A consensus on the biostratigraphic age and depositional environment of the Navidad, Ranquil, and Lacui formations exposed along the tectonic margin of central Chile has been elusive due to conflicting evidence. This study resolves this dilemma and gains further insight regarding the history of the Chilean coast. Problematic interpretations stem primarily from the remarkable similarity between the molluscan fauna of these units with those well documented for the late Oligocene to early Miocene of Peru. Planktic foraminifers, however, indicate that the Chilean sections accumulated in the late Miocene to early Pliocene interval following a regional hiatus that extends into the Eocene. The prevalence of mixed-depth bathyal assemblages of benthic foraminifers and ostracodes, the majority of which include lower-bathyal (>2000 m) indicators, reveals that downslope displacement was a primary mode of deposition in the basins. Although the molluscan assemblages are dominated by shallow marine taxa, most include species that range into or are restricted to deeper waters. Sedimentary features connote rapid subsidence and deep-water deposition of gravity flows. Although older Tertiary and Cretaceous planktic foraminifers in several assemblages indicate reworking of older units, lack of data on pre-Tortonian faunas of this region precludes recognition of other age-discordant components that could constitute a significant portion of the recovered fauna. The findings of this study revise the prevailing conception of the region's geologic history that considered these units to be early to middle Miocene shelf deposits and indicate that infilling and uplift have characterized the nearshore basins since the late Pliocene.

Outcrops of the Lower Triassic (Spathian) Virgin Limestone Member (Moenkopi Formation) in the southwestern United States contain the oldest known metazoan bioherms formed in the aftermath of the end-Permian mass extinction. These small buildups, up to 1.0 m in diameter and 0.2 m high, were constructed by cementing bivalves. The bivalve bioherms accreted in a shallow, subtidal environment above storm wave base atop an oolitic hardground on a carbonate ramp. Similarities in shell microstructure and bioherm morphology between the Lower Triassic buildups reported here and previously described Middle Triassic occurrences suggest that the Lower Triassic bioherms were likely built by a bivalve assignable to Placunopsis. Although taxonomic assignment of the bivalve remains uncertain, the presence of cemented bivalve bioherms in Lower Triassic sections of the southwestern United States demonstrates that cementing bivalves were geographically widespread, even early in their Mesozoic evolutionary history. Despite their bioherm-building ecology, cementing bivalves do not occur in Middle Triassic platform-margin reefs, underscoring the decoupling of the recovery of framework-building metazoans from the return of large carbonate platform-margin reefs in the wake of the end-Permian mass extinction. These first Mesozoic bioherms built by metazoans represent a significant ecological advance in the evolutionary history of bivalves in that the cementing life-mode had reappeared before the end of the Early Triassic.

A quantitative study based on unionoid bivalve presence-absence data, species abundance, shell morphology, and sedimentological data provides a more detailed paleoecological interpretation of the Upper Cretaceous Hell Creek Formation. The Proparreysia and the Pleurobema faunal assemblages can be separated on the basis of taxonomic diversity and species composition. While the first consists of 19 species, including trigonal and elongate shell morphologies, the latter consists of only 3 species characterized by elongate shells. A riverine environment is interpreted for most species from the quantitative analysis of shell morphology. Only one species (cf. Pleiodon sp.) is from a lacustrine habitat. The main river channels of the Hell Creek paleodrainage system are the habitat of bivalves of the Proparreysia assemblage through a combined interpretation of the morphology and diversity data. In contrast, the bivalves of the Pleurobema assemblage are from secondary channels and tributaries of the main river channels. The mode of deposition of the two assemblages is very similar, as they are preserved predominantly in crevasse-splay deposits. The long-term ecosystem stability, high habitat heterogeneity, and a variable degree in floodplain connectivity of the habitats in the midreach of the Hell Creek paleodrainage system resulted in the high taxonomic diversity of the unionoid bivalves and the separation of the unionoid faunal assemblages.

Drillholes interpreted as the products of gastropod predation have become the most widely applied proxy for predator-prey interactions in the fossil record. In a broader sense, they have also become accepted as reflecting the evolution of many aspects of predator-prey interactions; e.g., intensity, behavior, and efficiency. Because of the relative paucity of published studies, the generality of long-term trends revealed by recent compilations of drilling intensity data has not been widely tested. The present study examines predatory gastropod drilling intensity in bivalves from the late early to early late Maastrichtian Fox Hills Formation within the Western Interior Seaway (WIS). These data allow a new comparison to be made to drilling intensity values reported previously from coeval United States Coastal Plain collections. 6,910 valves and 4,343 articulated specimens representing 53 bivalve species were examined for evidence of drilling predation. Although the approach employed was designed to maximize the number of drillholes recorded, only 236 unequivocal drillholes, 20 possible drillholes, 11 partial drillholes, and a single specimen with multiple drillholes were found, resulting in a maximum drilling intensity of 3.3%. These drillholes are thought to have been largely produced by naticids, which are abundant in these deposits. When compared to other published studies of Maastrichtian gastropod drilling, these data document that drilling intensities in the latest Cretaceous varied considerably both spatially and temporally, and that the WIS record provides a lower baseline for Cretaceous drilling than that derived from coeval Coastal Plain localities.

The Yakataga Formation contains mudstones, sandstones, and diamictites that represent fluctuating marine and glaciomarine deposition in the Gulf of Alaska since the latest Miocene. These rocks contain distinctive benthic foraminiferal assemblages that provide insight into the depositional, structural, and climatic history of the northeastern Pacific Ocean. Qualitative analyses of benthic foraminiferal distribution patterns have been used previously to define eight stratigraphic sequences in the offshore Yakataga Formation. Results of multivariate quantitative methods are presented here to provide additional insight into the nature of foraminiferal faunas and to demonstrate the potential for using quantitative methods in sequence biostratigraphy. Cluster and polytopic vector analyses of 158 samples from the offshore Yakataga Formation indicate distinct mixtures of foraminiferal faunas within the samples. Polytopic vector analysis suggests that samples contain mixtures of seven end members representing the neritic through bathyal environments: EM1: Elphidium excavatum clavatum biofacies (inner neritic); EM2: Epistominella pacifica biofacies (upper bathyal and middle bathyal); EM3: sharp-margined Cassidulina spp. biofacies (outer neritic); EM4: round-margined Cassidulina spp. biofacies (outer neritic); EM5: Cassidulina californica biofacies (outer neritic); EM6: Uvigerina ex gr. peregrina biofacies (upper to middle bathyal); and EM7: Haplophragmoides spp. biofacies (outer neritic through upper bathyal). Identification of several outer neritic biofacies indicates heterogeneity within this environment, probably due to differences in substrates and nutrient levels. Mixing of biofacies is primarily due to downslope transport of faunas across the shelf and slope and may also be the result of constriction of environmental zones due to advances of the tidewater glacier margins across the shelf.

Images in the monographic literature represent an important but relatively untapped resource for paleontologists. In particular, they could provide vast amounts of body size data. It is possible, however, that images of specimens represent a biased sample of the fossil record. Thus, the quality of these data must be assessed before body size estimates from the literature can be used in analyses.

Two complementary datasets were constructed for a group of bivalve and brachiopod species from the Paleozoic and the Cenozoic. The monograph dataset consisted of length measurements taken from all unique images of a species in a monograph. The counterpart bulk dataset consisted of comparable measurements taken from a set (n > 10) of bulk-collected specimens of the same species acquired from the same locality as those figured in the monograph. These paired datasets were used to assess the quality of monographic data.

Bias direction and magnitude were assessed by using the bulk sample of a species as an estimate of its underlying size-frequency distribution. Bias was estimated for each monographed specimen by calculating its percentile-value in relation to the size-frequency distribution for that species. All species groups had mean values within the 70th to 85th percentile range, indicating a significant bias toward monograph specimens that are larger than the mean of the bulk sample. The consistency of bias was evaluated by comparing the monograph sample mean to the bulk sample mean for each species. When compared in bivariate scatter plots, all species groups yielded significant regression lines with slopes near unity, indicating highly consistent, yet predictable, bias in each case. This trend persisted when the data were grouped taxonomically, geographically, or by year of monograph publication.

These results indicate that size measurements of monographed specimens of bivalves and brachiopods consistently record similar size classes for most species. This bias is easy to remove and doing so renders size data from images in monographs useful for macroevolutionary studies of body size.

The environmental distribution of lingulide brachiopods in western Canadian Triassic marine successions, their relationship with other infaunal organisms occupying the same ecospace, and their role in the aftermath of the Permian-Triassic extinction event is summarized. Western Canada is an ideal location to assess lingulide distribution patterns as upper Paleozoic and lower Mesozoic strata are extensively exposed, and lingulides (cf. Lingularia Biernat and Emig) and the trace fossil Lingulichnus Hakes are both common. A distribution comparison of in situ lingulides and Lingulichnus Hakes with concordantly emplaced lingulide shells and shell beds shows clearly that the latter is a poor indicator of true environmental distribution of these infaunal suspension feeders.

Lingulides are rare in uppermost Paleozoic strata in the study area. Most occurrences consist of isolated valves or abraded material in erosional lags. Lingulides remain minor components of infaunal communities during the earliest Triassic (Griesbachian). Although lingulide valves and valve fragments are the dominant body fossil observed, trace fossil analysis indicates that lingulides were minor components of earliest Triassic infaunal communities. Lingulides increase in abundance and importance during the Dienerian and Smithian. Shallow and marginal marine trace-fossil assemblages of this age are dominated commonly by Lingulichnus. Lingulide fossils are less abundant but are found in many shallow and marginal marine lithofacies. Lingulides comprise only a minor component of late Smithian through Anisian infaunal communities.

Canadian lingulide abundance reached an acme during the latest Middle Triassic (Ladinian). Fossil material is common in many environments, however, in situ lingulides and the trace fossil Lingulichnus occur primarily in tempestites in proximal offshore through lower shoreface settings and in intertidal flat settings. Although quantitatively more abundant in the Middle Triassic, lingulides were proportionally more abundant in Lower Triassic successions. Regardless of relative changes in abundance, the environmental distribution of lingulides did not differ between Early and Middle Triassic successions. Lingulides comprise only a minor component of Upper Triassic infaunal communities.

Early Triassic lingulides did not occupy any environmental settings from which they were excluded prior to the Permian-Triassic extinction or after the postextinction recovery interval. Thus, lingulides were not postextinction disaster taxa but rather were ecological opportunists that dominated some Early Triassic shallow and marginal marine successions.

Stable isotopic values were measured on micrite, sparry calcite, dolomite, inarticulated brachiopods, and conodonts from the Lange Ranch section (central Texas) of the Lower Ordovician Tanyard Formation. The section spans the upper Cordylodus angulatus Zone through the lower Rossodus manitouensis Zone. An ∼2‰ negative δ¹³C shift from >0‰ to <−1.5‰_VPDB through the section suggests the lower third of the Rossodus manitouensis Zone was sampled. Consistent with previous studies, the δ¹⁸O values of carbonates are low, ranging from −3.3‰ to −8.1‰_VPDB. Phosphate δ¹⁸O values range from 15.4‰ to 17.1‰_VSMOW. Paleotemperature estimates calculated from micrite δ¹⁸O values assuming an ice-free seawater δ¹⁸O value of −1‰_VSMOW indicate Early Ordovician tropical seawater temperatures averaged 42°C, whereas δ¹⁸O values of co-occurring biogenic phosphate assuming the same seawater value yield paleotemperature estimates averaging 37°C. The phosphate values are interpreted as less affected by diagenesis than carbonate values and suggest Early Ordovician tropical paleotemperatures were not more than 10°C warmer or the oxygen isotopic composition of Early Ordovician hydrosphere was not more than 2‰ lower than present.

This work describes the occurrence of numerous, nearly intact Mecochirus rapax populations within Thalassinoides suevicus burrows in the Lower Cretaceous Boca do Chapim Formation. This exceptional preservation allows for unquestionable attribution of a specific producer to a biogenic structure. Analysis of sedimentological features combined with functional morphology and ichnological inferences suggests that the unique preservation of the fauna resulted from river flood depositional events that buried successive Mecochirus populations in a shallow marine setting.