Miocene hominoids and ecosystems

 

     Much of my work focuses on Miocene hominoids, with a goal of determining whether Miocene apes had habitat requirements similar to those of modern apes and thereby understand what role changing climate played in their extinction.  If fossil apes differed in their habitat and dietary requirements from modern apes, then how, with similar body and brain sizes as well as life history regimes, could they ecologically afford to exploit harsher habitats?  Much of my work has focused on Sivapithecus, a fossil ape from the Siwaliks of Pakistan.  The Siwaliks are a rare 20 million year sequence offering the opportunity to examine changes in an ape’s habitat through time, including through that ape’s extinction.  My work involves isotopic and dental microwear analyses to provide reconstructions of forest type, vegetation mosaic, fruit availability, and seasonality.  My current Siwalik collaboration involves expanding our isotopic sampling of faunas to include rodents.  Little is known of fossil rodent diets, and given their small home ranges, they provide a different perspective of the landscape.  

     My current fossil hominoid projects also include paleoecological reconstructions for two of the most enigmatic fossil apes, Gigantopithecus and Oreopithecus.  Gigantopithecus’ extreme body size has led to much speculation regarding its diet and habitat.  I am interested in Oreopithecus because it is found in Europe long after other apes there went extinct.  A question remains, why did Oreopithecus survive outside of modern ape habitat range when no other ape could?  I address these questions using stable isotopic analyses of these apes and their contemporaneous faunas.

      I also work on fossil equids because they are essential to understanding the expansion of grasslands in the Miocene as well as changes in climate such as increasing seasonality. My colleagues and I have documented the oldest C4 diet in Africa, and we have also found the first evidence for C4 grazing diets in Europe. 

 

Collaborators include David Pilbeam, John Barry, Lawrence Flynn, and Michele Morgan (Harvard University); Thure Cerling (University of Utah); Catherine Badgley (University of Michigan); Kay Behrensmeyer (Smithsonian Institute); Lorenzo Rook (University of Florence); and Ray Bernor (Howard University).

 

 

 

Modern ecosystems

 

     To improve out resolution in paleoecological reconstructions, I work in a modern chimpanzee site, Kibale National Park, Uganda.  My research there includes the first isotopic analyses of a large community of wild chimpanzees and sympatric fauna, thus providing a means of comparing fossil ape and early hominin paleoecologies to those of a modern ape.  While many paleoecological studies focus on carbon isotopes, my study showed that oxygen isotopes distinguish between feeding on the ground vs. in trees, and feeding on canopy fruits vs. canopy leaves.  When applied to fossils, these distinctions yield insights into the evolution of traits such as bipedalism and a high-quality diet necessary for brain growth.  I am currently expanding my Kibale study to incorporate isotopic and phytolith load analyses of Kibale primate foods.  The goals are to better determine how well tooth enamel isotopically captures niche breadth, and to understand how phytolith loads may drive increasing enamel thickness, a feature of early hominin evolution.  Additionally, I am studying isotopic stratification of fruits and leaves throughout the rainforest canopy, with this work involving tree climbing! 

 

Collaborators include Martin Muller and Marian Hamilton (University of New Mexico); Richard Wrangham (Harvard University); John Mitani (University of Michigan); and Alain Houle (College Jean de la Mennais).

 

 

 

     

Chimpanzee life histories and the evolution of human life histories

     

     My Kibale colleagues and I are collaborating to provide the first detailed information on development in wild chimpanzees in order to provide a more accurate understanding of the evolution of human life history. My laboratory is attempting to determine timing of weaning through isotopic analyses of urine and feces from mother-infant pairs. Weaning time is critical to understanding energetic trade-offs of reproduction from the mother’s point of view, and energetic requirements of morphological, cognitive, and behavioral development from the infant’s.  Isotopic analyses from mother-infant pairs will allow us to monitor infants’ weaning transitions, which we will compare to timing of M1 eruption.  Weaning, M1 eruption, and near completion of brain growth have been heralded as isochronic relationships in primate life history. Yet, chimpanzees breastfeed well after their offspring erupt first molars and complete most of their brain growth. By combining isotopic measurements of weaning, growth measurements in offspring, and energetic measurements of mothers, our study will be the first to address chimpanzee mothers' continued nutritional investment.  Given the use of M1 eruption as a life history marker in hominin evolution, understanding what M1 eruption means in terms of maternal energetics and infant development is critical. 

 

 

Collaborators include Martin Muller, Melissa Emery Thompson, and Kristin Sabbi (University of New Mexico); and Richard Wrangham and Zarin Machanda (Harvard University).