Welcome to the C4-world: Ecological change and evolution in the Neogene

Thure Cerling

Distinguished Professor of Geology & Geophysics,
College of Mines and Earth Sciences,
Univeristy of Utah

Global vegetation changed in the late Miocene to that similar to that of today: modern grassland and savannas where grasses use the C4 photosynthetic pathway were absent or rare before 8 million years ago, but by ca. 7 million years ago were evident in North and South America, Africa, and Asia. Within this context of the change in food source, we study evolutionary changes in different mammalian groups. The Turkana Basin in Kenya contains Neogene sediments ranging in age from about 25 million years to the present. Volcanic ash correlation by Brown and others provides excellent chronological control in which to test hypotheses about dietary change during the Neogene. In our studies of large ungulate diets, we have used stable isotopes to document the fraction of C3 to C4 vegetation eaten by modern ungulates, and to study dietary change over millions of years. For modern mammals, we find the stable isotope record agrees with most observational data but some field observations tend to overestimate the fraction of grass selected on occasions where both small dicots and grass are available. In the fossil record we find rapid dietary change in equids and elephantids during the Late Miocene, but more gradual changes in suids and giraffids. The latter display changes in anatomy that reflect dietary change.

These assumptions are analytically and logically false. They derive from a misunderstanding of the relations between facts and values in science and politics. I will present a more realistic framework for viewing the role of science in decision making, and then discuss the implications of this framework for climate change research priorities, and environmental science more generally.

About the Lecturer
www.mines.utah.edu
www.biology.utah.edu

Thure Cerling