Given estimates of the variation in total standing species richness through the periods of the Phanerozoic, mean species duration, and the relative intensity of the sampling of the fauna from each of the periods, the expected number of described species can be predicted for each period of the Phanerozoic using an analytic sampling model. This model is based on the assumption that the relative abundances of species in any geologic period can be approximated by the canonical (lognormal) species-abundance distribution.

Three commonly cited models of standing species richness (Valentine, 1973; Gould et al., 1977; Bambach, 1977) each suggest different patterns of species richness in the Phanerozoic. By assuming that sampling of the fossil record is proportionate to sediment volume, it can be shown with the sampling model that the Empirical, Equilibrium, and Species-Richness Models each predict that the number of described species will be strongly correlated with sediment volume. Equally high correlations are predicted if it is assumed that sampling is proportionate to sediment area or to paleontological interest. The correlations predicted for each of the three models are remarkably similar. The impact of sampling effects is so strong that the variations in species richness postulated by these three models are almost completely obscured. Preservational biases will probably only further obscure the relationship between the number of described species and total species richness. Therefore, it seems likely that analysis of trends in the total number of described species will be of little use in determining trends in worldwide species richness in the Phanerozoic.

Comparison of the actual patterns of variation in the number of described species and the expected numbers of described species predicted by the sampling model reveals that more species are known from the Cenozoic than would be predicted from the abundance of Cenozoic sediments or from the amount of paleontological interest in the Cenozoic. This might have resulted from the Cenozoic sediments remaining relatively free of diagenetic effects which might have destroyed the fossils entombed in the sediments.

Truth, goes an old proverb, is the daughter of time. Fifty years ago, G. G. Simpson (1944) brought paleontology into the Neodarwinian fold, arguing that evolutionary tempo can be documented in the geological record and used to inform debate about evolutionary mode. Today, increasingly sophisticated paleontological investigations of rate—be it diversification, extinction, migration, morphological change, or divergence in macromolecular sequence—require calibration of the geological time scale with a precision far greater than Simpson could have anticipated. Expanding research on the relationships between environmental history and evolution also requires unprecedented resolution in correlation and geochronometry.

The exceptionally preserved Triassic (Anisian) Grès à Voltzia fauna from the Vosges of northeastern France is compared with four major Carboniferous Konservat-Lagerstätten. The problem of comparing faunas with different types of preservation and degrees of taxonomic determination is addressed with a newly devised similarity coefficient. This coefficient quantifies and combines data from different levels in the taxonomic hierarchy and allows comparisons between biotas in a consistent direction regardless of relative diversity. The rank order of similarity between the four Carboniferous Konservat-Lagerstätten and the Grès à Voltzia is as follows: 1. Mazon Creek (Westphalian D) of Illinois; 2. Glencartholm (Visean) of southern Scotland; 3. Bear Gulch (Namurian) of Montana; and 4. Blanzy-Montceau (Stephanian) of France. These occurrences represent conditions transitional between nearshore fully marine and fresh water. The Grès à Voltzia fauna is significantly closer to the Mazon Creek fauna than to the others; the taxonomic overlap with Blanzy-Montceau and Bear Gulch is limited.

Stratigraphic age has an insignificant influence on the result; indeed, the fauna closest in age to the Grès à Voltzia, that of Blanzy-Montceau, is least similar. Taphonomic factors are important in determining the range of organisms preserved. The Glencartholm fauna is represented only by forms with either mineralized or robust chitinous skeletons, implying a greater degree of decay prior to the onset of diagenetic mineralization than in the other Konservat-Lagerstätten. Environment, however, is the major control on similarity. The Mazon Creek biota, like that of Grès à Voltzia, represents settings transitional between terrestrial and marine-influenced delta. Groups common to both Konservat-Lagerstätten include medusae, brachiopods, polychaetes, bivalve and gastropod molluscs, limulids, scorpions, spiders, branchiopods, ostracodes, malacostracans, cycloids, euthycarcinoid and myriapod uniramians, insects, fish, and tetrapods. There is a striking continuity between the faunas of Carboniferous and Triassic transitional sedimentary environments. Groups that were adapted to fluctuating conditions (e.g., shifting salinity) show strong congruence at the family and lower levels and were little affected by Permian extinctions. The major taxonomic contrasts are in the eumalacostracans and insects: many of the groups represented in the Grès à Voltzia appeared in the Permian and radiated across the Permo-Triassic boundary as Paleozoic forms became extinct.

Several groups of siliceous microorganisms possess a skeletal latticework of interconnected rods. Skeletal configurations of one of these groups, the silicoflagellates, can be produced by a simple mathematical model that minimizes the apical surface area for a given basal area and internal volume. A similar model that minimizes the total length of the skeletal elements, and thus the silica utilization and skeletal weight, produces configurations that are generally less common in silicoflagellates. The diversity of silicoflagellate skeletal morphologies suggests that both the minimization of apical surface area and the conservation of skeletal material may be important factors in skeletal design. The two most important morphologies found in modern oceans, the four-sided Dictyocha and the six-sided Distephanus, can co-occur in an environment where both factors have some relative importance. However, these models do not explain the range of silicoflagellate skeletal morphology found in nature.

The hypothesis is proposed that mean level of heterozygosity is functionally related to rate of speciation in evolutionary phylads. Under this hypothesis, phylads which speciate more rapidly do so because of increased level of within-species genetic variability which is then available to conversion to species differences under appropriate ecological or environmental conditions. An important corollary is that rate of speciation could be limited in phylads with low genetic variability, irrespective of environmental considerations.

This hypothesis has been tested with respect to electrophoretically detectable variation in products of structural genes in two families of North American fishes characterized by grossly different rates of speciation. Totals of 69 species of the highly speciose Cyprinidae, and 19 species of the relatively depauperate Centrarchidae, were assayed for mean level of heterozygosity at 11–24 genetic loci. Since Cyprinidae and Centrarchidae exhibit on the average nearly identical levels of genic variation (Ĥ = 0.052 ± 0.004, and Ĥ = 0.049 ± 0.009, respectively), the hypothesis that level of heterozygosity affects rate of speciation in these fishes is not supported.

Nonetheless, the amount of genic variability in both Cyprinidae and Centrarchidae is large, comparable to mean levels in previously studied vertebrates. The great wealth of genome variability, reflected in the electrophoretic variation present in virtually all outcrossing organisms, apparently can accommodate considerable flexibility in rate and pattern of evolutionary response to the various environmental regimes challenging organisms.

Body size is one of the most studied phenotypic attributes because it is biologically important and easily measured. Despite a long history of study, however, the pattern of body-size change in diverse higher taxa over the Phanerozoic remains largely unknown because few relevant data sets span more than a single geological period or provide comprehensive, global coverage. In this study, we measured representative specimens of 3414 brachiopod genera illustrated in the Treatise on Invertebrate Paleontology. We applied these size data to stage-resolved stratigraphic ranges from the Treatise and the Paleobiology Database to develop a Phanerozoic record of trends in brachiopod size. Using a model comparison approach, we find that temporal variation in brachiopod size exhibits two distinct modes—a Paleozoic mode of size increase and a post-Paleozoic mode indistinguishable from a random walk. This transition reflects a change in the identities of the most diverse brachiopod orders rather than a shift in mode within any given order. Paleozoic size increase reflects a small, persistent bias toward the origination of new genera larger than those surviving from the previous stage and is identifiable as a statistically supported trend in three orders representing both Class Strophomenata (Order Productida) and Class Rhynchonellata (orders Atrypida and Spiriferida). Extinction exhibits no consistent bias with respect to size. The shift in evolutionary mode across the end-Permian mass extinction adds to long-standing evidence from studies of diversity and abundance that this biotic catastrophe suddenly and permanently altered the evolutionary history of what was, until that time, the most diverse animal phylum on Earth.

It has been suggested that a sudden event at the end of the Cretaceous period caused a major extinction that was felt disproportionately by creatures in the water column. It also has been argued that benthic deposit feeders, being relatively independent of abundance of organic particles in the water column, should have survived the crisis more readily than suspension feeders, which depended more upon feeding upon phytoplankton. I argue that the hypothesis of relative immunity of deposit feeders is insufficient, because deposit feeders by and large depend upon a supply of organic matter from the water column and would have succumbed to food shortage nearly as rapidly as suspension feeders, possibly within a maximum of three to six months. This near simultaneity of extinction would have been especially true of continental shelf environments. Even in some parts of the deep sea, it is likely that a dependence upon the water column above might have caused deep-sea deposit feeders to succumb rapidly. Therefore, deposit feeders would not necessarily have outsurvived suspension feeders during a crisis of depleted water-column phytoplankton, increased shading by inert particles, or poisoning of the water column and killing of phytoplankton. The relatively lower rate of extinction of nuculoid bivalves may relate instead to their presence in deeper-water refuge habitats, their apparent relative ability to diversify in higher latitudes, or their resistance to factors other than food shortage.

Fibrous ligament and aragonitic shell material have been found preserved in two specimens of radiolitid rudists [cf. Radiolites angeoides (De Lapeirouse)] from the Lower to Middle Coniacian of Tirol, Austria. The invaginated ligament apparently comprised two torn and overgrown non-functional strings, one in each valve, connected medially by a thin strip of active ligament. The original dimensions of the active ligament have been estimated, for shells of 4 to 5 cm commissural diameter, at 0.58 mm2 cross-sectional area and 1.3 mm length, with the shell closed. Using data on the adductor muscle of Recent oysters and the results of compression tests carried out on samples of oyster fibrous ligament, it is estimated that these radiolitid shells opened less than 1 mm in life; their gaping was highly restricted. This is taken to support the proposal that the expanded mantle margins (principally that of the right, attached valve) were responsible for food particle entrapment, rather than the gills as in most other bivalves. It is suggested that a tentaculate mantle flange was extruded through the narrow gap between the valves during feeding. The pair of pronounced radial bands on the posterior flanks of the shell are interpreted as marking pseudofaecal and faecal ejection sites. Finally, it is speculated that slime (possibly poisonous or foul-tasting) on the mantle tentacles inhibited predators.

We describe three giant palaeobatrachid fossil tadpoles of the genus Palaeobatrachus (Nieuwkoop-Faber [NF] stages 60–64) from the Miocene of Randecker Maar, Germany. The largest was 150 mm at the beginning of metamorphosis (stage 60), whereas the smallest was 100 mm and approaching the end of metamorphosis (stage 64). In contrast, normal palaeobatrachid tadpoles and their pipid relatives, both extinct and extant, rarely exceed 60 mm in length. We review here both ecological and pathological conditions that are conducive to the development of gigantism in tadpoles. Tadpoles that lack a thyroid gland become exceptionally large and arrest development at early hindlimb stages (NF stages 53–56). However, the advanced metamorphic stages of the giant Palaeobatrachus tadpoles indicate that they were able to metamorphose, and thus were not athyroid. Environmental factors—pond size and permanence, predators, duration of the growing season—may all contribute to tadpole gigantism in certain extant anuran species. We identify suites of ecological features that distinguish extant anurans with large tadpoles from high-latitude and high-altitude permanent lakes in temperate regions (e.g., certain Rana and Telmatobius) from tropical species, such as Pseudis paradoxa, whose tadpoles normally achieve large size in temporary seasonal ponds. The paleoecology of Randecker Maar suggests that Palaeobatrachus tadpoles lived in a permanent semitropical lake, but one with few predators.

A large body of paleontological literature concerns the importance of ontogeny as a source of morphological variation for evolution; morphologies that appear during one stage of an organism's development are made available for use in another simply by modifying the developmental program. Paleontologists need to know why this occurs, so they can study the process of evolution in extinct animals and so they can discuss the fossil record in terms that are applicable to modern forms. If most cases of heterochrony can be attributed to life-history evolution then the fossil record provides evidence of the nature of selection (in particular the age-specific mortality) that extinct animals experienced. The hypothesis of interest here is that species in which maturity is accelerated will also show generalized morphology and small size, while those with delayed maturity will have more specialized morphology and large size.

Four species of the ostracode genus Cyprideis were studied to determine whether differences in age at maturity are correlated with heterochrony in the expected manner. For each species the changes in size and shape through geological time were evaluated in the statistical context of modern geographic and seasonal variation. Living populations were sampled regularly to detect differences in seasonality and to estimate the duration of development.

Evolution of ontogeny is apparent at the level of species in this group, but it is not simply related to differences in life-history. In comparisons among species, we find evidence of heterochrony where there is no difference in the age at maturity, and a difference in age at maturity where there is no heterochrony. Similarly, three of the four species show the expected positive correlation between size and age at maturity, yet the fourth species is relatively large and matures rapidly. Cyprideis does not support the generalization that life-history evolution causes heterochrony, and casts doubt on the inference of life-history evolution from heterochrony where the data are drawn exclusively from extinct forms.

The fossil record provides an important source of data on adaptive radiations, and indeed some of the earliest theoretical insights on the nature of these radiations were made by paleontologists. Here we focus on the diverse Devonian Metacryphaeus group calmoniid trilobites, known from the Malvinokaffric Realm, which have been considered a classic example of an adaptive radiation preserved in the fossil record. We use a geometric morphometric analysis in conjunction with phylogenetic and biogeographic patterns and data on speciation rates. Using ancestral character state reconstruction during speciation events, we quantify patterns of morphological change in order to assess the role ecological and geographical factors may have played in mediating this radiation. We found no significant differences between the amount of morphological change that occurred during speciation events when ancestors and descendants were in the same area as opposed to when they occupied different areas. Further, the magnitude of morphological divergence did not change through time or with cladogenetic rank. These patterns, in conjunction with the fact that the radiation occurs in a geographically heterogeneous region subjected to repeated episodes of sea-level rise and fall, suggest that at the macroevolutionary scale this radiation may have been motivated more by phenomena that facilitated geographic isolation than by competition.

A central premise of bioclimatic envelope modeling is the assumption of niche conservatism. Whereas such assumptions are testable in modern populations, it is unclear whether niche conservatism holds over deeper time spans and over very large geographic ranges. Hyaenids occupied a diversity of ecological niches over time and space, and until the end-Pleistocene they occurred in Europe and most of Asia, with Asian populations of Crocuta suggested as being genetically distinct from their closest living relatives. Further, little is known regarding whether and how the dietary ecology of extinct populations of Crocuta differed from those of their extant African counterparts. Here, we use a multiproxy approach to assess an assumption of conserved dietary ecology in late Pleistocene extant spotted hyenas via finite element analysis, dental microwear texture analysis, and a novel dental macrowear method (i.e., whether teeth are minimally, moderately, or extremely worn, as defined by degree of dentin exposure) proposed here. Results from finite element simulations of the masticatory apparatus of Chinese and African Crocuta demonstrate lower skull stiffness and higher stress in the orbital region of the former when biting with carnassial teeth, suggesting that Chinese Crocuta could not process prey with the same degree of efficiency as extant Crocuta crocuta. Dental microwear texture data further support this interpretation, as Chinese Crocuta have intermediate and indistinguishable complexity values (indicative of hard-object feeding) between the extant African lion (Panthera leo) and extant hyenas (C. crocuta, Hyaena hyaena, and Parahyaena brunnea), being most similar to the omnivorous P. brunnea. The use of dental macrowear to infer dietary behavior may also be possible in extinct taxa, as evinced by dietary correlations between extant African feliforms and dental macrowear assignments. Collectively, this multiproxy analysis suggests that Chinese Crocuta may have exhibited dietary behavior distinct from that of living C. crocuta, and assumptions of niche conservatism may mask significant dietary variation in species broadly distributed in time and space.

The fossil record has been used to show that in some geologic intervals certain traits of taxa may increase their survivability, and therefore that the risk of extinction is not randomly distributed among taxa. It has also been suggested that traits that buffer against extinction in background times do not confer the same resistance during mass extinction events. An open question is whether at any time in geologic history extinction probabilities were randomly distributed among taxa. Here we use a method for detecting random extinction to demonstrate that during both background and mass extinction times, extinction of marine invertebrate genera has been nonrandom with respect to species richness categories of genera. A possible cause for this nonrandom extinction is selective clustering of extinctions in genera consisting of species which possess extinction-biasing traits. Other potential causes considered here include geographic selectivity, increased extinction susceptibility for species in species-rich genera, or biases related to taxonomic practice and/or sampling heterogeneity. An important theoretical result is that extinction selectivity at the species level cannot be smoothly extrapolated upward to genera; the appearance of random genus extinction with respect to species richness of genera results when extinction has been highly selective at the species level.

Phyletic speciation arising from a shift between adaptive peaks in the selective surface is modeled. At a locus initially monomorphic, a new allele is introduced that triggers phenotypic evolution by making a new adaptive peak available. A phenotypic model is used to describe the evolution of a quantitative character that is important for fitness but not directly affected by the new allele. Recursion equations are derived for both the allele frequency and the mean of the quantitative character. It is shown that the dynamics of the quantitative trait fit a “punctuated equilibrium” pattern of evolution. Phyletic speciation is seen to occur over a time span so short as to make observation of the transition in the fossil record unlikely.

Attempts to use Fourier methods to quantify ammonoid suture shape have failed to yield robust, repeatable results because sutures are complex curves that violate the assumptions of Fourier mathematics. In particular, sampled sutures are artificially truncated such that the first and last sampled points are not equivalent, the folds are non-stationary, and a position along a horizontal reference axis may map to multiple amplitudes along the suture path. Here I introduce an alternative Fourier method—the windowed short-time Fourier transform (STFT)—that accommodates these characteristics of complex curves. For each suture, digitized landmarks were parameterized using a tangent angle function and then smoothed by convolving with an apodization function. Piece-wise Fourier transforms were then calculated and averaged, resulting in a robust, unique quantification of line morphology. STFT coefficients and estimated power spectra describing the relative weights of harmonics were generated for 576 Paleozoic-basal Triassic ammonoid genera, representative of the range of suture morphotypes. While insensitive to major episodes of taxonomic turnover (Frasnian/Famennian, end-Devonian, and Permian/Triassic extinctions), the summed power data support the previously observed trend toward increasing suture complexity through time. Moreover, partitioning the summed power statistic into harmonic ranges allows novel insight into Paleozoic suture evolution. In particular, the data show significant shifts in the dominant morphotypes during periods of rebound and radiation and suggest that basal Triassic ammonoids possessed unique suture morphotypes when compared with those of the Paleozoic.

The mammalian fossil record of Spain is long and taxonomically well resolved, offering the most complete record of faunal change for the Neogene of Europe. We evaluated changes in diversification, composition, trophic structure, and size structure of large mammals over the middle and late Miocene with methods applied to this record for the first time, including ordination of fossil localities to improve temporal resolution and estimation of confidence intervals on taxa temporal ranges. By contrast, analysis within the traditional Mammal Neogene (MN) biochronology obscures important aspects of diversification. We used inferred temporal ranges of species and evaluated per capita rates of origination, extinction, diversification, and turnover over 0.5-Myr time intervals.

Three periods of significant faunal change occurred between 12.0 and 5.5 Ma: (1) From 12.0 to 10.5 Ma, elevated origination rates led to an increase in diversity without significant change in ecological structure. Immigrants and geographic-range shifts of species to lower latitudes during an interval of global cooling contributed to these faunal changes. (2) From 9.5 to 7.5 Ma, high extinction rates followed by high origination rates coincided with significant changes in taxonomic composition and ecological structure. These changes represent the Vallesian Crisis, with replacement of a fauna of forest affinities (with frugivores and browsers) by a fauna of open woodlands (with grazers and mixed feeders). (3) From 6.5 to 5.5 Ma, high extinction rates reduced diversity without substantial changes in ecological structure, and large mammal faunas became highly endemic across the northern Mediterranean region. This interval includes the Messinian Salinity Crisis, the desiccation of the Mediterranean basin. Extinction may have been caused by geographic isolation and aridification, with evolution of endemic lineages giving rise to new species in the early Pliocene. These distinct macroevolutionary patterns of faunal change correspond to different geographic scales of inferred climatic and tectonic drivers.

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferal Globorotalia (Globoconella) puncticulata-inflata plexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage, G. puncticulata, is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks of Globoconella occurred at about 3.5 Ma and gave rise to the G. inflata lineage. The descendant lineage, G. inflata, appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of the G. inflata lineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology of G. inflata are attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in the Globoconella clade has been modulated by changes in paleoceanographic conditions.

Magadina cumingi (Davidson) lives in an environment of high current energy and mobile sediments using the pedicle as an elevating device. This previously undescribed substrate relationship is reflected in pedicle form, the muscular system, distribution of secondary thickening and characters of the beak. The cardinalia provide the evidence of key differences in the muscular system from an attached species Magellania australis (Quoy and Gaimard) and a free lying species with atrophied pedicle Neothyris lenticularis (Deshayes). The possession of an open foramen in articulate brachiopods is not synonymous with permanent attachment.

Cladistic analysis of osteological and dental characters in a monophyletic group of Miocene and younger tayassuids demonstrates a pattern of changes in the degree of sexual dimorphism in canine tooth diameter and zygomatic arch width, and in phenotypic correlations between these characters. Primitively, tayassuids have canine teeth that are sexually dimorphic and discretely bimodal in size, and zygomatic arches that are narrow in both sexes. Many late Miocene and Pliocene tayassuids have broad, winglike zygomatic processes. In some species, these processes are large in both sexes, but in others, those of females are much smaller than those of males. The presence of large processes in both sexes is primitive relative to the condition of strong sexual dimorphism. In five separate clades, the zygomatic processes of both sexes become reduced in size, and the degree of sexual dimorphism in canine size becomes reduced as well. The pattern is congruent with predictions derived from a theoretical model of the evolution of sexual dimorphism, and it further indicates the emergence of a new phenotypic correlation between two previously uncorrelated characters, canine size and zygoma size. The advent of this new correlation coincides with the advent of pronounced sexual dimorphism in zygomatic processes. Although such a pattern could be explained by genetically modifying phenotypic expression of homologous characters in one sex or the other, an epigenetic modification of expression is equally plausible: the evolution of sexual dimorphism in homologous characters could be accomplished by placing phenotypic expression of an originally monomorphic character under the control of steroid sex hormones. This hypothesis is consistent with evidence from many vertebrate groups, and it provides testable predictions.

Probabilistic approaches to phylogenetic inference have recently gained traction in paleontological studies. Because they directly model processes of evolutionary change, probabilistic methods facilitate a deeper assessment of variability in evolutionary patterns by weighing evidence for competing models. Although phylogenetic methods used in paleontological studies have generally assumed that evolution proceeds by splitting cladogenesis, extensions to previous models help explore the potential for morphological and temporal data to provide differential support for contrasting modes of evolutionary divergence. Recent methodological developments have integrated ancestral relationships into probabilistic phylogenetic methods. These new approaches rely on parameter-rich models and sophisticated inferential methods, potentially obscuring the respective contributions of data and models. In this study, we describe a simple likelihoodist approach that combines probabilistic models of morphological evolution and fossil preservation to reconstruct both cladogenetic and anagenetic relationships. By applying this approach to a data set of fossil hominins, we demonstrate the capability of existing models to unveil evidence for anagenesis presented by morphological and temporal data. This evidence was previously recognized by qualitative assessments, but largely ignored by quantitative phylogenetic analyses. For example, we find support for directly ancestral relationships in multiple lineages: Sahelanthropus is ancestral to later hominins; Australopithecus anamensis is ancestral to Australopithecus afarensis; Australopithecus garhi is ancestral to Homo; Homo antecessor is ancestral to Homo heidelbergensis, which in turn is ancestral to both Homo sapiens and Homo neanderthalensis. By accommodating direct ancestry in phylogenetics, quantitative results align more closely with previous qualitative expectations.