Search

Confidence in fossil ages is a recognized constraint for understanding changes in archaeological and palaeontological records. Poor estimates of age can lead to erroneous inferences—such as timing of species arrival, range expansions and extinctions—preventing robust hypothesis testing of the causes and consequences of past events. Therefore, age reliability must be demonstrated before patterns and mechanisms are inferred. Here we present a generalized quality-rating scheme based on a two-stage set of objective criteria: first, our method assesses the reliability of an age regarding the dating procedure, and second, if the age is based on association, it assesses the confidence in its association with the target vertebrate fossil. We developed this quality rating specifically for Australian applications, but it could be applied to other regions and to longer timescales with some modification. Our method ranks ages in four categories of reliability (A* and A are reliable; B and C are unreliable). In our case study of the late Pleistocene megafauna of Sahul, accounting for reliability (i.e., accepting only reliable ages) reduced the number of useful records within chronologies by 70%; for most species, this greatly affects any inferences regarding the timing and possible drivers of extinction. Our method provides a simple, replicable and general tool for assessing the age quality of dated fossils, as well as provides a guide for selecting useful protocols and samples for dating. [ABSTRACT FROM AUTHOR]

Abstract: Recent discussion on the late Pleistocene extinction of the Australian megafauna has revolved around interpretation of several key fossil sites in Tasmania. It has been suggested that humans did not arrive in Tasmania until after the megafauna became extinct, or did not hunt now extinct megafauna, and therefore that humans cannot be implicated in the extinctions. Radiocarbon results from these sites indicate that the youngest extinct megafauna are close to charcoal ages from the oldest archaeological deposits, although difficulties have arisen in establishing chronologies because most relevant sites have ages near the limit for radiocarbon analysis. We report a series of new radiocarbon ages, δ13C, δ15N and C:N ratios on collagen and dentine fractions from skeletal remains in the Mount Cripps karst area and the Mowbray Swamp, both in northwestern Tasmania, and discuss the reliability of ages from these and other sites. We also report the discovery of an articulated Simosthenurus occidentalis skeleton at Mt Cripps, that represents only the second directly-dated extinct megafaunal taxon with a reliable age <50 ka cal BP from Tasmania. Our results suggest that C:N ratios measured on collagen or dentine are not an infallible guide to radiocarbon age reliability. We confirm previous reports of a temporal overlap between the megafaunal and archaeological records in Tasmania, but the presence of archaeological evidence and megafauna with the same age at the same site has not yet been demonstrated. At least two megafaunal taxa—the now-extinct Protemnodon anak and a giant Pleistocene form of the extant Macropus giganteus—were still present in Tasmania after 43 ka, when human crossing of the Bassian landbridge from mainland Australia first became sustainable. [Copyright &y& Elsevier]

The juxtaposition of stone tools, charcoal and bones at Cuddie Springs has been used to support claims that people were butchering now-extinct animals, and grinding seeds about 30,000 BP. Statistical analysis of dates for the site shows significant sediment disturbance, and the anomalous presence of hair residues in the absence of bone collagen suggests that bones and stone tools are not the same age. We argue that the published studies on the Cuddie Springs claypan deposits do not show a stratified and undisturbed Late Pleistocene archaeological site, as proposed by the excavators, instead revealing a palimpsest of Late Holocene and European occupational debris superimposed on a much longerterm record of Quaternary landscape evolution. There is no reliable evidence that extinct Australian megafauna coexisted with people using seed-grinding technology at Cuddie Springs, nullifying the excavators' support for climate change models of extinction and dietary choice. [ABSTRACT FROM AUTHOR]