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Climate Change and Paleontology: Back to the Future

PLOS Blogs Climate Change PLOS ONE

This week and next at PLOS Blogs, we are doing a focus on climate change. This is leading up to a great collection of papers that will be released at the Ecological Society of America meeting very soon (the link to the collection will be live on August 5th).

As paleontologists, we are frequently thinking about changes in climates over longer time spans that most people ever consider. Decades and centuries seem like small drops in a vast, overflowing bucket. Even though we often deal with thousands or millions of years of climate data obtained from proxies, we still are very concerned with how our science can help understand the current state of rapidly accelerated climate alteration and its impact on global ecology. Paleontology is indeed relevant to this discussion because we can gain perspective on the magnitude of events, such as extinction, in the face of normal climate change, but also in response to rarer, more extreme climate events.

Certain proxies in paleontology allow us to understand how past climate change impacted biodiversity, and we can use this information to make an attempt at predicting the future. As I have previously posted, ancient and modern small mammal communities are strong indicators of how climate change will impact the survival of vertebrates around the world. For example, research has shown certain rodents that feed mainly on seeds dominated past desert faunal assemblages during warm periods. Since warming is predicted to increase in many of the world’s deserts, this gives a strong indication of what may happen to certain key species of rodents over the coming decades.

It is no secret my favorite proxy for studying how climate change has impacted animals in the past is stable isotope paleoecology. By quantitatively studying what vertebrates ate and the types of environments they lived in at different points in time, we can visualize how changes in environments will impact the diets, ranges, and survival of certain species. Climate change will strongly impact the food webs of both marine and terrestrial ecosystems, and looking into how these changes have played out in the fossil record could give us an idea of what will happen in vulnerable areas in the future.

Using stable isotopes to assess diet in a unique, changing environment was the basic premise behind my most recent paper that came out on June 12th in PLOS ONE. My co-authors and I used carbon and oxygen stable isotopes to characterize the environment these extinct large marsupials lived in 3 million years ago based on the diets reflected in their tooth enamel. This locality that we analyzed was Pliocene in age, and represents the time preceding large scale megafauna extinctions in Australia. Being able to understand the environment these animals lived in is critical for assessing how the subsequent shift to grasslands in the region may have impacted biodiversity and factored in to future extinction events.

Euryzygoma dunense, one of the animals I sampled tooth enamel from for stable isotope analysis. Image by Nobu Tamura, distributed under GNU Free Documentation.
Euryzygoma dunense, one of the animals I sampled tooth enamel from for stable isotope analysis. Image by Nobu Tamura, distributed under GNU Free Documentation.

In this study, I compared the stable isotope values in the tooth enamel of fossil marsupials, such as kangaroos and giant wombats, to that of modern kangaroo tooth enamel in order to characterize the ancient environment. According to stable isotope data, this area of Queensland was much wetter than previously thought. Today, this same region is classified as grassland when, during the Pliocene, it probably more closely resembled a temperate or subtropical forest. Now that this is known about the past environment, with more sampling of later localities, we can better understand how climatic and environmental factors could have lead to a decline of certain species. While doing this research, I was struck by the vast range of plant fodder modern kangaroo species consume—it spans a vast range of carbon stable isotope values over their different habitats. While kangaroos may be generalist herbivores that can survive over a range of habitats, other animals may not be, which exposes them to a greater danger of losing their food source in areas strongly impacted by climate change.

Figure 2 from Montanari et al. 2013. This illustrates the range in plant diet in modern kangaroos, and also that the stable isotope values in the paleoenvironment indicate it may have been similar to a modern temperate or subtropical environment.
Figure 2 from Montanari et al. 2013. This illustrates the range in plant diet in modern kangaroos, and also that the stable isotope values in the paleoenvironment indicate it may have been similar to a modern temperate or subtropical environment. (Click to enlarge)

Typically in the megafauna extinction debate we talk about a binary cause of extinction: climate change or humans? In this day and age, it isn’t so clear. We have caused an accelerated shift in the carefully orchestrated conditions that allow us to have such a great diversity of life on Earth. In the future, we cannot really think of extinction debates in the same binary fashion—as almost all extinction can now be traced back to humans. The work of paleontologists to understand past climate change and its impact on global ecology and biodiversity will clearly only become more relevant in the near future.

 

References:

Montanari S, Louys J, Price GJ (2013) Pliocene Paleoenvironments of Southeastern Queensland, Australia Inferred from Stable Isotopes of Marsupial Tooth Enamel. PLoS ONE 8(6): e66221. doi:10.1371/journal.pone.0066221

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