Gilbert J. Price

Climate change frames debate over the extinction of megafauna in Sahul (Pleistocene Australia-New Guinea)

Around 88 large vertebrate taxa disappeared from Sahul sometime during the Pleistocene, with the majority of losses (54 taxa) clearly taking place within the last 400,000 years. The largest was the 2.8-ton browsing Diprotodon optatum, whereas the ∼100- to 130-kg marsupial lion, Thylacoleo carnifex, the world’s most specialized mammalian carnivore, and Varanus priscus, the largest lizard known, were formidable predators. Explanations for these extinctions have centered on climatic change or human activities. Here, we review the evidence and arguments for both. Human involvement in the disappearance of some species remains possible but unproven. Mounting evidence points to the loss of most species before the peopling of Sahul (circa 50–45 ka) and a significant role for climate change in the disappearance of the continent’s megafauna.

Heavy metal pollution recorded in Porites corals from Daya Bay, northern South China Sea.

We examined metal-to-calcium ratios (Fe/Ca, Mn/Ca and Zn/Ca) in the growth bands of two Porites corals from Daya Bay, South China Sea, in order to trace long-term trends in local ambient pollution levels. Although Fe and Mn did not show any obvious increasing trends over 32 years in the period 1976-2007, peak values of Fe/Ca and Mn/Ca occurred in the mid-late 1980s, temporally-coeval with the local construction of a nuclear power station. Furthermore, both corals showed rapid increases in Zn concentrations over the past 14 years (1994-2007), most likely due to increases in domestic and industrial sewage discharge. The Daya Bay corals had higher concentrations of metals than other reported corals from both pristine and seriously polluted locations, suggesting that acute (Fe and Mn) and chronic (Zn) heavy metal contamination has occurred locally over the past approximately 32 years.

Cryptic meteoric diagenesis in freshwater bivalves: Implications for radiocarbon dating

Shells of freshwater bivalves are commonly used for radiocarbon dating late Pleistocene archaeological and vertebrate fossil sites, thus providing important constraints on late Pleistocene human dispersal and megafauna extinction hypotheses. The reliability of bivalve shells for dating rests partly on the ease with which subsequent diagenetic alteration can be recognized; typically, wherein original shell aragonite is replaced by calcite in meteoric environments. Here we document late Pleistocene freshwater bivalve shells wherein meteoric diagenesis involved syntaxial overgrowth of aragonite cement on original aragonite shell biocrystals. Aragonite cement was identified in situ using Raman microspectroscopy and formed rather than calcite as a result of unusually high Mg:Ca ratios in local groundwaters. Thus, altered shells contain diagenetic 14C, rendering their dates unreliable, but they may slip past common vetting techniques because (1) epitaxial cements are not readily apparent petrographically because they are in optical continuity with adjacent biocrystals; (2) X-ray diffraction indicates that no calcite is present; (3) alteration is not apparent in cathodoluminescence studies; and (4) stable isotopes of C and O are difficult to interpret in shells that originate in terrestrial-meteoric environments. Hence, although freshwater with a high Mg:Ca ratio is not common, groundwater chemistry should be considered before accepting bivalve-based radiocarbon dates uncritically. More broadly, meteoric diagenesis in carbonate rocks is generally characterized by the dissolution of aragonite or its conversion to calcite. Our data show that such is not invariably the case, even in fully terrestrial, freshwater systems.

An early modern human presence in Sumatra 73,000–63,000 years ago

Genetic evidence for anatomically modern humans (AMH) out of Africa before 75 thousand years ago (ka) and in island southeast Asia (ISEA) before 60 ka (93–61 ka) predates accepted archaeological records of occupation in the region. Claims that AMH arrived in ISEA before 60 ka (ref. 4) have been supported only by equivocal or non-skeletal evidence. AMH evidence from this period is rare and lacks robust chronologies owing to a lack of direct dating applications, poor preservation and/or excavation strategies and questionable taxonomic identifications. Lida Ajer is a Sumatran Pleistocene cave with a rich rainforest fauna associated with fossil human teeth. The importance of the site is unclear owing to unsupported taxonomic identification of these fossils and uncertainties regarding the age of the deposit, therefore it is rarely considered in models of human dispersal. Here we reinvestigate Lida Ajer to identify the teeth confidently and establish a robust chronology using an integrated dating approach. Using enamel–dentine junction morphology, enamel thickness and comparative morphology, we show that the teeth are unequivocally AMH. Luminescence and uranium-series techniques applied to bone-bearing sediments and speleothems, and coupled uranium-series and electron spin resonance dating of mammalian teeth, place modern humans in Sumatra between 73 and 63 ka. This age is consistent with biostratigraphic estimations, palaeoclimate and sea-level reconstructions, and genetic evidence for a pre-60 ka arrival of AMH into ISEA. Lida Ajer represents, to our knowledge, the earliest evidence of rainforest occupation by AMH, and underscores the importance of reassessing the timing and environmental context of the dispersal of modern humans out of Africa.

Long-term decline of a fringing coral reef in the Northern South China Sea

Abstract Zhao, M.; Yu, K.; Zhang, Q.; Shi, Q., and Price, G.J., 2012. Long-term decline of a fringing coral reef in the northern South China Sea. The Luhuitou coral reef is a fringing reef at Hainan Island in the northern South China Sea. Since the 1960s, the reef has experienced several significant ecological changes. During that interval, the mean coral cover decreased dramatically from 80–90% in 1962–65 and to just 12% in 2009. In the 1960s, the coral community structure was divided into three well-defined zones: a Goniastrea zone and Montipora zone (both on the reef flat) and an Acropora zone (on the reef slope). However, by 2009, Porites lutea became the dominant species on the reef flat, whereas the predominance of Acropora on the reef slope weakened significantly. There are few long-established Porites lutea colonies present, with approximately 80% being younger than 30 years old. This demographic pattern differs significantly from healthy coral reefs, which are typically dominated by large, well-established (and mature) coral colonies. The long-term decline of the Luhuitou coral reef has most likely been driven as a result of anthropogenic activities, such as overfishing, destructive fishing, reef rock digging, and mariculture and tourism activities. Our study reinforces previous works and highlights the vulnerability of coral reefs to anthropogenic impacts.

Fossil bandicoots (marsupialia, peramelidae) and environmental change during the pleistocene on the darling downs, Southeastern Queensland, Australia

Synopsis Systematic collecting from fluviatile Pleistocene fossil deposits of the Darling Downs, southeastern Queensland, Australia, has led to an increase in the regions fossil record of bandicoots. Isoodon obesulus, Perameles bougainville and P. nasuta are reported for the first time in the Darling Downs fossil record. Accelerator mass spectrometry 14C dates based on charcoal from bandicoot fossil‐bearing stratigraphic horizons indicates deposition 45–40 ka. Additional material attributed to the recently described Darling Downs P. sobbei is also described. P. sobbei retains plesiomorphic characters in the upper dentition including reduction of the metaconule on M3 and the lack of posterior cingula on M2 and M3. Phylogenetic interpretation of dental characters suggests that P. sobbei has closer affinities to the Pliocene P. bowensis than to any modern species. The presence of extant species such as P. bougainville and I. obesulus as fossils provides evidence that scrublands and closed woodlands with dense understories existed on the Darling Downs during the Pleistocene. The Darling Downs bandicoot assemblage represents the only known fauna, fossil or modern, where I. obesulus, P. bougainville and P. nasuta occur sympatrically. The Pleistocene Darling Downs may have had a more equable climate than occurs today and a greater range of habitat niches to support such populations. The southern and western contraction of the geographical ranges of I. obesulus and P. bougainville between the Pleistocene and the present was probably the result of significant environmental change that may have involved the contraction of woodlands and expansion of grasslands. The persistence of P. nasuta populations on the Darling Downs from the Pleistocene to the present may reflect that species’ ability to adapt to a wide range of habitats.

Late Pleistocene sedimentology, taphonomy and megafauna extinction on the Darling Downs, southeastern Queensland

The Kings Creek catchment, southeastern Queensland, contains a variety of Pleistocene – Holocene depositional settings. Fluvial depositional accumulation processes in the catchment reflect both high-energy channel and low-energy episodic overbank deposition. The lithofacies and depositional environments of locality QML796 were examined in detail to aid interpretation of taphonomic accumulation patterns of large and small taxa in the deposit. The basal fossiliferous unit was deposited in a meandering channel and passes upward into overbank deposits that include ephemeral interfluve channels and splays. The most striking taphonomic observations on vertebrates at the locality include: (i) low representation of post-cranial elements; (ii) high degree of bone breakage; (iii) variable abrasion with most identifiable bone elements having a low to moderate degree of abrasion; (iv) low rates of bone weathering; (v) a low degree of carnivore bone modification; and (vi) a low degree of articulated or associated specimens. Collectively, these data suggest that the material was transported into the deposit from the surrounding proximal floodplain and that the assemblages reflect substantial hydraulic sorting. However, despite that, sequential faunal horizons show a stepwise decrease in taxonomic diversity that cannot be explained by sampling or taphonomic bias. The decreasing diversity includes loss of some, but not all, megafauna and is consistent with a progressive local loss of megafauna in the catchment over an extended interval of time. Data are consistent with a climate change model for megafauna extinction but not with nearly simultaneous extinction of megafauna as required by the human-induced blitzkrieg extinction hypothesis.

Mid-Holocene sea-level and coral reef demise: U-Th dating of subfossil corals in Moreton Bay, Australia:

It is increasingly apparent that sea-level data (e.g. microfossil transfer functions, dated coral microatolls and direct observations from satellite and tidal gauges) vary temporally and spatially at regional to local scales, thus limiting our ability to model future sea-level rise for many regions. Understanding sea-level response at ‘far-field’ locations at regional scales is fundamental for formulating more relevant sea-level rise susceptibility models within these regions under future global change projections. Fossil corals and reefs in particular are valuable tools for reconstructing past sea levels and possible environmental phase shifts beyond the temporal constraints of instrumental records. This study used abundant surface geochronological data based on in situ subfossil corals and precise elevation surveys to determine previous sea level in Moreton Bay, eastern Australia, a far-field site. A total of 64 U-Th dates show that relative sea level was at least 1.1 m above modern lowest astronomical tide (LAT) from at least ~6600 cal. yr BP. Furthermore, a rapid synchronous demise in coral reef growth occurred in Moreton Bay ~5800 cal. yr BP, coinciding with reported reef hiatus periods in other areas around the Indo-Pacific region. Evaluating past reef growth patterns and phases allows for a better interpretation of anthropogenic forcing versus natural environmental/climatic cycles that effect reef formation and demise at all scales and may allow better prediction of reef response to future global change.

Pliocene Paleoenvironments of Southeastern Queensland, Australia Inferred from Stable Isotopes of Marsupial Tooth Enamel

The Chinchilla Local Fauna is a diverse assemblage of both terrestrial and aquatic Pliocene vertebrates from the fluviatile Chinchilla Sand deposits of southeastern Queensland, Australia. It represents one of Australias few but exceptionally rich Pliocene vertebrate localities, and as such is an important source of paleoecological data concerning Pliocene environmental changes and its effects on ecosystems. Prior inferences about the paleoenvironment of this locality made on the basis of qualitative observations have ranged from grassland to open woodland to wetland. Examination of the carbon and oxygen isotopes in the tooth enamel of marsupials from this site represents a quantitative method for inferring the paleoenvironments and paleoecology of the fossil fauna. Results from Chinchilla show that Protemnodon sp. indet. consumed both C3 and C4 photosynthesis plant types (mean δ13C = −14.5±2.0‰), and therefore probably occupied a mixed vegetation environment. Macropus sp. indet. from Chinchilla also consumed a mixed diet of both C3 and C4 plants, with more of a tendency for C4 plant consumption (mean δ13C = −10.3±2.3‰). Interestingly, their isotopic dietary signature is more consistent with tropical and temperate kangaroo communities than the sub-tropical communities found around Chinchilla today. Other genera sampled in this study include the extinct kangaroo Troposodon sp. indet. and the fossil diprotodontid Euryzygoma dunense each of which appear to have occupied distinct dietary niches. This study suggests that southeastern Queensland hosted a mosaic of tropical forests, wetlands and grasslands during the Pliocene and was much less arid than previously thought.

Pleistocene frogs from the Darling Downs, southeastern Queensland, and their palaeoenvironmental significance

Systematic collecting from fluvial late Pleistocene deposits from the Darling Downs, southeast Queensland, Australia, has led to the recovery of the first fossil frogs from the region, ail from the Myobatrachidae, a family of ground dwelling and burrowing frogs. The most common species recovered, Limnodynastes tasmaniensis, is extant on the Darling Downs. The fossil taxa include species whose extant populations inhabit arid zones(Limnodynastes sp. cf. L. spenceri), montane forests (Kyarranus spp.), and open woodlands (Neobatrachus sudelli), and indicate the existence of a mosaic of habitats during the Pleistocene. The absence of the Hylidae (tree frogs), a family common throughout the Darling Downs today, may be explained by a taphonomic bias that favours non-arboreal forms. Alternatively, hylids may have been rare or absent on the Darling Downs during the Pleistocene.