Small buildups of chaetetids and associated biota in the Higginsville Limestone Member of the Fort Scott Formation (Desmoinesian, Middle Pennsylvanian) are well exposed in three dimensions in an abandoned quarry in Crawford County, Kansas. Regional studies indicate that the buildups were deposited during a relative sea-level highstand, but within normal wave-base, on the southern flank of the Bourbon Arch. The chaetetid facies consists of a fusulinid wackestone to packstone that encloses the chaetetids. In the lower part of the chaetetid interval, chaetetids are small and tabular, but gradually upsection they grade into larger domical forms that sometimes form tall, ragged columns. These, in turn, coalesce upward to form large masses (boundstone) up to 6 m across. At the top of the bed, the chaetetid masses and surrounding matrix are covered by intertidal to supratidal, coastal, and/or terrigenous facies, indicating a shallowing of sea level to the point that chaetetid growth was terminated.

Attachment surfaces for individual chaetetids initially involved partially lithified sediment or shell fragments, whereas within the columns they attached to underlying chaetetids, Multithecopora or algal overgrowths on underlying chaetetids, or thin sediment layers that define growth interruptions within the columns. Apparent maximum relief of chaetetids relative to the seafloor during growth was from 30 to 45 cm. Cross laminations in the matrix and some toppling of chaetetids indicate a moderately high-energy paleoenvironment. Ragged margins of the chaetetids accompanied by overlying thin sediment layers, and periodic overgrowths by the tabulate coral Multithecopora and encrusting algae, indicate growth interruptions instigated by periodic influxes of sediment or other environmental factors. Abundant fossils are present on and among the chaetetids, including brachiopods, bryozoans, rugose corals, crinoids, echinoids, gastropods, encrusting algae, ostracodes, and foraminiferids. Many of them are apparently in life positions, indicating a diverse, stenohaline biota living in this environment.

Chaetetid masses are relatively evenly distributed throughout the quarry and, thus, give no indication of an end to the buildup in any direction, or of a windward or leeward orientation. Directional indicators within the rocks and linear trends of the buildups suggest a paleocurrent that moved in a northeasterly direction. Apparently the environment of deposition was relatively uniform, flat, shallow, well-aerated, and open marine, at some distance from shore.

At the time of deposition, this area was within 10 degrees of the paleoequator. Changes in rainfall, ocean circulation, mixing, aeration, and nutrient input are reflected in the rocks and by their preserved biota. Black shale represents the least mixing and aeration, the phylloid algal limestone suggests low turbidity and possibly low salinity but well-aerated and nutrient-rich marine conditions, and the chaetetid interval represents normal marine salinity and low nutrient input with the best circulation, mixing, and aeration.

Recent studies of growth rates in extant coralline sponges suggest that the chaetetid bed of this study represents a minimum of 10,000 to nearly 20,000 years of deposition, and the largest individual chaetetid in this bed may have lived over 3,000 years. The relatively thin transitional bed between the underlying phylloid algal limestone and the chaetetid bed represents several hundred years of deposition. The limestone bed overlying the chaetetid bed contains a few chaetetids that may have lived up to 400–800 years, and it contains evidence of a tidal cycle of strong and weak tides.

The aim of this study was to determine whether biotic associations of Pennsylvanian-Permian brachiopods and bivalves from the northern Midcontinent differ in their degree of recurrence through time. The study interval includes 2.5 Myr that can be divided into 5 full and 2 partial composite depositional sequences separated by subaerial unconformities. These stratigraphic packages represent replicate natural experiments in establishing the benthic marine ecosystem of the basin. Based on cluster and ordination analyses, two discrete biofacies can be recognized—one dominated by brachiopods and the other by bivalves. Within each of these, environmental gradients can be recognized. The brachiopod gradient is interpreted to reflect the degree of water-column oxygenation, whereas the bivalve gradient is interpreted to reflect the transition from restricted to open-marine conditions. Comparison of measured recurrence with randomized data indicates that the ecological segregation of the two biofacies is maintained to a significant degree through the succession of depositional sequences in the study interval. In contrast, the gradients within each biofacies, although recognizable, are not maintained rigidly from sequence to sequence. There is also no significant difference in gradient recurrence between the two biofacies. These results imply that there is no need to call upon strong interspecific interactions to maintain the structure of these paleocommunities through time.

The enigmatic concretionary exposures that typify the Chañares Formation (Ladinian, northwestern Argentina) long have defied precise paleoenvironmental characterization. Recent work indicates that the formation accumulated in an alluvial-to-lacustrine setting within an active rift basin that received sedimentary detritus from surrounding highlands, as well as copious amounts of volcanic ash. Ash- flow sheets were emplaced presumably as secondary mass flows on alluvial surfaces characterized by small fluvial channels and shallow lakes. Thin bentonite beds intercalated in the Chañares Formation indicate that ash also accumulated via direct airfall, although this mode of emplacement accounts for a very small fraction of the overall section. A shift to widespread lacustrine deposition is recorded by the superjacent Los Rastros Formation, which preserves at least six shallowing-upward hemicycles, five of which commenced amidst explosive volcanic activity as evidenced by intercalated bentonite beds.

Volcanism played an important role in the generation and preservation of the Chañares Formation's exceptional tetrapod fossil record. This is especially true of the classic Los Chañares locality, where more than 100 individuals representing a diverse array of taxa (archosaurs, cynodonts, dicynodonts) are entombed in volcanogenic concretions with matrices of relic glass shards diagenetically replaced by calcite. Taphonomic attributes of the Los Chañares locality are consistent with the scenario of mass mortality, and several clues hint at the nature of the event. The killing agent was lethal to a variety of taxa, killed both adults and juveniles, and led to the concentration of taxa that under normal circumstances would tend to dissociate, such as carnivores and their potential prey. It also produced a counterintuitive bias against the preservation of large-bodied taxa, which may have been largely unsusceptible to the death event, or perhaps were excluded from the Los Chañares death assemblage via post-mortem sorting. The spatial arrangement of skeletal material in a small sample of concretions is consistent with the stranding of tetrapod carcasses along a strandline, and it is feasible that volcanism led to catastrophic flooding of the landscape via damming and/or diversion of local drainages. Uncompacted skeletal elements and relic outlines of glass shards indicate that carbonate concretions formed shortly after skeletal material was buried in reworked volcanic ash. The microbial decay of organic matter presumably catalyzed concretion diagenesis. There is no indication that bone hydroxyapatite diffused into the entombing glassy matrix and contributed to concretion formation. Bones entombed within early diagenetic concretions were safeguarded from subsequent destructive pedogenic and/or diagenetic processes, and were incorporated in exquisite quality into the fossil record.

Bone bed 43 is one of at least eight paucispecific Centrosaurus bone beds located in the Dinosaur Park Formation (Upper Campanian) in Dinosaur Provincial Park, Alberta, Canada. It long has been used as a case example for evidence of herding and social behavior in dinosaurs, but a detailed analysis of the site has not been presented until this study. The bone bed is dominated by the disarticulated, mostly fragmentary and slightly abraded remains of Centrosaurus apertus, with minor occurrences of other taxa, notably teeth from the large tyrannosaurid Albertosaurus libratus. Fossils occur in a stacked to amalgamated succession of lag deposits, deposited and reworked at the erosional base of a paleochannel. The most parsomonious scenerio suggests that Centrosaurus material represents part of a large aggregation of animals (possibly numbering in the thousands) that died by drowning on the alluvial plain. Disarticulation occurred at a point upriver from the bone-bed site. Scavenging by theropods, primarily Albertosaurus, at or near the original site of death is suggested by the high number of shed theropod teeth. A subsequent event prior to fossilisation moved the material to its present location removing many juvenile-sized and hydrodynamically light elements from the original death assemblage. Evidence for distinct size classes amongst the preserved elements is not supported by the data, but the size range of elements preserved are representative of living individuals that would have ranged from small juveniles to mature adults. The large data base of specimens from bone bed 43 allows for the illustration of the ontogenetic changes that occurred in the diagnostic cranial elements of Centrosaurus.

The extinction of the Morozovella velascoensis lineage, a group of planktonic foraminifera that dominated tropical assemblages for ∼6.3 m.y., is investigated using an upper Paleocene/lower Eocene section from the central Pacific Ocean (ODP Site 865). Uppermost stratigraphic occurrences of the lineage consist solely of diminutive M. edgari, a species roughly half the size of its ancestor, M. velascoensis. Eigenshape analysis indicates that adult specimens of M. edgari are morphologically similar to small, presumably juvenile, forms of M. velascoensis. The overall stratigraphic succession, where the uppermost occurrences of a lineage are represented by relict populations of minute, juvenilized forms, is consistent with a process called “terminal progenesis.” Various lines of evidence indicate that stress-induced size reduction foreshadowed the extinction of other planktonic foraminiferal lineages as well.

The ecological cause(s) for the extinction of ancestral M. velascoensis is unclear. Stable isotopic evidence for a progressive deterioration of algal symbiosis was not detected. Specifically, none of the individually-analyzed shells of M. velascoensis were depleted significantly in ¹³C, nor was there a decrease in the covariance of the δ¹³C/size relationship.

Planktonic foraminiferal δ¹⁸O values exhibit a subtle increase over the stratigraphic interval in which the M. edgari extinction is recorded. This inferred tropical cooling appears to be correlative with terrestrial records of cooling from the North American continental interior and northwestern Europe. Thus, it is postulated that climatic variation during the earliest Eocene (∼54.02Ma) played a significant role in shaping biodiversity in the pelagic realm, sealing the doom of the declining M. velascoensis lineage.