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 Permian/Triassic mass extinction marks a permanent phylogenetic shift in the composition of the sessile benthos, from one largely dominated by articulate brachiopods to one dominated by mollusks. Widespread evidence of oceanic hypoxia and anoxia at this time provides a possible selective kill mechanism that could help explain the large taxonomic losses in brachiopods compared to the morphologically and ecologically similar bivalve molluscs. Our study compared the oxygen consumption of an articulate brachiopod, Terebratalia transversa, with that of two pteriomorph bivalves, Glycymeris septentrionalis and Mytilus trossulus, under normoxia and hypoxia, as well as their tolerance to anoxia, to gain insight into the relative metabolic characteristics of each group. We found no significant difference in the oxygen consumption of the three species when normalized to the same dry-tissue mass. However, when calculated for animals of the same external linear dimensions, bivalve oxygen consumption was two to three times greater than that of brachiopods. Our results also showed no significant decrease in the oxygen consumption of the three species until measured at a partial pressure of oxygen ∼10% of normoxic values. Finally, T. transversa and M. trossulus showed no significant difference in their tolerance to complete anoxia, but both showed a much lower tolerance than another bivalve, Acila castrensis. Findings from this study suggest that oxygen limitation is unlikely to account for the observed selective extinction of brachiopods during the Permian/Triassic mass extinction. Results may provide valuable information for assessing hypotheses put forth to explain why articulate brachiopods continue to remain a relatively minor group in marine environments.

Interpretations of morphologic radiations and macroevolutionary patterns are dependent on a priori choices of taxonomic and geographic scales of study. The results of disparity analysis at varying taxonomic (species and genus) and geographic (regional, biofacies, and community) scales are examined in a study of Ordovician though Early Silurian crinoids. Using discrete morphologic characters, we examined the disparity of 421 crinoids from 65 Laurentian biofacies. Crinoid disparity differs when analyzed at the regional and biofacies levels. Regardless of fluctuations in regional crinoid disparity, average within-biofacies disparity was static throughout the Ordovician, deviating only during the Silurian because of the proliferation of the morphologically aberrant myelodactylid crinoids. The choice of taxonomic level does not have an effect at the biofacies level. However, at the regional level, the two taxonomic scales (genus and species) can produce different results because of variation in the number of species per genus through time and the amount of morphologic variation within individual genera. Weighting disparity by abundance provides a metric combining morphology and community structure. Average weighted disparity at the community level showed patterns similar to that of the biofacies-level disparity curve, but this metric has a greater degree of variation between biofacies. Biofacies with a low ratio of weighted to unweighted disparity display the distinctive community structure (based on aerosol filtration theory) that is often reported in crinoid assemblages.

We investigate potential microevolutionary mechanisms of phenotypic change in a lineage of brackish-water gastropods from Lake Pannon. The lineage exhibits a threefold increase in body size and a pronounced increase in shell shouldering over a roughly 2.5-Myr interval. We use the stable oxygen isotope profiles of 13 shells to address the question of whether large size is due to more rapid growth or to greater longevity.

Results indicate that larger individuals have significantly greater longevity. Growth rates in large snails are comparable to those of their smaller-bodied ancestors.

Potentially relevant selective advantages of large size include escape from predators, avoidance of resource competition, and increased fecundity. We argue that the first two advantages may have accrued to larger individuals but are not likely to have driven the trend because selection for them would favor more rapid growth rates. Fecundity selection, on the other hand, is readily envisioned in a stable, predictable environment in which the need for early reproduction is relaxed. The evolution of large body size in Lake Pannon molluscs may be comparable to evolution on many islands, where reduced pressure from competition and predation lead to characteristic changes in body size.

Large-scale trends in planktonic foraminiferal diversity have so far been based on utilization of synoptic biostratigraphic range charts. Although this approach ensures the taxonomic consistency and quality of the data being used, it takes no formal account of any sampling biases that might exist in the fossil record. We demonstrate that the occurrence data of planktonic foraminifera, as recorded in the primary literature, are strongly biased by sampling. We do this by demonstrating that raw diversity curves derived from the land-based and deep-sea records are strikingly different, but that they each correlate with the intensity of sampling in their respective environments, and thus are ultimately controlled by the structure of the geological record in each setting. Because sampling of the Mesozoic record is best in our land record whereas sampling of the Cenozoic is best in our deep-sea record, we combine the two to generate the best-supported estimates of species and genus diversity over time from these data. We correct for sampling bias using shareholder quorum subsampling and a modeling approach. The data are then transformed to generate a range-through plot of species richness that is compared with two earlier estimates of the diversity history where comparable species-in-bin data can be recovered. No robust statistical correlation is found among the three estimates. Although differences in amplitude are to be expected, differences in the actual shape of the curve are surprising. We conclude that these differences stem from the nature of the data themselves, namely the taxonomic scheme adopted and the taxonomic coverage used.

In this paper we present a method for estimating soil pCO₂ in ancient environments using the measured carbon-isotope values of pedogenic carbonates and plant-derived organic matter. The validity of soil pCO₂ estimates proves to be highly dependent on the organic δ¹³C values used in the calculations. Organic matter should be sourced from the same paleosol profiles as sampled carbonates to yield the most reliable estimates of soil pCO₂. In order to demonstrate the potential use of soil pCO₂ estimates in paleoecological and paleoenvironmental studies, we compare samples from three Upper Jurassic localities. Soil pCO₂ estimates, interpreted as a qualitative indicator of primary paleoproductivity, are used to rank the Late Jurassic terrestrial environments represented by the Morrison Formation in western North America, the informally named Lourinhã formation in Western Europe, and the Stanleyville Group in Central Africa. Because modern terrestrial environments show a positive correlation between primary productivity and faunal richness, a similar relationship is expected in ancient ecosystems. When the relative paleoproductivity levels inferred for each study area are compared with estimates of dinosaur generic richness, a positive correlation emerges. Both the Morrison and Lourinhã formations have high inferred productivity levels and high estimated faunal richness. In contrast, the Stanleyville Group appears to have had low primary productivity and low faunal richness. Paleoclimatic data available for each study area indicate that both productivity and faunal richness are positively linked to water availability, as observed in modern terrestrial ecosystems.

Analysis of dental wear and damage is becoming an increasingly important tool in unraveling the trophic ecology of a wide range of vertebrates, and when applied to fossils it can provide evidence of both diet and feeding kinematics that is independent of morphological analysis. Conodonts have the best fossil record among vertebrates and their skeletal elements are known to exhibit surface wear and damage generated in vivo as a consequence of their function as teeth. We report the results of the first systematic survey and analysis of the frequency and extent of this wear and damage in conodonts (based on P₁ elements from a range of Carboniferous genera). This has revealed that wear and damage are remarkably common, present in all conodont elements sampled. Multivariate analysis reveals that patterns of wear and damage differ significantly among different conodont taxa, and exploratory ANOVA and linear discriminant analyses show that wear and damage differ according to the position of taxa in an onshore-offshore gradient, and whether they are likely to have had a benthic or pelagic mode of life. The incidence of denticle tip spalling in particular is higher in more-offshore environments and in taxa likely to have had a pelagic mode of life. Aspects of the data also reflect the occlusal kinematics of the elements, providing a means of testing hypotheses of element function. Our results have wide-ranging implications for unlocking the fossil record of conodonts, by, for example, furnishing direct evidence of the diet-mediated processes that may have driven observed patterns of evolutionary change, and reducing the confounding effects of depth segregation when using conodonts in isotope-based paleotemperature studies.

One of the best-recognized patterns in the evolution of organismal size is the tendency for mean and maximum size within a clade to decrease following a major extinction event and to increase during the subsequent recovery interval. Because larger organisms are typically thought to be at higher extinction risk than their smaller relatives, it has commonly been assumed that size reduction mostly reflects the selective extinction of larger species. However, to our knowledge the relative importance of within- and among-lineage processes in driving overall trends in body size has never been compared quantitatively. In this study, we use a global, specimen-level database of foraminifera to study size evolution from the Late Permian through Late Triassic. We explicitly decompose size evolution into within- and among-genus components. We find that size reduction following the end-Permian mass extinction was driven more by size reduction within surviving species and genera than by the selective extinction of larger taxa. Similarly, we find that increase in mean size across taxa during Early Triassic biotic recovery was a product primarily of size increase within survivors and the extinction of unusually small taxa, rather than the origination of new, larger taxa. During background intervals we find no strong or consistent tendency for extinction, origination, or within-lineage change to move the overall size distribution toward larger or smaller sizes. Thus, size stasis during background intervals appears to result from small and inconsistent effects of within- and among-lineage processes rather than from large but offsetting effects of within- and among-taxon components. These observations are compatible with existing data for other taxa and extinction events, implying that mass extinctions do not influence size evolution by simply selecting against larger organisms. Instead, they appear to create conditions favorable to smaller organisms.

Recovery of marine biodiversity following the Permo-Triassic extinction is thought to have been delayed relative to other mass extinctions. Terrestrial vertebrate biodiversity is said to have taken as much as 15 Myr longer to recover than the marine. The present study tests, at the scale of an individual fossil community, whether a disparity in biodiversity existed in the American Southwest, between the Moenkopi Formation, containing an early Middle Triassic (Anisian) terrestrial tetrapod fauna, and the Chinle Formation, containing a successor Late Triassic (Norian) tetrapod fauna. Taking Chinle faunal biodiversity to represent full biotic recovery, comparison of taxonomic and guild diversity of faunas from similar depositional and taphonomic environments in these two formations allowed us to assess the possibility of incipient terrestrial recovery of biodiversity in the Anisian.

Comparisons were made between the Holbrook Member fauna of the Moenkopi, a unit best characterized as a low-sinuosity medium- to coarse-grained fluvial deposit, and each of four Chinle stratigraphic units, representing fluvial settings from sandy low-sinuosity to muddy high-sinuosity. Three metrics were applied: generic and familial taxonomic diversity and guild diversity; these were compared by rarefaction. Simpson and Shannon diversity metrics augmented the analysis. Units of extraordinary preservation in the Chinle—the so-called blue layers—were removed from the analysis. In all tests the biodiversity of the Holbrook Member fauna is within the variation seen in Chinle faunas.

If the results of our study represent global conditions, they suggest that by at least early Anisian time (∼6 Myr after the P/T extinction) biodiversity had reached levels comparable to those seen in the Late Triassic. This potentially brings the terrestrial vertebrate recovery in line with the 4–8 Myr it took for recovery in the marine realm.

Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The “Nearshore Refugium Model” of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.