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There is evidence that human influence may be forcing the global ecosystem towards a rapid, irreversible, planetary-scale shift into a state unknown in human experience. Forecasting the biological impact of global change Most forecasts of how the biosphere will change in response to human activity are rooted in projecting trajectories. Such models tend not anticipate critical transitions or tipping points, although recent work indicates a high probability of those taking place. And, at a local scale, ecosystems are known to shift abruptly between states when critical thresholds are passed. These authors review the evidence from across ecology and palaeontology that such a transition is being approached on the scale of the entire biosphere. They go on to suggest how biological forecasting might be improved to allow us to detect early warning signs of critical transitions on a global, as well as local, scale. Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds. Here we review evidence that the global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence. The plausibility of a planetary-scale ‘tipping point’ highlights the need to improve biological forecasting by detecting early warning signs of critical transitions on global as well as local scales, and by detecting feedbacks that promote such transitions. It is also necessary to address root causes of how humans are forcing biological changes.

Adaptive radiation of Mesozoic-era multituberculate mammals began at least 20 million years before the extinction of non-avian dinosaurs and continued across the Cretaceous–Paleogene boundary—probably as a result of dietary expansion towards herbivory during the ecological rise of angiosperms—and is supported by increases in generic richness and disparity in dental complexity and body size. Mammals in the age of dinosaurs Conventional wisdom has it that when dinosaurs ruled Earth, mammals were small shrew-like creatures living on the margins. Not so — the rodent-like multituberculates were a group of very successful mammals that prospered under the dinosaurs and survived the mass extinction at the end of the Cretaceous period (66 million years ago) to become extinct only in the Eocene epoch (35 million years ago). An innovative method of analysing three-dimensional fossil-tooth surfaces shows that the ecological diversity of multituberculates actually increased during the Cretaceous, some 20 million years or so before the dinosaurs' demise. Many new multituberculate species seem to have evolved to eat flowering plants, which were also thriving at the time. The fact that multituberculate radiation continued across the Cretaceous–Palaeogene boundary suggests that their food resources were relatively unaffected by this mass-extinction event. The Cretaceous–Paleogene mass extinction approximately 66 million years ago is conventionally thought to have been a turning point in mammalian evolution 1 , 2 . Prior to that event and for the first two-thirds of their evolutionary history, mammals were mostly confined to roles as generalized, small-bodied, nocturnal insectivores 3 , presumably under selection pressures from dinosaurs 4 . Release from these pressures, by extinction of non-avian dinosaurs at the Cretaceous–Paleogene boundary, triggered ecological diversification of mammals 1 , 2 . Although recent individual fossil discoveries have shown that some mammalian lineages diversified ecologically during the Mesozoic era 5 , comprehensive ecological analyses of mammalian groups crossing the Cretaceous–Paleogene boundary are lacking. Such analyses are needed because diversification analyses of living taxa 6 , 7 allow only indirect inferences of past ecosystems. Here we show that in arguably the most evolutionarily successful clade of Mesozoic mammals, the Multituberculata, an adaptive radiation began at least 20 million years before the extinction of non-avian dinosaurs and continued across the Cretaceous–Paleogene boundary. Disparity in dental complexity, which relates to the range of diets, rose sharply in step with generic richness and disparity in body size. Moreover, maximum dental complexity and body size demonstrate an adaptive shift towards increased herbivory. This dietary expansion tracked the ecological rise of angiosperms 8 and suggests that the resources that were available to multituberculates were relatively unaffected by the Cretaceous–Paleogene mass extinction. Taken together, our results indicate that mammals were able to take advantage of new ecological opportunities in the Mesozoic and that at least some of these opportunities persisted through the Cretaceous–Paleogene mass extinction. Similar broad-scale ecomorphological inventories of other radiations may help to constrain the possible causes of mass extinctions 9 , 10 .

Cutting edge palaeontology Palaeontologists can reconstruct the diets of extinct animals as a pointer to their lifestyles by painstaking comparison of fossil teeth with those of comparable living animals . A new method, based on a 'virtual' teeth database compiled from 441 digital images of teeth from 81 carnivore and rodent species, is less time consuming and may be more accurate. In the example of the carnivores and rodents, the dental comparisons show that the surface complexity of tooth crowns directly reflects the food that is eaten. The sheer variety of different diets adopted by living species means that the new method is particularly useful for fossils with no close analogues among living species. The study of mammalian evolution depends greatly on understanding the evolution of teeth and the relationship of tooth shape to diet. Links between gross tooth shape, function and diet have been proposed since antiquity, stretching from Aristotle 1 to Cuvier 2 , Owen 3 and Osborn 4 . So far, however, the possibilities for exhaustive, quantitative comparisons between greatly different tooth shapes have been limited. Cat teeth and mouse teeth, for example, are fundamentally distinct in shape and structure as a result of independent evolutionary change over tens of millions of years 5 . There is difficulty in establishing homology between their tooth components or in summarizing their tooth shapes, yet both carnivorans and rodents possess a comparable spectrum of dietary specializations from animals to plants. Here we introduce homology-free techniques 6 , 7 , 8 to measure the phenotypic complexity of the three-dimensional shape of tooth crowns. In our geographic information systems (GIS) analysis of 441 teeth from 81 species of carnivorans and rodents, we show that the surface complexity of tooth crowns directly reflects the foods they consume. Moreover, the absolute values of dental complexity for individual dietary classes correspond between carnivorans and rodents, illustrating a high-level similarity between overall tooth shapes despite a lack of low-level similarity of specific tooth components. These results suggest that scale-independent forces have determined the high-level dental shape in lineages that are widely divergent in size, ecology and life history. This link between diet and phenotype will be useful for inferring the ecology of extinct species and illustrates the potential of fast-throughput, high-level analysis of the phenotype.

The extinction of dinosaurs at the Cretaceous/Paleogene (K/Pg) boundary was the seminal event that opened the door for the subsequent diversification of terrestrial mammals. Our compilation of maximum body size at the ordinal level by sub-epoch shows a near-exponential increase after the K/Pg. On each continent, the maximum size of mammals leveled off after 40 million years ago and thereafter remained approximately constant. There was remarkable congruence in the rate, trajectory, and upper limit across continents, orders, and trophic guilds, despite differences in geological and climatic history, turnover of lineages, and ecological variation. Our analysis suggests that although the primary driver for the evolution of giant mammals was diversification to fill ecological niches, environmental temperature and land area may have ultimately constrained the maximum size achieved.

Venta Micena is an area containing several palaeontological sites marking the beginning of the Calabrian stage (Early Pleistocene). The richness of the fossil accumulation including species of Asian, African and European origin, makes Venta Micena a key site for the the palaeoecological and palaeoenvironmental study of southern Europe during the Early Pleistocene. Thus, research has been focused on Venta Micena 3, which was originally interpreted as a single palaeosurface associated with a marshy context, in which most of the fauna was accumulated by Pachycrocuta brevirostris . Recent excavations have unearthed a new site, Venta Micena 4, located in the same stratigraphic unit (Unit C) and in close proximity to Venta Micena 3. Here we show the first analyses regarding the taphonomic and spatial nature of this new site, defining two stratigraphic boundaries corresponding to two different depositional events. Furthermore, the taphonomic analyses of fossil remains seem to indicate a different accumulative agent than Pachycrocuta , thus adding more complexity to the palaeobiological interpretation of the Venta Micena area. These results contribute to the discussion of traditional interpretations made from Venta Micena 3.

Despite much interest in the ecology and origins of the extensive grassland ecosystems of the modern world, the biogeographic relationships of savannah palaeobiomes of Africa, India and mainland Eurasia have remained unclear. Here we assemble the most recent data from the Neogene mammal fossil record in order to map the biogeographic development of Old World mammalian faunas in relation to palaeoenvironmental conditions. Using genus-level faunal similarity and mean ordinated hypsodonty in combination with palaeoclimate modelling, we show that savannah faunas developed as a spatially and temporally connected entity that we term the Old World savannah palaeobiome. The Old World savannah palaeobiome flourished under the influence of middle and late Miocene global cooling and aridification, which resulted in the spread of open habitats across vast continental areas. This extensive biome fragmented into Eurasian and African branches due to increased aridification in North Africa and Arabia during the late Miocene. Its Eurasian branches had mostly disappeared by the end of the Miocene, but the African branch survived and eventually contributed to the development of Plio–Pleistocene African savannah faunas, including their early hominins. The modern African savannah fauna is thus a continuation of the extensive Old World savannah palaeobiome. Savannah faunas developed in a spatially and temporally connected palaeobiome that flourished in the mid Miocene, before fragmenting into Eurasian and African branches in the late Miocene.

The Late Miocene development of faunas and environments in western Eurasia is well known, but the climatic and environmental processes that controlled its details are incompletely understood. Here we map the rise and fall of the classic Pikermian fossil mammal chronofauna between 12 and 4.2 Ma, using genus-level faunal similarity between localities. To directly relate land mammal community evolution to environmental change, we use the hypsodonty paleoprecipitation proxy and paleoclimate modeling. The geographic distribution of faunal similarity and paleoprecipitation in successive timeslices shows the development of the open biome that favored the evolution and spread of the open-habitat adapted large mammal lineages. In the climate model run, this corresponds to a decrease in precipitation over its core area south of the Paratethys Sea. The process began in the latest Middle Miocene and climaxed in the medial Late Miocene, about 7-8 million years ago. The geographic range of the Pikermian chronofauna contracted in the latest Miocene, a time of increasing summer drought and regional differentiation of habitats in Eastern Europe and Southwestern Asia. Its demise at the Miocene-Pliocene boundary coincides with an environmental reversal toward increased humidity and forestation, changes inevitably detrimental to open-adapted, wide-ranging large mammals.

Do large mammals evolve faster than small mammals or vice versa? Because the answer to this question contributes to our understanding of how life-history affects long-term and large-scale evolutionary patterns, and how microevolutionary rates scale-up to macroevolutionary rates, it has received much attention. A satisfactory or consistent answer to this question is lacking, however. Here, we take a fresh look at this problem using a large fossil dataset of mammals from the Neogene of the Old World (NOW). Controlling for sampling biases, calculating per capita origination and extinction rates of boundary-crossers and estimating survival probabilities using capture-mark-recapture (CMR) methods, we found the recurring pattern that large mammal genera and species have higher origination and extinction rates, and therefore shorter durations. This pattern is surprising in the light of molecular studies, which show that smaller animals, with their shorter generation times and higher metabolic rates, have greater absolute rates of evolution. However, higher molecular rates do not necessarily translate to higher taxon rates because both the biotic and physical environments interact with phenotypic variation, in part fueled by mutations, to affect origination and extinction rates. To explain the observed pattern, we propose that the ability to evolve and maintain behavior such as hibernation, torpor and burrowing, collectively termed \"sleep-or-hide\" (SLOH) behavior, serves as a means of environmental buffering during expected and unexpected environmental change. SLOH behavior is more common in some small mammals, and, as a result, SLOH small mammals contribute to higher average survivorship and lower origination probabilities among small mammals.

How fast can a mammal evolve from the size of a mouse to the size of an elephant? Achieving such a large transformation calls for major biological reorganization. Thus, the speed at which this occurs has important implications for extensive faunal changes, including adaptive radiations and recovery from mass extinctions. To quantify the pace of large-scale evolution we developed a metric, clade maximum rate, which represents the maximum evolutionary rate of a trait within a clade. We applied this metric to body mass evolution in mammals over the last 70 million years, during which multiple large evolutionary transitions occurred in oceans and on continents and islands. Our computations suggest that it took a minimum of 1.6, 5.1, and 10 million generations for terrestrial mammal mass to increase 100-, and 1,000-, and 5,000-fold, respectively. Values for whales were down to half the length (i.e., 1.1, 3, and 5 million generations), perhaps due to the reduced mechanical constraints of living in an aquatic environment. When differences in generation time are considered, we find an exponential increase in maximum mammal body mass during the 35 million years following the Cretaceous–Paleogene (K–Pg) extinction event. Our results also indicate a basic asymmetry in macroevolution: very large decreases (such as extreme insular dwarfism) can happen at more than 10 times the rate of increases. Our findings allow more rigorous comparisons of microevolutionary and macroevolutionary patterns and processes.

Ouranopithecus turkae, from the late Miocene of Çorakyerler in Central Anatolia, is considered one of the last known occurrences of great ape in the eastern Mediterranean. The Çorakyerler fauna has previously been correlated with MN 11 to early MN 12 on the basis of biochronology, and its faunal composition has been found to contrast with those from contemporaneous sites. In this paper, we present the magnetostratigraphy of the Çorakyerler site and an expanded interpretation of its paleobiogeographical and paleoecological contexts. The paleomagnetic results reveal two intervals of normal polarity and an intervening interval of reversed polarity in the main fossiliferous section. Of the three likely age correlations spanning 8.13–7.15 Ma (MN 11-MN 12), we favor correlation with chron 4n, with a possible age range of the fossiliferous deposit between 8.11 and 7.64 Ma (late MN 11). The geographic distribution of genus-level faunal similarity and mean hypsodonty show that Çorakyerler is a typical representative of the Pikermian chronofauna with a wide range of faunal similarity, including late Miocene localities from the eastern Mediterranean, eastern Asia, and eastern Africa. Lithological and sedimentological characteristics of the fossiliferous horizon, however, indicate a lacustrine depositional environment and relatively humid local conditions within the more arid regional context. This special setting could explain the unexpected occurrence of a hominid primate at Çorakyerler.