We investigate evolution and ecosystem assembly in deep time, using mainly plant silica (phytoliths) and macrofossils. We also use modern plants and ecosystem data to develop proxies and methods that allow us to better interpret the fossil record. Major foci are:
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• Evolution of grasses and assembly of grassland ecosystems
• Biotic responses to climate change in deep-time
• Evolution and functional role of silica in land plants
• Evolutionary ecology of plant communities in the Late Cretaceous-Paleocene

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Evolution of Grasses and Assembly of Grassland Ecosystems

 

Grasslands cover more than 40% of the continents and vitally influences global climate, geochemical cycling, and the animals (including humans!) that depend on them. Given the central role that the grasses (Poaceae) play on Earth today, we ask:

• When/where did Poaceae originate and diversify, and how did it reach its current, world-wide distribution?
• When did grasses able to cope with the open, arid conditions typical of today's grasslands evolve—and when did grasslands start spreading? What drove these changes?
• How and why have grasslands changed through evolutionary time, and how have they influenced faunas and faunal evolution? 
• How did grasses themselves respond to the spread of open, grass-dominated habitats through changes in dispersal mode and defense?

We document the evolutionary history of Poaceae and the assembly of grassland ecosystems in multiple regions on different continents (North and South America, Eurasia, Africa) to better understand the unique paths and common factors that have shaped the formation of the grassy biome.

Former graduate student Regan Dunn excavating section at Gran Barranca, Patagonia, Argentina.

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Biotic Responses to Climate Change in Deep-Time

 

Paleontologists have a unique opportunity to study how plants and animals have responded to major environmental changes over long timescales (104-106 years), providing information that can potentially improve predictions for future ecosystem change. Environmental changes of interest include changes in climate, atmospheric CO2 levels, disturbance (e.g. fire regime). We wonder:

• How are major global climatic events manifested at the local-regional level and how does vegetation respond?
• What can geographic variation in climatic alteration and biotic responses tell us about major drivers and global impacts during these events?
• What role do plants play in faunal responses during environmental change?
• ​To what extent does ecosystem history influence how vegetation responds to environmental change?

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In collaboration with geochemists, geologists and vertebrate palentologists, we address these questions for several major Earth events (e.g., Eocene-Oligocene cooling, middle Miocene warming, end-Cretaceous warming and cooling) on different continents (North and South America, India). 

Sediment samples collected to study Eocene vegetation change, Montana.

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Evolution and Functional Role of Silica in Land Plant

 

​Plants have had to ‘deal’ with silica in their environment since they emerged on land some 450 million years ago. Today, many plants appear to benefit from incorporating Si/silica in their tissues for several reasons, ranging from enhanced protection against parasites and heavy metal poisoning, to mechanical support and herbivore deterrence. To better understand how and why plants accumulate silica in their bodies we ask:

• When did plants start actively accumulating silica in their tissues? Did it happen more than once?
• Did certain groups (e.g., grasses) enhance their silica content relative to others for functional (adaptive) reasons, such as structural support or herbivore defense?
• How have the amounts and shapes of silica bodies evolved across Poaceae? Can we use this shape variation to better track specific grass lineages or to better understand ecological change in the fossil record?

Using phylogenetic comparative methods, modern experiments, and 2D/3D morphometric analyses of silica bodies in both modern and fossil plants, we tackle these questions by reconstructing phylogenetic patterns of silica levels and phytolith shape across land plants in general, and grasses specifically.

Confocal images of grass silica short cell phytoliths.

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Evolutionary Ecology of Plant Communities in the Late Cretaceous-Paleocene

 

Plant communities underwent major changes in the Late Cretaceous and Paleocene. Flowering plants (angiosperms), although taxonomically diverse, transitioned from being marginal in many ecosystems to becoming ecological dominants, as they are today. The end-Cretaceous saw environmental changes (e.g. Deccan volcanism, warming/cooling), and a major faunal collapse culminating in the extinction of dinosaurs and other animals at the Cretaceous-Paleogene (K-Pg) boundary. In light of these ecosystem transformations, we wonder:

• What ecological role did angiosperms play in ecosystems before they rose to dominance in North America?
• How did plant communities in northeastern Montana and India respond to environmental change leading up to and across the K-Pg boundary?
• What part, if any, did vegetation (change) have in the collapse of Late Cretaceous faunas and foodwebs?

In collaboration with other paleobotanists, neo-ecologists, vertebrate paleontologists (in particular the Wilson lab and colleagues), geologists, and geochemists, we use plant macrofossils and microfossils to reconstruct plant ecological strategies, vegetation types, and environments through time and space during this critical time. 

Fossil leaf of flowering plant from the Late Cretaceous Hell Creek Formation, Montana.