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.

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.

The history of diversity, origination and extinction of Cambro-Ordovician nautiloid cephalopods is explored to determine if differences in evolutionary rates between nautiloid orders are sufficient to document significantly high or low rates of evolutionary turnover (taxotely of Raup and Marshall 1980). The stratigraphic ranges of 425 nautiloid genera are analyzed for this purpose.

Evolutionary rates for five of the seven time intervals analyzed fall within frequency distributions of rates which are thought to be characteristic for a given time interval (horotelic distribution of Simpson 1944). Sufficient heterogeneity is present among extinction rates of Arenigian orders and origination rates of Caradocian orders to reject the null hypotheses of horotely in favor of taxotely. The orders Ellesmerocerida and Tarphycerida, each with a significantly high rate of extinction (P ≥ 0.99), and the Actinocerida, with a significantly low rate of extinction (P ≥ 0.99), were responsible for taxotely during the Arenigian. The Oncocerida and Discosorida, each with a significantly high rate of origination (P ≥ 0.99), were responsible for taxotely during the Caradocian. In each case, taxotely is attributable to the influence of North American endemics. This effect is believed to be more the result of real biological aspects of nautiloid evolution than an artifact of the fossil record.

Analysis of relative changes in plate position during ontogeny was made on a number of Cenozoic spatangoid echinoids: species of Breynia, Lovenia, Protenaster and Echinocardium. Contrary to the generally held view that adjacent ambulacral and interambulacral columns in echinoids always remain in a fixed relative position during ontogeny, many spatangoids show great fluidity in plate growth, with adjacent columns ‘sliding past’ one another during ontogeny. Furthermore, in many genera plates from one column may undergo strong lateral growth and bisect pairs of plates in adjacent rows. This phenomenon of relative plate movement, both meridional and equatorial, is herein termed ‘plate translocation’. It is considered to occur by localized resorption and redeposition in a narrow zone along adjacent plate boundaries. Plate translocation has been of considerable phylogenetic significance to spatangoids and, combined with an increase in differential allometries between plates, has been one of the most important factors in the evolution of the Spatangoida. Furthermore, the initiation of plate translocation in the apical system in certain Jurassic echinoids may have been the trigger for the migration of the periproct out of the apical system, and a major factor in the evolution of irregular echinoids. Heterochrony in plate growth has been critical in controlling the course of evolution in many lineages of spatangoid echinoids.

We compare refined data sets for Atlantic benthic foraminiferal oxygen isotope ratios and for North American mammalian diversity, faunal turnover, and body mass distributions. Each data set spans the late Paleocene through Pleistocene and has temporal resolution of 1.0 m.y.; the mammal data are restricted to western North America. We use the isotope data to compute five separate time series: oxygen isotope ratios at the midpoint of each 1.0-m.y. bin; changes in these ratios across bins; absolute values of these changes (= isotopic volatility); standard deviations of multiple isotope measurements within each bin; and standard deviations that have been detrended and corrected for serial correlation. For the mammals, we compute 12 different variables: standing diversity at the start of each bin; per-lineage origination and extinction rates; total turnover; net diversification; the absolute value of net diversification (= diversification volatility); change in proportional representation of major orders, as measured by a simple index and by a G-statistic; and the mean, standard deviation, skewness, and kurtosis of body mass. Simple and liberal statistical analyses fail to show any consistent relationship between any two isotope and mammalian time series, other than some unavoidable correlations between a few untransformed, highly autocorrelated time series like the raw isotope and mean body mass curves. Standard methods of detrending and differencing remove these correlations. Some of the major climate shifts indicated by oxygen isotope records do correspond to major ecological and evolutionary transitions in the mammalian biota, but the nature of these correspondences is unpredictable, and several other such transitions occur at times of relatively little global climate change. We conclude that given currently available climate records, we cannot show that the impact of climate change on the broad patterns of mammalian evolution involves linear forcings; instead, we see only the relatively unpredictable effects of a few major events. Over the scale of the whole Cenozoic, intrinsic, biotic factors like logistic diversity dynamics and within-lineage evolutionary trends seem to be far more important.

In this paper we reconstruct the phylogeny of a clade of pachypleurosaurs (Reptilia: Sauropterygia) occurring in Triassic-age deposits in the Monte San Giorgio region, Switzerland. We also present the phylogeny of this clade as a case study for two paradigms of phylogeny reconstruction: cladistics and phenetic/stratigraphic methods. While this dichotomy is not held rigidly by all workers, its advancement by cladists leads us to retain it initially for rhetorical purposes. We review the philosophical bases of species, species concepts, and speciation, as well as cladograms and phylogenies, before introducing the experimental system.

Data are presented from cladistic analyses, phenetic analyses, and stratigraphic information. Phylogeny of the clade is interpreted from both paradigms, and the interpretations are found to be inconsistent. Resolution of the phylogeny rests on the emphasis of one type of data over another. An interpretation of cladogenesis within the genus Neusticosaurus entails rejection of suggestive phenetic and stratigraphic data, whereas an anagenetic interpretation entails reversal of autapomorphies in ancestral taxa. Anagenesis is deemed to be the more probable interpretation, based on the strength of the stratigraphic and phenetic data relative to the character data. Implications of the test case results for phylogeny reconstruction in general are discussed, ending with a call for pluralism in approach.

All else being equal, species with short life spans are expected to be overrepresented in time-averaged death assemblages relative to their standing abundance in the living community, but the magnitude of the distortion of proportional abundance and assemblage evenness has received little attention. Here, information from 30 data sets on the living and dead abundances of marine bivalves in local habitats is combined with a global compilation of bivalve life spans to determine whether bias from mortality rate can explain observed differences in species proportional abundances. Although bivalve maximum life spans range from one to 75 years in these data sets, indicating annual mortality rates of 0.97 to 0.09, the “life span bias” (LB) of a species–the difference between its proportional abundance expected dead and that observed alive–is consistently small in magnitude (average change <2%, maximum about 20%) and random in sign relative to observed discordance (OD = difference between that species' proportional abundance observed dead and that observed alive). The aggregate result for 413 living species occurrences is a significantly positive but weak correlation of OD to LB, with only 10% of variation in OD explained. The model performs better among longer-lived species than among shorter-lived species, probably because longer-lived species conform better to the model assumption that species maintain a constant proportional abundance in the living assemblage over time. Among individual data sets, only seven exhibit significant positive correlations between OD and LB. The model also under-predicts the cases where a death assemblage is dominated by a species that is shorter lived than the dominant species in the living assemblage, indicating that some factor(s) other than or in addition to mortality rate is responsible for OD. We can find no evidence of preservational bias linked to life span, for example through body size. This negative outcome reflects a weak biological relationship between life span and living abundance among bivalves in local habitats, contrary to the terrestrial paradigm, and points toward a simpler model of time-averaged death assemblage formation where higher abundances reflect (under-sampled) past populations. Contrary to long-held expectations, variation in population turnover among species is not a major source of taphonomic bias in time-averaged death assemblages among bivalves and perhaps among other marine groups: bias must arise largely from other factors.

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.

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.

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 concept of evolvability—the capacity of a population to produce and maintain evolutionarily relevant variation—has become increasingly prominent in evolutionary biology. Paleontology has a long history of investigating questions of evolvability, but paleontological thinking has tended to neglect recent discussions, because many tools used in the current evolvability literature are challenging to apply to the fossil record. The fundamental difficulty is how to disentangle whether the causes of evolutionary patterns arise from variational properties of traits or lineages rather than being due to selection and ecological success. Despite these obstacles, the fossil record offers unique and growing sources of data that capture evolutionary patterns of sustained duration and significance otherwise inaccessible to evolutionary biologists. Additionally, there exist a variety of strategic possibilities for combining prominent neontological approaches to evolvability with those from paleontology. We illustrate three of these possibilities with quantitative genetics, evolutionary developmental biology, and phylogenetic models of macroevolution. In conclusion, we provide a methodological schema that focuses on the conceptualization, measurement, and testing of hypotheses to motivate and provide guidance for future empirical and theoretical studies of evolvability in the fossil record.

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.

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.

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.

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.

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.

It has generally been argued that the majority of fossil benthic foraminifera, the most common proxy for paleo bottom oceanic conditions, could not tolerate anoxia. Here we present evidence that fossil foraminifera were able to successfully colonize anoxic–dysoxic bottom waters, by using adaptations similar to those found in living species. Our study is based on a multi proxy micropaleontological and geochemical investigation of the Upper Cretaceous sediments from the Levant upwelling regime. A shift from buliminid to diverse trochospiral dominated assemblages was recorded in an interval with a distinct anoxic geochemical signature coinciding with a regional change in lithology. This change was triggered by an alteration in the type of primary producers from diatoms to calcareous nannoplankton, possibly causing modifications in benthic foraminiferal morphological and physiological adaptations to life in the absence of oxygen.

Our data show that massive blooms of triserial (buliminid) benthic foraminifera with distinct apertural and test morphologies during the Campanian were enabled by their ability to sequester diatom chloroplasts and associate with bacteria, in a similar manner as their modern analogs. Diverse trochospiral forms existed during the Maastrichtian by using nitrate instead of oxygen for their respiratory pathways in a denitrifying environment. Species belonging to the Stilostomellidae and Nodosariidae families might have been affected by the change in food type arriving to the seafloor after the phytoplankton turnover at the Campanian/Maastrichtian boundary, in a similar manner as their mid Pleistocene descendants prior to their extinction. This study promotes the need for a re-evaluation of the current models used for interpreting paleoceanographic data and demonstrates that the identification of adaptations and mechanisms involved in promoting sustained life under anoxic to dysoxic conditions should become a standard in faunal paleoceanographic studies.

Previous attempts to quantify the test-flattening trend in Heterostegina depressa with water depth have been rather unsuccessful. Due to its broad depth distribution, H. depressa is a perfect model species to calibrate test flattening as a bathymetric signal for fossil assemblages. This might enable us to better reconstruct paleoenvironments of fossil communities of larger foraminifera or even provide clues to the degree of transport in allochthonous deposits. In this study, we used growth-independent functions to describe the change of test thickness throughout ontogeny. Four growth-invariant characters, deriving from these functions, clearly quantify a transition of individuals with thicker to thinner central parts along the water-depth gradient. This transition is probably controlled by light intensity, because the photosymbionts of H. depressa (diatoms) are most effective at low irradiation levels. Thus, specimens at shallower depths grow thicker to reduce light penetration, whereas specimens living deeper than the light optimum increase their surface by flattening to obtain better exposure to light.

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.