This project, led by University of Oxford researchers in collaboration with colleagues in the US (University of Utah and University of California, San Diego) and Kenya (National Museums of Kenya), aims to investigate the evolution of dietary variability in fossil hominins in eastern Africa from 4 to 1 million years ago. Dietary change is a major driver of evolution amongst mammals, including early hominins (members of the human lineage). Recent developments in stable isotope analysis have revolutionized our understanding of early hominin biology and behaviour by allowing quantification of aspects of the diets of individual fossil hominins. Carbon isotope analyses of fossil hominin teeth have revealed a major dietary transition after 4 million years ago (Ma), from a concentration on C3 plants (leaves, fruit and nuts from trees, shrubs, and herbs) to diets extended to include tropical C4 plants (grasses and sedges) and/or animals. The biological significance of this innovation, and its relationship to the expansion of seasonal grass dominated environments, remains unclear. Indirect evidence from living human and non-human primates suggests that hominin diets may also have varied seasonally, yet there is no direct evidence on the scale and pattern of such variability over time.
Right hand image from Sponheimer M, Passey BH, de Ruiter D, et al. 2006. Isotopic Evidence for Dietary Variability in the Early Hominin Paranthropus robustus. Science 314:980–982. All other images courtesy of Dr S Blumenthal’s personal collection.
Mammal teeth grow incrementally from crown (earlier) to root (later), and, histological studies of modern and fossil hominoid tooth crown formation times demonstrate that multi-year records can be recovered, depending on the tooth and state of preservation. By measuring the within-tooth enamel stable carbon isotopes, the team can examine seasonal-scale diet changes in fossil hominins and other primates. Thus intra-tooth stable isotope profiles represent life-history archives of individual humans or animals. The RLAHA team will compare high-resolution tooth enamel-based isotopic records from fossil hominins and papionins (classification of monkeys including baboons) in order to better understand how seasonal-scale dietary variability evolved in two distinct lineages of terrestrial, large-bodied, omnivorous primates that shared the East African landscape over the last 4 million years.
This project aims to better establish how isotopic variability relates to dietary variability by measuring isotopic variation in faeces and teeth from well-studied modern savanna-dwelling baboons in central Kenya known to seasonally consume C4 foods. A further aim is to determine seasonal-scale dietary niche separation among co-existing fossil hominins Homo and Paranthropus.