarkably consistent, the sterol profiles from these organisms contain both dietary and environmental information. The skeletons of filter feeders generally have two to three times the variety of sterols as compared with carnivores and grazers. In addition, specific steroidal contributions from several plant and algal groups (including dinosterol, 22-dehydrocholesterol, and β- and γ-sitosterol) can be identified. The limited nature and distribution of sterols in the carnivore skeleton implies that both sterol-recycling and some degree of molecular selectivity may be occurring in this taxon. Taxa living in nearshore shallow marine habitats have significant sterol contributions from higher plants, while deepwater organisms have relatively little. Since the geologically stable form of sterols often retains the three-dimensional structure necessary to recognize the biological precursor, these compounds may be used for determining the ecology of fossil invertebrates.

The identification of randomness and nonrandomness is a perennial problem in evolutionary research. Stochastic thinking in evolutionary biology and paleobiology has solidified the use of a statistical notion of chance, but the idea of chance in evolutionary studies goes beyond statistics. A duality arises from the use of a statistical meaning on the one hand, and a more strictly evolutionary meaning on the other. The former implies a combination of indiscriminate sampling and unpredictability due to multiple causes; the latter codifies independence from adaptation and the directionality imposed by natural selection. Often these meanings are kept separate in evolutionary research, used in isolation according to the empirical situation or the goal of the investigator (recognition of pattern versus process). I argue that evolutionary studies in general and paleobiological studies in particular can benefit from the simultaneous application of statistical and evolutionary notions of chance. Following some background on the notion of chance and its use, I discuss a series of examples in which insight can be gained by explicit consideration of both meanings. Thus, typologies of extinction become clearer when phenomena like wanton extinction are made explicit; exaptive radiations are exposed as an alternative to adaptive radiations; the possible nonadaptive nature of deterministic chaos becomes sensible; the nonrandomness of community-assembly is put into question; parallel taxonomies of sorting rooted in different notions of nonrandomness are suggested as a means of facilitating understanding of relationships across the hierarchy; developmental constraints and self-organization are more easily distinguished from selective constraints; and a new term, “incidentals,” is suggested to refer to both exaptations and nonaptations. Finally, I point to ways in which the dichotomy between chance and necessity can be approached in evolutionary theory, by showing that the dual nature of chance in evolution entails a distinction between functional and structural necessity, and that chance ultimately becomes a unifying concept for a number of criticisms to neo-Darwinism.

Fish eagles (genus Haliaeetus) potentially have contributed the bones of their prey to many late Cenozoic concentrations of vertebrate microfossils. To evaluate possible biases in the taxa and skeletal elements preserved in assemblages accumulated by fish eagles, which could affect paleoecological and evolutionary interpretations derived from Cenozoic microfaunal localities, a sample of 1883 bones accumulated by modern African fish eagles (H. vocifer) was collected from a roost near Lake Turkana, Kenya. Characteristics of the bone assemblage include (1) taxonomic composition dominated by fish; (2) diverse but small-sized and ecologically restricted animals including inshore fish, aquatic birds, very small nocturnal mammals (which may have been contributed by other raptors), and small reptiles (possible predators on the roost); (3) poor survivorship for specific categories of skeletal elements; (4) considerable bone breakage for all but the smallest animals; and (5) a distinctive pattern of postcranial fragmentation for bird and mammal elements. The fish eagle element profile has some similarities to those of other diurnal raptors, but its cumulative signature can be distinguished from those of other bone accumulators and includes characteristics that would also be manifest in fossil assemblages. Examination of fossil microfaunas from the Plio-Pleistocene localities of Kanapoi (Kenya), Inolelo (Tanzania), and Olduvai Gorge (Tanzania) shows that the patterns of element preservation for Kanapoi and Inolelo do not match those of the Lake Turkana fish eagle roost. Nonetheless, some aspects of the Olduvai Gorge FLKN assemblage show taxonomic and skeletal similarites. In light of the selective choices of prey by fish eagles, the fauna recovered from Olduvai Gorge FLKN might not accurately reflect faunal diversity or patterns of abundance at this locality during the Pleistocene. Because fish eagles of the genus Haliaeetus are found on three continents, have a fossil record extending to the Miocene, and deposit bones in a habitat conducive to preservation, the taxa preserved at many other late Cenozoic microfaunal sites also might be biased. Therefore, taphonomic profiles of late Cenozoic microfaunal assemblages should be compared against the taphonomic profiles typical of fish eagle roosts before faunal characterizations of sites are applied in analyses of paleoecological evolution.

A mathematical-computational method for determining the volume, mass, and center of mass of any bilaterally symmetric organism is presented. Cavities within the body of an organism such as lungs are easily accommodated by this method. Sagittal and frontal profiles, obtained from tracings of “fleshed-out” skeletal reconstructions, are used to provide limits for defining transverse slices of the body. Any internal cavities are defined by their own sagittal and frontal profiles. The computations consist of mathematically slicing the body and any cavities into independent sets of transverse laminae and computing their masses, centroids, and moments with respect to the three coordinate axes. Further calculations produce the masses and the (x,y,z) coordinates for the centers of mass of the body, any cavities, and the body + cavities. Predicted body masses of large, extant mammals (elephant, giraffe, hippopotamus, and rhinoceros) are in close agreement with actual body masses. New, lower estimates for body masses of selected large dinosaurs, based on modern skeletal reconstructions, are also presented, along with numerical estimates of their centers of mass. This method is an improvement over earlier ones that relied on measuring displaced volumes of water or sand by scale models to estimate the masses, and suspending models by threads to estimate their centers of mass.

A number of natural events can cause ozone depletion, including asteroid and comet impacts, large-scale volcanism involving the stratospheric injection of chlorine, and close cosmic events such as supernovae. These events have previously been postulated to have been sole or contributory causes of mass extinctions. Following such events, UV-B radiation would have been elevated at the surface of the earth. The possibilities for detecting elevated UV-B as a kill mechanism in the fossil record are discussed. In the case of impact events and large-scale volcanism, the taxa affected by increases in UV-B radiation are likely to be similar to those affected by cooling and by the initial drop in irradiance caused by stratospheric dust injection. Thus UV-B may synergistically exacerbate the effects of these other environmental changes and contribute to stress in the biosphere, although UV-B alone is unlikely to cause a mass extinction. By the same token, however, this similarity in affected taxa is likely to make delineating the involvement of UV-B radiation in the fossil record more difficult. Cosmic events such as supernovae may produce smaller extinction events, but ones that are “cleaner” UV catastrophes without the involvement of other environmental changes.

The origin of the Neogene planktonic foraminifer Globorotalia (Globoconella) pliozea in the subtropical southwest Pacific has been attributed to its isolation resulting from intensification of the Subtropical Divergence (Tasman Front). Oxygen isotopic analyses suggest that, although the Subtropical Divergence may have played a role, the evolution of Gr. (G.) pliozea was facilitated by depth segregation of Gr. (G.) conomiozea morphotypes (low and high conical) during an interval of near-surface warming and increasing thermal gradient. Oxygen isotopic analyses suggest that low conical morphotypes of Gr. (G.) conomiozea inhabited greater depths than high conical morphotypes. Low conical forms of Gr. (G.) conomiozea are considered ancestral to the low conical species, Gr. (G.) pliozea. Oxygen isotopes indicate that Gr. (G.) pliozea inhabited greater depths than its ancestor, Gr. (G.) conomiozea.

These data are consistent with depth-parapatric and depth-allopatric models, but not with a sympatric model of speciation. In the allopatric model, reproduction at different water depths acts as a barrier between morphotypes. In the parapatric model, clinal variation along a depth gradient acts as a barrier between morphotypes living at the limits of the gradient. Depth segregation in both models results in genetic isolation and evolutionary divergence. Our data support a correlation between morphological evolution and habitat changes in the Globoconella clade, implying separation of populations as a driving force for morphological evolution.

Ecological segregation of morphotypes and species may be related to morphology (height of the conical angle), based on the data from Gr. (G.) conomiozea and Gr. (G.) pliozea. However, morphological differences alone do not necessarily produce depth differences. Large morphological differences between Gr. (G.) pliozea and closely related Gr. (G.) puncticulata did not result in isotopic and therefore depth differences between these species. These species coexisted at the same water depths for nearly 1 m.y. Thus, it is unlikely that the extinction of Gr. (G.) pliozea in the middle Pliocene resulted from competition with Gr. (G.) puncticulata, as previously suggested.

One of the major obstacles in dealing with any form of data derived from fossils is the effects of time-averaging, which are the result of mixing the remains of organisms that did not live contemporaneously. Although this process results in loss of temporal resolution, it also serves to filter out short-term variations. Temporal resolution of a collection depends not only on the range of fossil ages, but also on their frequency distribution. Previous studies of marine molluscs indicate that most shells in an accumulation are relatively young. Such a distribution of shell ages can be fit by an exponential curve (assuming both a constant probability of shell loss and a constant rate of shell addition), which implies that 90% of the shells were added during the last 50% of the time interval represented by the collection. That is to say, differences between two collections can be discerned even if they overlap 50% in time, because the proportion of shells with shared ages is only 10%. Applying the exponential model to previously published data suggests that long-term rates of destruction are controlled by how frequently shells from the taphonomically active zone are re-exposed to rapid destruction. To take advantage of the “noise-filtering” property of time-averaging, samples need to be large enough to catch the full range of environmental variation recorded by an accumulation. A simple probability formula indicates that samples of easily achievable size can give satisfactory time-averaged results depending on the level of confidence and sampling density defined by the researcher.

Outline-based morphometric methods have been more or less restricted to the consideration of closed curves and plagued by problems related to the maintenance of close biological correspondence across all forms within a sample. Methods developed herein generalize and extend the eigenshape method of outline analysis along the following lines: (1) consideration of open curves, (2) improvement of interobject correspondence via incorporation of information provided by landmarks, and (3) extension to the analysis of three-dimensional (open and closed) curves. In addition, techniques for using eigenshape results to create models of shape variation and for more consistently assessing the digital resolution necessary to represent an object are discussed and illustrated. These improvements are then placed in context via discussions of previous attempts to extend morphometric outline analysis methods, the relation between landmark and outline-based morphometric methods, the use of morphometric analyses to test biological hypotheses, and the nature of morphometric shape spaces (with special reference to studies of morphological disparity).

In this paper we analyze the ontogenies of four species of pachypleurosaur (Reptilia: Sauropterygia) occurring in Triassic-age deposits in the Monte San Giorgio region, Switzerland. Preservation of multiple complete specimens representing a growth series from each taxon allows the comparison of ontogenetic trajectories through a space composed of nine variables important in the evolution of the clade. Trajectories are characterized using the multivariate generalization of the allometry equation and then compared through calculations of the angles between allometry vectors. Individual coefficients of vectors are compared after calculation of bootstrapped confidence intervals. Pachypleurosaur ontogeny is found to be allometric and generally conserved, although significant differences between taxa exist. Shape-disassociated allometric changes characterize the transition between Serpianosaurus and Neusticosaurus, while allometric changes within Neusticosaurus are less significant. N. edwardsii is inferred to have arisen through hypermorphosis. Interpretation of whole-body heterochrony in multivariate analysis is discussed.

The origins and maintenance of morphological diversity through the Phanerozoic have been documented in several groups of invertebrates. By using shape analysis of the ventral valve, we quantify morphological diversity within the inarticulate brachiopods, which have a species-rich lower Paleozoic history followed by low richness through the rest of the Phanerozoic. Morphological diversity peaked during the Cambrian, and was subsequently maintained despite significant decreases in richness at all taxonomic levels. The loss of morphological diversity, associated with late-Paleozoic decreases in the number of orders and the Permo-Triassic mass extinction, was followed by rapid morphological rediversification without concordant taxonomic diversification. Any limits upon the generation of diverse morphologies were established early in the Cambrian and were maintained and approached through the history of this group.

Variance and taxonomic selectivity were studied as functions of time across the Phanerozoic for duration of genera and families in the fossil record and for habitat of fossil families. The variance of duration increases temporarily before mass extinctions but otherwise decreases across the Phanerozoic, and the variance of habitat increases to an asymptote. For both duration and habitat, the percentage of variance explained by differences among orders and classes shows no temporal trend, whereas the percentage of variance explained by differences among phyla decreases across the Phanerozoic. The latter decrease depends upon the time elapsed since the origination of classes within phyla in the early Paleozoic; a similar decrease appears in differences among classes if the analysis is restricted to orders that originate before the Silurian. The observed patterns can be described by bounded random walks that include some infrequent but large steps.

In this paper we reconstruct the phylogeny of a clade of pachypleurosaurs (Reptilia: Sauropterygia) occurring in Triassic-age deposits in the Monte San Giorgio region, Switzerland. We also present the phylogeny of this clade as a case study for two paradigms of phylogeny reconstruction: cladistics and phenetic/stratigraphic methods. While this dichotomy is not held rigidly by all workers, its advancement by cladists leads us to retain it initially for rhetorical purposes. We review the philosophical bases of species, species concepts, and speciation, as well as cladograms and phylogenies, before introducing the experimental system.

Data are presented from cladistic analyses, phenetic analyses, and stratigraphic information. Phylogeny of the clade is interpreted from both paradigms, and the interpretations are found to be inconsistent. Resolution of the phylogeny rests on the emphasis of one type of data over another. An interpretation of cladogenesis within the genus Neusticosaurus entails rejection of suggestive phenetic and stratigraphic data, whereas an anagenetic interpretation entails reversal of autapomorphies in ancestral taxa. Anagenesis is deemed to be the more probable interpretation, based on the strength of the stratigraphic and phenetic data relative to the character data. Implications of the test case results for phylogeny reconstruction in general are discussed, ending with a call for pluralism in approach.

If your undergraduate experience in stratigraphy was anything like mine, it was overwhelmingly dull. It was all about nomenclature and classification and endless lists of formation names. There were apparently no questions to be asked and the goal of stratigraphy was to devise boxes into which to place all types of geologic data. Notwithstanding the important work of correlation, the perception was that it was the sedimentologists who did the real science, science that focused on the processes of sediment accumulation and their controlling factors. Since then, stratigraphy has undergone a conceptual revolution, and it is necessary to examine how the field has changed and what those advances mean for paleobiology.

In his 1932 book Brave New World, Aldous Huxley laid out a satirical blueprint of a future so strange to people of the time that it became a symbol of the frightening and unyielding momentum of scientific progress. Literature and popular culture have since been littered with images of a future earth so transformed by human progress (or extraterrestrial intervention) that we can hardly recognize it. Earth historians and paleontologists, however, have taken a different path into the bizarre. This group of time travelers has used the kind of technology that Huxley foreshadowed to recreate past worlds of similar disparity. These worlds are neither based on, nor entirely limited by, human imagination, but are based instead on scientific observation. In short, these strange old worlds are real, not imagined. As often is the case, however, truth can b e stranger than fiction.

Two major ichnotypes of sauropod trackways have been described: “narrow-gauge,” in which both manus and pes prints approach or intersect the trackway midline, and “wide-gauge,” in which these prints are well apart from the midline. This gauge disparity could be the result of differences in behavior, body size, or morphology between the respective trackmakers. However, the biomechanics of locomotion in large terrestrial vertebrates suggest that sauropods were probably restricted in locomotor behavior, and the lack of systematic size differences between footprint gauges argues against body-size-related influences. We argue that skeletal morphology is responsible for gauge differences and integrate data from locomotor biomechanics and systematics with the track record to predict the hindlimb morphology of wide-gauge trackmakers. Broader foot stances in large, graviportal animals entail predictable mechanical consequences and hindlimb modifications. These could include outwardly angled femora, offset knee condyles, and a more eccentric femoral midshaft cross-section. A survey of sauropod hindlimb morphology reveals that these features are synapomorphies of titanosaurs, suggesting that they were the makers of wide-gauge trackways. The temporal and geographic distribution of titanosaurs is consistent with this hypothesis because wide-gauge trackways predominate during the Cretaceous and are found worldwide. Additional appendicular synapomorphies of titanosaurs are interpreted in light of identifying these animals as wide-gauge trackmakers. We suggest that titanosaurs may have used a bipedal stance more frequently than did other sauropods. These correlations between ichnology, biomechanics, and systematics imply that titanosaurs were unique among sauropods in having a more varied repertoire of locomotor habits.

Addition of the recently discovered fossil Nalacetus to a phylogenetic analysis of basicranial, cranial, dental, postcranial, and soft morphological characters reveals that it is the most basal cetacean, and that mesonychians form the monophyletic sister group to Cetacea. The molars of Nalacetus elucidate transformations in dental morphology that occurred early in the cetacean radiation and clarify certain derived differences in molar cusp position between cetaceans and the extinct clade, Mesonychia, hypothesized to be their sister taxon. Nalacetus and other archaic cetaceans share derived vertically elongate shearing facets on the lower molars. Applying the Extant Phylogenetic Bracket, we advance the hypothesis that these facets are an osteological correlate of aquatic predation. Our functional interpretation of this character and its distribution within Cetacea indicates that a behavioral change in tooth use characterized the origin of the clade. Comparison of the transformation of this dental character with that of the cetacean pelvis indicates that a change in tooth use (feeding behavior) occurred before loss of the ability to engage in terrestrial locomotion.

The most parsimonious phylogenetic hypothesis presented here has a significant fit with the stratigraphic record as determined by the Manhattan Stratigraphic Measure, which is corroborated by retention indices of stratigraphic data. Ghost lineages necessitated by the phylogenetic hypothesis extend the stratigraphic range of Cetacea into the middle Paleocene (Torrejonian), ten million years earlier than the oldest cetacean fossil currently known. Primitive features of Nalacetus, the large number of synapomorphies diagnosing Cetacea, and the implied ghost lineage suggest that the early cetacean radiation was much more extensive than has been previously recognized.