One of the most enduring evolutionary metaphors is Van Valen's (1973) Red Queen. According to this metaphor, as one species in a community adapts by becoming better able to acquire and defend resources, species with which it interacts are adversely affected. If those other species do not continuously adapt to compensate for this biotically caused deterioration, they will be driven to extinction. Continuous adaptation of all species in a community prevents any single species from gaining a long-term advantage; this amounts to the Red Queen running in place. We have critically examined the assumptions on which the Red Queen metaphor was founded. We argue that the Red Queen embodies three demonstrably false assumptions: (1) evolutionary adaptation is continuous; (2) organisms are important agents of extinction; and (3) evolution is a zero-sum process in which living things divide up an unchanging quantity of resources. Changes in the selective regime need not always elicit adaptation, because most organisms function adequately under many “suboptimal” conditions and often compensate by demonstrating adaptive flexibility. Likewise, ecosystems are organized in such a way that they tend to be robust and capable of absorbing invasions and extinctions, at least up to a point. With a simple evolutionary game involving three species, we show that Red Queen dynamics (continuous adaptation by all interacting species) apply in only a very small minority of possible outcomes. Importantly, cooperation and facilitation among species enable competitors to increase ecosystem productivity and therefore to enlarge the pool and turnover of resources. The Red Queen reigns only under a few unusual circumstances.

656 mandibles and isolated teeth of the bovid Pachytragus solignaci Robinson from two localities in the Miocene Beglia Formation, Gafsa, Tunisia, have been individually aged on the basis of ontogenetic development and state of dental wear. The sample probably represents normal but seasonally restricted mortality. Life table analysis indicates an annual mortality rate of 25–30%, increasing in old animals. Dental dimensions are affected by stabilizing selection which sets in as the tooth comes into function, earlier mortality being nonselective in that respect.

Toothed cetacean (Odontoceti) lineages in the Miocene and Pliocene evolved rostra that are proportionally more elongate than any other aquatic mammal or reptile, living or extinct. Their similarities in cranial proportions to billfish may suggest a convergent feeding style, where the rostrum is swept through the water to hit and stun prey. Here we calculated second moment of area from rostral cross sections of these fossil odontocete taxa, as well as from extant ecological analogues, to infer variation in feeding behavior. Our results show that the extremely long rostra of extinct toothed whales vary considerably in functionally relevant measures of shape and likely exhibited a diversity of feeding behaviors, ranging from those similar to modern odontocetes to those convergent with billfish. Eustatic sea-level and temperature maxima of the Miocene likely led to changes in prey characteristics or abundance that enabled the repeated evolution of this extreme morphotype, which later went extinct during late Pliocene climatic deterioration.

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.

The evolutionary history of shell geometry of Early Jurassic ammonoids during the Pliensbachian–Toarcian second-order mass extinction is explored at both adult and ontogenetic levels. The ontogenetic approach builds on the concept of allometric space to get insights into the developmental aspects of morphological evolution. Investigation of the deployment of taxa in adult morphospace and allometric space allows the appraisal of the temporal evolution of morphological and allometric disparities. Curves of taxonomic diversity, adult morphological disparity, allometric disparity, and average adult size are contrasted. Results show that during the Pliensbachian–Toarcian interval, ammonoids underwent two successive and drastic declines in taxonomic diversity. Patterns of morphospace and allometric space occupancy suggest nonselective extinction at both morphological and developmental levels. Another measure of allometric disparity suggests the occurrence of two heterochronic trends, a peramorphocline followed by a paedomorphocline, during the Toarcian. These trends are concomitant with changes in average adult size that compensate for the heterochronic effects and explain the striking stability of morphological disparity despite changes in diversity. The results also emphasize the existence of two contrasted evolutionary dynamics in Pliensbachian and Toarcian ammonoids. Methodologically, the allometric disparity approach appears to be a fruitful tool to analyze the rather understudied clade-wide ontogenetic aspects of morphological evolution. Combining multiple approaches to describe clade morphological dynamics leads to a better characterization and understanding of the diversity-disparities relationships and a better distinction of the potential processes driving these macroevolutionary patterns.

Here I test the hypothesis that temporal variation in geographic range size within genera is affected by the expansion and contraction of their preferred environments. Using occurrence data from the Paleobiology Database, I identify genera that have a significant affinity for carbonate or terrigenous clastic depositional environments that transcends the Database's representation of these environments during the stratigraphic range of each genus. These affinity assignments are not a matter of arbitrarily subdividing a continuum in preference; rather, genera form distinct, nonrandom subsets with respect to environmental preference. I tabulate the stage-by-stage transitions in range size within individual genera and the stage-by-stage changes in the extent of each environment. Comparing the two shows that genera with a preference for a given environment are more likely to increase in geographic range, and to show a larger average increase in range, when that environment increases in areal extent, and likewise for decreases in geographic range and environmental area. Similar results obtain for genera with preferences for reefal and non-reef settings. Simulations and subsampling experiments suggest that these results are not artifacts of methodology or sampling bias. Nor are they confined to particular higher taxa. Genera with roughly equal preference for carbonates and clastics do not have substantially broader geographic ranges than those with a distinct affinity, suggesting that, at this scale of analysis, spatial extent of preferred environment outweighs breadth of environmental preference in governing geographic range. These results pertain to changes over actual geologic time within individual genera, not overall average ranges. Recent work has documented a regular expansion and contraction when absolute time is ignored and genera are superimposed to form a composite average. Environmental preference may contribute to this pattern, but its role appears to be minor, limited mainly to the initial expansion and final contraction of relatively short-lived genera.

The most abundant and diverse graptolite assemblages are found in offshore, deep-water black shales—the classical “graptolite fades” (deep-water or isograptid biofacies). The mean duration of Ordovician graptolite species confined to the deep-water facies (here referred to as “group 1” species) is 2.19 Myr, significantly shorter than the mean duration of species in the deep-water facies that are also known in sediments of the shallow-water shelf or platform (“group 2” species) −4.42 Myr, indicating a significantly higher extinction probability (p = <0.001). These figures are based on the precise age ranges of species derived from the time-calibrated composite sequence of 1446 Ordovician to early Devonian graptolites, built by the constrained optimization procedure (CONOP) from 256 measured sections worldwide, and exclude the effects of the Hirnantian mass extinction. The difference between groups cuts across families, morphological types, and pandemic/endemic distributions. An environmental influence is strongly suggested, and although both groups were planktonic, they were unlikely to have shared the same habitat in the water column. The new duration measurements therefore are interpreted as favoring a depth-stratification of graptolite habitats in the water column.

The Scleractinia, which are one of the most important builders of modern reefs, have been considered to have first appeared in the Middle Triassic. Recently, Paleozoic scleractiniamorphs have been reported from both the Ordovician and the Permian, suggesting that the scleractinian-like body plan was already established in the Paleozoic. Those Paleozoic scleractiniamorphs are considered either unsuccessful skeletonized offshoots (extinct experiments) or Paleozoic progenitors of the post-Paleozoic Scleractinia. Permian scleractiniamorphs are characterized by “ancestral” features and have no specific morphologies that deny scleractinian affinities. Molecular phylogenetics also indicate that extant scleractinians are monophyletic and originated long before their Triassic appearance. A Paleozoic origin for the Scleractinia is supported by morphological and molecular phylogenetic data. On the other hand, there is no positive evidence to show that different groups of scleractinians had separate soft-bodied precursors.

The Paleozoic scleractinians evolved within the framework of their basic body plan, and a direct derivation of the Scleractinia from the Rugosa is not probable. The Anthozoa are characterized by a bilaterally symmetrical body plan, which is traditionally considered to have been derived from other radially symmetrical Cnidaria. The problem of the origin of scleractinian body plan may provide a key for deciphering the early anthozoan radiation within the Bilateria. Other examples of Paleozoic Scleractinia and scleractiniamorphs will be found, probably in shallow-water reefal facies or deeper-water communities, bridging the stratigraphic gaps in occurrence and elucidating the origin of the Scleractinia and their body plan.

The stratigraphic distribution of graptoloid species within the upper Middle Ordovician strata of New York State represents a complex pattern of origination, extinction, faunal migration, and fluctuating relative abundances. In particular, the observed patterns of species turnover at graptolite biozone boundaries are apparently strongly correlated with lithofacies, sampling strategies, and the depositional effects of relative sea-level change.

Vertical facies changes that occur within third-order depositional sequences and fourth- or fifth-order parasequences are mirrored by changes in the graptoloid faunal composition. Large-scale faunal turnovers at biozone boundaries tend to occur either at sequence boundaries or at flooding surfaces within sequences (e.g., the base of Highstand System Tracts). The base of the Corynoides americanus and Climacograptus (D.) spiniferus Zones coincide with major onlap events, and the Orthograptus ruedemanni Zone fauna appears just below a Lowstand Systems Tract. Within individual biozones, smaller-scale changes such as the fluctuating relative abundances of graptoloid species coincide with higher-order parasequence cyclicity. These distribution patterns resemble recent computer-generated models for the sequence stratigraphic distribution of hypothetical taxa.

By combining good biogeographic control with a detailed sampling program, we are able to see through the patterns attributable to depositional cyclicity and identify the different components of faunal turnover (migration, speciation, and extinction).

The unique holotype of the Triassic reptile Sharovipteryx (initially Podopteryx) mirabilis has been reexamined and redescribed, correcting the original account. It is a small lizard-like reptile with an elongate head and densely tubular femur and tibia each longer than the (estimated) intergirdle distance. (Part of the pectoral region has been lost and the remnants remain encased in the matrix.) The matrix retains the impression of portions of the integument, including a patagium that reached from the hindlimbs to the base of the tail. Unlike the original account, the patagium did not extend to the pectoral limbs. Experiments with models indicate that Sharovipteryx could have maintained a shallow glide if the femora were held at a shallow angle to the vertebral column and the tibia and feet extended out at right angles to it, thus stretching the integument. The pectoral limbs (with or without a fringing membrane) might have produced a variable canard; alternatively vertical bending of the tail could have applied drag, each making the glide more stable.

Kelps and other fleshy macroalgae—dominant reef-inhabiting organisms in cool seas—may have radiated extensively following late Cenozoic polar cooling, thus triggering a chain of evolutionary change in the trophic ecology of nearshore temperate ecosystems. We explore this hypothesis through an analysis of body size in the abalones (Gastropoda; Haliotidae), a widely distributed group in modern oceans that displays a broad range of body sizes and contains fossil representatives from the late Cretaceous (60–75 Ma). Geographic analysis of maximum shell length in living abalones showed that small-bodied species, while most common in the Tropics, have a cosmopolitan distribution, whereas large-bodied species occur exclusively in cold-water ecosystems dominated by kelps and other macroalgae. The phylogeography of body size evolution in extant abalones was assessed by constructing a molecular phylogeny in a mix of large and small species obtained from different regions of the world. This analysis demonstrates that small body size is the plesiomorphic state and largeness has likely arisen at least twice. Finally, we compiled data on shell length from the fossil record to determine how (slowly or suddenly) and when large body size arose in the abalones. These data indicate that large body size appears suddenly at the Miocene/Pliocene boundary. Our findings support the view that fleshy-algal dominated ecosystems radiated rapidly in the coastal oceans with the onset of the most recent glacial age. We conclude with a discussion of the broader implications of this change.

Bryozoans are colonial animals and this permits the partitioning of their morphologic variability into components of within colony (i.e. within a single genotype) and between colony (i.e. between genotype) variance. These data have been obtained for four species of the endemic deep-sea genus Euginoma for a series of characters. In 8 comparisons, one component of the total variance dominated at the 5% level. Population (between colony) variance contributed significantly to the total variance in 63% of the comparisons (5 of 8); individual (within colony) variance contributed significantly to the total variance in 37% of the comparisons (3 of 8).

Compared to shallow water species, the surprising feature of the deep-sea data is that the between colony component of variance is as high as it is. Possibly in the more stable, deep-sea environment, the genotypic contribution to the variance of each individual colony is expressed to a greater degree than in the more variable, shallow water regime. If so, then analyses of variability in colonial animals may be an independent means of ascertaining stability gradients in the fossil record.

Issues of directionality in the history of life can be framed in terms of six major evolutionary steps, or megatrajectories (cf. Maynard Smith and Szathmáry 1995): (1) evolution from the origin of life to the last common ancestor of extant organisms, (2) the metabolic diversification of bacteria and archaea, (3) evolution of eukaryotic cells, (4) multicellularity, (5) the invasion of the land and (6) technological intelligence. Within each megatrajectory, overall diversification conforms to a pattern of increasing variance bounded by a right wall as well as one on the left. However, the expanding envelope of forms and physiologies also reflects—at least in part—directional evolution within clades. Each megatrajectory has introduced fundamentally new evolutionary entities that garner resources in new ways, resulting in an unambiguously directional pattern of increasing ecological complexity marked by expanding ecospace utilization. The sequential addition of megatrajectories adheres to logical rules of ecosystem function, providing a blueprint for evolution that may have been followed to varying degrees wherever life has arisen.

Primary vascular architecture of members of the Paleozoic Aneurophytales (Progymnosper-mopsida) is described. This architecture is somewhat more complex but fundamentally similar (homologous) to that of members of the Trimerophytina, putative ancestors of aneurophytes. It is suggested that the presence of complex stelar morphology in aneurophytes was epiphenomenal, a passive result of changes in growth and development in a trimerophyte-like ancestor. Specifically, I suggest that the evolutionary transformation in primary vascular architecture from haplostele to ribbed protostele was a direct consequence of changes that affected the vertical spacing and degree of organization of lateral appendages in early vascular plants. This view is in sharp contrast to adaptationist explanations of change in stelar morphology expressed by other authors and provides an example of non-adaptive change in evolution.

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.

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

Evolutionary trends observed over large clades have the potential to mask underlying trends that occur within their constituent subclades. A recent study of encephalization in the Caniformia (Carnivora, Mammalia) found evidence for an abrupt increase in median log-encephalization quotients (logEQs), indicating higher brain volume relative to body mass, at the end-Miocene, but gradual increase in the variance of logEQs. In this study, new endocranial volume estimates for fossil taxa in the well-sampled caniform subclade Canidae are reported. Using the encephalization data for the Canidae, hypotheses of evolution in encephalization allometries were tested with respect to canid phylogeny. The Akaike Information Criterion and likelihood ratios recovered support for a preferred hypothesis of the evolution of canid encephalization, which proposed two distinct allometric relationships: (1) a plesiomorphic grade of encephalization in the subfamilies Hesperocyoninae and Borophaginae and the paraphyletic canine genus Leptocyon, and (2) an apomorphic grade in the crown radiation of Caninae. This defines a shift in to higher encephalization, but without an associated change in the variance around the allometry. Increased canid encephalization coincides with a reorganization of the brain and the observed trend may reflect the evolution of complex social behavior in this clade.

Biomechanical models illustrate how the principles of physics and physiology determine function in organisms, allowing ecological inferences and functional predictions to be based on morphology. Dynamic lever and linkage models of the mechanisms of the jaw and skull during feeding in fishes predict function from morphology and have been used to compare the feeding biomechanics of diverse fish groups, including fossil taxa, and to test ideas in ecological morphology. Here we perform detailed computational modeling of the four-bar linkage mechanism in the skull and jaw systems of Dunkleosteus terrelli, using software that accepts landmark morphological data to simulate the movements and mechanics of the skull and jaws during prey capture. The linkage system is based on the quadrate and cranio-thoracic joints: Cranial elevation around the cranio-thoracic joint forces the quadrate joint forward, which, coupled with a jaw depressor muscle connecting the jaw to the thoracic shield, causes the jaw to rotate downward during skull expansion. Results show a high speed transmission for jaw opening, producing a rapid expansion phase similar to that in modern fishes that use suction during prey capture. During jaw closing, the model computes jaw and skull rotation and a series of mechanical metrics including effective mechanical advantage of the jaw lever and kinematic transmission of the skull linkage system. Estimates of muscle cross-sectional area based on the largest of five specimens analyzed allow the bite force and strike speed to be estimated. Jaw-closing muscles of Dunkleosteus powered an extraordinarily strong bite, with an estimated maximal bite force of over 6000 N at the jaw tip and more than 7400 N at the rear dental plates, for a large individual (10 m total length). This bite force capability is among the most powerful bites in animals. The combination of rapid gape expansion and powerful bite meant that Dunkleosteus terrelli could both catch elusive prey and penetrate protective armor, allowing this apex predator to potentially eat anything in its ecosystem, including other placoderms.

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.

Standard techniques of energy exchange analysis are applied to modelling the thermal regimes of several species of sailback pelycosaurs. Of particular interest is the role played by the sail in thermoregulation. Although the sail did increase the rate at which the model could warm up in the morning, its effectiveness fell short of previous estimates. The sail increased the daytime internal temperature by typically 3°C to 6°C. The more massive subjects had the highest temperature increases owing partly to their higher thermal inertia and partly to their disproportionately large sails. The sail had no impact upon the nocturnal minimums in temperature.

Overheating does not appear to have been a significant problem in the Permian environment, particularly in view of the high thermal inertia of the subjects modeled. When overheating occurred, the sail was of limited value for dumping excess heat.