—Stable isotope ratios of carbon and nitrogen in archaeological and modern bone samples have been used to reconstruct the dietary changes of the South American sea lion Otaria flavescens from the late Holocene to the present in the southwestern Atlantic. We sampled bones from archaeological sites in northern-central and southern Patagonia, Argentina, and bones housed in modern scientific collections. Additionally, we analyzed the stable isotope ratios in ancient and modern shells of intertidal molluscs to explore changes in the isotope baseline and allow comparison between bone samples from different periods after correction for baseline shifts. Results confirmed the trophic plasticity of the South American sea lion, demonstrated the much larger impact of modern exploitation of marine resources as compared with that of hunter-gatherers, and underscored the dissimilarity between the past and modern niches of exploited species. These conclusions are supported by the rather stable diet of South American sea lions during several millennia of aboriginal exploitation, in both northern-central and southern Patagonia, and the dramatic increase in trophic level observed during the twentieth century. The recent increase in trophic level might be related to the smaller population size resulting from modern sealing and the resulting reduced intraspecific competition. These results demonstrate how much can be learned about the ecology of modern species thanks to retrospective studies beyond the current, anthropogenically modified setting where ecosystem structure is totally different from that in the pristine environments where current species evolved.

Changes in shape and in the pattern of the reticulate carapace ornament of 63 representative female ostracode specimens of the deep-sea genus Poseidonamicus from 28 Deep Sea Drilling Project Sites, extending over a geographic distance of 40,000 miles and a geologic age of 40 × 106 yr, have been analyzed by Resistant Fit Theta-Rho Analysis, conventional least-squares Theta-Rho Analysis, and by inspection of homologies in the fossae of the reticulum. Through comparison of the relative rates of morphological change on at least three levels of integrated complexity, it is possible to demonstrate that a sudden evolutionary change in the architectural framework of the carapace can be the product of mechanical accommodation under stress to more gradual and general changes in carapace shape. Certain geometric imperatives related to these mechanical needs determine morphologic stability and consequently rates of evolutionary change. In the western deep South Atlantic (near the Vema Channel on the Rio Grande Rise), an important evolutionary “punctuational event” seems to have taken place at about 14 Myr, whereas its concomitant, more gradual transformation is traceable in the shallower eastern South Atlantic (Walvis Ridge). This evolutionary event in Poseidonamicus probably reflects the relatively sudden invasion of deep Antarctic Bottom Water through the Vema Channel resulting from the formation of the East Antarctic Ice Cap, while the more gradual transition in shallower depths of Walvis Ridge represents a temporary transitory refuge. The problems of recognizing allopatric origins of species in the deep sea compared to in situ sudden transitions caused by biomechanical instability are considered.

The late Albian (Early Cretaceous) lineage of Actinoceramus sulcatus (Parkinson 1819) is a remarkable example of macro- and microevolution within the Bivalvia. Immediately following cladogenesis from ancestral A. concentricus, the lineage displays a conspicuous, short-term excursion through morphospace followed by a return to the ancestral form. This excursion is marked by the acquisition, and subsequent loss, of large radial folds affecting some part or all of the shell. The pattern is noteworthy because of the gross scale and rate of morphological evolution, the relatively short life span of an “extreme” morphology, an apparent evolutionary reversal, the presence of phenotypic clines through time, the extent of phenotypic variation within populations and abundance of morphological intermediates between disparate end-member types, the wide geographic distributions of phenotypic clines and variants, and the subtle asymmetry of morphological transitions bounding the evolutionary excursion.

From census and biometric analyses of stratigraphically constrained samples, we conclude that morphological change was not focused at speciation and the pattern of evolution does not conform to the classical paradigm of punctuated equilibrium. Instead, we infer that observed patterns are best explained by phyletic evolution, at widely varying rates, combined with ecophenotypic plasticity. Evolution targeted the potential to form radial folds; the expression of those in any individual was determined, in part at least, by environmental cues. Ecophenotypic plasticity in A. sulcatus was itself probably an evolutionary response favored by the presence of long-lived planktotrophic larvae and wide dispersal of the species. In A. sulcatus, there is a continuum of pattern between intrapopulational, ecophenotypic variation that can be observed on bedding planes, interregional variation, and phyletic change through time. We argue that this continuity of pattern is most easily explained by continuity of process: in the case of the visually striking radial folds in A. sulcatus, there is no reason to invoke distinct hierarchies of macro- and microevolution; instead, these seem to be parts of a continuum.

Pelagic (open-ocean) species have enormous population sizes and broad, even global, distributions. These characteristics should damp rates of speciation in allopatric and vicariant evolutionary models since dispersal should swamp diverging populations and prevent divergence. Yet the fossil record suggests that rates of evolutionary turnover in pelagic organisms are often quite rapid, comparable to rates observed in much more highly fragmented terrestrial and shallow-marine environments. Furthermore, genetic and ecological studies increasingly suggest that species diversity is considerably higher in the pelagic realm than inferred from many morphological taxonomies.

Zoogeographic evidence suggests that ranges of many pelagic groups are much more limited by their ability to maintain viable populations than by any inability to disperse past tectonic and hydrographic barriers to population exchange. Freely dispersing pelagic taxa resemble airborne spores or wind-dispersed seeds that can drift almost anywhere but complete the entire life cycle only in favorable habitats. It seems likely that vicariant and allopatric models for speciation are far less important in pelagic evolution than sympatric or parapatric speciation in which dispersal is not limiting. Nevertheless, speciation can be quite rapid and involve cladogenesis even in cases where morphological data suggest gradual species transitions. Indeed, recent paleoecological and molecular studies increasingly suggest that classic examples of “phyletic gradualism” involve multiple, cryptic speciation events.

Paleoceanographic and climatic change seem to influence rates of turnover by modifying surface water masses and environmental gradients between them to create new habitats rather than by preventing dispersal. Changes in the vertical structure and seasonality of water masses may be particularly important since these can lead to changes in the depth and timing of reproduction. Long-distance dispersal may actually promote evolution by regularly carrying variants of a species across major oceanic fronts and exposing them to very different selection pressures than occur in their home range. High dispersal in pelagic taxa also implies that extinction should be difficult to achieve except though global perturbations that prevent populations from reestablishing themselves following local extinction. High rates of extinction in some pelagic groups suggests either that global perturbations are common, or that the species are much more narrowly adapted than we would infer from current taxonomies.

In the past decade, evolutionary paleoecology has shifted away from corroborative research of the “me-too-ecology” type toward its proper domain—the evolutionary consequences of ecological properties, roles, and strategies at the individual, population, community, and species levels. The science of evolutionary paleoecology tests for linkage between a species' ecology and its macroevolutionary history. Do the ecological characters of species within clades influence differential rate dynamics, particularly rates of faunal turnover and diversification? Intellectual coequality, once hampered by the misunderstanding that the role of paleoecology is to find examples of past ecology imperfectly entombed in the fossil record, is strengthened by the increasing number of evolutionary ecologists who have called for explicit paleontological contributions to resolve theoretical issues. The fossil record provides a necessary perspective to an understanding of process.

The covariation patterns of the postcranial skeleton in eight species of moas (Aves, Dinornithidae) from the Pleistocene of New Zealand are described using multiple factor analysis. Rotation schemes include an orthogonal Varimax and oblique (direct quartimin) simple structure solutions.

Four major patterns of covariation are resolved: a length factor, primarily that of leg length; a width factor, including pelvis width and long bone widths; a sternal breadth factor; and a sternal length-posterior pelvis length factor. The first two patterns represent a functional separation between body size and those aspects of the skeleton, scaling allometrically, adapted to support body weight. The sternal breadth factor may indicate that features contributing to trunk support are independent from those width measurements of the pelvis and hindlimb bones. The sternal length-posterior pelvis length factor reveals a pattern of covariation that is somewhat independent of other patterns (long bone lengths) determining variability in body size.

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

Several very large, taxonomically standardized data sets have been compiled and utilized to investigate biogeographic and evolutionary patterns of continental margin benthic foraminifera. Mean partial species durations for 87 frequently occurring and 180 rarely occurring species on the Atlantic continental margin of North America are the same, namely 21 m.y. The global fossil record of these species indicates no center or centers of origin and indicates very rapid dispersal. The Miocene had the greatest number of first occurrences with 46%, followed by the Pleistocene, Pliocene and Oligocene with approximately 13% each. The remaining 14% first occur in the Eocene, Paleocene, and Cretaceous. Species with a wide geographic distribution often exhibit longer species durations than those with narrow geographic ranges. The vast majority of endemic species (150 of 175) occur rarely and have no fossil record.

In studies of heterochrony, timing of development is generally measured relative to some intrinsic dimension, usually size, which serves as a proxy for time. A complementary approach is to measure timing relative to chronological time, an extrinsic dimension. Here, colony growth of a marine hydroid, Hydractinia echinata, is used to compare size- and age-based approaches to rate heterochronies. Colonies consist of feeding polyps; a basal, encrusting mat; and, in some cases, stolons which extend from the mat. Size is measured by the area covered by the mat and, if present, the stolons. Rate of polyp production was compared between colonies using clonal replicates grown in a common environment. Age-based comparisons employed polyp specific growth rates calculated over the same ontogenetic time interval for each replicate. Specific growth rates for colony area were also calculated; rates-ratios (polyp/area) provided size-based measures of polyp growth, analogous to allometric coefficients commonly used in studies of rate heterochronies. These comparisons show that size can be a misleading referent for between-colony comparisons because the rate of areal growth is not constant among colonies. Size-based measures of changes in developmental rates may provide insight into patterns, but not necessarily processes, of heterochrony. The implications of the pattern-oriented framework of size-based heterochrony should be considered in paleontological studies.

As paleobiology continues to address an ever broader array of questions, it becomes increasingly important to interpret confidently the meaning of the pattern of fossil occurrences as found in outcrop. To this end, sequence stratigraphy is an important tool for paleobiologists because it predicts the distribution of unconformities, facies changes, and changes in sedimentation rate, all factors known from numerous previous studies to affect the quality of the fossil record. Computer simulations now make it possible not only to model sequence architecture within sedimentary basins, but also to model the occurrence of fossils within those basins. These models generate predictions regarding the stratigraphic distribution of first and last occurrences, changes in species abundance, changes in species morphology, and the distribution of gaps in fossil ranges. Although confirmation of some of these predictions has been found in field studies, the extent to which these predictions describe the fossil record in general is still unknown. If the predicted patterns of fossil occurrences are found to be widespread, it will suggest that a relatively simple model of fossil occurrences in outcrops could become a new tool for solving a wide array of paleobiologic and biostratigraphic problems. With such models, paleobiologists and biostratigraphers will be able to use model data to test the accuracy of newly developed methods of analysis.

Paleobiologists must propose a priori hypotheses of homology when conducting a phylogenetic analysis of extinct taxa. The distributions of such “primary” homologies among species are fundamental to phylogeny reconstruction because they reflect a prior belief in what constitutes comparable organismal elements and are the principal determinants of the outcome of phylogenetic analysis. Problems arise when fossil morphology presents seemingly equivocal hypotheses of homology, herein referred to as antinomies. In groups where homology recognition has been elusive, such as echinoderms, these problems are commonly accompanied by the presence (and persistence) of poor descriptive terminology in taxonomic literature that confounds an understanding of characters and stymy phylogenetic research. This paper combines fossil morphology, phylogenetic systematics, and insights from evolutionary developmental biology to outline a research program in Phylogenetic Paleo-ontogeny. A “paleo” ontogenetic approach to character analysis provides a logical basis for homology recognition and discerning patterns of character evolution in a phylogenetic context. To illustrate the utility of the paleo-ontogenetic approach, I present a reassessment of historically contentious plate homologies for “pan-cladid” crinoids (Cladida, Flexibilia, Articulata). Developmental patterns in living crinoids were combined with the fossil record of pan-cladid morphologies to investigate primary posterior plate homologies. Results suggest the sequence of morphologic transitions unfolding during the ontogeny of extant crinoids are developmental relics of their Paleozoic precursors. Developmental genetic modules controlling posterior plate development in pan-cladid crinoids have likely experienced considerable constraint for over 250 million years and limited morphologic diversity in the complexity of calyx characters. Future phylogenetic analyses of pan-cladids are recommended to consider the presence of a single plate in the posterior region homologous with the radianal, rather than the anal X, as is commonly assumed.

The internal structures of the third metacarpals of Merychippus and Mesohippus are assessed from thin sections and from radiographs, and systems of trabeculae differing in orientation and density are described. The principal forces transmitted to the articular surfaces of these bones are reconstructed and are used to estimate the pressure of contact on each surface. The major correlations made between the structure and the function of the third metacarpal of Equus (Thomason, 1985a) are also observed in this bone in Merychippus and Mesohippus. More important, the differences in trabecular structure among the recent and fossil bones may be interpreted in terms of the differences in inferred function. Thus the functional interpretation of the internal structure of fossil bones may reasonably be attempted.

Ecological theory predicts an inverse association between population size and extinction risk, but most previous paleontological studies have failed to confirm this relationship. The reasons for this discrepancy between theory and observation remain poorly understood. In this study, we compiled a global database of gastropod occurrences and collection-level abundances spanning the Early Permian through Early Jurassic (Pliensbachian). Globally, the database contains 5469 occurrences of 496 genera and 2156 species from 839 localities. Within the database, 30 collections distributed across seven stages contain at least 75 specimens and ten genera—our minimum criteria for within-collection analysis of extinction selectivity. We use logistic regression analysis, based on global and local measures of population size and stage-level extinction patterns in Early Permian through Early Jurassic marine gastropods, to assess the relationship between abundance and extinction risk. We find that global genus occurrence frequency is inversely associated with extinction risk (i.e., positively associated with survival) in 15 of 16 stages examined, statistically significantly so in five stages. Although correlation between geographic range and occurrence frequency may account for some of this association, results from multivariable regression analysis suggest that the association between occurrence frequency and extinction risk is largely independent of geographic range. Within local assemblages, abundance (number of individuals) is also inversely associated with extinction risk. The strength of association is consistent across time and modes of fossil preservation. Effect strength is poorly constrained, particularly in analyses of local collections. In addition to limited power due to small sample size, this poor constraint may result from confounding by ecological variables not controlled for in the analyses, by taphonomic or collection biases, or from non-monotonic relationships between abundance and extinction risk. Two factors are likely to account for the difference between our results and those of most previous studies. First, many previous studies focused on the end-Cretaceous mass extinction event; the extent to which these results can be generalized to other intervals remains unclear. Second, previous findings of nonselective extinction could result from insufficient statistical power rather than the absence of an underlying effect, because nonselective extinction is generally used as the null hypothesis for statistical convenience. Survivorship patterns in late Paleozoic and early Mesozoic gastropods suggest that abundance has been a more important influence on extinction risk through the Phanerozoic than previously appreciated.

Manifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of extant plants, the ones of M. talaris are exceptional in that they have variable morphology. They bore two wings that produced a range of wing configurations, from seeds with two equal-sized wings to single-winged specimens, via various stages of underdevelopment of one of the wings. To examine the effects of various seed morphologies on aerodynamics and dispersal potential, we studied the flight performance of paper models of three morphotypes: symmetric double-winged, asymmetric double-winged, and single-winged. Using a high-speed camera we identified the mode of descent (plummeting, gliding, autorotation) and quantified descent speed, autorotation frequency, and other flight characteristics. To validate such modeling as an inferential tool, we compared descent of extant analogues (kauri; Agathis australis) with descent of similarly constructed seed models. All three seed morphotypes exhibited autorotating flight behavior. However, double-winged seeds, especially symmetric ones, failed to initiate slow autorotative descent more frequently than single-winged seeds. Even when autorotating, symmetric double-winged seeds descend faster than asymmetric double-winged ones, and descent is roughly twice as fast compared to single-winged seeds. Moreover, the relative advantage that (effectively) single-winged seeds have in slowing descent during autorotation becomes larger as seed weight increases. Hence, the range in seed wing configurations in M. talaris produced a wide variation in potential dispersal capacity. Overall, our results indicate that the evolutionarily novel autorotating winged seeds must have improved conifer seed dispersal, in a time when animal vectors for dispersion were virtually absent. Because of the range in wing configuration, the early evolution of autorotative flight in conifers was a functionally imperfect one, which provides us insight into the evolutionary developmental biology of autorotative seeds in conifers.

Two speciation events occurred in the Eocene lineage beginning with Echinocythereis isabenana Oertli (Aragon, Spain). After a long period of stasis in ornament and shape/size, this species underwent a relatively rapid decrease in size, accompanied by ornamental changes. The transition required about 30,000 yr. The new species E. aragonensis Oertli is significantly smaller (20% decrease in size). The lateral papillation is denser and less regular, the papillae being significantly smaller than in the ancestral form. This ornament gradually yields to increasing frequencies of individuals with reduced papillae superimposed on a progressively better developed network of filaments. This change, which is regionally valid, is ultimately replaced by fully expressed reticulations, on which minute pustules may occur; this development typifies the third species, E. posterior Oertli. Some ornamental characteristics of E. aragonensis are anticipated in rare individuals of E. isabenana. Ornamental features of E. posterior appear in late larvae of E. isabenana. Generally, E. aragonensis and E. posterior do not differ significantly in size. A trend toward smaller carapaces in the upper samples of E. posterior could be related to ecophenotypic effects.

All species are highly polymorphic for both shape and ornament; the morphs are not sharply bounded and are mostly of uncertain evolutionary status. The transition from isabenana to aragonensis is heralded by a sharp rise in the coefficient of variation for length measures of the carapace. There is a pronounced multivariate morphometric discontinuity between isabenana and the descendant forms, which are largely multivariately homogeneous. The isabenana-aragonensis transition could have occurred by selection or by random genetic drift. Both models can be accommodated by the data; however, the weight of evidence favors the former hypothesis. Evolution in the Echinocythereis lineage seems to have occurred by two different mechanisms. The first transition was rather rapid, with many disjunct features. The second was slow, the changes being more of degree than of kind.

Plant–insect associations have been a significant component of terrestrial ecology for more than 400 Myr. Exploring these interactions in the fossil record through novel perspectives provides a window into understanding evolutionary and ecological forces that shaped these interactions. For the past several decades, researchers have documented, described, and categorized fossil evidence of these interactions. Drawing on powerful tools from network science, we propose here a bipartite network representation of fossilized plants and their herbivore-induced leaf damage to understand late Paleozoic plant–insect interactions at the local community level. We focus on four assemblages from north-central Texas, but the methods used in this work are general and can be applied to any well-preserved fossil flora. Network analysis can address key questions in the evolution of insect herbivory that often would be difficult to summarize using standard herbivory metrics.

Species duration data for living benthic foraminifera derived from an extensive literature search have been compiled and analyzed to investigate rates and patterns of species origination. The same data subjected to taxonomic standardization through examination of many specimens lodged in museum collections indicate strikingly different, and more realistic, rates and patterns.

Evolutionary generalizations based on data generated from the literature only are often unreliable and may be directly in opposition to reality. Extensive attempts at taxonomic standardization should be the norm in paleobiological investigations.

Synchronous episodes of phenotypic change in five lineages of the endemic land snail genus Mandarina of the oceanic Bonin (Ogasawara) Islands through 40,000 years were documented by morphological analyses of radiocarbon-dated fossil specimens. Adult shell traits of these lineages show mostly synchronous patterns of change with longer intervals of stability and rapid shifts to other states of stability. Although there are intermediates between these different phenotypic states, the net interval of the phenotypic shift was relatively short, i.e., no longer than 7000 years. Extinction of a lineage and speciation occurred during the intervals of the rapid phenotypic shift. This period of abrupt change corresponds to the period of lowest sea level and end of the last glacial period. This implies that climatic change is one of the causes of these episodes of simultaneous rapid phenotypic shifts, speciation, and extinction in different lineages. These findings suggest that major phenotypic changes in phyletic evolution, separation of different species, and extinction of lineages may occur synchronously in many lineages during an extremely short interval.