Dietary responses of Sahul (Pleistocene Australia-New Guinea) megafauna to climate and environmental change

Throughout the late Quaternary, the Sahul (Pleistocene Australia-New Guinea) vertebrate fauna was dominated by a diversity of large mammals, birds, and reptiles, commonly referred to as megafauna. Since ca. 450-400 Ka, approximately 88 species disappeared in Sahul, including kangaroos exceeding 200 kg in size, wombat-like animals the size of hippopotamuses, flightless birds, and giant monitor lizards that were likely venomous. Ongoing debates over the primary cause of these extinctions have typically favored climate change or human activities. Improving our understanding of the population biology of extinct megafauna as more refined paleoenvironmental data sets become available will assist in identifying their potential vulnerabilities. Here, we apply a multiproxy approach to analyze fossil teeth from deposits dated to the middle and late Pleistocene at Cuddie Springs in southeastern Australia, assessing relative aridity via oxygen isotopes as well as vegetation and megafaunal diets using both carbon isotopes and dental microwear texture analyses. We report that the Cuddie Springs middle Pleistocene fauna was largely dominated by browsers, including consumers of C4 shrubs, but that by late Pleistocene times the C4 dietary component was markedly reduced. Our results suggest dietary restriction in more arid conditions. These dietary shifts are consistent with other independently derived isotopic data from eggshells and wombat teeth that also suggest a reduction in C4 vegetation after ∼ 45 Ka in southeastern Australia, coincident with increasing aridification through the middle to late Pleistocene. Understanding the ecology of extinct species is important in clarifying the primary drivers of faunal extinction in Sahul. The results presented here highlight the potential impacts of aridification on marsupial megafauna. The trend to increasingly arid conditions through the middle to late Pleistocene (as identified in other paleoenvironmental records and now also observed, in part, in the Cuddie Springs sequence) may have stressed the most vulnerable animals, perhaps accelerating the decline of late Pleistocene megafauna in Australia

Dental microwear textures across cheek teeth in canids: Implications for dietary studies of extant and extinct canids

Dental microwear texture analysis (DMTA) has been instrumental in reconstructing dietary ecology of extinct and extant carnivorans. Current sampling methods for canids focus on lower second molars (m2), where the grinding of flesh and bone captures dental microwear indicative of diet. However, dental microwear on other biomechanically analogous grinding facets (i.e. the talonid basin on the lower carnassial, m1) might be comparable and could help dramatically increase sample sizes of fossil specimens, as carnassials are more frequently recovered and identifiable than lower m2s. Here, we quantify the degree to which dental microwear textures between grinding facets on lower first and second molars are similar in two species of extant canids, coyotes (Canis latrans) and gray wolves (Canis lupus). Casts of paired m1s and m2s for each individual were sampled from museum collections and analyzed for three microwear parameters that correlate with diet in carnivorans: anisotropy, complexity, and textural fill volume. Within wolves, the m1 talonid and m2 are indistinguishable in all DMTA parameters. In coyotes, grinding facets of the ml talonid and m2 are indistinguishable in complexity and textural fill volume, but anisotropy values of m1s are significantly lower than those of m2s. Differences in anisotropy between species were unlikely to be driven by biomechanical shifts in bite force between the ml talonid and m2, but could stem from a combination of subtle morphological variation and intra-tooth variation. Overall, these data suggest that regions across molars with similar functions yield similar dental microwear textures. Finally, to demonstrate the effect of increased sample size, we show how the combination of DMTA data from lower m1 talonids and lower m2s of the hypocarnivorous Phlaocyonini canids from the John Day Formation of eastern Oregon, USA, alters the size and shape, but not position, of their reconstructed dietary "niche" space and hence interpretations about dietary behavior

Effects of Global Warming on Ancient Mammalian Communities and Their Environments

Current global warming affects the composition and dynamics of mammalian communities and can increase extinction risk; however, long-term effects of warming on mammals are less understood. Dietary reconstructions inferred from stable isotopes of fossil herbivorous mammalian tooth enamel document environmental and climatic changes in ancient ecosystems, including C(3)/C(4) transitions and relative seasonality.Here, we use stable carbon and oxygen isotopes preserved in fossil teeth to document the magnitude of mammalian dietary shifts and ancient floral change during geologically documented glacial and interglacial periods during the Pliocene (approximately 1.9 million years ago) and Pleistocene (approximately 1.3 million years ago) in Florida. Stable isotope data demonstrate increased aridity, increased C(4) grass consumption, inter-faunal dietary partitioning, increased isotopic niche breadth of mixed feeders, niche partitioning of phylogenetically similar taxa, and differences in relative seasonality with warming.Our data show that global warming resulted in dramatic vegetation and dietary changes even at lower latitudes (approximately 28 degrees N). Our results also question the use of models that predict the long term decline and extinction of species based on the assumption that niches are conserved over time. These findings have immediate relevance to clarifying possible biotic responses to current global warming in modern ecosystems

Was the giant short-faced bear a hyper-scavenger? A new approach to the dietary study of ursids using dental microwear textures.

Dramatic environmental changes associated with global cooling since the late Miocene, and the onset of glacial-interglacial cycles in the Pleistocene served as a backdrop to the evolutionary radiation of modern bears (family Ursidae). These environmental changes likely prompted changes in food availability, and triggered dietary adaptations that served as motive forces in ursid evolution. Here, we assess correspondence of dental microwear textures of first and second lower molars with diet in extant ursids. We use the resulting baseline data to evaluate the hypothesis that the Pleistocene giant short-faced bear, Arctodus simus, was a bone consumer and hyper-scavenger at Rancho La Brea, California, USA. Significant variation along the tooth row is consistent with functional differentiation, with the second molar serving as a better dietary recorder than the first. Results evince significant variation among species: carnivorous and omnivorous ursids (Ursus maritimus, U. americanus) have significantly higher and more variable complexity (Asfc) than more herbivorous ones (Ailuropoda melanoleuca, Tremarctos ornatus, U. malayanus), and A. melanoleuca is differentiated from U. maritimus and U. americanus by significantly higher and more variable anisotropy (epLsar) values. Arctodus simus from Rancho La Brea exhibits wear attributes most comparable to its closest living relative (T. ornatus), which is inconsistent with hard-object (e.g., bone) consumption, and the hypothesis that short-faced bears were bone consuming hyper-scavengers across their range

Implications of Diet for the Extinction of Saber-Toothed Cats and American Lions

<div><p>The saber-toothed cat, <em>Smilodon fatalis</em>, and American lion, <em>Panthera atrox</em>, were among the largest terrestrial carnivores that lived during the Pleistocene, going extinct along with other megafauna ∼12,000 years ago. Previous work suggests that times were difficult at La Brea (California) during the late Pleistocene, as nearly all carnivores have greater incidences of tooth breakage (used to infer greater carcass utilization) compared to today. As Dental Microwear Texture Analysis (DMTA) can differentiate between levels of bone consumption in extant carnivores, we use DMTA to clarify the dietary niches of extinct carnivorans from La Brea. Specifically, we test the hypothesis that times were tough at La Brea with carnivorous taxa utilizing more of the carcasses. Our results show no evidence of bone crushing by <em>P. atrox</em>, with DMTA attributes most similar to the extant cheetah, <em>Acinonyx jubatus</em>, which actively avoids bone. In contrast, <em>S. fatalis</em> has DMTA attributes most similar to the African lion <em>Panthera leo</em>, implying that <em>S. fatalis</em> did not avoid bone to the extent previously suggested by SEM microwear data. DMTA characters most indicative of bone consumption (i.e., complexity and textural fill volume) suggest that carcass utilization by the extinct carnivorans was not necessarily more complete during the Pleistocene at La Brea; thus, times may not have been “tougher” than the present. Additionally, minor to no significant differences in DMTA attributes from older (∼30–35 Ka) to younger (∼11.5 Ka) deposits offer little evidence that declining prey resources were a primary cause of extinction for these large cats.</p> </div

Pairwise comparisons using Dunn’s procedure of extinct taxa from different pits spanning ∼35,000 years at Rancho La Brea, California.

*<p>Significant values (<i>p</i><0.05, critical value is 5.5) represent analyses performed absent of the Bonferroni correction (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052453#s4" target="_blank">methods</a>).</p><p><i>Asfc</i>, area-scale fractal complexity; <i>epLsar</i>, anisotropy; <i>Smc</i>, scale of maximum complexity; <i>Tfv</i>, texture fill volume; <i>HAsfc</i>_(3×3), <i>HAsfc</i>_(9×9) heterogeneity of complexity in a 3×3 and 9×9 grid, respectively.</p

Three-dimensional photosimulations of microwear surfaces of all extant and extinct carnivorans analyzed.

<p>Examples include: (A) <i>A. jubatus</i> (AMNH 161139), (B) <i>P. leo</i> (USNM236919), (C) <i>C. crocuta</i> (AMNH 83592), (D) <i>P. atrox</i> (LACMHC 6996), and (E) <i>S. fatalis</i> (LACMHC 2002-298).</p