Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration

Abstract

Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world's largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change.

Fig. 1. Map of Sahul (Australia and New Guinea) showing the distribution of reliably-dated megafauna sites within MIS 3 (57–29 ka) and locations mentioned in the text.

Red star indicates South Walker Creek. a The Fitzroy River Basin (FRB). b The Lake Eyre Basin (LEB). c The northern Darling and d southern Murray River catchments of the Murray-Darling Basin (MDB). e Over three quarters of the continental area of Sahul is missing reliably-dated sites from MIS 3, here indicated north of the dashed line. Other localities mentioned in text, 1. ODP 820, 2. Lynch’s Crater, 3. Capricorn Caves, 4. North Stradbroke Island, 5. Kati Thanda–Lake Eyre, 6. Ned’s Gully, 7. Cuddie Springs, 8. Lake Mungo, 9. Mt. Cripps, 10. Titan’s Shelter, 11. Tight Entrance Cave, 12. Kudjal Yolgah Cave, 13. Kenniff Cave, 14. Gledswood Shelter and 15. Ngarrabullgan. Blue arrows indicate catchment flow direction. bmsl = below mean present day sea level indicating outline of the Sahul continent. The baseline map was generated in QGIS using shoreline data from https://www.ngdc.noaa.gov/mgg/shorelines/ under GNU Lesser General Public License v3 or later; and drainage basin data from https://data.gov.au/data/dataset/f55ec9b3-ab74-4056-93a2-b4b8aa65ead1 under Creative Commons Attribution 4.0 International; and bathymetry data from https://data.gov.au/data/dataset/australian-bathymetry-and-topography-grid-june-2009 under Creative Commons Attribution 4.0 International. The base map was composited using Corel Draw and altered to delineate ‘Lake Carpentaria’.

Fig. 2. Summary of field sites and diversity of fossil remains from South Walker Creek (QML1420).

a Aerial map of main South Walker Creek fossil sites SW9, SWJ and SW3 with downstream site SWCC indicated by arrow. Megafauna taxa recovered from each site indicated by numbered silhouette: 1. Pallimnarchus sp. 2. ‘Quinkana’ sp., 3. Crocodylus sp. cf. C. porosus, 4. Varanus priscus, 5. Varanus sp. (large), 6. Dromaius sp., 7. Diprotodon optatum, 8. Phascolonus gigas, 9. Sedophascolomys sp. cf. S. medius, 10. Thylacoleo sp., 11. Palorchestes sp., 12. Macropus sp. (giant), 13. Protemnodon sp., 14. Notamacropus sp. (giant), 15. Osphranter sp. cf. O. rufus, 16. sthenurine. b Stratigraphic section A–Aʹ crossing through SW9, SWJ and SW3 (indicated by dashed line in (a)). Quaternary (Qa) alluvial sediment overlies dipping basement Permo-Triassic Rewan Group (Rw) bedrock (vertical exaggeration 5×). Fossil deposit surface expression at SW9 (c), SW3 (d) and SWCC (e). Summary of the diverse fossil remains recovered from SWC sites (see Supplementary Note 1 for detailed descriptions): f leaves and bivalves in situ at SW9; g Goodeniaceae seed; h Velesunio wilsoni bivalve; i insect elytron (?Curculionidae); j Pallimnarchus sp. osteoderm; k Crocodylus sp. cf. C. porosus osteoderm; isolated crocodile teeth from l Pallimnarchus, m Crocodylus sp. and n ‘Quinkana’; o Varanus priscus tooth; p Macropus sp. (giant) tibia in situ at SW9; q Varanus priscus dorsal vertebra; associated appendicular elements from Thylacoleo sp., r metacarpal, s phalange and t fibula; u Diprotodon optatum right dentary; v Macropus sp. (giant) humerus with crocodile puncture marks (indicated by arrows); w Articulated pelvis and caudal vertebrae of Phascolonus gigas from SW9; x associated hind limb of juvenile Protemnodon sp. from SW9. Scale bars equal 1 mm in (g, i); 5 mm in (h, j–t, v, x); 10 mm in (u); and 50 mm in (w).

Fig. 3. Regional hydroclimate and local palaeoenvironmental proxies since 100 ka compared with young megafauna sites from the Lake Eyre, Murray-Darling and Fitzroy River basins.

a Hydroclimatic proxies include Kati Thanda–Lake Eyre levels (adapted from ref. ). b Palaeodischarge of the Darling River (adapted from ref. ). c Mungo Lake levels and dune development (adapted from ref. ). d FRB catchment activity (adapted from refs. ^, ). e Hydroclimate relative to present day of northern monsoonal Australia (adapted from ref. ). f Local palaeoenvironmental proxies including counts of grass pollen (Poaceae) (f) and micro-charcoal (g) from ODP 820 (adapted from ref. ). Young megafauna sites within each basin are plotted using A or A* quality-rated ages (black plots) (Table 1). All SWC sites are plotted here for completeness. Published OSL ages for Cuddie Springs and the Willandra Lakes Zygomaturus are B-rated here but are equivocal so we have included them (plotted in grey). Extinctions are interpreted as occurring sometime after the youngest A or A* age. Note the timing of onset of trajectory of hydroclimatic deterioration (light grey bars) within each region and megafauna ages. Closed circles denote OSL ages (1σ); open diamonds denote U-series minimum ages (2σ); filled diamonds denote US-ESR ages (2σ); open circles denote combined radiocarbon and OSL ages (Progura egg shell) (1σ); and open square denotes combined OSL and US-ESR ages (1σ).