Our knowledge of the diversity, ecology, and phylogeny of Mesozoic birds has increased significantly during recent decades, yet our understanding of their flight competence remains poor. Wing loading (WL) and aspect ratio (AR) are two aerodynamically relevant parameters, as they relate to energy costs of aerial locomotion and flight maneuverability. They can be calculated in living birds (i.e., Neornithes) from body mass (BM), wingspan (B), and lift surface (S L). However, the estimates for extinct birds can be subject to biases from statistical issues, phylogeny, locomotor adaptations, and diagenetic compaction. Here we develop a sequential approach for generating reliable multivariate models that allow estimation of measurements necessary to determine WL and AR in the main clades of non-neornithine Mesozoic birds. The strength of our predictions is supported by the use of those variables that show similar scaling patterns in modern and stem taxa (i.e., non-neornithine birds) and the similarity of our predictions with measurements obtained from fossils preserving wing outlines. In addition, although our WL and AR values are based on estimates (BM, B, and S L) that have an associated error, there is no cumulative error in their calculation, and both parameters show low prediction errors. Therefore, we present the first taxonomically broad, error-calibrated estimation of these two important aerodynamic parameters in non-neornithine birds. Such estimates show that the WL and AR of the non-neornithine birds here analyzed fall within the range of variation of modern birds (i.e., Neornithes). Our results indicate that most modern flight modes (e.g., continuous flapping, flap and gliding, flap and bounding, thermal soaring) were possible for the wide range of non-neornithine avian taxa; we found no evidence for the presence of dynamic soaring among these early birds.

Stick-like bryozoans from 1 to 5 cm tall, and of varying degrees of colony robustness, are common in deposits from Ordovician through Cenozoic in age; their occurrence has been used to infer strength of bottom currents. Three species which are modern analogues of this mode of growth occur abundantly at subtidal depths near Friday Harbor, Washington; we studied one of these forms, the calcitic cyclostome Heteropora pacifica. Branch diameter was used as an indication of colony robustness because it can be measured in both living and fossil material. Branch diameter decreases significantly with depth (in collections from approximately 9, 15 and 30 m depth) at each of 4 transect localities.

At each locality, currents 6 to 10 cm above the bottom were measured continuously in water depth of ≃ 15 m, for several hours at a time. Under these conditions, the maximum sustained current through the several hour tidal cycle was 70 to 90 cm/sec at one locality, and 20 cm/sec or less at each of the other 3 localities. Suspended matter was determined at heights of 0.2, 0.5 and 1.0 m above the bottom. The amount of suspended matter 0.2 m above the bottom was 40 to 45 mg/cm2/day at the locality with the high current (depth of 15 and 30 m), and usually 5 to 10 mg/cm2/day at the localities with the low current (depth 15 and 30 m). Despite these several fold differences in current strength and suspended matter between localities, for any given depth bryozoan branch diameter does not vary. Branch breaking strength (23 MN/m2) and elastic modulus (30 GN/m2) were measured using small (.16 mm) strain gauges affixed to dry branches of Heteropora. These values are typical of carbonate skeletons of corals. Although Heteropora branch diameter (and colony robustness) decreases significantly with depth, this trend probably is unrelated to current strength.

A nonparametric analysis of the extinction patterns of 10 major marine invertebrate groups at the five most profound mass extinction events leads to five observations: (1) At each event some taxonomic groups were affected much more than others. (2) There is little consistency among events in terms of which taxonomic groups were most or least affected; however, adaptive groupings do exhibit consistency: benthic, mobile organisms suffered significantly fewer extinctions than sessile suspension feeders, while the pelagic organisms apparently suffered the most. (3) There are no convincing patterns of interrelated extinctions among taxonomic groups. (4) No group exhibits a persistent tendency through time for a relative increase or decrease in their extinction rate at the events. (5) Some relationships are seen between the extinction patterns of three pairs of events; the Late Ordovician and Late Devonian events exhibit a significantly similar pattern (the same taxonomic groups suffered the most extinction in both cases) as do the Late Triassic and Late Cretaceous events. The Late Permian and Late Cretaceous events show a significantly inverse pattern (the most affected groups in the former were among the least affected in the latter). Upon examination, these observations, notably 1, 2, and 5, are consonant with current scenarios of the effects of catastrophic bolide impacts on marine fauna.

Understanding the relationships between morphological disparity and environment, geography, and scale require examination at the local level. Even with disparity metrics that are inherently sample size independent, the nature of rare species and the segregation of common and rare species within morphospace can create substantial sampling issues. Eight well-sampled, Late Ordovician crinoid assemblages were examined for potential biases in the study of local disparity. Disparity is based on the ordination of discrete characters. The rare and common species within these assemblages contributed equally to disparity. In spite of this pattern, rare species in some localities occupy a different area of morphospace, causing disparity to vary greatly with sampling intensity. Morphological rarefaction based on the number of specimens shows that disparity weighted by abundance is constant past a sample size of approximately 30 individuals. This metric is dependent on the evenness within an assemblage as well as the abundance within subgroups in morphospace. Disparity weighted according to abundance gives a view of the functional disparity of an assemblage, which is more applicable in studies of local disparity, though unweighted disparity is still preferred in regional-scale studies and in investigations of morphospace filling through a clade's history.

Computer-generated searches through hypothetical fitness landscapes for progressively more fit variants were used to assess the effects of developmental barriers (mimicked by barring specific types of morphological transformations) and abruptly shifting environmental conditions (mimicked by sudden shifts in how fitness was defined) on the number and accessibility of optimal phenotypes. Relative fitness was defined in terms of maximizing light interception, mechanical stability, or reproductive success, or minimizing surface area, or optimizing the performance of various combinations of these tasks. Developmentally obstructed and unobstructed walks located, on average, equivalent numbers of phenotypic optima. The number of optima identified by both kinds of walks increased in proportion to the number of simultaneously performed tasks used to measure fitness. Walks passing from more complex to less complex fitness landscapes located more optima than walks passing through unchanging, stable landscapes. The model thus suggests that there are no a priori reasons to assume that (1) the morphological options available to adaptive evolution become more restrictive as biological complexity increases, (2) “developmental barriers” necessarily restrain a lineage from evolving well-adapted morphologies, and (3) generalist organisms are less successful than specialists. Also, because the number and accessibility of fitness peaks were proportional to the complexity of fitness landscapes, the model predicts that the probability of cladogenesis will increase as landscape complexity increases, while anagenesis will be encouraged when fitness is defined in terms of performing one or a few tasks simultaneously.

The Mesozoic marine revolution theory postulates a causal connection between the Cretaceous radiations of durophagous predators and the decline of suspension-feeding echinoderms in shallow-water habitats. In order to test the temporal distribution of dense ophiuroid populations for such a decline, I present a method of calculating the expected distribution of populations or communities in different geologic timespans. This statistical null hypothesis may then be compared with data from the fossil record to draw paleoecological inferences. The model takes into account the relative lengths of time blocks, the decay of sedimentary rock, and changes in shallow sea area through time. Although mass extinctions did not cause the immediate disappearance of shallow-water “brittlestar beds,” brittlestar beds show a significant decline in the Early Cretaceous. Results of several studies suggest that predators were at least partially responsible for reducing the distribution of dense ophiuroid populations.

All evolution attributable to natural selection, at any level, is due to a causal covariance between fitness and phenotype. Over macroevolutionary time scales, species selection is one of many possible mechanisms for generating large-scale morphological trends. For species selection to sort morphology, a correlation between morphology and taxonomic diversification rate must be present. Other trend mechanisms (driven mechanisms, e.g., a bias in the direction of speciation) produce a systematic change in the mean phenotype over time. All mechanisms can co-occur. Here I demonstrate (1) an inverse correlation between diversification rate and calyx complexity that demonstrates the effect of species selection on morphology. Genera with simple calyces tend to increase in diversity, whereas genera with complex calyces have a net decrease in diversity; and (2) the presence of a driven trend mechanism in monobathrid crinoids where descendant genera tend to be simpler than their ancestors. The separate effects of these two classes of trend mechanisms can be combined by using the Price's Theorem, which partitions the contribution to the overall change in calyx complexity over time accurately among selection and driven mechanisms. Price's Theorem provides significant conceptual and methodological clarification of the contribution of multiple and interacting hierarchical mechanisms in generating large-scale trends.

A paradoxical relationship exists between the genetic and morphologic adaptive strategies of benthic marine invertebrates; morphologically variable species from unstable environments have been shown to possess less genetic variability than species with more constant phenotypes from stable habitats. The mode of growth of Ordovician bryozoans provides an insight into this paradox. These bryozoans exhibit morphologic gradients within zooidal subcolonies that change throughout colony development. Entire clusters of zooids begin and cease growth as a function of their spatial position with respect to neighboring clusters. A comparison of the within-colony and among-colony components of developmental and morphologic variability was made from populations inhabiting Ordovician environments of differing stability. In four stratigraphically persistent species, the level of developmental variability is homogeneous within species, but varies significantly across taxa. The two species with the highest levels of developmental variability (less canalized development) fit the concept of r-selected opportunistic species and are most abundant in communities of lowest diversity. The other two species have much lower levels of variability (more canalized development), fit the concept of K-selected equilibrium species, and are most abundant in the communities of highest diversity. Within-colony morphologic variability is also higher in the opportunistic rather than the equilibrium species, indicating that the higher morphologic variability observed in unstable environments is the product of within-genotype deregulation, and not the result of higher genetic polymorphism. The equilibrium species in stable environments have lower levels of morphologic deregulation and correspondingly greater variation among genotypes than within genotypes in fossil populations.

Earliest Paleocene megafloras from North America are hypothesized to be low diversity and dominated by long-lived cosmopolitan species following the Cretaceous/Paleogene (K/Pg) mass extinction. However, megafloras used to develop this hypothesis are from the Northern Great Plains (NGP) of North America, and relatively little is known about floras from southern basins. Here, we present a quantitative analysis of an earliest Paleocene megaflora (<350 kyr after K/Pg boundary) from the Ojo Alamo Sandstone in the San Juan Basin (SJB), New Mexico. The megaflora, comprising 53 morphotypes, was dominated by angiosperms, with accessory taxa composed of pteridophytes, lycophytes, and conifers. Diversity analyses indicate a species-rich, highly uneven, and laterally heterogeneous flora. Paleoclimate estimates using multivariate and univariate methods indicate warm temperatures and relatively high precipitation consistent with a modern tropical seasonal forest.

When compared with contemporaneous floras from the Denver Basin (DB) of Colorado and the Williston Basin (WB) of North Dakota, the SJB flora had significantly higher species richness but lower evenness. Paleoclimate estimates from the SJB were 7–14°C warmer than the estimates for the DB and WB, indicating a shift from a temperate forest in the NGP to a tropical forest in the SJB. These results demonstrate the presence of a latitudinal floral diversity and paleoclimatic gradient during the earliest Paleocene in western North America. We hypothesize that the warm, wet conditions in the earliest Paleocene SJB drove rapid rates of speciation following the K/Pg boundary, resulting in a diverse and heterogeneous flora.

Cosmopolitanism occurred recurrently during the geologic past, especially after mass extinctions, but the underlying mechanisms remain poorly known. Three theoretical models, not mutually exclusive, can lead to cosmopolitanism: (1) selective extinction in endemic taxa, (2) endemic taxa becoming cosmopolitan after the extinction and (3) an increase in the number of newly originated cosmopolitan taxa after extinction. We analyzed an updated occurrence dataset including 831 middle Permian to Middle Triassic ammonoid genera and used two network methods to distinguish major episodes of ammonoid cosmopolitanism during this time interval. Then, we tested the three proposed models in these case studies. Our results confirm that at least two remarkable cosmopolitanism events occurred after the Permian–Triassic and late Smithian (Early Triassic) extinctions, respectively. Partitioned analyses of survivors and newcomers revealed that the immediate cosmopolitanism event (Griesbachian) after the Permian–Triassic event can be attributed to endemic genera becoming cosmopolitan (model 2) and an increase in the number of newly originated cosmopolitan genera after the extinction (model 3). Late Smithian cosmopolitanism is caused by selective extinction in endemic taxa (model 1) and an increase in the number of newly originated cosmopolitan genera (model 3). We found that the survivors of the Permian–Triassic mass extinction did not show a wider geographic range, suggesting that this mass extinction is nonselective among the biogeographic ranges, while late Smithian survivors exhibit a wide geographic range, indicating selective survivorship among cosmopolitan genera. These successive cosmopolitanism events during severe extinctions are associated with marked environmental upheavals such as rapid climate changes and oceanic anoxic events, suggesting that environmental fluctuations play a significant role in cosmopolitanism.

Fragments of cheilostome and cyclostome bryozoans are the most common fossils in the mound structures commonly found in the Lower Danian limestones of southern Scandinavia. Sedimentological investigations and measurement of colony morphology combined with flume channel experiments indicate that: 1) The mounds were affected by unidirectional currents which created relatively high current velocities on the upstream flanks and summits, and low velocities on the downstream flanks and in the basins. 2) Colonies with slender stems and thin walls dominated in areas with low current velocities and those with thick stems and thick walls dominated in areas with high velocities. 3) The specific variability of the stem diameter was mainly controlled by the geometrical arrangement of the zooids. In general, species with a bilamellar arrangement of the zooids show high variability, whereas species with a radial arrangement show small variability. 4) Variation in the wall thickness is primarily related to the mode of growth of the individual zooids. In the ascophorans deposition was confined to the external surface of the stems. On the other hand, in the coilostegoid anascans the secondary skeletal material was deposited on all the internal surfaces of the zooids as well as on the external side of the cryptocyst. Cuticles do not seem to have been present in the secondary thickened part of the frontal wall of either the coilostegoid anascans or the ascophorans. 5) Calcareous material was deposited predominantly on the lower and older portions of the colony.

We documented changes in the relative abundance of bivalve genera and functional groups in the southwest Caribbean over the past 11 Myr to determine their response to oceanographic changes associated with the closure of the Central American Seaway ca. 3.5 Ma. Quantitative bulk samples from 29 localities yielded 106,000 specimens in 145 genera. All genera were assigned to functional groups based on diet, relationship to the substrate, and mobility. Ordinations of assemblages based on quantitative data for functional groups demonstrated strong shifts in community structure, with a stark contrast between assemblages older than 5 Ma and those younger than 3.5 Ma. These changes are primarily due to an increase in the abundance of attached epifaunal bivalves (e.g., Chama, Arcopsis, and Barbatia) and a decrease in infaunal bivalves (e.g., Varicorbula and Caryocorbula). Taxa associated with seagrasses, including deposit-feeding and chemosymbiotic bivalves (e.g., Lucina), also increased in relative abundance compared to suspension feeders. The composition of bivalve assemblages is correlated with the carbonate content of sediments and the percentage of skeletal biomass that is coral. Our results strongly support the hypothesis that increases in the extent of coral reefs and Thalassia communities were important drivers of biologic turnover in Neogene Caribbean benthic communities.

The fossil stickleback, Gasterosteus doryssus, is highly variable for pelvic girdle structure and the number of dorsal spines. Six “sampling pits” were dug at known stratigraphic positions within a continuous section which contains abundant G. doryssus, and the stratigraphic position of each specimen within each pit was determined. The deposit apparently is composed of annual layers (varves), allowing relatively precise conversion of stratigraphic distance to years. The temporal distribution of phenotypes is heterogeneous but can be grouped into two temporally contiguous, nonheterogeneous sets. However, absence of heterogeneity for pelvic phenotypes within the two groups of pits could be an artifact of small sample size. The number of sample pits was insufficient to determine whether the observed phenotypic heterogeneity among pits represents temporal trends. Differences also occurred between mean temporal distributions of stickleback phenotypes within one of the pits located within a nonheterogeneous set of pits. Thus, there is within-pit temporal heterogeneity that is unresolved by between-pit comparisons, although the sampling pits are separated by an average of only about thirty thousand years. Larger time intervals usually used in paleontology may seriously underestimate evolutionary rates because fine scale reversals of evolutionary trajectory are undetected. Temporal variation in G. doryssus provides a system in which most limitations of other fossil systems for measuring the rate of evolution can be circumvented. As in virtually all paleontological studies, spatial variation cannot be entirely eliminated as a potential cause of stratigraphic variation.

Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity, and funnel point to a relationship with the cephalopods. However, aspects of this reinterpretation, including the relevance of the group to cephalopod evolution, have been called into question.

Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.

Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.

This paper takes an alternative approach to the problem of inferring patterns of phenotypic evolution in the fossil record. Reconstructing temporal biological signal from noisy stratophenetic data is an inverse problem analogous to subsurface reconstructions in geophysics, and similar methods apply. To increase the information content of stratophenetic series, available geological data on sample ages and environments are included as prior knowledge, and all inferences are conditioned on the uncertainty in these geological variables. This uncertainty, as well as data error and the stochasticity of fossil preservation and evolution, prevents any unique solution to the stratophenetic inverse problem. Instead, the solution is defined as a distribution of model parameter values that explain the data to varying degrees. This distribution is obtained by direct Monte Carlo sampling of the parameter space, and evaluated with Bayesian integrals. The Bayesian inversion is illustrated with Miocene stratigraphic data from the ODP Leg 174AX Bethany Beach borehole. A sample of the benthic foraminifer Pseudononion pizarrensis is used to obtain a phenotypic covariance matrix for outline shape, which constrains a model of multivariate shape evolution. The forward model combines this evolutionary model and stochastic models of fossil occurrence with the empirical sedimentary record to generate predicted stratophenetic series. A synthetic data set is inverted, using the Neighbourhood Algorithm to sample the parameter space and characterize the posterior probability distribution. Despite small sample sizes and noisy shape data, most of the generating parameter values are well resolved, and the underlying pattern of phenotypic evolution can be reconstructed, with quantitative measures of uncertainty. Inversion of a stratigraphic series into a time series can significantly improve our perception and interpretation of an evolutionary pattern.

We studied the morphological diversity of gastropod shell forms from the viewpoint of theoretical morphology, emphasizing the relationships of shell form to postural stability and the available space for soft body, which we assessed in terms of the moment of force and soft-tissue ratio calculations, respectively. The results of computer simulations suggest a functional trade-off between postural stability and available space for soft body: a compact shell possessing a low spire and small umbilicus exhibits high postural stability, whereas a less overlapped shell form with a high spire and large umbilicus makes available space for soft body. A functional morphospace analysis using theoretical models reveals that outward and downward inclination of the aperture moderates the functional trade-off between these parameter values and permits compatibility between stable posture and efficient shell construction. The hypothetical optimum that realizes this compatibility is consistent with the observed range of forms estimated from 359 extant gastropod species. The biometric results also suggest that land snails are more highly constrained than marine species in achieving a balance between postural stability and available space for soft body.

We report a detailed study of the different categories and types of abnormal morphologies in planktic foraminifera recognizable in the lowermost Danian, mainly from the El Kef and Aïn Settara sections, Tunisia. Various types of abnormalities in the test morphology were identified, including protuberances near the proloculus, abnormal chambers, double or twinned ultimate chambers, multiple ultimate chambers, abnormal apertures, distortion in test coiling, morphologically abnormal tests, attached twins or double tests, and general monstrosities. Detailed biostratigraphic and quantitative studies of the Tunisian sections documented a major proliferation of aberrant planktic foraminifera (between approximately 5% and 18% in relative abundance) during the first 200 Kyr of the Danian, starting immediately after the Cretaceous/Paleogene (K/Pg) boundary mass extinction (spanning from the Guembelitria cretacea Zone to the lower part of the P. pseudobulloides Zone). This contrasts with the proportionately low frequency of aberrant tests (generally <2%) identified within the uppermost Maastrichtian, suggesting more stable environmental conditions during the last ~50–100 Kyr of the Cretaceous. Two main pulses with abundant aberrant tests were recognized in the earliest Danian, the one recorded in the well-known K/Pg boundary clay being the more intense of those (maxima of >18%). These main pulses of aberrants coincide approximately with relevant quantitative and evolutionary turnovers in the planktic foraminiferal assemblages. In this paper, we explore the relation of these high values of the foraminiferal abnormality index with the environmental changes induced by the meteorite impact of Chicxulub in Yucatan, Mexico, and the massive eruptions of the Deccan Traps, India.

The “niche-variation” model predicts that increase in environmental stability should be accompanied by increase in homozygosity and reduction in morphological variability. All Late Cambrian trilobite biomeres show an increase in regional species diversity from low in the biomere toward the top. This change in diversity is believed to reflect increasing environmental stability and consequently affords the opportunity to indirectly test the “niche-variation” hypothesis in a paleontological context. Measurements were made of eight cranidial features of samples of 17 species populations from the Pterocephaliid Biomere of the Great Basin. Coefficients of variation and a multivariate analog of them failed to reveal a relationship between morphological variability and species diversity. Consideration of these data together with contradictory, but limited, informaton for other organisms suggests that the predicted decrease in genetic variability may either be absent or be readily masked in naturally occurring populations, which typically retain a high degree of genetic polymorphism. If heterozygosity is common, it would appear that accidents of geography, rather than the genetic consequences of stable or unstable environments, are among the primary factors controlling the probability of speciation.