No egg of any fossil nautiloid has yet been discovered. However, anomalies of embryonic shell growth, described for the first time in several Mesozoic Nautilida, provide important clues on morphology, structure, and size of their egg capsules; on the physical characteristics where egg laying occurred; and on the hatching processes. Roughness inside the inner egg capsule–caused by hard and uneven egg-laying substrate, locally and temporarily slowing down or stopping the apertural shell growth–could cause temporary deformations of growth lines. Such roughness, caused by stone, is described inside an egg capsule of Nautilus, which was fixed obliquely relative to the egg-laying substrate. This reduced the space between the inner and outer capsules, which locally fused together. The lateral-umbilical grooves, furrows, and deformations of growth lines were probably caused by the inner egg capsule during the prehatching stage. In fossil Nautilida, as in Nautilus, the size of this capsule was relatively small compared with the shell diameter at hatching. During the last stages of embryonic development, the shell extended backwards outside the egg capsule before hatching. This prehatching stage, during which the egg capsule continued to press against the shell, can be marked by a prehatching constriction. In fossil species, as in Nautilus, the inner capsule constituted a kind of “straitjacket” during the last stages of embryonic development. The expansion in whorl width at hatching, in normal as well as in abnormal shells, marks release of this straitjacket. Important deformations of the whorl section probably result from an abnormal form and size of the egg capsules mainly caused by the manipulations by the female during the egg laying on a hard and hollow substrate, increasing the straitjacket effect. An alternative explanation could be that the chorion did not expand adequately. From relatively early embryonic stages (approximately 180° adapical of the nepionic constriction) to hatching, both flaps of the hyponome could be turned backward under the shell, jammed between the inner wall of the egg capsule and the mantle margin, resulting in the formation of paired ventral parallel grooves. Many normal features of the embryonic development of nautiloids can be clarified through the study of the anomalies of embryonic shell growth.

Theoretical models of skeletal structures provide suitable frameworks to assess macroevolutionary patterns of form change. We discuss three theoretical approaches to account for morphological patterns of the pelvic girdle in archosaurs. Every approach targets a different level of organization within the concept of morphospace. First, we build a morphocline by applying a mathematical transformation to the outline of the hip of the theropod dinosaur Deinonychus antirrhopus, in order to look at theoretical paths of evolutionary change based on changes of proportion. Second, we analyze the variability of a sample of 86 hips within a theoretical construction that incorporates information about the spatial orientation of the three paired bones that build this skeletal compound. Finally, we look at boundary patterns within these hips as a basis for generating a formalism based on graph theory. Insights about the evolution and development of the archosaur triradiate pelvis and its morphological trends are suggested in the light of each theoretical approach, with a special focus on the convergent evolution of a retroverted pubis in ornithischians and birds.

This paper assesses the reliability with which fossil reefs record the diversity and community structure of adjacent Recent reefs. The diversity and taxonomic composition of Holocene raised fossil reefs was compared with those of modern reef coral life and death assemblages in adjacent moderate and low-energy shallow reef habitats of Madang Lagoon, Papua New Guinea. Species richness per sample area and Shannon-Wiener diversity (H′) were highest in the fossil reefs, intermediate in the life assemblages, and lowest in the death assemblages. The taxonomic composition of the fossil reefs was most similar to the combination of the life and death assemblages from the modern reefs adjacent to the two fossil reefs. Depth zonation was recorded accurately in the fossil reefs. The Madang fossil reefs represent time-averaged composites of the combined life and death assemblages as they existed at the time the reef was uplifted.

Because fossil reefs include overlapping cohorts from the life and death assemblages, lagoonal facies of fossil reefs are dominated by the dominant sediment-producing taxa, which are not necessarily the most abundant in the life assemblage. Rare or slow-growing taxa accumulate more slowly than the encasing sediments and are underrepresented in fossil reef lagoons. Time-averaging dilutes the contribution of rare taxa, rather than concentrating their contribution. Consequently, fidelity indices developed for mollusks in sediments yield low values in coral reef death and fossil assemblages. Branching corals dominate lagoonal facies of fossil reefs because they are abundant, they grow and produce sediment rapidly, and most of the sediment they produce is not exported.

Fossil reefs distinguished kilometer-scale variations in community structure more clearly than did the modern life assemblages. This difference implies that fossil reefs may provide a better long-term record of community structure than modern reefs. This difference also suggests that modern kilometer-scale variation in coral reef community structure may have been reduced by anthropogenic degradation, even in the relatively unimpacted reefs of Madang Lagoon. Holocene and Pleistocene fossil reefs provide a time-integrated historical record of community composition and may be used as long-term benchmarks for comparison with modern, degraded, nearshore reefs. Comparisons between fossil reefs and degraded modern reefs display gross changes in community structure more effectively than they demonstrate local extinction of rare taxa.

Recently, there has been much interest in detecting and measuring patterns of change in disparity. Although most studies have used one or two measures of disparity to quantify and characterize the occupation of morphospace, multiple measures may be necessary to fully detect changes in patterns of morphospace occupation. Also, the ability to detect morphological trends and occupation patterns within morphospace depends on using the appropriate measure(s) of disparity. In this study, seven measures were used to determine and characterize sensitivity to sample size of the data, number of morphological characters, percentage of missing data, and changes in morphospace occupation pattern. These consist of five distance measures—sum of univariate variances, total range, mean distance, principal coordinate analysis volume, average pairwise dissimilarity—and two non-distance measures—participation ratio and number of unique pairwise character combinations. Evaluation of each measure with respect to sensitivity to sample size, number of morphological characters, and percentage of missing data was accomplished by using both simulated and Ordovician crinoid data. For simulated data, each measure of disparity was evaluated for its response to changes of morphospace occupation pattern, and with respect to simulated random and nonrandom extinction events. Changes in disparity were also measured within the Crinoidea across the Permian extinction event.

Although all measures vary in sensitivity with respect to species sample size, number of morphological characters, and percentage of missing data, the non-distance measures overall produce the lowest estimates of variance (in bootstrap analyses). The non-distance measures appear to be relatively insensitive to changes in morphospace occupation pattern. All measures, except average pairwise dissimilarity, detect changes in occupation pattern in simulated nonrandom extinction events, but all measures, except number of unique pairwise character combinations and principal coordinate analysis volume, are relatively insensitive to changes in pattern in simulated random extinction events. The distance measures report similar changes in disparity over the Permian extinction event, whereas the non-distance measures differ. This study suggests that each measure of disparity is designed for different purposes, and that by using a combination of techniques a clearer picture of disparity should emerge.

We infer the absolute completeness of the mammalian fossil record of the Iberian Neogene, from a compiled database of preserved stratigraphic ranges for both species and genera and by means of the analytical tools developed by Foote and Raup (1996). We conclude that the mammalian fossil record from the Neogene of the Iberian Peninsula is very complete (more than 75% at the specific level, and more than 90% at the generic one), being a good indicator of how complete the record of terrestrial organisms can be at least under certain favorable conditions. Comparison with previously published results for well-known marine invertebrates indicates that the continental Iberian Neogene record is not significantly less complete, thus raising doubts about the importance of more episodic deposition in continental environments. It remains to be seen if continental faunas in general are as complete as the marine invertebrate record.

Evolutionary interpretation of paleontological patterns requires a hypothesis of phylogeny, but our phylogenetic hypotheses may not perfectly mirror organismal phylogeny. Tree summary methods less conservative than strict consensus may increase resolution, but these methods may present a biased summary of the full set of most parsimonious trees. When we fail to acknowledge all equally optimal topologies, we risk disregarding trees that are closer to the correct phylogeny. We discuss a case where two subsets of trees were recovered in the set of most parsimonious trees, each with a profoundly different interpretation of character evolution near the root of Echinodermata. This was caused by the presence of a bimodally labile taxon in the matrix with two different topological subsets, each equally parsimonious but differing in the number of consistent trees. Majority-rule consensus favors the subset with the largest number of trees consistent with the placement of the rogue taxon. This bias favors clusters not because of the biological implications of the tree, but on the basis of great inequality in the sizes of the islands of parsimony. We thus recommend that majority-rule consensus trees not be used to summarize the results of a phylogenetic analysis.

Two models of faunal turnover patterns, one with constant turnover and another with climatically induced turnover pulses, were tested against the empirical fossil data of first and last appearances of large mammals from the late Pliocene and Pleistocene of East Africa. Computer simulations of each model were generated by first creating change in hypothetical faunal communities and then sampling the evolving communities in a manner scaled to the specific contingencies of the East African fossil record. Predictions of the two turnover models were compared with the empirical data. Neither model yielded predictions that deviated significantly from the observed patterns of first and last appearances of species, and both models produced extremely similar results. The implication is that the fossil data of East Africa are not refined enough to detect variations in the pace of turnover; the patterns of first- and last-appearance frequencies are determined more by the contingencies of the fossil record than by the underlying evolutionary and migrational patterns. Whereas these results undermine the primary basis of empirical support for the turnover-pulse hypothesis, they do not imply that other models are more likely. However, the simulation results were highly suggestive of significant reduction in species biodiversity of large mammals during the past 2 Myr.

An example of actual shell growth in the pentameride brachiopod Lycophoria nucella (Dalman) reveals that the axis-computing morphometric technique (Aldridge 1998; Van Osselaer and Grosjean 2000) produces hypothetical ideal logarithmic spirals that fail to morphometrically characterize the biological realities determined by the actual geometry of the shells to which the axis-computing technique is applied. In contrast, the actual-outline morphometric technique (McGhee 1980) links the measurement coordinate system directly to the ontogeny of the animal under analysis, and it yields morphometric parameterizations of geometric aspects of the shell of direct biological significance to the animal (the presence or absence of ontogenetic alterations in shell convexity, rates of change of shell convexity in the case of anisometric growth, and the nature of anisometric changes in shell convexity—i.e., whether the shell becomes increasingly more convex with growth, or whether the shell becomes increasingly flatter with growth).

A phylogeny of 54 Recent and fossil species of Soritacea (Foraminifera) was used to test the hypothesis that endosymbiosis has driven the evolution of the clade. Endosymbiosis with photosynthetic eukaryotes is the plesiomorphic condition for the entire clade Soritacea. Living species dwell in tropical-subtropical, shallow-water habitats and are characterized by the possession of rhodophyte, chlorophyte, or dinophyte photosymbionts. Two distinct changes in endosymbiont type are recognized when endosymbiont type is mapped in the cladogram of Soritacea: (1) a change from rhodophyte to chlorophyte endosymbionts occurred in the stem lineage of the least inclusive clade containing New clade B, Orbiculinida, and Soritida; and (2) a change from chlorophyte to dinophyte endosymbionts occurred in the stem lineage of the least inclusive clade containing New clade G, New clade H, New clade I, Sorites, Amphisorus, and Orbitolites. When habitat and ontogeny are optimized on the cladogram of Soritida, the acquisition of dinophyte endosymbionts appears as a key innovation that facilitated a switch in habitat from free-living to attached living on nonphytal and phytal substrata. A subsequent change in the attached habitat from nonphytal to predominantly phytal (seagrasses and macroalgae) substrata is accompanied by a peramorphic trend in the megalospheric tests. The diversification (adaptive radiation) of the crown Soritida subclade resulted from the interplay between the acquisition of a key innovation (dinophyte endosymbionts) and the subsequent change in the ecology of the group (radiation to phytal substrates).

The processes of fossilization have usually been perceived by paleontologists as destructive ones, leading to consecutive (and in most cases irretrievable) losses of paleobiological information. However, recent developments of conceptual issues and methodological approaches have revealed that the decrease in paleobiological information runs parallel to the gain of taphonomic information. This taphonomic imprinting often makes it possible to decode the fraction of paleobiological information that was lost during fossilization, and may also contribute new data for deciphering paleobiological information that was not originally preserved in the assemblage, such as paleoethology. A good example is the study of the macrovertebrate assemblage from the lower Pleistocene site at Venta Micena (Orce, southeastern Spain). Taphonomic analysis showed that the giant, short-faced hyenas (Pachycrocuta brevirostris) selectively transported ungulate carcasses and body parts to their maternity dens as a function of the mass of the ungulates scavenged. The fracturing of major limb bones in the dens was also highly selective, correlating with marrow content and mineral density. Important differences in bone-cracking intensity were related to which species the bones came from, which in turn biased the composition of the bone assemblage. The analysis of mortality patterns deduced for ungulate species from juvenile/adult proportions revealed that most skeletal remains were scavenged by the hyenas from carcasses of animals hunted by hypercarnivores, such as saber-tooths and wild dogs. Analytical study of the Venta Micena assemblage has unlocked paleobiological information that was lost during its taphonomic history, and has even provided paleobiological information that was not preserved in the original bone assemblage, such as the paleoethology of P. brevirostris, which differed substantially from modern hyenas in being a strict scavenger of the prey hunted by other carnivores.

Many Tertiary species of Crassostrea appear to have inhabited shallow-marine environments where they produced extremely large and thick shells. In contrast, living Crassostrea species are restricted primarily by marine predation to brackish, hypersaline, and intertidal environments where they produce comparatively smaller and thinner shells. If Crassostrea populations have used estuarine environments as a refuge from predation since the Cretaceous, then their presence in fully marine environments after the Cretaceous is puzzling. In order to interpret differences in environment and shell size, I examined the paleoecology and sclerochronology of two marine and two estuarine populations. Results are consistent with the hypothesis that thicker shells in Tertiary Crassostrea titan deterred increased exposure to fully marine predation. Life spans and growth rates estimated from annually formed growth increments show that C. titan grew significantly faster in shell thickness, as well as lived two to three times longer, than Quaternary Crassostrea virginica. Similar or lower valve-height growth rates in C. titan, as well as thinner shell walls in the attachment area, are consistent with exposure to marine predation, but not with alternative factors, such as higher salinity or alkalinity. Thicker valves in C. titan resulted from the successive addition of chalky deposit layers, in contrast to C. virginica valves, which contain significantly less of this unusual shell structure. A high incidence of incomplete drill holes in juvenile C. titan shells demonstrates that their thick valves were successful in deterring muricid predation. The association of C. titan with other large suspension feeders (barnacles and pectenids), as well as with phosphatic-pellet sediments, suggests that elevated planktic productivity may have supported this reefal community and enabled C. titan to grow thicker shells. The occurrence of both shallow-marine and estuarine Crassostrea since the Cretaceous raises the possibility that estuaries have served as refugia from which populations have dispersed into fully marine environments multiple times through the Cenozoic.

Hypotheses about constraints, selection, and other evolutionary processes often predict different rates of change among different characters. For example, it is thought that gross soft anatomical characters change less frequently than do general shell characters. However, some shell characters on primitive gastropods, such as the sinus and selenizone, are thought to be linked to soft anatomy. If both premises are true, then selenizone/sinus characters should change less frequently than other characters. Workers also have documented active trends among gastropod shell characters. One explanation is a driven trend, where the rate of change in one direction (i.e., gain or loss, increase or decrease) is greater than the rate of change in the opposite direction.

Hypotheses about relative rates and biased change are tested here for lophospiroid gastropods. Likelihood analyses test whether hypotheses positing many different rates predict data significantly better than do hypotheses positing few rates. One tree-based approach assumes that a phylogeny is known and thus treats a tree as a model. A second tree-based approach treats phylogeny as an additional hypothesis. This multiparameter approach allows competing rate hypotheses to “assume” a phylogeny that maximizes their likelihoods.

Likelihood tests reject hypotheses of low rate heterogeneity among lophospiroid characters. The most likely hypothesis (which treats phylogeny as an unknown) posits seven rates, with biased changes among three characters (preferential reduction of both sinus depth and sinus width and preferential addition of ornament). The distribution of rates among different character classes is consistent with the prediction that characters associated with internal anatomy should show generally lower rates of change than those associated with gross shell morphology. Evaluating significance when contrasting hypotheses posit different phylogenies is problematic, but the difference in support (log-likelihood) is overwhelming. Even if a model phylogeny is used, we still reject all hypotheses using fewer than six rates and not invoking trends in sinus characters. Thus, it is difficult to avoid rejecting the hypothesis that shell characters are uniformly plastic.

Co-ossified pygal and caudal vertebrae in Late Cretaceous mosasaurs from the southeast Netherlands, northeast Belgium, and North America are compared with lumbar and caudal vertebrae from fossil and extant whales. Both infectious spondylitis and idiopathic vertebral hyperostosis afflicted these marine tetrapods. The causes of the infectious disease and of the idiopathic disease are similar in the compared life forms. The location of idiopathic hyperostosis along the vertebral column implicates axial locomotion in mosasaurs, as in whales.

Globorotalia truncatulinoides is an extant species of planktic foraminiferans commonly used for stratigraphic and paleoenvironmental analyses. It originated ∼2.8 m.y. ago in subtropical areas of the South Pacific, spread to all subtropical and temperate regions of the world ocean, and expanded its range to southern subantarctic waters between 500 and 200 Ka. The wide geographic distribution of G. truncatulinoides is associated with a latitudinal morphological variability considered as an ecophenotypic variation within a single species. Here, we present the first molecular, morphological, and ecological evidence that G. truncatulinoides corresponds to a complex of four genetic species adapted to particular hydrographic conditions. The different species are separated by significant genetic distances in several ribosomal genes (SSU, ITS-1, 5.8S, ITS-2). Species 1 and species 2 characterize subtropical waters, species 3 is abundant exclusively in the Subantarctic Convergence, while species 4 inhabits subantarctic waters. By using an absolute molecular clock, we deduce the time of divergence between the subtropical and frontal/subantarctic species at ∼300 Ka, which is in agreement with stratigraphic data and suggests an adaptive radiation of the species allowing it to colonize the nutrient-rich and cold subantarctic waters. This genetic dichotomy is associated with a morphological differentiation identified using outline analysis. Species of the same regions are more similar in test shape but can be distinguished by coiling direction. The evolutionary patterns recognized here by combining DNA and morphological analyses from plankton-tow specimens mirror and allow a new interpretation of the data available from Recent sediments. They highlight the importance of adaptation and heterochronic processes, leading to cryptic speciation, in planktic foraminifera.

Growth rings of Mesozoic fossil woods have often been used for paleoclimatological inferences. Most of the studies, however, rest upon uniformitarian deductions based on the observation of conifers from the present boreal temperate realm, whereas warm climates dominated during the Mesozoic. We propose a new approach, based on the study of the distribution of growth ring types among 643 samples from the Jurassic-Cretaceous interval. A clear picture emerges from analysis, consistent with what is known of Mesozoic climates from other sources. Woods with no rings are encountered in a wide latitudinal zone, extending up to 75°N and 65°S during the Late Cretaceous. Woods with well-developed latewood do not occur at low latitude and disappeared from the Northern Hemisphere during the Late Cretaceous. Our data set also shows that the taxonomic distribution of growth ring types is not regular. Among the genera encountered, 40% can build only one type of ring. The genus Agathoxylon never displays thick latewood, although it ranges from 75°S to 70°N. This demonstrates that growth ring studies must include a taxonomic analysis.

In computational studies of the body mass and surface area of vertebrates, it is customary to assume that body cross-sections are approximately elliptical. However, a review of actual vertebrate cross-sections establishes that this assumption is not usually met. A new cross-sectional model using superellipses is therefore introduced, together with a scheme that allows estimates to be given with ranges. Tests of the new method, using geometrical shapes, miniature vertebrate models, and actual animals, show that the method has a high accuracy in body mass estimation. A new computer program to perform the computation is introduced. The application of the method to some Mesozoic marine reptiles suggests that the tuna-shaped ichthyosaur Stenopterygius probably had body masses comparable to those of average cetaceans of the same body length.

Radiations are commonly believed to be linked to the evolutionary appearance of a novel morphology or ecology. Previous studies have demonstrated a close relationship between the evolutionary appearance of algal photosymbiosis in planktonic foraminifera and evolutionary diversification of Paleogene photosymbiotic clades. For example, the evolution of photosymbiosis was synchronous with the abrupt evolution of four major groups of Paleogene planktonic foraminifera including two clades within the genus Morozovella, as well as the genera Acarinina and Igorina. Our new isotopic and biogeographic data suggest that the acarininids evolved from a photosymbiotic ancestor (which we identify as Praemurica inconstans or early representatives of Praemurica uncinata), but also demonstrate that photosymbiosis did not trigger an immediate species-level radiation in this group. Instead, the acarininids remained a low-diversity taxon restricted to high latitudes for nearly 1.8 million years before radiating ecologically and taxonomically. The eventual radiation of the acarininids is tied to an expansion of their geographic range into the mid and low latitudes. Biogeographic analyses of modern plankton suggest that high-latitude environments may be less conducive to establishing radiations simply because there are fewer niches available to be filled than there are in the tropics. Accordingly, the acarininids may have initially failed to diversify because they started off in environments that presented few opportunities to sustain a large radiation. The high-latitude origin of the acarininids continued to retard their overall diversification until they were able to develop strategies that allowed them to expand into tropical environments and fully exploit their photosymbiotic ecology.

During the first 10–20 Kyr of the Eocene temperatures warmed by 4–8°C in middle and high latitudes, then cooled again over the succeeding ∼200 Kyr. Major changes in the composition of marine and terrestrial faunas, including one of the largest mammalian turnover events of the Cenozoic, occurred during this temperature excursion. To better understand the effects of rapid climatic change on continental biotas, we studied 60 fossil pollen samples collected from 900 m of section spanning approximately three million years of the late Paleocene and early Eocene; the samples come from the Fort Union Formation and Willwood Formation in the Bighorn Basin of northwestern Wyoming, paleolatitude approximately 47°N. There are 40 samples from the 500 m of rock deposited during the one million year interval centered on the Paleocene/Eocene boundary, although pollen was not preserved well in rocks representing the short warm interval at the base of the Eocene.

Overall, the palynoflora shows moderate change in composition and diversity. Two pollen taxa clearly expanded their ranges to include North America in the first 400 Kyr of the Eocene, Platycarya (Juglandaceae), and Intratriporopollenites instructus (cf. Tilia), but they account for less than 5% of pollen grains in the early Eocene. There are no last appearances of common taxa associated with the Paleocene/Eocene boundary. The most noticeable palynological changes are the decrease in abundance of Caryapollenites spp. and Polyatriopollenites vermontensis (Juglandaceae), and the increase in abundance of Taxodiaceae (bald cypress family), Ulmaceae (elm family), and Betulaceae (birch family), particularly Alnipollenites spp. (alder). There are 22% more species in the Eocene samples than in the Paleocene samples; mean richness of Eocene samples is 17% higher than the mean of Paleocene samples. The mean evenness of Eocene samples is higher than that of Paleocene samples, but the difference is not significant.

The modest level of floral change during the late Paleocene and early Eocene contrasts with the major taxonomic turnover and ecological rearrangement of North American mammalian faunas observed at the same time. Faunal change probably resulted from intercontinental range expansion across Arctic land bridges that became habitable as a result of high-latitude warming, so it is surprising that climatically sensitive plants did not also experience a major episode of interchange. The absence of fossil plants from the temperature excursion interval itself could prevent us from recognizing a transient shift in floral composition, but it is clear that the flora did not undergo a major and permanent restructuring like that seen in the mammals. The contrast between the moderate floral response to warming and the strong faunal response is consistent with the idea that interactions between immigrant and native taxa, rather than climate directly, were the primary cause of terrestrial biotic change across the Paleocene/Eocene boundary.

Recent works have suggested that the fossil record exhibits a fractal structure; i.e., that processes, such as extinction, follow a power-law size distribution and their time series show a 1/f power spectrum. This structure has been used as evidence that evolutionary dynamics are an example of a self-organized critical (SOC) process. We have reexamined this claim by analyzing a detailed record of marine genus-level extinctions and originations. Our results indicate that neither extinctions nor origination metrics show the power-law size distribution or a 1/f power spectrum characteristic of SOC and related models. We also believe that the underlying assumptions of SOC are incompatible with our understanding of the processes controlling macroevolutionary patterns.

Statistical analyses of the data sets are compatible, however, with the presence of multifractal self-similarity in both records, consistent with a hierarchical and multiplicative generating process. This model assumes that multiple causal mechanisms, acting over many spatial and temporal scales, interact to promote or inhibit originations and extinctions. In this view, the same event can have quite different impacts depending on the state of the biotic or physical system at the time that it occurs. This may at least partially explain such phenomena as the imperfect correlation between eustatic sea-level changes and macroevolutionary processes and the apparent nonlinear response of biotic systems to bolide impacts.

The estimation and interpretation of temporal patterns in origination and extinction rates is a major goal of paleobiology. However, the possibility of coincident variation in the quality and completeness of the fossil record makes the identification of such patterns particularly difficult. Previously, Nichols and Pollock (1983) proposed that capture-mark-recapture (CMR) models be adapted to address this problem. These models can be used to estimate both sampling and turnover rates, reducing the risk of confounding the two quantities. Since that time, theoretical advances have made possible the application of these tools to a much broader range of problems. This paper reviews those advances likely to be of greatest relevance in paleobiological studies. They include (1) joint estimation of per-taxon origination and extinction rates, (2) modeling sampling or turnover rates as explicit functions of causal variables, (3) ranking of alternative models according to their fit to the data, and (4) estimation of parameter values using multiple models. These are illustrated by application to an Ordovician database of benthic marine genera from key higher taxa. Robustness of these methods to violation of assumptions likely to be suspect in paleobiological studies further suggests that these models can make an important contribution to the quantitative study of macroevolutionary dynamics.