Late Pleistocene human occupation of inland rainforest, Birds Head, Papua

This paper reports new AMS dates for Late Pleistocene occupation of the Ayamaru Plateau in the central Bird's Head of Papua. Two cave sites, Kria Cave and Toé Cave, together provide occupation sequences that span the Holocene and extend back to the Las

The Genyornis egg: A commentary on Grellet-Tinner et al., 2016

When humans colonized Australia three giant flightless birds were on the landscape, of which the largest, Genyornis newtoni, the sole remaining taxon of the mihirungs, became extinct. Although nearly complete skeletons of Genyornis have been found, they never have been linked directly to an egg. Williams (1981) recognized and described distinct morphological characteristics demonstrating that eggshell fragments from two different taxa were preserved in arid-zone sand dunes. One type had characteristics identical to those of emu (Dromaius novaehollandiae), whereas the other was dissimilar to any extant bird. Based on its estimated volume exceeding that of modern emu egg, he attributed the newly discovered eggshell to Genyornis. Attribution of these eggshell to a Genyornis parent was recently challenged by Grellet-Tinner et al. (2016), who suggested that an extinct megapode of the genus Progura was a more likely candidate parent. They refer to the eggshell Williams (1981) assigned to Genyornis as “putative Genyornis oological material” (PGOM), which for convenience we follow here. The goal of this commentary is to support our claim that Genyornis is by far the most likely candidate parent bird for PGOM, and to show why it is highly unlikely that any megapode could be parent to PGOM.Primary funding for our research on the Quaternary history of the Australian arid zone was provided through U.S. National Science Foundation grants BCS-0914821, EAR-0949398, ATM0502632, ATM-0082254, ATM-9709806, ATM-9311303 to GHM and MLF, and Australian Research Council grants F00103660 and A00102515 to JWM, with additional support from the University of Colorado Boulder, Carnegie Institution of Washington, University of California Merced, the Australian National University, and Curtin Universit

Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65-60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae), an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans. We also suggest that altered climate feedbacks linked to changes in vegetation may have weakened the penetration of monsoon moisture into the continental interior, explaining the failure of the Holocene monsoon. Climate modeling suggests a vegetation shift may reduce monsoon rain in the interior by as much as 50%

Continuous 150 k.y.monsoon record from Lake Eyre, Australia: Insolation-forcing implications and unexpected Holocene failure

Our reconstructed history of Lake Eyre provides the first continuous continental proxy record of Australian monsoon intensity over the past 150 k.y. This continental record's broad correspondence to the marine isotope record demonstrates that this very large catchment, with its hydrology dependent on a planetary-scale climate element, responds to Milankovitch-scale climate forcing. Abrupt transitions from dry phases to wet phases (ca. 125 and 12 ka) coincide with Northern Hemisphere winter insolation minima rather than Southern Hemisphere summer insolation maxima, indicating that Northern Hemisphere insolation exerts a dominant control over the intensity of the Australian monsoon. Stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but, within the uncertainties, are consistent with Northern Hemisphere forcing. Regardless of the hemispheric forcing, the low intensity of the early Holocene Australian monsoon-by comparison with the last interglacial and particularly the last high-level lacustrine event at 65-60 ka when all forcing elements were modest-is an enigma that can be explained by a change in boundary conditions within Australia

Quaternary record of aridity and mean annual precipitation based on delta N-15 in ratite and dromornithid eggshells from Lake Eyre, Australia

The cause(s) of the late Pleistocene megafauna extinction on the Australian continent remains largely unresolved. Unraveling climatic forcing mechanisms from direct or indirect human agents of ecosystem alteration has proven to be extremely difficult in Australia due to the lack of (1) well-dated vertebrate fossils and (2) paleo-environmental and -ecological records spanning the past approximately 100 ka when regional climatic conditions are known to have significantly varied. We have examined the nitrogen isotope composition (δ15N) of modern emu (Dromaius novaehollandiae) eggshells collected along a precipitation gradient in Australia, along with modern climatological data and dietary δ15N values. We then used modern patterns to interpret an approximately 130-ka record of δ15N values in extant Dromaius and extinct Genyornis newtoni eggshells from Lake Eyre to obtain a novel mean annual precipitation (MAP) record for central Australia spanning the extinction interval. Our data also provide the first detailed information on the trophic ecology and environmental preferences of two closely related taxa, one extant and one extinct. Dromaius eggshell δ15N values show a significant shift to higher values during the Last Glacial Maximum and Holocene, which we interpret to indicate more frequent arid conditions (<200 mm MAP), relative to δ15N from samples just prior to the megafauna extinction. Genyornis eggshells had δ15N values reflecting wetter nesting conditions overall relative to those of coeval Dromaius, perhaps indicating that Genyornis was more reliant on mesic conditions. Lastly, the Dromaius eggshell record shows a significant decrease in δ13C values prior to the extinction, whereas the Genyornis record does not. Neither species showed a concomitant change in δ15N prior to the extinction, which suggests that a significant change in vegetation surrounding Lake Eyre occurred prior to an increase in local aridity

A GIS-based reconstruction of late Quaternary paleohydrology: Lake Eyre, arid central Australia

Lake Eyre is the terminal playa in a large closed basin which receives the majority of its moisture from the summer monsoon. Modern Lake Eyre receives intermittent floodings at times of increased monsoon intensity, generally associated with the La Niña

Evaluating quaternary dating methods: Radiocarbon, U-series, luminescence, and amino acid racemization dates of the last Pleistocene emu egg

A whole emu egg, with infilling sediment believed to be coeval with egg laying and burial, was found in late Pleistocene lunette sediments near Lake Eyre, central Australia. The stratigraphic context and initial amino acid racemization (AAR) results suggested an age between 25 ka and 35 ka, ideal for a multiple cross-dating comparison. The sediment infilling the egg provided material for luminescence dating that minimized problems of association. Age estimations from AAR, 14C and U series methods were obtained from the eggshell and optically stimulated luminescence (OSL) of the infilling sediment. All methods agreed within their respective dating uncertainties confirming the utility of all four methods. They indicate an age for the emu egg of 31.24 ± 0.34 ka

The geochronological potential of isoleucine epimerisation in cassowary and megapode eggshells from archaeological sites

Our research demonstrates that the extent of isoleucine epimerisation (A/I) in fragments of avian eggshells provides geochronological information in archaeological contexts. In the archaeological sequence of Hay Cave, northern Queensland, Australia, there is an excellent correspondence between the A/I values of Australian brush-turkey (Alectura lathami) eggshells (n = 99) and independent geochronological control (n = 16 radiocarbon ages including 4 on eggshell calcite). The A/I values identify three phases of deposition during the Holocene at Hay Cave. In contrast to the Alectura eggshell A/I values, a poor correspondence was observed between the A/I values of cassowary (Casuarius) eggshells from Toé (n = 35) and Kria caves (n = 23) (Ayamaru Plateau, Papua) and the depths from which the specimens were recovered in these stratified sequences. Given coherent archaeofauna trends and radiocarbon chronologies (n = 8 and 2 eggshell calcite radiocarbon ages at Toé and Kria, respectively) with respect to depth, the variable A/I values are not explicable in terms of mixing. Rather, the variability is most likely due to exposure of the eggshells to the high temperatures of campfires. Despite the variability, eggshells with relatively low A/I values amongst specimens recovered from similar depths (and therefore presumably least influenced by high temperatures) exhibit a gradual increase in A/I with respect to depth, as expected in a stratified deposit. From this observation it is suggested that the identification of heated eggshells will increase confidence in geochronological information provided by A/I. These studies illustrate the complications that arise from campfire-induced acceleration of amino acid racemisation and emphasise that although this phenomenon is common, it is not universally encountered in archaeological contexts