What Drove the Giant Marsupial Predators (sparassodontans) of South America to Extinction?

Extinction of South American sparassodontans (Metatheria): environmental fluctuations or complex ecological processes?

Authors:

Lópes-Aguirre et al

Abstract:

Sparassodontans are a diverse but now extinct group of metatherians that were apex predators in South America during most of the Cenozoic. Studying their decline has been controversial mainly due to the scarcity of the fossil record, and different methodological approaches have led to contradictory hypotheses. In an effort to explore questions about their extinction, we developed a novel multi-model statistical approach to analyse all of the currently available data at a continental scale. Using multiple regression analysis and new advances in beta diversity analysis, we used all currently available fossil data at a continental scale to test four competing hypotheses to account for the decline of sparassodontans: competition with placental carnivorans, competition with avian phorusrhacids, non-competitive ecological interactions, and environmental fluctuations. Our results show that the sparassodontan extinction was a gradual process with species disappearing throughout the Cenozoic. Multiple regression analysis supported non-competitive ecological interactions as the best extinction model. Native South American ungulates, African migrants (caviomorph rodents and platyrrhine primates) and didelphimorphians were the groups with the highest statistical significance. Sparassodontan beta diversity increased between South American Land Mammal Ages after the Paleocene–Eocene boundary. Our results demonstrate that ecological modelling techniques illuminate aspects of extinction processes whilst mitigating the limitations of the fossil record. Our study suggests that non-competitive ecological interactions could have been the main driver for sparassodontan extinction rather than, as commonly assumed, a result of competition and/or abiotic fluctuations.

St Paul Mammoths Went Extinct 5,600 Years ago

While the Minoan culture on Crete was just beginning, woolly mammoths were disappearing from St. Paul Island, Alaska, according to an international team of scientists who have dated this extinction to 5,600 years ago.

"It's amazing that everything turned out so precisely with dating of extinction at 5,600 plus or minus 100 years," said Russell Graham, professor of geosciences, Penn State."

St. Paul Island lies about 400 miles north of the Aleutian Islands and was part of the Bering Land Bridge before sea level rose when the last glacial period ended. Previous researchers radiocarbon-dated remains of five mammoths to about 6,480 years ago, but there was no way to know if these were the last five animals.

The researchers used a variety of proxies to date the demise of the mammoths on the island. Proxies are things in the environment that can be used to independently document the presence of an organism, even though they are not parts of it. In this study, three different spores from fungi that grow on large animal dung were extracted from lake cores and used to determine when the mammoths were no longer on the island. Proxies in sediments from cores from a lake near the cave were used to determine the time of the demise of the mammoth population.

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Ichthyosaurs Went Extinct due to Extreme Global Warming

Why ichthyosaurs — marine Mesozoic reptiles — disappeared before the dinosaur extinction has remained a mystery. New research suggests they may have gone extinct stepwise, during one of the most extreme greenhouse periods in the history of complex life-forms.

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Megalodon Went Extinct due to Competition and Prey Scarcity

It lived millions of years ago and was three times as large as the great white shark: the megalodon. So far its extinction has been explained with the onset of an ice age. However, researchers at the University of Zurich have now come to the conclusion that responsibility for the decline of the monster shark lays not with the climate, but with other species.

Is there anyone out there who doesn't know Jaws, the film about the great white shark and the devastation it wreaked? But there have been even bigger and more dangerous sharks in the past: The largest shark in the history of the planet, Carcharocles megalodon, lived between 23 million and 2.6 million years ago, reaching body lengths of up to 18 meters and probably feeding on marine mammals. Then it became extinct. In the past, climate changes have generally been blamed for its disappearance. Now, for the first time, researchers from the University of Zurich have examined the geographical distribution of the megalodon over time and arrived at the following conclusion: The giant shark became extinct because the diversity of its prey decreased and new predators appeared as competitors.

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Does Climate Change Threaten the Primates?

This is the battle that nobody wins. According to a new study, climate change will adversely affect every single primate species on Earth. That’s every ape, monkey, gibbon, lemur and loris, no matter how super or strong they might be.

The study, published in the International Journal of Primatology, reveals that primate habitats will, on average, feel the pinch of a warming world 10 percent more severely than non-primate habitats. Not only will temperatures change, so will rainfall, with some species experiencing 7.5 percent more or less precipitation per degree C of global warming.

This is troubling news for the world’s primates, as many species rely on narrow habitats or have extremely specialized diets. Some primates only eat one or two things, so their food and habitats are particularly sensitive to disruption. Many primates are already endangered by habitat loss, hunting, or the illegal pet trade, so this additional threat could push several species over the brink.

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How Many Dinosaur Species Were There?

How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model

Authors:

Starrfelt et al

Abstract:

The fossil record is a rich source of information about biological diversity in the past. However, the fossil record is not only incomplete but has also inherent biases due to geological, physical, chemical and biological factors. Our knowledge of past life is also biased because of differences in academic and amateur interests and sampling efforts. As a result, not all individuals or species that lived in the past are equally likely to be discovered at any point in time or space. To reconstruct temporal dynamics of diversity using the fossil record, biased sampling must be explicitly taken into account. Here, we introduce an approach that uses the variation in the number of times each species is observed in the fossil record to estimate both sampling bias and true richness. We term our technique TRiPS (True Richness estimated using a Poisson Sampling model) and explore its robustness to violation of its assumptions via simulations. We then venture to estimate sampling bias and absolute species richness of dinosaurs in the geological stages of the Mesozoic. Using TRiPS, we estimate that 1936 (1543–2468) species of dinosaurs roamed the Earth during the Mesozoic. We also present improved estimates of species richness trajectories of the three major dinosaur clades: the sauropodomorphs, ornithischians and theropods, casting doubt on the Jurassic–Cretaceous extinction event and demonstrating that all dinosaur groups are subject to considerable sampling bias throughout the Mesozoic.

Why did the Stegosaurs go Extinct in the Cretaceous?

Without doubt, stegosaurs were adversely affected by new conditions in the Cretaceous. Available data suggests that, right after their Jurassic heyday, stegosaurs suffered a loss of diversity similar to what sauropods endured - 57-89%. After this first setback, they were further battered, by Barremian time c. 127 Ma. Plated dinosaurs apparently vanished everywhere, except in Asia, where their last occurrences are dated Aptian-Albian. By mid K at the latest, Stegosauria was entirely gone. What caused plated beasts to wane and die out?

In their 2009 paper, Diversity patterns amongst herbivorous dinosaurs and plants during the Cretaceous, Butler et al. note an apparent correlation between the waning of certain plants (cycads, cycadophytes and bennattitalles) and the demise of stegosaurs. Citing earlier works suggesting an ecological association of plated dinosaurs and cycads (and close relatives) they suggest the disappearance of stegosaurs, from the start of the early Cretaceous to its end, mirrored the decline of such vegetation.

With their narrow snouts, stegosaurs do appear to have been specialized feeders, essentially limited to a specific type of plant. Ergo, they may have been vulnerable to loss of such flora. The available evidence however, suggests other factors may have been equally important, if not more so.

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What Environmental Factor Wiped out so Many Crocodyliforms Across the Jurassic-Cretaceous Boundary?

Environmental drivers of crocodyliform extinction across the Jurassic/Cretaceous transition

Authors:

Tennant et al

Abstract:

Crocodyliforms have a much richer evolutionary history than represented by their extant descendants, including several independent marine and terrestrial radiations during the Mesozoic. However, heterogeneous sampling of their fossil record has obscured their macroevolutionary dynamics, and obfuscated attempts to reconcile external drivers of these patterns. Here, we present a comprehensive analysis of crocodyliform biodiversity through the Jurassic/Cretaceous (J/K) transition using subsampling and phylogenetic approaches and apply maximum-likelihood methods to fit models of extrinsic variables to assess what mediated these patterns. A combination of fluctuations in sea-level and episodic perturbations to the carbon and sulfur cycles was primarily responsible for both a marine and non-marine crocodyliform biodiversity decline through the J/K boundary, primarily documented in Europe. This was tracked by high extinction rates at the boundary and suppressed origination rates throughout the Early Cretaceous. The diversification of Eusuchia and Notosuchia likely emanated from the easing of ecological pressure resulting from the biodiversity decline, which also culminated in the extinction of the marine thalattosuchians in the late Early Cretaceous. Through application of rigorous techniques for estimating biodiversity, our results demonstrate that it is possible to tease apart the complex array of controls on diversification patterns in major archosaur clades.

pop sci link.

Ichthyosaurs Went Extinct During Cenomanian Cretaceous due to Inability to Adapt to Radical Climate Change

Ichthyosaurs - shark-like marine reptiles from the time of dinosaurs - were driven to extinction by intense climate change and their own failure to evolve quickly enough, according to new research by an international team of scientists.

The study provides an explanation for one of the longest-standing enigmas in palaeobiology: how and why ichthyosaurs died out. Unlike other marine reptile groups, ichthyosaurs disappeared tens of millions of years before the end-Cretaceous extinction (65 million years ago) that marked the end for dinosaurs and the beginning of the age of mammals.

The research is published in the journal Nature Communications.

First author Dr Valentin Fischer, of the University of Liège, Belgium, and the University of Oxford, UK, said: "We analysed the extinction of this crucial marine group thoroughly for the first time. We compared the diversity of ichthyosaurs with the geological record of global change, emphasising the dynamics of these datasets.

"Ichthyosaurs were actually well diversified during the last chapter of their reign, with several species, body shapes and ecological niches present. However, their evolution was much slower than earlier in their history. Additionally, they were seemingly negatively affected by the profound global changes going on during the Cretaceous, as their extinction rate correlates with environmental volatility."

Causes of extinctions - including the demise of the ichthyosaurs, or 'sea dragons' - have often remained elusive and conjectural, particularly when they cannot be linked to an obvious geological or geochemical event such as a large meteorite or massive volcanic eruption. Ichthyosaurs were regarded as undiversified for a prolonged period before their extinction, and their dying out has previously been linked to minor events including increased competition with other marine predators and a decline in their assumed principal source of food.

However, using a battery of cutting-edge techniques to quantify ancient biodiversity and its fluctuations, the team was able to reconstruct the evolution of the ichthyosaurs during the last 120 million years of their lifetime and assess the causes of their extinction. The researchers - comprising Belgian, British, French and Russian scientists - demonstrated that before their extinction, ichthyosaurs were in fact highly diverse, both in terms of body shape and ecological role.

A two-phase event then suppressed their ecological diversity and wiped out the group at the beginning of the Late Cretaceous period, about 100 million years ago. At that time, the Earth's poles were essentially ice-free, and sea levels were much higher than today. Analyses revealed that this two-phase extinction can be associated both with reduced evolutionary rates (a failure to evolve novel body plans for a prolonged period) and intense climate change (strong variations in sea surface temperatures and sea levels).

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High Extinction Rates Trigger Diversification in Amniotes

Elevated Extinction Rates as a Trigger for Diversification Rate Shifts: Early Amniotes as a Case Study

Authors:

Brocklehurst et al

Abstract:

Tree shape analyses are frequently used to infer the location of shifts in diversification rate within the Tree of Life. Many studies have supported a causal relationship between shifts and temporally coincident events such as the evolution of “key innovations”. However, the evidence for such relationships is circumstantial. We investigated patterns of diversification during the early evolution of Amniota from the Carboniferous to the Triassic, subjecting a new supertree to analyses of tree balance in order to infer the timing and location of diversification shifts. We investigated how uneven origination and extinction rates drive diversification shifts, and use two case studies (herbivory and an aquatic lifestyle) to examine whether shifts tend to be contemporaneous with evolutionary novelties. Shifts within amniotes tend to occur during periods of elevated extinction, with mass extinctions coinciding with numerous and larger shifts. Diversification shifts occurring in clades that possess evolutionary innovations do not coincide temporally with the appearance of those innovations, but are instead deferred to periods of high extinction rate. We suggest such innovations did not cause increases in the rate of cladogenesis, but allowed clades to survive extinction events. We highlight the importance of examining general patterns of diversification before interpreting specific shifts.

Most Climate Change Vulnerable Marine Fauna Often NOT in Fastest Warming Locales

Thermal biases and vulnerability to warming in the world’s marine fauna

Authors:

Stuart-Smith et al

Abstract:

A critical assumption underlying projections of biodiversity change associated with global warming is that ecological communities comprise balanced mixes of warm-affinity and cool-affinity species which, on average, approximate local environmental temperatures. Nevertheless, here we find that most shallow water marine species occupy broad thermal distributions that are aggregated in either temperate or tropical realms. These distributional trends result in ocean-scale spatial thermal biases, where communities are dominated by species with warmer or cooler affinity than local environmental temperatures. We use community-level thermal deviations from local temperatures as a form of sensitivity to warming, and combine these with projected ocean warming data to predict warming-related loss of species from present-day communities over the next century. Large changes in local species composition appear likely, and proximity to thermal limits, as inferred from present-day species’ distributional ranges, outweighs spatial variation in warming rates in contributing to predicted rates of local species loss.

Animal Populations do NOT Respond Uniformly to Climate Change

Geographical variation in species' population responses to changes in temperature and precipitation

Authors:

Pearce-Higgins et al

Abstract:

Despite increasing concerns about the vulnerability of species' populations to climate change, there has been little overall synthesis of how individual population responses to variation in climate differ between taxa, with trophic level or geographically. To address this, we extracted data from 132 long-term (greater than or equal to 20 years) studies of population responses to temperature and precipitation covering 236 animal and plant species across terrestrial and freshwater habitats. Our results identify likely geographical differences in the effects of climate change on populations and communities in line with macroecological theory. Temperature tended to have a greater overall impact on populations than precipitation, although the effects of increased precipitation varied strongly with latitude, being most positive at low latitudes. Population responses to increased temperature were generally positive, but did not vary significantly with latitude. Studies reporting significant climatic trends through time tended to show more negative effects of temperature and more positive effects of precipitation upon populations than other studies, indicating climate change has already impacted many populations. Most studies of climate change impacts on biodiversity have focused on temperature and are from middle to high northern latitudes. Our results suggest their findings may be less applicable to low latitudes.

Pleistocene Quaternary Giant Mammals Became Extra Vulernable to Extinction due to Habitat Fragmentation?

Life and extinction of megafauna in the ice-age Arctic

Authors:

Mann et al

Abstract:

Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes.

A More Precise Method for Determining the Speciation and Extinction Rates

A more precise speciation and extinction rate estimator

Author:

Alroy

Abstract:

A new turnover rate metric is introduced that combines simplicity and precision. Like the related three-timer and gap-filler equations, it involves first identifying a cohort of taxa sampled in the time interval preceding the one of interest (call the intervals i 0 and i 1 ). Taxa sampled in i 0 and i 1 are two-timers (t 2 ); those sampled in i 0 and i 2 but not i 1 are part-timers (p); and taxa sampled only in either i 1 , i 2 , or i 3 are newly notated here as either s 1 , s 2 , or s 3 . The gap-filler extinction proportion can be reformulated as (s 1 −s 3 )/(t 2 +p). The method proposed here is to substitute s 3 with the second-highest of the three counts when the expected ordering s 1 ≥s 2 ≥s 3 is violated. In simulation, this new estimator yields values that are highly correlated with those produced by the gap-filler equation but more precise. In particular, it rarely produces highly negative values even when sample sizes are quite small. It is mildly upwards biased when sampling is extremely poor and turnover rates are extremely low, but it is otherwise highly accurate. Examples of Phanerozoic extinction rates for four major marine invertebrate groups are given to illustrate the method’s improved precision. Based on the results, the procedure is recommended for general use.

The Americas Loss of Megafauna Caused Significant Ecological Shifts

Variable impact of late-Quaternary megafaunal extinction in causing ecological state shifts in North and South America

Authors:

Barnosky et al

Abstract:

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.

Extinction of Pleistocene Megafauna Allowed Forests to Expand

Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation

Authors:

Bakker et al

Abstract:

Until recently in Earth history, very large herbivores (mammoths, ground sloths, diprotodons, and many others) occurred in most of the World’s terrestrial ecosystems, but the majority have gone extinct as part of the late-Quaternary extinctions. How has this large-scale removal of large herbivores affected landscape structure and ecosystem functioning? In this review, we combine paleo-data with information from modern exclosure experiments to assess the impact of large herbivores (and their disappearance) on woody species, landscape structure, and ecosystem functions. In modern landscapes characterized by intense herbivory, woody plants can persist by defending themselves or by association with defended species, can persist by growing in places that are physically inaccessible to herbivores, or can persist where high predator activity limits foraging by herbivores. At the landscape scale, different herbivore densities and assemblages may result in dynamic gradients in woody cover. The late-Quaternary extinctions were natural experiments in large-herbivore removal; the paleoecological record shows evidence of widespread changes in community composition and ecosystem structure and function, consistent with modern exclosure experiments. We propose a conceptual framework that describes the impact of large herbivores on woody plant abundance mediated by herbivore diversity and density, predicting that herbivore suppression of woody plants is strongest where herbivore diversity is high. We conclude that the decline of large herbivores induces major alterations in landscape structure and ecosystem functions.

pop sci write up. 2nd one.

Holy Mammoth Farts! Estimating the Atmospheric Methane Budget With Global PreExtinction Megafauna

Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget

Authors:

Smith et al

Abstract:

Globally, large-bodied wild mammals are in peril. Because “megamammals” have a disproportionate influence on vegetation, trophic interactions, and ecosystem function, declining populations are of considerable conservation concern. However, this is not new; trophic downgrading occurred in the past, including the African rinderpest epizootic of the 1890s, the massive Great Plains bison kill-off in the 1860s, and the terminal Pleistocene extinction of megafauna. Examining the consequences of these earlier events yields insights into contemporary ecosystem function. Here, we focus on changes in methane emissions, produced as a byproduct of enteric fermentation by herbivores. Although methane is ∼200 times less abundant than carbon dioxide in the atmosphere, the greater efficiency of methane in trapping radiation leads to a significant role in radiative forcing of climate. Using global datasets of late Quaternary mammals, domestic livestock, and human population from the United Nations as well as literature sources, we develop a series of allometric regressions relating mammal body mass to population density and CH4 production, which allows estimation of methane production by wild and domestic herbivores for each historic or ancient time period. We find the extirpation of megaherbivores reduced global enteric emissions between 2.2–69.6 Tg CH4 y−1 during the various time periods, representing a decrease of 0.8–34.8% of the overall inputs to tropospheric input. Our analyses suggest that large-bodied mammals have a greater influence on methane emissions than previously appreciated and, further, that changes in the source pool from herbivores can influence global biogeochemical cycles and, potentially, climate.

Nearly Wiping out Sea Otters Helped Drive Stellar Sea Cows to Extinction

Sea otters, kelp forests, and the extinction of Steller’s sea cow

Authors:

Estes et al

Abstract:

The late Pleistocene extinction of so many large-bodied vertebrates has been variously attributed to two general causes: rapid climate change and the effects of humans as they spread from the Old World to previously uninhabited continents and islands. Many large-bodied vertebrates, especially large apex predators, maintain their associated ecosystems through top-down forcing processes, especially trophic cascades, and megaherbivores also exert an array of strong indirect effects on their communities. Thus, a third possibility for at least some of the Pleistocene extinctions is that they occurred through habitat changes resulting from the loss of these other keystone species. Here we explore the plausibility of this mechanism, using information on sea otters, kelp forests, and the recent extinction of Steller's sea cows from the Commander Islands. Large numbers of sea cows occurred in the Commander Islands at the time of their discovery by Europeans in 1741. Although extinction of these last remaining sea cows during early years of the Pacific maritime fur trade is widely thought to be a consequence of direct human overkill, we show that it is also a probable consequence of the loss of sea otters and the co-occurring loss of kelp, even if not a single sea cow had been killed directly by humans. This example supports the hypothesis that the directly caused extinctions of a few large vertebrates in the late Pleistocene may have resulted in the coextinction of numerous other species.

Common Lizards Face Threat From Climate Change

While there is no doubt that climate change is affecting many organisms, some species might be more sensitive than others. Reptiles, whose body temperature depends directly on environmental temperature, may be particularly vulnerable. Scientists have now shown experimentally that lizards cope very poorly with the climate predicted for the year 2100.

In a new study, publishing in the Open Access journal PLOS Biology on October 26th, Elvire Bestion, Julien Cote and colleagues examined the consequences of a 2°C warmer climate on the persistence of populations of common lizards (Zootoca vivipara), a widespread European reptile. Their results show that many common lizard populations could disappear rapidly as a consequence of such warmer temperatures.

"Breed fast and die young" seems to be the new mantra of common lizards in the face of climate change; it is also the conclusion reached by researchers from the Station d'écologie expérimentale du CNRS à Moulis (SEEM) and the Laboratoire Evolution et Diversité Biologique (EDB, CNRS/Université Toulouse 3 Paul Sabatier/ENFA) who studied this small European reptile species.

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Giant Monitor Lizards Survived in Australia at Least Until Humans Arrived

As if life wasn't hard enough during the last Ice Age, research led by the University of Queensland has found Australia's first human inhabitants had to contend with giant killer lizards.

UQ vertebrate palaeoecologist Dr Gilbert Price said researchers working in Central Queensland were amazed when they unearthed the first evidence that Australia's early human inhabitants and giant apex predator lizards had overlapped.

"Our jaws dropped when we found a tiny fossil from a giant lizard during a two metre deep excavation in one of the Capricorn Caves, near Rockhampton," Dr Price said.

"The one-centimetre bone, an osteoderm, came from under the lizard's skin and is the youngest record of a giant lizard on the entire continent."

Dr Price and his colleagues used radiocarbon and uranium thorium techniques to date the bone as about 50,000 years old, coinciding with the arrival of Australia's Aboriginal inhabitants.

"We can't tell if the bone is from a Komodo dragon -- which once roamed Australia -- or an even bigger species like the extinct Megalania monitor lizard, which weighed about 500kg and grew up to six metres long," Dr Price said.

"The find is pretty significant, especially for the timeframe that it dates."

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