Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.

Conservation of species and ecosystems is increasingly difficult because anthropogenic impacts are pervasive and accelerating. Under this rapid global change, maximizing conservation success requires a paradigm shift from maintaining ecosystems in idealized past states toward facilitating their adaptive and functional capacities, even as species ebb and flow individually. Developing effective strategies under this new paradigm will require deeper understanding of the long-term dynamics that govern ecosystem persistence and reconciliation of conflicts among approaches to conserving historical versus novel ecosystems. Integrating emerging information from conservation biology, paleobiology, and the Earth sciences is an important step forward on the path to success. Maintaining nature in all its aspects will also entail immediately addressing the overarching threats of growing human population, overconsumption, pollution, and climate change.

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South America lost around 52 genera of mammals during a worldwide event known as the Late Quaternary Extinction episode. More than 80% of South American mammals weighing > 44 kg succumbed. Analysis of the megafaunal extinction chronology in relation to human arrival and major climate changes have revealed slightly different extinction patterns in different eco‐regions of the continent, highlighting the importance of detailed regional analysis in order to understand how the possible drivers of extinction operated. Here we present an analysis of the megafaunal extinction in the Última Esperanza (UE) area of southwestern Patagonia, Chile. We have compiled a comprehensive chronology of megafaunal extinctions and earliest human occupation between 18–7 cal ka BP, based on radiocarbon dates from published literature. We calculated confidence intervals using the GRIWM method to estimate the times of human arrival and megafaunal local extinctions, and then compared these events to the timing of major climate and vegetation changes, fire frequency increase, and the Reclús volcanic eruption. Our results suggest that a combination of human impacts and climate–vegetation change drove megafaunal extinctions in the UE area, with the balance of factors being taxon specific; the volcanic eruption does not seem to have exacerbated extinctions. Competition between humans and mega‐carnivores seems to be the most plausible cause for the extinction of the mega‐carnivores. Coexistence of humans with extinct horses, extinct camels, and mylodonts for several thousand years rules out a scenario of blitzkrieg overkill of megafauna by humans. The transition of vegetation from cold grasslands to Nothofagus forests corresponds with the disappearance of Hippidion saldiasi and Lama cf. owenii. The later full establishment of Nothofagus forests and an increasing fire frequency coincided with the disappearance of mylodonts. A climate‐driven reduction of open environments plausibly reduced herbivore's populations making them susceptible to local extinction.

Loss of megafauna, an aspect of defaunation, can precipitate many ecological changes over short time scales. We examine whether megafauna loss can also explain features of lasting ecological state shifts that occurred as the Pleistocene gave way to the Holocene. We compare ecological impacts of late-Quaternary megafauna extinction in five American regions: southwestern Patagonia, the Pampas, northeastern United States, northwestern United States, and Beringia. We find that major ecological state shifts were consistent with expectations of defaunation in North American sites but not in South American ones. The differential responses highlight two factors necessary for defaunation to trigger lasting ecological state shifts discernable in the fossil record: (i) lost megafauna need to have been effective ecosystem engineers, like proboscideans; and (ii) historical contingencies must have provided the ecosystem with plant species likely to respond to megafaunal loss. These findings help in identifying modern ecosystems that are most at risk for disappearing should current pressures on the ecosystems' large animals continue and highlight the critical role of both individual species ecologies and ecosystem context in predicting the lasting impacts of defaunation currently underway. megafauna | extinction | Quaternary | North America | South America D efaunation is occurring at a rapid pace presently (1-3).Losses are particularly severe for megafauna (1) (considered here as animals with an average body size ≥44 kg), whose removal can trigger the following: changes in vegetation structure and species composition; reductions in environmental heterogeneity, species richness, evenness, seed dispersal, nutrient cycling and distribution, and ecosystem services; coextinction of dependent species; and increases in disease-transmitting organisms (1, 4-14) and fire frequency and/or intensity (15-17).Most work on defaunation has been in contemporary ecosystems. Much less is known about how it manifests over millennial time scales. A natural experiment to assess lasting effects of megafauna loss is provided by the extinctions of late-Quaternary megafauna in the Americas, part of global-scale ecological state shift (18), during which about half of the world's large-bodied mammal species (19,20) disappeared. In North America, ∼60 megafaunal species died out, with the youngest occurrences of dated species typically falling between ∼13,000 and 11,000 y ago (19). In South America, ∼66 species were lost over a longer time span (21-23).With a few important exceptions (6, 17, 24-29), the major changes in vegetation and mammalian community structure that accompanied Quaternary extinctions have been interpreted as responses to changing climate (17-19, 21, 23, 25-27, 29-35). Here, we build on recent work of paleoecologists (17,25,28,29,32,36) and ecologists (1, 3-7, 9, 10, 15, 16, 37) ApproachThe late-Quaternary impact of losing 70-80% of the megafauna genera in the Americas (19) would be expected to trigger biotic transitions that would b...

Human impacts have left and are leaving distinctive imprints in the geological record. Here we show that in North America, the human-caused changes evident in the mammalian fossil record since c. 14,000 years ago are as pronounced as earlier faunal changes that subdivide Cenozoic epochs into the North American Land Mammal Ages (NALMAs). Accordingly, we define two new North American Land Mammal Ages, the Santarosean and the Saintagustinean, which subdivide Holocene time and complete a biochronologic system that has proven extremely useful in dating terrestrial deposits and in revealing major features of faunal change through the past 66 million years. The new NALMAs highlight human-induced changes to the Earth system, and inform the debate on whether or not defining an Anthropocene epoch is justified, and if so, when it began.

Understanding extinction drivers in a human-dominated world is necessary to preserve biodiversity. We provide an overview of Quaternary extinctions and compare mammalian extinction events on continents and islands after human arrival in system-specific prehistoric and historic contexts. We highlight the role of body size and life-history traits in these extinctions. We find a significant size-bias except for extinctions on small islands in historic times. Using phylogenetic regression and classification trees, we find that while life-history traits are poor predictors of historic extinctions, those associated with difficulty in responding quickly to perturbations, such as small litter size, are good predictors of prehistoric extinctions. Our results are consistent with the idea that prehistoric and historic extinctions form a single continuing event with the same likely primary driver, humans, but the diversity of impacts and affected faunas is much greater in historic extinctions.

Biogenic habitat can structure marine communities by serving as both a complex substrate and food source for adult and recruiting organisms. We investigated the role played by biogenic habitats (Mytilus edulis and Crepidula spp. beds) in influencing the subtidal distribution (kilometers scale) of the mud crab Dyspanopeus sayi in Narragansett Bay, New England (USA). In field surveys, D. sayi were 1 to 2 orders of magnitude more abundant on M. edulis and Crepidula spp. beds than at sites lacking these habitats, and a laboratory experiment confirmed that D. sayi will consume both of these species. In a field-based, substrate-choice experiment, modules containing rocks had higher D. sayi recruit densities than those containing M. edulis or Crepidula spp. This indicates that structural complexity of those biogenic substrates, rather than their availability as prey, is the primary factor influencing patterns of D. sayi recruitment. Densities of recruit and adult D. sayi on recruitment modules were higher at bare sites than at sites with biogenic habitat, where modules represented islands of structure in otherwise simple habitat. This suggests small-scale habitat selection by D. sayi. Adult D. sayi occupied modules indiscriminately at bare sites, but exhibited a preference for modules containing mussels at sites with biogenic habitats. The importance of structure for adult and recruit D. sayi, reinforced by adults' response to prey presence, likely explains this organism's association with hard, biogenic habitats in the studied system.