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.

link.

Pleistocene Megafauna Extinctions Were Caused by BOTH Humans AND Climate Change?

Giant Ice Age species including elephant-sized sloths and powerful sabre-toothed cats that once roamed the windswept plains of Patagonia, southern South America, were finally felled by a perfect storm of a rapidly warming climate and humans, a new study has shown.

Research led by the Australian Centre for Ancient DNA (ACAD) at the University of Adelaide, published today in Science Advances, has revealed that it was only when the climate warmed, long after humans first arrived in Patagonia, did the megafauna suddenly die off around 12,300 years ago.

The timing and cause of rapid extinctions of the megafauna has remained a mystery for centuries.

"Patagonia turns out to be the Rosetta Stone - it shows that human colonisation didn't immediately result in extinctions, but only as long as it stayed cold," says study leader Professor Alan Cooper, ACAD Director. "Instead, more than 1000 years of human occupation passed before a rapid warming event occurred, and then the megafauna were extinct within a hundred years."

link.

Greatest Megafauna Mammal Extinctions in Europe Began 3,000 Years Ago

Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene

Authors:

Crees et al

Abstract:

The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18 700 mammalian zooarchaeological records for the last 11 700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of ‘static’ past baselines to inform current-day environmental management and restoration.

End of all Things #1: a Mass Extinction Aggregation Post

Ediacaran/Cambrian Extinction:

Were the Ediacaran's wiped out, in part and the Cambrian Explosion initiated by greatly increased UV radiation?

Permian Triassic Mass Extinction:

The Permian Triassic boundary has been geochronologically located in the Spanish Pyrenees and produced an interesting and diverse fauna from the early Triassic.

The early Triassic locales of the Persian Gulf show evidence of repeated and sustained conditions like during the mass extinction itself.

Cretaceous-Paleogene (KT) Mass Extinction:

Another extraordinary claim that the KT/K-Pg mass extinction was caused by dark matter has been made.

Sixth Mass Extinction:

The carbon dates in North America appear to match well with the Human Overkill Hypothesis for the reason why the megafauna (mammoths, sloths, dire wolves, etc) went extinct.

What were the implications of the loss of large Pleistocene carnivores on the ecosystem?

Or for that matter for the impact of the loss of ALL the missing megafauna on the ecosystem?  Or more specifically on the forests?  Was the impact uniform or variable on the ecosystems of North and South America?

What were the changes on the nutrient cycle with the extinctions taking place?

Or!  Gasp!  The lack of mammoths farts on the atmosphere?

Or in the sea coast, what about the impacts of the extinction of the stellar's sea cow?

The data strongly supports the extinction of Australia's giant bird, Genyornis, as being caused by humans.

In fact, multiple sources of data suggest humanity was the cause of the extinctions in the Sahul (greater Australia).

META:

The proposed planet 9, proposed by Caltech astronomers, is unlikely to have anything to do with the mass extinctions on Earth.  Even so, if it pans out, for historical reasons, I hope they name the new planet 'Nemesis.'

The World May ALREADY Have a Mass Extinction Fossil Record in the Holocene

Rarity in mass extinctions and the future of ecosystems

Authors:

Hull et al

Abstract:

The fossil record provides striking case studies of biodiversity loss and global ecosystem upheaval. Because of this, many studies have sought to assess the magnitude of the current biodiversity crisis relative to past crises—a task greatly complicated by the need to extrapolate extinction rates. Here we challenge this approach by showing that the rarity of previously abundant taxa may be more important than extinction in the cascade of events leading to global changes in the biosphere. Mass rarity may provide the most robust measure of our current biodiversity crisis relative to those past, and new insights into the dynamics of mass extinction.

A Study of Modern African Fauna and the Ecological Implications for the Megafaunal Extinctions Elsewhere

A continent-wide assessment of the form and intensity of large mammal herbivory in Africa

Authors:

Hempson et al

Abstract:

Megafaunal extinctions and a lack of suitable remote sensing technology impede our understanding of both the ecological legacy and current impacts of large mammal herbivores in the Earth system. To address this, we reconstructed the form and intensity of herbivory pressure across sub-Saharan Africa ~1000 years ago. Specifically, we modeled and mapped species-level biomass for 92 large mammal herbivores using census data, species distributions, and environmental covariates. Trait-based classifications of these species into herbivore functional types, and analyses of their biomass surfaces, reveal four ecologically distinct continental-scale herbivory regimes, characterized by internally similar forms and intensities of herbivory pressure. Associations between herbivory regimes, fire prevalence, soil nutrient status, and rainfall provide important insights into African ecology and pave the way for integrating herbivores into global-scale studies.

Academic Bun Fight: the Pleistocene/Holocene Boundary and the Younger Dryas Impact Hypothesis

Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

Authors:

Kennett et al

Abstract:

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835–12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

That was really bad science

Problematic dating of claimed Younger Dryas boundary impact proxies

Author:

Holliday

Extract:

The PNAS paper by Kennett et al. (1) uses statistical methods in an attempt to improve the geochronological control for purported Younger Dryas boundary (YDB) impact proxies. The underpinning data for these analyses are problematic, however, as discussed by Meltzer et al. (2) and Holliday et al. (3). Several examples illustrate the problems. At Barber Creek the YDB zone is at ∼100 cm below the surface, but in situ wood charcoal dated to 10,500 ± 50 14C y B.P. (∼12.5 k cal yrs) is documented below 100 cm (3). The large SD for the modeled age of the YDB here (1) (12,865 ± 535 cal yrs) easily accommodates the high-precision date on the charcoal from below the spherule zone. At Blackville the sediments dated by optically stimulated luminescence are mixed and thus the dates cannot be considered reliable (3). The supposed impact proxies at Bull Creek are from 307- to 312-cm depth (3). The radiocarbon date of ∼12,960 cal yrs is from 298 to 307 cm and is a bulk sample on soil organic matter, thus representing a mean residence time for the soil carbon. Impact proxies are, therefore, older than ∼12,960 y by some unknown amount; they are also found in abundance in strata less than 3,000 y old. The Usselo soil in northwest Europe spans ∼1,400 y based on ∼50 radiocarbon ages, dating primarily to the Allerød and into the YD (2).

Thbbbbbppppt:

Reply to Holliday and Boslough et al.: Synchroneity of widespread Bayesian-modeled ages supports Younger Dryas impact hypothesis

Authors:

Kennett et al

Extract:

Holliday (1) rejects age-depth models for the Younger Dryas boundary layer (YDB) in Kennett et al. (2), claiming that they are incorrect for several reasons, including age reversals, high age uncertainties, and use of optically stimulated luminescence (OSL) dating. These same claims previously were presented in Meltzer et al. (3) and were discussed and refuted in Kennett et al. (2). These criticisms apply to nearly all dated archaeological and geological sequences, including the Odessa meteorite impact crater, where paradoxically, Holliday et al. (4) modeled an impact age using OSL dating (greater than 70% of dates used) with large uncertainties (to greater than 6,000 y) and age reversals (greatre than 40% of dates are reversals). Thus, Holliday (1) argues against a practice that he and many other researchers have used and continue to use today. In an ideal world, all dates would be in perfect chronological order with high accuracy and certainty, but such scenarios are rarely possible (2). It is because of such dating difficulties that Bayesian analysis is a powerful chronological tool, and is rapidly becoming the archaeological standard.

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.

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.

Pleistocene/Holocene Megafaunal Extinction has Significantly Altered Inland Nutrient Transport

Global nutrient transport in a world of giants

Authors:

Doughty et al

Abstract:

The past was a world of giants, with abundant whales in the sea and large animals roaming the land. However, that world came to an end following massive late-Quaternary megafauna extinctions on land and widespread population reductions in great whale populations over the past few centuries. These losses are likely to have had important consequences for broad-scale nutrient cycling, because recent literature suggests that large animals disproportionately drive nutrient movement. We estimate that the capacity of animals to move nutrients away from concentration patches has decreased to about 8% of the preextinction value on land and about 5% of historic values in oceans. For phosphorus (P), a key nutrient, upward movement in the ocean by marine mammals is about 23% of its former capacity (previously about 340 million kg of P per year). Movements by seabirds and anadromous fish provide important transfer of nutrients from the sea to land, totalling ∼150 million kg of P per year globally in the past, a transfer that has declined to less than 4% of this value as a result of the decimation of seabird colonies and anadromous fish populations. We propose that in the past, marine mammals, seabirds, anadromous fish, and terrestrial animals likely formed an interlinked system recycling nutrients from the ocean depths to the continental interiors, with marine mammals moving nutrients from the deep sea to surface waters, seabirds and anadromous fish moving nutrients from the ocean to land, and large animals moving nutrients away from hotspots into the continental interior.

pop sci write up.

Large Pleistocene Carnivores had a Huge Impact on the Ecology

The impact of large terrestrial carnivores on Pleistocene ecosystems

Authors:

Van Valkenburgh et al

Abstract:

Large mammalian terrestrial herbivores, such as elephants, have dramatic effects on the ecosystems they inhabit and at high population densities their environmental impacts can be devastating. Pleistocene terrestrial ecosystems included a much greater diversity of megaherbivores (e.g., mammoths, mastodons, giant ground sloths) and thus a greater potential for widespread habitat degradation if population sizes were not limited. Nevertheless, based on modern observations, it is generally believed that populations of megaherbivores (>800 kg) are largely immune to the effects of predation and this perception has been extended into the Pleistocene. However, as shown here, the species richness of big carnivores was greater in the Pleistocene and many of them were significantly larger than their modern counterparts. Fossil evidence suggests that interspecific competition among carnivores was relatively intense and reveals that some individuals specialized in consuming megaherbivores. To estimate the potential impact of Pleistocene large carnivores, we use both historic and modern data on predator–prey body mass relationships to predict size ranges of their typical and maximum prey when hunting as individuals and in groups. These prey size ranges are then compared with estimates of juvenile and subadult proboscidean body sizes derived from extant elephant growth data. Young proboscideans at their most vulnerable age fall within the predicted prey size ranges of many of the Pleistocene carnivores. Predation on juveniles can have a greater impact on megaherbivores because of their long interbirth intervals, and consequently, we argue that Pleistocene carnivores had the capacity to, and likely did, limit megaherbivore population sizes.

Radiocarbon Dating Further Supports Human Overkill Hypothesis

Radiocarbon analysis of the decline and extinction of large mammals in the Americas lends support to the idea that hunting by humans led to the animals' demise -- and backs the generally accepted understanding of when humans arrived in, and how they colonized, the Western Hemisphere.

Those findings by University of Wyoming researchers are reported this week in an article published in the Proceedings of the National Academy of Sciences, a major scientific journal. The study was conducted by Professor Todd Surovell and graduate student Spencer Pelton in UW's Department of Anthropology; Professor Richard Anderson-Sprecher in the Department of Statistics; and Assistant Professor Adam Myers in the Department of Physics and Astronomy.

Their work supports a hypothesis forwarded in 1973 by well-known geoscientist Paul Martin that the chronology of the extinction of animals such as mammoths, mastodons, camels, horses and ground sloths in the Americas could be used to map the spread of humans through the New World.

"The heavy ecological footprint of human societies throughout prehistory is becoming increasingly apparent through a variety of environmental (indicators) independent of the archeological record," the researchers wrote. "Past human societies have disrupted ecological communities in dramatic ways for many tens, if not hundreds of thousands, of years."

The study involved compiling radiocarbon dates from fossils of now-extinct animals from North and South America, and looking at how those dates correspond with initial evidence of human colonization. The researchers found that, as Martin predicted, decline and extinction of the large mammals began between 13,300-15,000 years ago in Alaska and areas near the Bering Strait; between 12,900-13,200 years ago in the contiguous United States; and between 12,600-13,900 years ago in South America.

That supports the generally accepted understanding of how humans colonized the Americas: first, that they crossed from Siberia to Alaska across a Bering Strait land bridge; and then that they moved southward across North America and into South America. Hunting of the native large mammals is thought to have fueled rapid human population growth and expansion.

A number of hypotheses have been forwarded to explain the extinction of those animals. The "overkill hypothesis" connects their demise directly to overhunting by humans, and that is supported by the north-to-south extinction trend observed in the new study.

link.

paper link.

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."

link.

Pleistocene Quaternary Megafaunal Communities Became More Vulnerable After Human Arrival

Pleistocene megafaunal interaction networks became more vulnerable after human arrival

Authors:

Pires et al

Abstract:

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions.

A Finer Resolution Timeline for the South American Megafauna Component of the Sixth Mass Extinction

Megafauna Extinction in South America: A new chronology for the Argentine Pampas

Authors:

Prado et al

Abstract:

The megafauna extinction in South America was one of the most profound events, with the loss of 50 genera (~ 83%). Three orders disappeared (Notoungulata, Proboscidea, Litopterna), as did all large xenarthrans, but how this fits into global extinction is uncertain, mainly due to the lack of chronological resolution. In recent years there has been an increase in the number of radiocarbon dating at archaeological and paleontological sites, but this information varies greatly from area to area in South America, and few data can be considered to constitute a taxon-date.

The timing of the late Pleistocene extinction in the Pampas is poorly established. Most taxa only appear in the biostratigraphic context and many reported 14C dates do not meet rigorous criteria for accepting dates, including reports suggesting survival of megafauna into the Holocene. In the present paper, we evaluate the published radiocarbon dates in the pampas and present 20 new radiocarbon dates for paleontological sites in order to establish a more accurate “extinction window” for the key taxa. These new dates are sufficiently robust to assess correspondences among last-appearance records of megafauna, first-appearance records of humans, and the Younger Dryas to Holocene climatic transition in the Argentine Pampas. These results highlight the need for greater effort in taxa selection for dating.

Impacts of Human Colonization of Pleistocene Quaternary Sahul

The process, biotic impact, and global implications of the human colonization of Sahul about 47,000 years ago

Authors:

O’Connell et al

Abstract:

Comprehensive review of archaeological data shows that Sahul (Pleistocene Australia-New Guinea) was first occupied by humans ca. 47 ka (47,000 years ago); evidence for earlier arrival is weak. Colonizing populations remained low – perhaps two orders of magnitude below those estimated at European contact – for many millennia, and were long restricted to relatively favorable habitats. Though human arrival coincided with changes in native flora and fauna, these were mainly the products of climatic factors, not human interference. The genetic makeup of founding populations and their arrival date are consistent with the Late Dispersal Model of anatomically modern humans beyond SW Asia, beginning ca. 50 ka. Early Dispersal Models (120-70 ka) are not refuted, but draw no support from the Sahul record as currently understood.

15 Sites are Considered Undisputed Examples of Clovis Era Human Predation of Megafauna

Revisiting Paleoindian Exploitation of Extinct North American Mammals

Authors:

Grayson et al

Abstract:

In 2002, we assessed all sites known to us that had been suggested to provide evidence for the association of Clovis-era archaeological material with the remains of extinct Pleistocene mammals in North America. We concluded that, of the 76 sites we assessed, 14 provided compelling evidence for human involvement in the death and/or dismemberment of such mammals. Of these sites, 12 involved mammoth (Mammuthus), the remaining two mastodon (Mammut). Here, we update that assessment. We examine Clovis-era, and earlier, sites reported since 2002, as well as sites examined previously but for which additional information has become available. Our assessment leads us to exclude Hebior (Wisconsin) from the list of accepted sites, and to add El Fin del Mundo (Sonora) and Wally’s Beach (Alberta). There are now 15 sites on our list, providing what we find to be compelling evidence for human involvement in the death and/or dismemberment of five genera of now-extinct late Pleistocene mammals: Equus, Camelops, Cuvieronius, Mammut, and Mammuthus. As in 2002, however, we note this is a small fraction of the 37 genera that disappeared at the end of the Pleistocene, and for this and other reasons we remain highly skeptical that human overkill was responsible for their extinction.

Cause, Effect or Coincidence? Hydrological Cycle Changed at Pleistocene Quaternary Megafauna Extinction in Australia

Hydrological transformation coincided with megafaunal extinction in central Australia

Authors:

Cohen et al

Abstract:

Central to the debate over the extinction of many of Australia's last surviving megafauna is the question: Was climate changing significantly when humans arrived and megafauna went extinct? Here we present a new perspective on variations in climate and water resources over the last glacial cycle in arid Australia based on the study of the continent's largest lake basin and its tributaries. By dating paleoshorelines and river deposits in the Lake Eyre basin, we show that major hydrological change caused previously overflowing megalakes to enter a final and catastrophic drying phase at 48 ± 2 ka just as the giant bird, Genyornis newtoni, went extinct (50–45 ka). The disappearance of Genyornis and other megafauna has been previously attributed to "ecosystem collapse" coincident with the spread of fire-wielding humans. Our findings suggest a climate-driven hydrological transformation in the critical window of human arrival and megafaunal extinction, and the results call for a re-evaluation of a human-mediated cause for such extinctions in arid Australia.

The question becomes could people cause the hydrological change?  Fire was used extensively by the Aboriginals and that would have transformed things considerably.  Or did the climate change on its own and drive an extinction 30k years before the rest of the megafaunal extinctions?  Or was the arrival of humanity a coincidence?  or...?

Sixth Mass Extinction Academic Bun Fight: Tracking Ecological Change in Egypt Over 6k Years

Collapse of an ecological network in Ancient Egypt

Authors:

Yeakel et al

Abstract:

The dynamics of ecosystem collapse are fundamental to determining how and why biological communities change through time, as well as the potential effects of extinctions on ecosystems. Here, we integrate depictions of mammals from Egyptian antiquity with direct lines of paleontological and archeological evidence to infer local extinctions and community dynamics over a 6,000-y span. The unprecedented temporal resolution of this dataset enables examination of how the tandem effects of human population growth and climate change can disrupt mammalian communities. We show that the extinctions of mammals in Egypt were nonrandom and that destabilizing changes in community composition coincided with abrupt aridification events and the attendant collapses of some complex societies. We also show that the roles of species in a community can change over time and that persistence is predicted by measures of species sensitivity, a function of local dynamic stability. To our knowledge, our study is the first high-resolution analysis of the ecological impacts of environmental change on predator–prey networks over millennial timescales and sheds light on the historical events that have shaped modern animal communities.

Retort:

Mammalian extinction in ancient Egypt, similarities with the southern Levant

Authors:

Bar-Oz et al

Exert:

Yeakel et al. (1) find that wild mammal extinction in ancient Egypt during the Holocene was nonrandom and coincided with abrupt climatic changes and a local cultural collapse. The authors provide compelling evidence that the deterioration of the natural Egyptian ecosystem gradually progressed during the Holocene. The extinction patterns provided vividly show that decreasing predator and prey (ungulates) diversity mirror increased desertification, human population growth, and political instability. We see strong ecological logic in Yeakel et al.’s (1) scenario and point to the advantages of conducting detailed comparisons of local extinction data to illuminate particularities and to better fine-tune broader hypotheses concerning Holocene extinctions

Second Retort:

Ancient Egypt’s fluctuating fauna: Ecological events or cultural constructs?

Author:

Evans

Exert:

Yeakel et al. present an innovative examination of Egypt’s ecological history (1), in which they rely upon paleontological evidence and artistic representations of animals to reconstruct patterns of species extinctions over six millennia. Focusing on ungulates and their mammalian predators, and drawing upon mammalogist Dale Osborn’s 1998 volume, The Mammals of Ancient Egypt (2), Yeakel et al. (1) report dramatic changes in predator–prey ratios corresponding to periods in which Egypt may have experienced extreme aridification.

Yeakel et al.’s (1) efforts to link science and the humanities are valuable; indeed, the abundant depictions of animals found in ancient Egyptian cultural remains, especially in detailed tomb paintings, offer a ready source of material that can be approached in this way (3). However, scientific evaluation must be balanced with a clear understanding of Egyptian art, which was heavily constrained by both graphic and cultural rules (4).

Response:

Reply to Evans and Bar-Oz et al.: Recovering ecological pattern and process in Ancient Egypt

Authors:

Yeakel et al

Exert:

Our recent paper used artistic depictions of animals and fossil evidence to examine the community-level effects of local extinction events over 6,000 y of Egyptian history (1). We found that local extinctions were nonrandom, that changes to community structure (quantified by the species predator/prey ratio) seemed to correspond to local aridification pulses, and that the decline in species richness throughout Egyptian history resulted in a drop in dynamic stability because of the elimination of smaller-bodied herbivores.