Vertebrate paleontologists have proposed a model for the terrestrial end-Permian event in the Karoo Basin, South Africa. The scenario envisions vegetational collapse that resulted in a phased extinction of vertebrate taxa in the uppermost Daptocephalus Assemblage Zone and overlying Lystrosaurus Assemblage Zone. These biodiversity patterns are placed into composite stratigraphic sections at key localities, several of which are in close spatial proximity. We present a stratigraphic framework at two of these localities, Old Lootsberg Pass and Tweefontein, physically correlated over ∼ 2 km distance into which new and previously reported fossils are placed.

Glossopterid-dominated megafloras occur in both the Daptocephalus and Lystrosaurus biozones, along with palynological assemblages. Katbergia, a burrow used by others as an indicator of the transition and post-transition interval, occurs in paleosols much lower in the upper Daptocephalus Assemblage Zone, along with various subhorizontal cylindrical structures interpreted as vertebrate burrows. New vertebrate specimens include: (1) a large skull of either Daptocephalus leoniceps or Dicynodon sp.; (2) a partial skull with large canine assignable to either Dicynodon, Daptocephalus, or Lystrosaurus mccaigi; (3) a Lystrosaurus canine in grayish-red siltstone; (4) a skull of Lystrosaurus murrayi; and (5) a non-diagnostic post-cranial skeleton of lystrosaurid affinity.

These fossils are combined with the published Karoo-vertebrate dataset to test the stratigraphic position of the Daptocephalus and Lystrosaurus Assemblage Zone boundary. We conclude that: (1) glossopterids in the Lystrosaurus Assemblage Zone indicate persistence of the clade past what is considered to be an extinction event; (2) the presence of palynomorphs known from recovery clades above the proposed vertebrate-biozone boundary indicate that these groups were present in the basin, but outside of the megafloral taphonomic window; (3) the position of the proposed vertebrate assemblage-zone boundary is stratigraphically inconsistent and varies in its reported stratigraphic position at a minimum of 25 m, and up to 70 m, across a distance of only ∼ 2 km; and (4) terrestrial ecosystem dynamics only can be assessed when a high resolution stratigraphic framework is developed into which biostratigraphic data are placed and, thereafter, patterns can be evaluated.

The vertebrate fauna from the lower Carnian Chañares Formation of Argentina is dominated by well-preserved small- and medium-bodied archosauriforms and therapsids. Here we report the discovery of a non-mammalian therapsid dicynodont (of greater than 20 cm skull length) that was found partially articulated within the floodplain deposit. Taphonomic analysis of this specimen reveals details of its paleobiology and taphonomic history, including the cause of death, exposure to predation and/or scavenging, subsequent subaerial decay, and final entombment. The specimen studied also allowed for the documentation of the activity of micro-organisms involved in decay processes during the biostratinomic stage (soft tissue decomposition on surface) and diagenetic stages (anaerobic decay). Our results indicate that despite bones being found in concretions the formation of calcareous concretions is not required for bone preservation. Consequently, this study highlights the role of volcanic ash in promoting bone preservation.

Corals formed at least 15 symbiotic associations in the Devonian. Tabulates formed symbiotic associations more often than rugose corals, with the largest number of different taxa involved in stromatoporoid-syringoporid and brachiopod-auloporid symbioses. Eight of fifteen symbiotic associations first appeared in the Devonian, all of which except for the crinoid-tabulate association went extinct by the end of the Devonian. The general increase in symbiotic interactions involving corals in the Devonian can be explained by the increase in number of coral taxa. The influence of Ordovician/Silurian and Frasnian/Famennian mass extinctions on coral symbiosis was different: the Ordovician/Silurian mass extinction did not terminate coral symbiosis, whereas the Frasnian/Famennian mass extinction almost entirely terminated symbiotic interactions between the corals and other invertebrates.

Fossils preserving the anatomy of soft tissues provide rare but essential evidence for the reconstruction of metazoan evolutionary history. Decay is inherent to the fossilization process and features may be distorted, displaced, or missing even in exceptionally preserved fossils, and non-anatomical artifacts may be introduced. Here we describe the results of experimental decay of the epibenthic actinian (sea anemone) Metridium senile and document serial changes in its morphology. Decay proceeded rapidly and followed a consistent, reproducible trajectory, which we divide into six stages; in the final stage, no anatomically illuminating information remained. The column, one of the most salient anatomical features of actinians, contracted near the time of death and changed shape dramatically thereafter. The tentacles decayed from their distal ends. Fibrous bundles representing the interior musculature were among the morphological features most resistant to degradation, and taphonomically induced transverse bands were also long lasting. These experimental results provide a semi-quantitative and predictive framework which can be applied to the interpretation of putative polypoid cnidarian organisms. Furthermore, this decay series shows that diploblast- and triploblast-grade fossils are unlikely to be confused and provides the means to evaluate the taxonomic validity of the long-standing assumption that many enigmatic soft-bodied Ediacaran and lower Cambrian taxa are of actinian grade.

Continental deposits of the middle Miocene Barstow Formation formed in an extensional basin of the Mojave region. Mammalian faunas of the type section in the Mud Hills, California, are the basis for defining the Barstovian North American Land Mammal Age. Prior mapping, lithostratigraphy, geochronology, and fossil collecting have established a structural, chronostratigraphic, and biostratigraphic framework for the Barstow Formation. Here, we analyze the sedimentary facies of the lithostratigraphic sequence, infer the major depositional environments, and assess controls on fossil preservation in relation to major facies. We recognize six major facies associations that represent alluvial fans, shallow or seasonal lakes, and channels and floodplains. The transition from older, fan-dominated to younger, floodplain-dominated environments reflects changes in tectonics, accommodation, drainage, and depositional settings during the formation and filling of the basin. Fossil-mammal concentrations are common in four facies associations. Body fossils are abundant in two facies associations that represent well-drained floodplains and spring-fed wetlands. Fossil concentrations are moderately abundant in facies associations that represent floodplains and channel deposits, and fossils are rare in facies associations that represent alluvial fans and lake margins. The highest frequency of fossil localities occurs in the facies associations representing both suitable life habitats and high preservation potential for terrestrial mammals.

Here we present the first use of calcareous microfossils to examine the late Quaternary paleoecology of the endorheic Pozuelos Basin (Argentina). Modern deposition in the basin centers on Laguna de los Pozuelos (LP), a shallow playa-lake that is fed by axial rivers and groundwater and dominantly accumulates siliciclastic sediments. Today, the distribution of limnocytherid and cypridoidean ostracodes across southern LP is strongly influenced by distance to the Río Cincel delta, whereas the northern end of the playa-lake is characterized by a paucity of ostracodes due to frequent sub-aerial exposure. Ten ostracode biofacies define a sediment core retrieved from LP, which reveal progressive changes in aquatic environments that varied in salinity, depth, and proximity to deltas over the late Pleistocene. Closed lakes occupied the basin from ∼ 37.6–30.7 ka, ∼ 28.0–25.0 ka, and ∼ 23.0–16.6 ka, whereas saline wetlands occurred when these lakes contracted. Extant LP has no analog in the late Pleistocene record; it formed after ∼ 7.2 ka, following a hiatus that removed the Pleistocene–Holocene transition. Paleoecological evidence indicates that the core site was influenced by deltaic inflows from the eastern basin margin until ∼ 24.3 ka, an area where today dry alluvial fans are found. Reorganization of the watershed by normal faulting, most likely at ∼ 18.0 ka, appears to have reduced the influence of these deltaic inflows. Extensional neotectonics, perhaps induced by incorporation of the Pozuelos Basin into the Andean hinterland, is a mechanism that along with tropical climate change is potentially important to water balance and ecology in high-altitude convergent orogenic basins.