Mammals in an Arid World
As Australia is projected to experience more extreme droughts and intense precipitation events and ~0.8 to 2.8º C temperature increases by 2050, it has never been more critical to assess the effects of climate change and habitat modification on extant marsupials. Australia, being one of the hottest and driest places on the plant also serves as a ‘canary in the coal mine’ - alerting global citizens to the consequences of climate change on biotic organisms. The primary focus of a 5-year NSF CAREER grant is to clarify the paleoecology and paleobiology of marsupial mammals in Australia during the Cenozoic using a multi-proxy approach that integrates morphological data with stable isotopes, DMTA, and dental mesowear, with the aim of assessing how mammals responded to increased aridification.
First, we are studying extant marsupials to better assess how they record their diet (via stable carbon isotopes, DMTA, and dental mesowear) when occurring in different regions across their range (subjected to different climatic conditions and/or the presence of different competitors). This work encompasses ground dwelling macropodids (kangaroos and their close relatives) and arboreal marsupials (including tree kangaroos, koalas, and possums). We assess how diets are altered in response to both habitat modification and extreme drought events — of relevance to current climate change and helpful to assessing if fossil assemblages were accumulated during extreme drought events.
Second, we are expanding the application of these tools to carnivorous marsupials (dasyurids, thylacinids, and thylacoleonids) to help clarify their biology, including assessing effects of novel predators (e.g. Dingos and/or humans) on their ecology.
Third, we are applying knowledge gained from extant taxa to assess effects of aridification on the ecology of marsupial mammals in Australia since the Miocene, including longer term trends and more pronounced changes since ~350 thousand years ago. In collaboration with numerous colleagues, we are examining marsupial mammals from throughout Australia during the Miocene, Plio-Pleistocene, and today—assessing how dietary niches varied geographically, temporally, and potentially in response to climate change and/or human occupation. In collaboration with Judith Field (University of New South Wales), Steven Wroe (University of Newcastle), and John Dodson (University of New South Wales) we documented dramatic dietary shifts coincident with increased aridity, suggesting that increased aridity increased dietary resource competition and likely stressed megafauna during the Pleistocene—suggesting that climate played a role in megafaunal extinction in Australia.
Learn more about Australia’s ancient past and relevance to today from Dr. Larisa DeSantis, as part of A Diprotodon in the Coal Mine: Conservation Lessons from Australian Fossils (Paleo Talks Episode 22), a production by paleontologists at East Tennessee State University.
*Coal miners used to bring canaries in the coal mine to let them know when air quality declined to unsafe levels (i.e. when they stopped tweeting). Similarly, fossil can inform our understanding of biotic responses to climate change in the past—a warning for the future.
Australia’s Past
Much of our research is aimed at understanding the paleoecology of Australian marsupials from the Miocene to the present. We study the ecology of the largest pouched predator (the “marsupial lion” Thylacoleo carnifex), and why it went extinct. Reconstructing the diet of giant wombat-like animals the size of rhinos, giant kangaroos, and even thylacines and Tasmanian devils that occupied mainland Australia, we have begun to clarify the diets and behavior of these ancient prehistoric creatures and understand the profound consequences of aridification on numerous Australian marsupials, past and present.
Image of Thylacoleo carnifex: Peter Schulton
Australia’s Present
Modern marsupials can clarify the ecology of ancient animals by serving as a “Rosetta Stone.” Through the study of animals with observed locations and diets, we have developed methods of correlating modern climates and diets with tools like stable isotopes and dental microwear. With an understanding of living animals, we can apply these tools to fossil animals and clarify their biology and ecology. We can also clarify if and how mammals have altered their ecology in the historic and prehistoric past, allowing for more informed conservation decisions.
Quokka on Rottnest Island. Larisa DeSantis
Changes in the diets of the super-sized megafauna that ruled Australia during the last Ice Age indicates that climate change was a major factor in their extinction.
Megafaunal Extinctions
In collaboration with numerous colleagues throughout Australia, we are examining marsupial mammals from throughout Australia during the Pliocene (5.3 to 2.6 million years ago), Pleistocene, and today—assessing how dietary niches varied geographically, temporally, and potentially in response to climate change and/or human occupation. Specifically, we use stable oxygen isotopes in tooth enamel to document Pleistocene climate changes (e.g. increase aridity) and carbon isotopes and dental microwear to infer dietary responses to climate change. Our collaborative work on Cuddie Springs (New South Wales) has documented dramatic dietary shifts coincident with increased aridity, suggesting that increased aridity increased dietary resource competition and likely stressed megafauna during the Pleistocene—suggesting that climate played a role in megafaunal extinction in Australia (Paleobiology Letters-Rapid Communication). Our work on giant short-faced kangaroos (PNAS) also documented their increased vulnerability to extinction due to their diet of salt-bush, a food that requires the consumption of water from water holes (which may have been few in number, further apart, and risky places due to predation). Currently, we are completing work on the marsupial lion, thylacines, Tasmanian devils, and numerous herbivorous kangaroos, wallabies, and even quokkas from fossil localities spanning all states and territories throughout Australia.
Paleontologist Larisa DeSantis studies the teeth of ancient and modern mammals to determine how their diets changed across the millennia and, by extension, to clarify biotic responses to climate change.
Modern Marsupials
Before the paleoecology of extinct mammals can be inferred, it is critical to clarify how various tools record the dietary behavior and ecology of mammals—today. Specifically, we are studying extant marsupials to better assess how they record their diet (via stable isotopes, DMTA, and dental mesowear) when occurring in different regions across their range (subjected to different climatic conditions and/or the presence of different competitors). This work encompasses ground dwelling macropodids (kangaroos and their close relatives) and arboreal marsupials (including tree kangaroos, koalas, and possums). Much of the macropodid work is collaborative with Dr. Graeme Coulson from the University of Melbourne (a Vanderbilt University partner institution), integrating ecological data from radio-collared kangaroos with tools that can be applied to fossils; thus, knowledge gained from extant mammals will inform paleoecological interpretations of fossil marsupials. Additionally, we are assessing how diets are altered in response to both habitat modification and extreme drought events—of relevance to current climate change and helpful to tell if fossil assemblages were accumulated during extreme drought events. We are studying a diversity of species, including both herbivorous and carnivorous mammals, spanning the entirety of Australia.
Nashville Paleontologist Looks At Koalas, Kangaroos To Learn About Climate Change
Produced by News Channel 5 Nashville
Relevant Papers & Press (Australia)
(*graduate student, **undergraduate student) Bold = lab members
Scholtz, E.J.**, DeSantis, L.R.G. §. 2020. Invasive species, not environmental changes, restrict the population and geographical range of the quokka (Setonix brachyurus). Journal of Zoology 311:106-115 (https://doi.org/10.1111/jzo.12765)
Featured by UPI , Futurity, The Epoch Times, and more. Also, this work is being featured on a forthcoming podcast on The Wild Life. See the associated blog we wrote, published in the Journal of Zoology Blog.
DeSantis, L.R.G., Fortelius, M., Grine, F., Janis, C., Kaiser, T.M, Merceron, G., Purnell, M.A., Schulz-Kornas, E., Saarinen J., Teaford, M., Ungar, P.S., Žliobaité, I.§ 2018. The phylogenetic signal in tooth wear: what does it mean? Ecology and Evolution (https://doi.org/10.1002/ece3.4541)
DeSantis, L.R.G. §, **Alexander, J., *Biedron, E.M., *Johnson, P.S., **Frank, A.S., **Martin, J.M., **Williams, L. 2018. Effects of climate on dental mesowear of extant koalas and two broadly distributed kangaroos throughout their geographic range. PLoS ONE 13(8): e0201962. (https://doi.org/10.1371/journal.pone.0201962)
Featured in EveryONE, PLoS ONE's Blog, and News Channel 5.
DeSantis, L.R.G. §, **Hedberg, C. 2017. Stable isotope ecology of the koala (Phascolarctos cinereus). Australian Journal of Zoology 64: 343-349 (https://doi.org/10.1071/ZO16057)
DeSantis, L.R.G. §, Field, J.H., Wroe, S. Dodson, J. 2017. Dietary responses of Sahul (Pleistocene Australia-New Guinea) megafauna to climate and environmental change. Paleobiology Letters - Rapid Communications 43: 181-195 (https://doi.org/10.1017/pab.2016.50)
Rapid Communications are reserved for papers that represent "non-incremental research advancements of broad interdisciplinary interest." Featured in Scientific American and other news outlets including Smithsonian, Forbes, and several others.
**Hedberg, C., DeSantis, L.R.G. § 2017. Dental microwear texture analysis of extant koalas: clarifying causal agents of microwear. Journal of Zoology 301: 206-214 (http://onlinelibrary.wiley.com/doi/10.1111/jzo.12413/full)
DeSantis, L.R.G. § 2016. Dental microwear textures: reconstructing diets of fossil mammals. Surface Topography: Metrology and Properties 4: 023002 (http://iopscience.iop.org/article/10.1088/2051-672X/4/2/023002)
Invited Review Paper for a special issue titled: Exposing the past: what surfaces and their measurement can teach us about extinct species and the lives of ancient people.
Prideaux, G.J. §, Ayliffe, L.K., DeSantis, L.R.G., Schubert, B.W., Murray, P.F., Gagan, M.K., Cerling, T.E. 2009. Extinction implications of a chenopod browse diet for a giant Pleistocene kangaroo. PNAS 106: 11646-11650 (http://www.pnas.org/content/106/28/11646.full)
Featured in BBC News and several other on-line, print, and radio shows (including PRI).
