Organismal metabolic rates reflect the interaction of environmental and physiological factors. Thus, calcifying organisms that record growth history can provide insight into both the ancient environments in which they lived and their own physiology and life history. However, interpreting them requires understanding which environmental factors have the greatest influence on growth rate and the extent to which evolutionary history constrains growth rates across lineages. We integrated satellite measurements of sea-surface temperature and chlorophyll-a concentration with a database of growth coefficients, body sizes, and life spans for 692 populations of living marine bivalves in 195 species, set within the context of a new maximum-likelihood phylogeny of bivalves. We find that environmental predictors overall explain only a small proportion of variation in growth coefficient across all species; temperature is a better predictor of growth coefficient than food supply, and growth coefficient is somewhat more variable at higher summer temperatures. Growth coefficients exhibit moderate phylogenetic signal, and taxonomic membership is a stronger predictor of growth coefficient than any environmental predictor, but phylogenetic inertia cannot fully explain the disjunction between our findings and the extensive body of work demonstrating strong environmental control on growth rates within taxa. Accounting for evolutionary history is critical when considering shells as historical archives. The weak relationship between variation in food supply and variation in growth coefficient in our data set is inconsistent with the hypothesis that the increase in mean body size through the Phanerozoic was driven by increasing productivity enabling faster growth rates.

The set of environmental conditions under which a taxon can survive and maintain viable populations, known as the ecological niche, is a fundamental determinant of a taxon's distribution. Because of the central importance of ecological niches, they have been assumed to remain relatively stable during intervals of morphological stasis. However, the assumption of niche stability has rarely been tested directly with fossil data spanning multiple temporal intervals. Thus, the conditions under which this assumption is likely to be accurate are not well understood. In this study, we use ecological niche modeling (ENM) to reconstruct the ecological niche for 11 genera of marine benthos (crinoids, trilobites, molluscs, bryozoans, and corals) from the Type Cincinnatian Series (Late Ordovician, Katian Stage) across nine temporal intervals spanning approximately three million years. This interval includes both abiotic environmental change (gradual sea-level fall) and biotic change (rapid pulses of the Richmondian Invasion), thus allowing the relative effect of different environmental perturbations to be constrained. A previous symmetrical analysis of niche stability of brachiopod species recovered an increase in niche evolution following the Richmondian Invasion. Herein we test the generality of the brachiopod pattern within the community. Niche stability was evaluated in geographic space, ecological space, and niche parameter space. Niche stability varied through time; during the Pre-Invasion interval, taxa exhibited niche stability during gradual shallowing of sea level in the basin, whereas niche evolution became more common during the Richmondian Invasion. Taxa adjusted to the increased competition by altering aspects of their niche. Notably, surviving taxa contracted their niche into a subset of their previous niche parameters. This represents an adaptive response to increased competition for resources with the newly established invader taxa, and it was employed most successfully by generalist taxa. Patterns of niche evolution were congruent between clades, among feeding styles, and across taxonomic levels.

The latest Aalenian–early Bajocian time interval (ca. 171-169 Ma) is marked by a global reorganization of oceanic plates with the Central Atlantic opening and the formation of the Pacific plate. This time interval is also marked by a global geochemical perturbation of δ13C with a negative excursion at the Aalenian/Bajocian boundary and a positive excursion during the early Bajocian. Evolutionary diversifications of marine invertebrate taxa, namely ammonites, radiolarians, and coccolithophorids, are recorded at that time. Concerning coccolithophorids, this interval witnesses the diversification and expansion of the most successful Mesozoic genus: Watznaueria. In this study, we explore the potential environmental, ecological, and biological forcing at the origin of Watznaueria diversification and its effect on the coccolith assemblages through quantification of the absolute and relative abundances of calcareous nannofossils in two Middle Jurassic key sections: Cabo Mondego (Portugal) and Chaudon-Norante (France). In both sections, we find an increase in nannofossil absolute abundance and flux at the beginning of the lower Bajocian, coeval with an increase in absolute and relative abundances of Watznaueria spp., followed by a plateau in the middle and upper part of the lower Bajocian. The increase of Watznaueria spp. is synchronous with a decrease in relative abundance of other major coccolith taxa, whereas the absolute abundance of these species did not decrease. During the climatically driven early Bajocian eutrophication event, Watznaueria spp. integrated into the calcareous nannoplankton community in two successive evolutionary steps involving first W. contracta and W. colaccicchii, and second W. britannica and W. aff. manivitiae. Step 1 was driven by an increase in niche carrying capacities linked to the early Bajocian eutrophication. Step 2 was driven by specific adaptation of the newly evolved Watznaueria species to bloom in nutrient-rich environments not exploited before. These evolutionary events have initiated the 100-Myr reign of Watznaueria over the calcareous nannoplankton community.

Diversity and faunal turnover of North American land mammals are calibrated against the magnetic polarity time scale for million-year intervals for the latest Eocene through late Oligocene. A major, gradual Late Eocene decline in diversity, caused mostly by an extended period of extinction of archaic forms, seems to be related to the worldwide crisis known as the “Terminal Eocene Event.” Along with other evidence of gradual changes in deep-sea microfossils, this evidence argues against a catastrophic explanation for late Eocene extinctions.

Faunal stability characterized the rest of the Oligocene except for a wave of extinctions in the mid-Oligocene (Chadronian-Orellan boundary, about 32.4 ma). This mid-Oligocene event is sudden and severe, occurring in less than 200,000 yr, based on estimates from sedimentation rates calibrated from magnetic polarity interval boundaries. The mid-Oligocene event is found in many paleoclimatic records, but not in all of them. It may be related to the completion of the Circum-Antarctic Current and to increased mid-Oligocene glaciation.

Fossil specimens can be recovered easily only from exposed localities, so rock exposure area should represent a better proxy for rock availability than the frequently used outcrop (i.e., map) area. Data collected via remote sensing and GIS show that map area does not consistently correlate with exposure area in different regions. Proportional rock exposure is not geographically consistent and is influenced by a number of variables that are independent of outcrop area, including proximity to the coast, elevation, bedrock age, land use and lithology. These variables appear to be non-independent in their influence on rock exposure, and are not consistent in their effects across continents. The inconsistency in the correlation between outcrop and exposure area, and the variability in the influence of different factors on rock exposure, suggests that using outcrop area as a sampling proxy is poorly supported. The weaknesses in using outcrop area as a sampling proxy, highlighted by the lack of correlation with exposure area, suggest that a single accurate global sampling proxy may never be attained and it is premature to assume that paleodiversity curves can be corrected using such proxies. It is therefore preferable to work on a regional scale, comparing regional fossil collection data with a number of proxies representing all aspects of sampling. The lack of correlation between outcrop and exposure area suggests that the covariance detected between outcrop area and paleodiversity might be better explained by a common-cause model, and that geological megabiases may not have had as profound an effect on paleodiversity curves as previously thought.

Dental measurements are commonly used in the diagnosis of fossil elephant species, yet elephant teeth develop slowly, within a highly dynamic context that enhances opportunities for physical deformation (or its subtler manifestation, quantitative phenotypic variation). This paper examines intraspecific variation in elephant teeth and compares it with variability in other mammals (83 species in 7 orders). I conclude that (1) male elephants tend to have slightly larger cheek teeth than females, though the difference is not marked; (2) of the full complement of six cheek teeth per jaw quadrant, no single tooth consistently varies less than the others (so on this basis, for taxonomic decisions no tooth is preferable to the customarily used M3 = tooth VI); (3) single-population samples vary less than more inclusive, geographically heterogeneous samples of elephant teeth; (4) although differential wear and eruption are important sources of variation in dental measurements, complete elephant teeth are consistently more variable in length and width than the cheek teeth of other mammals; (5) variability in dental dimensions of recognized fossil species of elephants is in general not grossly inconsistent with variability noted in modern elephants, but there are some exceptions. With the information and guidelines presented here, consideration of variability, and assessment of the statistical power permitted by available samples, can enhance confidence and precision in the delimitation of species and provide a firmer basis for macroevolutionary inferences.

Study of the assemblage of encrusting organisms on co-occurring disarticulated valves of the bivalves Crassostrea virginica and Mercenaria mercenaria in Bogue Sound, North Carolina, indicates that there is little or no substrate specificity among the encrusting organisms but that the shape of the shells has an important influence on how extensively members of each higher taxon collectively inhabit the shells. Encrusting bryozoans, a dense low mat composed of many species from diverse phyla, and a unicellular film cover most of the area of both exterior and interior surfaces. The encrusting bryozoans most extensively cover both surfaces of C. virginica but are in second place behind the multispecies mat on exterior surfaces of M. mercenaria and behind the unicellular film on its interior surfaces. These differences are inferred to result from different physical stability of valves of the two bivalve species, which exhibit different frequencies of circumrotatory growth.

Degradation of the assemblage by sodium hypochlorite, to simulate loss of organic matter during fossilization, results in the complete loss of encrusting sponges, erect hydrozoans, erect bryozoans, and ascidians. Loss of these taxa results in overexposure and more apparently uniform distribution of skeletal taxa with respect to their surface representation in living assemblages and also in complete loss of the higher tiers present in the living assemblage. However, indications of the original structural organization of the living assemblage is indicated by preservation of the most abundant taxa in the lower tiers and by the retention in the reduced treated assemblage of the patterns of distribution that characterized the living assemblage.

We use Fourier analysis to investigate evolutionary dynamics related to periodicities in marine fossil biodiversity. Coherent periodic fluctuation in both origination and extinction of “short-lived” genera (those that survive <45 Myr) is the source of an observed ∼62 million year periodicity (which we confirmed in an earlier paper and also found to be ubiquitous in global compilations of marine diversity). We also show that the evolutionary dynamics of “long-lived” genera (those that survive >45 Myr) do not participate in the periodic fluctuation in diversity and differ from those of “short-lived” genera. The difference between the evolutionary dynamics of long- and short-lived genera indicates that the periodic pattern is not simply an artifact of variation in quality of the geologic record. Also, the interplay of these two previously undifferentiated systems, together with the secular increase in abundance of “long-lived” genera, is probably the source of observed but heretofore unexplained differences in evolutionary dynamics between the Paleozoic and post-Paleozoic as reported by others. Testing for cycles similar to the 62-Myr cycle in fossil biodiversity superimposed on the long-term trends of the Phanerozoic as described in Paper I, we find a significant (but weaker) signal in sedimentary rock packages, particularly carbonates, which suggests a connection. The presence of a periodic pattern in evolutionary dynamics of the more vulnerable “short-lived” component of the marine fauna demonstrates that a long-term periodic fluctuation in environmental conditions capable of affecting evolution in the marine realm characterizes our planet's history. Coincidence in timing is more consistent with a common cause than with sampling bias. A previously identified set of mass extinctions preferentially occur during the declining phase of the 62-Myr periodicity, supporting the idea that the periodicity relates to variation in biotically important stresses. Further work should focus on finding links to physical phenomena that might reveal the causal system or systems.

Although morphological variation is known to influence the evolutionary fates of species, the relationship between morphological variation and survivorship in the face of extinction-inducing perturbations is poorly understood. Here, we investigate this relationship for veneroid bivalves in association with the Plio-Pleistocene extinction in Florida. Fourteen pairs of related species were selected for analysis, with each pair including one species that survived the Plio-Pleistocene extinction and another that became extinct during the interval. Morphological landmark data were acquired for more than 1500 museum specimens, representing 19 localities that encompass four well-known Plio-Pleistocene units in the study region. Procrustes superimposition was applied to each sample, and overall multivariate variation was calculated as the mean squared partial Procrustes distance between specimens and their mean form. Morphological variation was calculated at three geographic scales for each species, and differences in variation between survivors and victims were examined within each species pair. Results indicate that species surviving the Plio-Pleistocene extinction were significantly more variable morphologically than victims. Greater morphological variation may promote survivorship by directly enhancing species adaptations to changing conditions or by permitting the occupation of a larger geographic range. Alternatively, high morphological variation and survivorship may both be mediated by a third variable, such as large geographic range.

Digitizing the third upper molars of Microtus pennsylvanicus reveals evolutionary change in some traits but stability in others during the last 30,000 years. Fossils from Strait Canyon, Virginia (radiocarbon dated between 29,870 + 1,800/-1,400 and 17,880 ± 150 yr B.P.) were compared with modern samples from the margin of the species' conterminous geographic range: Virginia, Colorado, Alaska, and Hudson Bay. Since the late Pleistocene a modification from narrow to wide teeth took place in the eastern populations but not in the western ones, and populations in Virginia apparently evolved wider confluence between triangles 1 and 2. Traits that remained stable through time in the Virginia area, but not necessarily elsewhere, include the numerical shape factors of the occlusal surface and the posterior loop. Potentially widespread stability is evident in the perimeter of the posterior loop relative to total tooth perimeter. Tooth length forms a geographic cline, in which both the fossil and modern populations from Virginia occupy the same position. A peripheral population from southern Colorado shows the most derived dental morphology. These morphological relationships suggest that mosaic evolution operates in arvicoline lineages and provide testable paradigms for future studies.

Oysters, whose inner shell layer contains chambers, vesicles, and sometimes chalky deposits, often have extraordinarily thick shells of large size, prompting the idea that there is something unusual about the process of shell fPormation in these and similarly structured bivalves with the oyster syndrome. I propose the hypothesis that calcifying microbes, especially sulfate-reducing bacteria growing on organic substrates in fluid-filled shell-wall chambers, are responsible for shell calcification away from the shell-secreting mantle of the host bivalve. Other phenomena, including the formation of cameral deposits in fossil cephalopods, the cementation of molluscs and barnacles to hard substrata, the formation of a calcified intriticalx on the shell's exterior, and cementation of objects by gastropods on the shell for camouflage, may also involve calcifying bacteria. Several lines of inquiry are suggested to test these hypotheses.

Insect taphonomy is a topic that has drawn interest because of its potential biases on diversity patterns and the ecological information recorded by ancient insect faunas. Other than the onset of common amber fossilization in the Cretaceous, very little is known about long-term trends in the nature and quality of insect preservation and, as a result, the effects of taphonomic biases are poorly constrained. We assembled a database of nearly 7000 Carboniferous–Pliocene insect adpression (compression and impression) species from the primary literature to assess changes in insect taphonomy over time and test biotic and environmental controls on preservation. We grouped the fossils into 10-Myr bins and scored preservation of holotype specimens as either articulated bodies or isolated wings; articulated specimens with a body implied a generally higher quality of preservation. Paleozoic and Triassic insect holotypes are known overwhelmingly from isolated wings (only 12% articulated bodies), but our database shows a significant increase in the percentage preserved as articulated bodies, to more than 70%, beginning about 160 Myr ago in the Late Jurassic. This transition could reflect variations in the robustness of different insect orders and shifts in the taxonomic composition of insect faunas, but all the major orders in the database exhibit significant increases in articulation. Instead, a shift to increased preservation in lacustrine paleoenvironments, which contain a greater proportion of articulated body fossils, explains most of the trend. The pronounced Late Jurassic increase in articulation has implications for evolutionary and ecological reconstructions, for example, suggesting that preserved insect diversity may be biased downward in the earlier part of their history when articulation was poor.

Bases of attachment of Archimedes colonies are very rare, but many colonies show evidence of origination from a pre-existing set of branches. The evidence consists of spiralled supports (axial screws) originating from fragments of pre-existing sets of branches, proximal taper of colonies or axial screws to a diameter smaller than that of bases of attachment, early stages of new colonies originating from the whorl margins of older colonies, and sets of laterally fused colonies. In the most favorable environments Archimedes populations were dominated by a few genets that consisted of hundreds to perhaps thousands of genetically identical colonies.

The ability to reproduce by colony fragmentation was probably an important cause of Archimedes' abundance in the Chesterian seas of eastern North America, especially where it occurred in dense populations in the lee of submarine carbonate shoals. Colony fragmentation, the importance of which is becoming increasingly recognized in modern corals and bryozoans, was also of importance in Paleozoic seas.

It has recently been argued that barren intervals of marine sedimentary rock are less common in the Cenozoic than in the Paleozoic, and that this arises as a direct consequence of widespread epeiric seas and the prevalence of dysaerobic conditions at such times. We show, using an independent and more direct measure of rock outcrop through time in western Europe, that barren marine sedimentary rocks do become less frequent toward the present, but that this is not linked to any epeiric-seas effect. The proportion of barren to fossiliferous rock outcrop correlates well with the inferred Phanerozoic marine diversity curve (although more so in the Paleozoic than in the post-Paleozoic), and shows no correlation or only a weak negative correlation with area over which the sediments have been deposited. We therefore concluded that the Phanerozoic trend in fossiliferousness most likely records the degree to which space is occupied in the shallow marine realm.

Stephen Jay Gould made impressive contributions to macroevolutionary theory; one of the topics in this area that particularly interested him was how to define and recognize species selection. Here we explore how and why Gould's ideas on concepts related to species selection evolved over 30 years, from the punctuated equilibria paper of 1972 to his “Structure of Evolutionary Theory” magnum opus published in 2002. Throughout his career his ideas on species selection shifted between three phases. Initially, Gould favored a definition of species selection that was more descriptive. Later, he came to distinguish between species sorting, which he called species selection in the broad sense, and true species selection, which is tied to the concept of species-level aptations. Finally, he came to view species selection in a broader, more inclusive way, effectively merging the two earlier viewpoints. His ideas on species selection changed over the years because he was trying to square his views on complex concepts like adaptation, natural selection, emergence, and the independence of macroevolutionary theory. Gould's thoughts on species selection not only help to define the history of debate on the concept but also help set a course for the future.

The placement of angiosperms and Gnetales in seed plant phylogeny remains one of the most enigmatic problems in plant evolution, with morphological analyses (which have usually included fossils) and molecular analyses pointing to very distinct topologies. Almost all morphology-based phylogenies group angiosperms with Gnetales and certain extinct seed plant lineages, while most molecular phylogenies link Gnetales with conifers. In this study, we investigate the phylogenetic signal present in published seed plant morphological data sets. We use parsimony, Bayesian inference, and maximum-likelihood approaches, combined with a number of experiments with the data, to address the morphological–molecular conflict. First, we ask whether the lack of association of Gnetales with conifers in morphological analyses is due to an absence of signal or to the presence of competing signals, and second, we compare the performance of parsimony and model-based approaches with morphological data sets. Our results imply that the grouping of Gnetales and angiosperms is largely the result of long-branch attraction (LBA), consistent across a range of methodological approaches. Thus, there is a signal for the grouping of Gnetales with conifers in morphological matrices, but it was swamped by convergence between angiosperms and Gnetales, both situated on long branches. However, this effect becomes weaker in more recent analyses, as a result of addition and critical reassessment of characters. Even when a clade including angiosperms and Gnetales is still weakly supported by parsimony, model-based approaches favor a clade of Gnetales and conifers, presumably because they are more resistant to LBA. Inclusion of fossil taxa weakens rather than strengthens support for a relationship of angiosperms and Gnetales. Our analyses finally reconcile morphology with molecules in favoring a relationship of Gnetales to conifers, and show that morphology may therefore be useful in reconstructing other aspects of the phylogenetic history of the seed plants.

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

Spinal ossified tendons are a defining character for Ornithischia, one of the two major clades of dinosaurs. The function of these bony rods has remained a mystery since their first detailed description in 1886. Qualitative approaches to understand ossified tendon function have resulted in different ecological and behavioral interpretations for ornithopod dinosaurs. To evaluate ossified tendon function, this study constructed finite element models of the vertebral column for two ornithopod taxa: Tenontosaurus, which shows the plesiomorphic condition of longitudinally arrayed tendons along the spinous processes, and Brachylophosaurus, which exhibits a lattice of tendons along the spinous processes. Both models predict that ossified tendons stiffened the vertebral column, especially the tail, but the derived lattice of ossified tendons in iguanodontoidean dinosaurs, like Brachylophosaurus, increased spinal stiffness more than the plesiomorphic condition. Caudofemoral muscles that retracted the hindlimb during locomotion attached the femur to the tail in ornithopods. Increased tail stiffness caused by intratendinous ossification may have influenced locomotion by rigidly anchoring M. caudofemoralis longus to the tail, thereby allowing a more forceful retraction of the hindlimb by reducing ventral flexion of the tail during muscle contraction. Ossified tendons may also have been important for storing elastic energy throughout the gait cycle. Moreover, the lattice of ossified tendons stiffened the trunk and tail nearly equally in Brachylophosaurus, indicating the evolution of a postural function by passively supporting the epaxial musculature in maintaining a horizontal vertebral column.

Decay experiments are becoming a more widespread tool in evaluating the fidelity of the fossil record. Character interpretations of fossil specimens stand to benefit from an understanding of how decay can result in changes in morphology and, potentially, total character loss. We performed a decay experiment for the Class Enteropneusta to test the validity of anatomical interpretations of the Burgess Shale enteropneust Spartobranchus tenuis and to determine how the preservation of morphological features compares with the sequence of character decay in extant analogues. We used three species of enteropneust (Saccoglossus pusillus, Harrimania planktophilus, and Balanoglossus occidentalis) representing the two major families of Enteropneusta. Comparisons between decay sequences suggest that morphological characters decay in a consistent and predictable manner within Enteropneusta, and do not support the hypothesis of stemward slippage. The gill bars and nuchal skeleton were the most decay resistant, whereas the gill pores and pre-oral ciliary organ were unequivocally the most decay prone. Decay patterns support the identification of the nuchal skeleton, gill bars, esophageal organ, trunk, and proboscis in Spartobranchus tenuis and corroborate a harrimaniid affinity. Bias due to the taphonomic loss of taxonomically informative characters is unlikely. The morphologically simple harrimaniid body plan can be seen, therefore, to be plesiomorphic within the enteropneusts. Discrepancies between the sequence of decay in a laboratory setting and fossil preservation also exist. These discrepancies are highlighted not to discredit the use of modern decay studies but rather to underline their non-actualistic nature. Paleoenvironmental variables besides decay, such as the timeframe between death and early diagenesis as well as postmortem transport, are discussed relative to decay data. These experiments reinforce the strength of a comprehensive understanding of decay sequences as a benchmark against which to describe fossil taxa and understand the conditions leading to fossilization.