Search

Abstract Previous assessments of thermally transferred optically stimulated luminescence (TT-OSL) signal resetting in natural sedimentary settings have been based on relatively limited numbers of observations, and have been conducted primarily at the multi-grain scale of equivalent dose (D e) analysis. In this study, we undertake a series of single-grain TT-OSL bleaching assessments on nineteen modern and geological dating samples from different sedimentary environments. Daylight bleaching experiments performed over several weeks confirm that single-grain TT-OSL signals are optically reset at relatively slow, and potentially variable, rates. Single-grain TT-OSL residual doses range between 0 and 24 Gy for thirteen modern samples, with >50% of these samples yielding weighted mean D e values of 0 Gy at 2σ. Single-grain OSL and TT-OSL dating comparisons performed on well-bleached and heterogeneously bleached late Pleistocene samples from Kangaroo Island, South Australia, yield consistent replicate age estimates. Our results reveal that (i) single-grain TT-OSL residuals can potentially be reduced down to insignificant levels when compared with the natural dose range of interest for most TT-OSL dating applications; (ii) the slow bleaching properties of TT-OSL signals may not necessarily limit their dating applicability to certain depositional environments; and (iii) non-trivial differences may be observed between single-grain and multi-grain TT-OSL bleaching residuals in some modern samples. Collectively, these findings suggest that single-grain TT-OSL dating may offer advantages over multi-grain TT-OSL dating in certain complex depositional environments. Highlights • TT-OSL bleaching assessments performed on 19 samples from different settings. • Modern sample TT-OSL residual doses range between 0 and 24 Gy. • Residuals are variable both within and between different depositional environments. • Differences were observed between single-grain and multi-grain TT-OSL residual doses. • Consistent OSL and TT-OSL ages obtained for late Pleistocene cave and beach deposits. [ABSTRACT FROM AUTHOR]

When pooled for extraction as a bulk sample, the DNA within morphologically unidentifiable fossil bones can, using next-generation sequencing, yield valuable taxonomic data. This method has been proposed as a means to rapidly and cost-effectively assess general ancient DNA preservation at a site, and to investigate temporal and spatial changes in biodiversity; however, several caveats have yet to be considered. We critically evaluated the bulk bone metabarcoding (BBM) method in terms of its: (i) repeatability, by quantifying sampling and technical variance through a nested experimental design containing sub-samples and replicates at several stages; (ii) accuracy, by comparing morphological and molecular family-level identifications; and (iii) overall utility, by applying the approach to two independent Holocene fossil deposits, Bat Cave (Kangaroo Island, Australia) and Finsch's Folly (Canterbury, New Zealand). For both sites, bone and bone powder sub-sampling were found to contribute significantly to variance in molecularly identified family assemblage, while the contribution of library preparation and sequencing was almost negligible. Nevertheless, total variance was small. Sampling over 80% fewer bones than was required to morphologically identify the taxonomic assemblages, we found that the families identified molecularly are a subset of the families identified morphologically and, for the most part, represent the most abundant families in the fossil record. In addition, we detected a range of extinct, extant and endangered taxa, including some that are rare in the fossil record. Given the relatively low sampling effort of the BBM approach compared with morphological approaches, these results suggest that BBM is largely consistent, accurate, sensitive, and therefore widely applicable. Furthermore, we assessed the overall benefits and caveats of the method, and suggest a workflow for palaeontologists, archaeologists, and geneticists that will help mitigate these caveats. Our results show that DNA analysis of bulk bone samples can be a universally useful tool for studying past biodiversity, when integrated with existing morphology-based approaches. Despite several limitations that remain, the BBM method offers a cost-effective and efficient way of studying fossil assemblages, offering complementary insights into evolution, extinction, and conservation. [ABSTRACT FROM AUTHOR]

Global ecosystems underwent major changes through the Quaternary, as climates cycled from cool and dry glacial conditions to relatively warm and humid interglacial conditions. How these changes affected the diversity and composition of small-mammal communities is mostly unknown, especially for the southern-temperate regions of Australia. We used fossil assemblages from owl regurgitates to investigate changes in small mammals from Tasmania's forest environments over the last 20,000 years, encompassing the transition from cold glacial conditions of the Last Glacial′ Maximum (LGM) into the warmer Holocene. During the early part of this period, Tasmania was connected to mainland Australia via a low-elevation land bridge, but was transformed into a large island by rising sea levels during the Late Pleistocene – Holocene transition. Despite these changes, the regional small-mammal fauna appears to have been persistent over this entire period, with no loss of species. However, the relative abundance of most species changed dramatically, apparently in response to habitat changes, which also provoked substantial shifts in community composition and diversity. A strong indicator of the magnitude of change is Mastacomys fuscus , a graminivorus specialist murid, which dominated the assemblage prior to and during the LGM, but declined as temperature and sea level rose during the Late Pleistocene – Holocene. In contrast, the generalist rodent Pseudomys higginsi , along with the small forest-dependent marsupials Cercartetus spp. and Antechinus spp., became more common during the Holocene. The continued survival of these species to the present, despite divergent environmental needs, implies that Tasmania's complex geomorphology provided multiple refugia that conferred resilience in the face of environmental change. • Last Glacial Maximum – present climate change did not cause extinctions in Tasmania. • Grassland species declined following Holocene global warming. • Forest–woodland species increased following Holocene global warming. • Species responses to Holocene global warming has conservation implications. [ABSTRACT FROM AUTHOR]

Abstract: Fossils and sediments preserved in caves are an excellent source of information for investigating impacts of past environmental changes on biodiversity. Until recently studies have relied on morphology-based palaeontological approaches, but recent advances in molecular analytical methods offer excellent potential for extracting a greater array of biological information from these sites. This study presents a thorough assessment of DNA preservation from late Pleistocene–Holocene vertebrate fossils and sediments from Kelly Hill Cave Kangaroo Island, South Australia. Using a combination of extraction techniques and sequencing technologies, ancient DNA was characterised from over 70 bones and 20 sediment samples from 15 stratigraphic layers ranging in age from >20 ka to ∼6.8 ka. A combination of primers targeting marsupial and placental mammals, reptiles and two universal plant primers were used to reveal genetic biodiversity for comparison with the mainland and with the morphological fossil record for Kelly Hill Cave. We demonstrate that Kelly Hill Cave has excellent long-term DNA preservation, back to at least 20 ka. This contrasts with the majority of Australian cave sites thus far explored for ancient DNA preservation, and highlights the great promise Kangaroo Island caves hold for yielding the hitherto-elusive DNA of extinct Australian Pleistocene species. [Copyright &y& Elsevier]

It is indisputable that much of Australia's modern biodiversity decline was triggered by European settlement. However, the driver(s) of pre-European extinctions and extirpations are more challenging to identify, particularly on islands where animals are faced with the additional pressures imposed by isolation. Kangaroo Island, South Australia, has been identified as a potential haven for the reintroduction of endangered animals, but the genetic relationship between reintroduction candidates on the mainland and their extinct relatives on Kangaroo Island is poorly understood. Here, we present a late Pleistocene to mid-Holocene genetic record from Kangaroo Island based on bulk bone metabarcoding of two thousand bone fragments excavated from Kelly Hill Cave. We detect 33 species of bird, reptile, fish and mammal and report additional intra-specific genetic diversity in Kangaroo Island's now extinct population of spotted-tailed quoll. Furthermore, we provide genetic evidence that the Eastern grey kangaroo formerly inhabited Kangaroo Island. Taken together, these data establish a more complete baseline of local biodiversity against which reintroduction programmes and bushfire recovery measures can be evaluated, which is more important than ever in light of the recent fires that devastated much of Kangaroo Island's flora and fauna. • A genetic biodiversity baseline for Kangaroo Island before European arrival. • Genetic identification of 33 species of bird, reptile, fish and mammal. • New haplotypes from the extinct Kangaroo Island population of spotted-tailed quoll. • Genetic evidence that the Eastern grey kangaroo once inhabited Kangaroo Island. [ABSTRACT FROM AUTHOR]

Understanding of Late Pleistocene megafaunal extinctions in Australia and New Guinea (Sahul) suffers from a paucity of reliably dated bone deposits. Researchers are divided as to when, and why, large-bodied species became extinct. Critical to these interpretations are so-called 'late survivors', megafauna that are thought to have persisted for tens of thousands of years after the arrival of people. While the original dating of most sites with purported late survivors has been shown to have been erroneous or problematic, one site continues to feature: Cloggs Cave. Here we report new results that show that Cloggs Cave's youngest megafauna were deposited in sediments that date to 44,500–54,160 years ago, more than 10,000 years older than previously thought, bringing them into chronological alignment with the emerging continental pattern of megafaunal extinctions. Our results indicate that the youngest megafauna specimens excavated from Cloggs Cave datedate to well before the Last Glacial Maximum (LGM), and their demise could not have been driven by climate change leading into the LGM, the peak of the last Ice Age. • The extinct megafauna remains from Cloggs Cave, a key 'late survival' Late Pleistocene megafauna site in SE Australia, are now conclusively shown to be older than 44,500 years old, more than 10,000 years older than previously thought. • We present 69 new AMS 14C and 10 new single-grain OSL ages from excavations undertaken in 2019–2020 at Cloggs Cave, to reveal significant new data on the deposit's chronostratigraphy, on what is now one of Sahul's best-dated archaeological sites. • We show that no purported 'late survival' extinct Late Pleistocene megafauna remains in Sahul are demonstrably significantly younger than c. 40,000 years old. • We argue that understanding Late Pleistocene megafaunal extinctions requires extensive chronostratigraphic examination of purported 'late survival' remainsthe. [ABSTRACT FROM AUTHOR]