What killed the Pleistocene megafauna?

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Levantine overkill: 1.5 million years of hunting down the body size distribution

Multiple large-bodied species went extinct during the Pleistocene. Changing climates and/or human hunting are the main hypotheses used to explain these extinctions. We studied the causes of Pleistocene extinctions in the Southern Levant, and their subsequent effect on local hominin food spectra, by examining faunal remains in archaeological sites across the last 1.5 million years. We examined whether climate and climate changes, and/or human cultures, are associated with these declines. We recorded animal abundances published in the literature from 133 stratigraphic layers, across 58 Pleistocene and Early Holocene archaeological sites, in the Southern Levant. We used linear regressions and mixed models to assess the weighted mean mass of faunal assemblages through time and whether it was associated with temperature, paleorainfall, or paleoenvironment (C3 vs. C4 vegetation). We found that weighted mean body mass declined log-linearly through time. Mean hunted animal masses 10,500 years ago, were only 1.7% of those 1.5 million years ago. Neither body size at any period, nor size change from one layer to the next, were related to global temperature or to temperature changes. Throughout the Pleistocene, new human lineages hunted significantly smaller prey than the preceding ones. This suggests that humans extirpated megafauna throughout the Pleistocene, and when the largest species were depleted the next-largest were targeted. Technological advancements likely enabled subsequent human lineages to effectively hunt smaller prey replacing larger species that were hunted to extinction or until they became exceedingly rare.

www.sciencedirect.com/science/article/abs/pii/S0277379121005230

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The Equus subgenus Sussemionus survived until the late Holocene based on radiocarbon dating of a high quality genome.

elifesciences.org/articles/73346

There is increasing evidence for some Pleistocene megafauna surviving well into the Holocene in certain parts of the globe. So the question of “why did they die out at the end of the ice age?” is simply that they didn’t.

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Re-evaluating the evidence for late-surviving megafauna at Nombe rockshelter in the New Guinea highlands

The causes of the Late Pleistocene extinction of most larger-bodied animals on the Australian continent have long been controversial. This is due, in no small part, to inadequate knowledge of exactly when these species were lost from different ecosystems. The Nombe rockshelter in the highlands of Papua New Guinea is one of very few sites on Sahul with as-yet-unrefuted evidence for the survival of megafaunal species until more recently than 40 thousand years (ka) ago. However, our understanding of the age of this site has been based on radiocarbon dating. Here we present new U–Th ages on large marsupial specimens from the deposit and identify a range of postcranial elements to species that include the diprotodontid Hulitherium tomasettii, kangaroo Protemnodon tumbuna and thylacine Thylacinus cynocephalus. Direct U–Th ages of 27–22 ka ago on faunal remains of Protemnodon tumbuna and another large unidentified macropodid are consistent with the existing radiocarbon chronology, yet are minimum ages due to the potential for post-depositional uptake of 238U and stratigraphic reworking. Pollen analyses indicate perhumid, montane forests dominated by Nothofagus persisted, with minimal human disturbance from at least c.26–20 ka ago up to the terminal Pleistocene. Collagen fingerprinting (ZooMS) demonstrates the potential of protein-based identification of megafaunal remains at Nombe in the future. This study leaves open the possibility of extended coexistence between some megafaunal species in the montane rainforests of New Guinea and intermittently visiting groups of people, and underscores the need for further investigation of the Nombe deposit. Although preliminary, these findings reinforce the view that debates regarding megafaunal extinctions on Sahul require a greater appreciation of species-specific temporalities and the degrees of human impact on diverse habitats across the continent.

onlinelibrary.wiley.com/doi/10.1002/arco.5274

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This is huge. This recent work suggests that Australia's megafauna may have survived as recently as 25,000 years ago. Also, Denisovans may have been present at some point in Australia too.

theconversation.com/new-dates-suggest-oceanias-megafauna-lived-until-25-000-years-ago-implying-coexistence-with-people-for-40-000-years-191857

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Some interesting papers advocating for at least some role of hyperdisease in the megafaunal extinctions. To be honest, I didn't think there was any potential evidence for one or more hyperdiseases. Of course, this doesn't mean it was the only, or even primary, reason for extinction.

pubmed.ncbi.nlm.nih.gov/16953418/

pubmed.ncbi.nlm.nih.gov/11438894/

journals.sagepub.com/doi/abs/10.1177/0959683620981673?journalCode=hola

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On the timing of megafaunal extinction and associated floristic consequences in Australia through the lens of functional palaeoecology

The timing and cause of megafaunal extinctions are an enduring focus of research interest and debate. Despite the developments in the analysis of coprophilous fungal spores (CFS), the proxy for reconstructing past megaherbivore changes, the environmental consequences of this fauna loss remain understudied. This is partly due to the general obscurity of such a signal in pollen records, as well as limitations in disentangling human and extinction ecological impact, and the lack of spatial information of megafauna changes in site-level sedimentary records. In Australia, the debate centres on the possibility that habitat loss through climate change, vegetation-fire change, human intervention, or a combination of these factors led to the extinction of some large animals during the Late Pleistocene. Pollen and plant isotope studies have also demonstrated that vegetation-fire responses following the Late Pleistocene megafaunal extinctions were characterized by increased vegetation density and fire activity due to reduced grazing/browsing pressure. Here, we use a well-dated marine sedimentary core record from the Murray Darling Basin in southern Australia and apply palynological and functional palaeoecological approaches to reconstruct the Late Pleistocene megafaunal abundance changes, the timing and potential cause of extinction across the basin and investigate if extinction was associated with any signal of trait-based vegetation changes. We infer megafaunal abundance changes from the abundance of CFS and compare this with climatic proxies from the same core. We then link modern observations of fruit, seed and fire response traits of plant genera within the basin to the fossil pollen record to reconstruct palaeo vegetation community traits and determine if extinction was associated with any changes in plant community trait composition. Closely-spaced ¹⁴C dates obtained from planktonic foraminifera and δ¹⁸O tie points place a major decline in CFS, and thus the timing of extinction, within the basin at ∼43.3 ka. While climate-driven environmental changes largely controlled megafaunal presence, human arrival and frequent landscape burning are considered the most likely primary cause of extinction or, at the very least, megafauna decline in the Murray Darling Basin. We also found that the proposed period of megafaunal decline was also accompanied and followed by a decline in the prevalence of plants with larger seeds and fruits that were likely to have been once dispersed by megaherbivores. Our study supports the idea of a human-driven megafaunal extinction in mainland Australia and that the extinction caused changes in vegetation due to reduced plant dispersal and herbivory. However, high fire activity primarily linked to these vegetation changes was not observed, as humans were already practicing landscape burning before the period of megafaunal extinction and likely continued to do so afterward.

www.sciencedirect.com/science/article/pii/S0277379123003116

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Pre–Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift

INTRODUCTION
At the end of the Pleistocene, most of Earth’s large mammals (megafauna) became extinct. These extinctions occurred at different times globally, resulting in a drastic reorganization of terrestrial ecosystems. Despite decades of research on extinction causality, the relative importance of late-Quaternary climate changes and spreading human impacts have been difficult to disentangle because poor chronological resolution in the fossil record has precluded alignment of these rapidly occurring, tightly linked phenomena.

RATIONALE
The Rancho La Brea (RLB) locality in Southern California provides a unique opportunity to investigate decadal-scale changes in megafaunal populations and community composition across the latest Pleistocene. At this site, naturally occurring asphalt seeps entrapped and preserved the bones of hundreds, and in some cases thousands, of individuals from numerous megafaunal species across the last 50,000 years of the Pleistocene. Nearly all of these osteological specimens preserve original collagen, which permits precise radiocarbon dating analysis.

RESULTS
We obtained radiocarbon dates on 172 specimens from seven extinct and one extant species: Smilodon fatalis, Aenocyon dirus, Panthera atrox, Bison antiquus, Equus occidentalis, Paramylodon harlani, Camelops hesternus, and Canis latrans, spanning 15.6 to 10.0 thousand calendar years before present (ka). We used the resulting high-resolution chronology of entrapment at RLB to analyze population dynamics across this time interval and the timing of local disappearance for different taxa. To investigate the potential roles of late-Quaternary environmental change and human activities in driving the observed patterns, we compared our analyses of population structure and megafaunal extirpation against well-resolved regional and continental paleoclimatic proxies, vegetation records, and modeled human demographic growth. We used time-series modeling to investigate the dynamics of ecosystem change and evaluate causal relationships among these different phenomena.
Modeling of extinction timing using several methods established that all taxa except coyotes were extirpated from RLB by 12.9 ka, before the onset of the Younger Dryas and well before the continental extinction of North American megafauna. The disappearance of all taxa was synchronous except for camels and sloths, which disappeared a few hundred years earlier in concert with aridification and tree loss during the Bølling–Allerød. The simultaneous disappearance of Smilodon, Aenocyon, Panthera, Equus, and Bison antiquus coincided with a regional ecological state shift characterized by floral community reorganization and unprecedented fire activity. Time-series modeling strongly implicates humans as the primary cause of the state shift and resulting extinctions.

CONCLUSION
Our data document a transition from a postglacial megafaunal woodland to a human-mediated chaparral ecosystem in Southern California before the onset of the Younger Dryas. This transition began with gradual opening and drying of the landscape over two millennia, and terminated in an abrupt (300-year) regime shift characterized by the complete extirpation of megafauna and unprecedented fire activity. This state shift appears to have been triggered by human-ignited fires in an ecosystem stressed by rapid warming, a megadrought, and a millennial-scale trend toward the loss of large herbivores from the landscape. This event parallels processes occurring in Mediterranean ecosystems today.

www.science.org/doi/10.1126/science.abo3594

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Worldwide Late Pleistocene and Early Holocene population declines in extant megafauna are associated with Homo sapiens expansion rather than climate change

The worldwide extinction of megafauna during the Late Pleistocene and Early Holocene is evident from the fossil record, with dominant theories suggesting a climate, human or combined impact cause. Consequently, two disparate scenarios are possible for the surviving megafauna during this time period - they could have declined due to similar pressures, or increased in population size due to reductions in competition or other biotic pressures. We therefore infer population histories of 139 extant megafauna species using genomic data which reveal population declines in 91% of species throughout the Quaternary period, with larger species experiencing the strongest decreases. Declines become ubiquitous 32–76 kya across all landmasses, a pattern better explained by worldwide Homo sapiens expansion than by changes in climate. We estimate that, in consequence, total megafauna abundance, biomass, and energy turnover decreased by 92–95% over the past 50,000 years, implying major human-driven ecosystem restructuring at a global scale.

www.nature.com/articles/s41467-023-43426-5

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The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene

Across the last ~50,000 years (the late Quaternary) terrestrial vertebrate faunas have experienced severe losses of large species (megafauna), with most extinctions occurring in the Late Pleistocene and Early to Middle Holocene. Debate on the causes has been ongoing for over 200 years, intensifying from the 1960s onward. Here, we outline criteria that any causal hypothesis needs to account for. Importantly, this extinction event is unique relative to other Cenozoic (the last 66 million years) extinctions in its strong size bias. For example, only 11 out of 57 species of megaherbivores (body mass ≥1,000 kg) survived to the present. In addition to mammalian megafauna, certain other groups also experienced substantial extinctions, mainly large non-mammalian vertebrates and smaller but megafauna-associated taxa. Further, extinction severity and dates varied among continents, but severely affected all biomes, from the Arctic to the tropics. We synthesise the evidence for and against climatic or modern human (Homo sapiens) causation, the only existing tenable hypotheses. Our review shows that there is little support for any major influence of climate, neither in global extinction patterns nor in fine-scale spatiotemporal and mechanistic evidence. Conversely, there is strong and increasing support for human pressures as the key driver of these extinctions, with emerging evidence for an initial onset linked to pre-sapiens hominins prior to the Late Pleistocene. Subsequently, we synthesize the evidence for ecosystem consequences of megafauna extinctions and discuss the implications for conservation and restoration. A broad range of evidence indicates that the megafauna extinctions have elicited profound changes to ecosystem structure and functioning. The late-Quaternary megafauna extinctions thereby represent an early, large-scale human-driven environmental transformation, constituting a progenitor of the Anthropocene, where humans are now a major player in planetary functioning. Finally, we conclude that megafauna restoration via trophic rewilding can be expected to have positive effects on biodiversity across varied Anthropocene settings.

www.cambridge.org/core/journals/cambridge-prisms-extinction/article/latequaternary-megafauna-extinctions-patterns-causes-ecological-consequences-and-implications-for-ecosystem-management-in-the-anthropocene/E885D8C5C90424254C1C75A61DE9D087?utm_campaign=shareaholic&utm_medium=twitter&utm_source=socialnetwork