Date of Award
Spring 6-15-2025
Document Type
Thesis (Ph.D.)
Department or Program
Ecology, Evolution, Environment and Society
First Advisor
Nathaniel J. Dominy
Abstract
This dissertation examines the functional and evolutionary impacts of Plio-Pleistocene C4 grassland expansion in the primate and hominin fossil records. I employ ecological, comparative primatological, and evolutionary modeling approaches to test hypotheses about the impact that shifting C4 resource landscapes had on the paleobiology and evolution of fossil hominins and sympatric fossil monkeys. In Chapter 1, I use a plains bison model system to test the “C4 challenge” hypothesis, which argues that C4 grasses pose unique mechanical demands for herbivore consumers that would require specialized dental adaptations to process. I find mixed support that C4 diets pose unique foraging challenges relative to C3 vegetation, with only the C3 forb to C4 grass transition being most impactful from a functional standpoint. In Chapter 2, I test the performance impacts of postcanine tooth enlargement in a forest primate community model system in West Africa, with the aim of modeling the functional consequences of postcanine enlargement during C4 expansion for some fossil hominin taxa (e.g., Paranthropus). I find that larger teeth promote increased chewing performance across the community, with the highest chewing performances being found in those primates that consume the hardest and toughest food objects. In Chapter 3, I utilize stable carbon and strontium isotope data to reconstruct the C4 foraging paleoecology of fossil Theropithecus, a lineage of large grassland monkeys contemporaneous with many fossil hominin species. I find that their greater commitment to C4 graminivory over the course of the Plio-Pleistocene was associated with a shift from selective graminivory with smaller body sizes to bulk-feeding graminivory with larger body sizes, a seemly stable strategy that shifted to an evolutionary trap as increasing seasonality made elevated ranging costs untenable to sustain. In Chapter 4, I fold in stable carbon and oxygen isotope data from fossil hominins and monkeys across the Plio- Pleistocene period to test the pillars of behavioral drive hypothesis, showing that rapid behavioral shifts in graminivory in both fossil hominins and Theropithecus proceeded attendant changes in dental morphology by ca. 700,000 years. I then utilized a novel comparative approach with oxygen isotopes to disambiguate the graminioid tissues contributing to behavioral drive.
Recommended Citation
Fannin, Luke D., "C4 grasslands and hominin paleoecology: comparative, functional, and evolutionary perspectives" (2025). Dartmouth College Ph.D Dissertations. 387.
https://digitalcommons.dartmouth.edu/dissertations/387
