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Studies on the effects of volcanic ash on fauna of the terrestrial realm have been numerous, however, this phenomenon has gone less well studied in the marine realm. Five localities within the Puerto Madryn Formation (Valdes Peninsula, Chubut Province, Argentina) were investigated in order to assess the effects of distal volcanic ash deposition on shallow marine communities during the middle Miocene (Tortonian). All five localities expose shallow marine deposits, and contain invertebrate fossils including abundant decapod crustaceans and bivalve mollusks. Sediments and fossils were analyzed using multiple geochemical and visual methods including scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), X-ray diffraction spectroscopy (XRD), petrographic microscopy, and reflected light microscopy. The sediments were found to uniformly contain a high percentage of very fine volcanic ash. Three previously unstudied localities including two paleosurfaces and a stratigraphic section which record a single mass mortality event were documented. Two paleosurfaces previously described by three of the authors (SC, RMF, CES) were revisited in order to assess the cause of death of the fossil assemblages at those sites. Although the field locality lies a minimum distance of 650 km from the Andean volcanic front, the effects of ash were nonetheless catastrophic; the crustaceans are interpreted to have been the victims of acute respiratory failure due to the introduction of volcanic ash to the branchial chamber.
The Waco Mammoth National Monument (WMNM) potentially represents the only recovered Columbian mammoth (Mammuthus columbi) herd to date, but the “herd” interpretation is dependent on the demographics of the accumulation as well as a catastrophic kill mechanism. The demographics are consistent with an extant elephant herd that is lacking only infants, and the generally accepted cause of death is a catastrophic flood and rapid burial based primarily on fossil articulation and associations with an ancient river channel and aquatic fauna. Herein we present new ichnological evidence of post-mortem biogenic bone modification contrary to a flood scenario with rapid burial. Traces on bone include branching furrows (Corrosichnia type), paired grooves (Machichnus regularis and M. bohemicus), arcuate grooves that penetrate the cortical material (Brutalichnus brutalis), roughly triangular punctures with jagged margins (Nihilichnus nihilicus), and hemispherical borings (Cubiculum isp.). The branching furrows are interpreted as root-dissolution features, whereas the remaining suite of traces demonstrate scavenging of the mammoths by rodents, carnivores, and hide beetles during a period of dry-decay and prolonged subaerial exposure. We propose that a drought scenario is a more plausible kill mechanism for this particular assemblage because: (1) a diminishing watering hole concentrating the local fauna explains the high taxonomic diversity; (2) migration to a distant water source explains the absence of M. columbi calves; and (3) a drought provides a parsimonious explanation for the site history in light of new observations regarding vertebrate and invertebrate scavenging. Under this scenario, the mammoths of WMNM represent at least one social group that perished during an anomalously dry season.
Predation is a key biotic interaction that shapes ecological communities. Defensive morphological traits are thought to improve prey survivorship, and knowing which traits aid survivorship is critical to understanding predator-prey dynamics and their impact on community composition. Paleontological studies that use optimal foraging theory and single species experiments suggest that shell size and thickness are traits that affect the outcome of mollusk drilling predation. We analyzed the effectiveness of these morphological traits using a tropical molluscan assemblage from the One Tree Reef lagoon (southern Great Barrier Reef, Australia). Shell mass, shape, thickness, and predation frequency were measured in five bivalve species (n = 804) constituting 80% of the predators' diet. Multiple regression determined that shell mass, shell thickness, and the interaction between the two were important predictors of predation. Drilling was more likely in thinner and larger individuals. However, support for the model that included species identity was markedly stronger, indicating that the morphological traits measured are not general predictors of predation across the five prey species we studied. That is, trait-only models are inadequate for explaining predator-prey dynamics at the community level. Alternatively, active behavioral defenses related to infaunality (like burrowing) appear to be stronger drivers of morphology in this system. Care should be taken when extrapolating results from experiments to communities or large temporal scales, as species with similar traits may not necessarily elicit the same response from predators.
Environmental changes since the late deglaciation are reconstructed from the sediment of Lake Hamoun. Lake Hamoun is located at the border of Iran and Afghanistan where inflowing rivers originate from the drainage basins of SW Hindu Kush Mountains and westernmost Himalaya. The lake has experienced a complex hydrological history during the late Quaternary due to climatic changes. Geochemical, sedimentological, and paleontological proxies as well as geomorphological data were used to investigate environmental changes of the lake. The results demonstrate that since the late glacial, the basin has directly and/or indirectly received its moisture from various climatic systems. During the early Holocene, both the Indian summer monsoon (ISM) and the mid-latitude westerlies (MLW) intensified and consequently the basin received higher precipitation. This interpretation is supported by higher content of total organic matter (mean: 8.2%), finer-grained sediments with low δ18O values (mean: -3.5‰), as well as rich fossil content. Lower organic matter content (< 5%), higher magnetic susceptibility values (5.8–10×10−4 SI unit), and coarser-grained sediments with no shell fragments support the dominance of an arid environment during the early-mid Holocene. The results of stable isotopes suggest weakening of ISM and intensification of MLW during the mid-late Holocene in the study area, when Bronze Age civilizations emerged in the Sistan Basin. In the late Holocene, lake levels experienced more severe fluctuations due to variations in the MLW. Shifts in settlement areas seen in the archaeological record may thus have been a response to climatic changes.