Research themes
Research themes
Triple oxygen isotopes (paired δ18O-δ17O, expressed as Δ17O) are a great proxy for aridity, physiology, drinking behavior, and global primary productivity. By measuring triple oxygen isotopes in incremental skeletal tissues (e.g., enamel, dentine) of large herbivores we can unlock high-resolution temporal records (weeks to months) that span months to several years.
1) Measure Δ17O in incremental tissues of modern herbivores with known ecology to understand the isotopic fractionation associated with tissue formation inside the body.
2) Measure Δ17O in incremental tissues of fossil herbivores to investigate the paleoecology of important fossil localities, with a focus on early hominin sites.
To date, my colleagues and I completed a pilot study in which we successfully measured large (i.e., ecologically meaningful) Δ17O variation within single teeth of fossil wildebeest (Connochaetes taurinus) and plains zebra (Equus quagga) from Malawi. Current efforts focus on larger taxa including the African elephant (Loxodonta africana) and the hippopotamus (Hippopotamus amphibius).
The Zambezian biome (ZB) of southern-central Africa is a biogeographically important area with high levels of endemism. Since the Pliocene, the ZB has been crucial for biotic exchanges between southern and eastern Africa, including the southernmost occurrence of the hominin Paranthropus boisei. Today the ZB is located at the southern edge of the Intertropical Convergence Zone (ITCZ) and therefore experiences one main wet season. Southward shifts of the ITCZ during cold periods would have caused a bimodal rainfall pattern instead of the modern unimodal pattern. By reconstructing rainfall seasonality across the ZB at various timepoints we can infer the oscillation of the ITCZ in response to global climate.
The Zambezian Paleoecology Project (ZAPP) aims to use geochemical proxies in herbivore tooth enamel to reconstruct rainfall seasonality at different times across the Quaternary, as well as infer animal behavioral responses to different climate regimes.
Currently, my colleagues and I collected data from the last 25,000 years from two localities: northern Malawi* (the Kasitu Valley) and southern Zambia (Leopard's Hill caves**). In northern Malawi, seasonality at the end of the Last Glacial Maximum (~19,000 years ago) was greater than today, but decreased to modern levels soon after. In southern Zambia the pattern appears reversed, possibly because of the absence of a large lake acting as a moisture reservoir. In both areas precipitation is unimodal throughout the last 25,000 years. Future work will include older samples, as well as expand to a new locality in central Malawi.
* Work in Malawi is carried out in partnership with the Malawi Department of Museums and Monuments and Dr. J.C. Thompson's Malawi Ancient Lifeways and Peoples Project.
** Work on Leopard's Hill caves material is carried out in partnership with the Livingstone Museum.
Several species of ungulates migrate seasonally to track high quality resources, reduce competition, or avoid predation and exposure to parasites and diseases. For predators, including hominins, this means that important prey is only available at specific times of the year. However, only few studies directly asses migration in the past using biogeochemical proxies. Radiogenic strontium ratios are a common proxy for mobility and provenience that can be used to investigate migratory behavior.
1) Use intra-tooth radiogenic strontium ratios (87Sr/86Sr) and oxygen isotope ratios (δ18O) to infer migratory behavior in fossil populations of taxa that are often migratory today.
2) Generate isoscapes (predictive models) of bioavailable strontium in selected areas to enable the use of 87Sr/86Sr as a geolocation tool.
To date, migratory behavior was investigated in Pleistocene reindeer (Rangifer tarandus) from southwestern France (read the paper here), as well as Pleistocene wildebeest (Connochaetes taurinus) and plains zebra (Equus quagga) from Malawi. In Malawi, we also generated the first isoscape of bioavailable strontium in the country (for an area of ~2,500 sqkm). We did not find evidence of long distance migratory behavior in either case. In combination with results from other groups, this suggests that long distance migration in the past may have been less common than previously thought. Current work is focusing on improving our ability to interpret intra-tooth 87Sr/86Sr ratios using a modelling approach, as well as studying another Pleistocene herbivore community from northwestern Italy.
The Economic Defendability Model (EDM) posits that dense and predictable resources should favor territorial behavior in mobile animals, such as birds and primates. In humans, there is ethnographic evidence from a variety of foraging and pastoral populations supporting this model, but archaeological tests have been mostly limited to coastal communities. The EDM has the potential to provide a productive interpretive framework for archaeological evidence within the theoretical realm of behavioral ecology, but requires multiple lines of high-quality data to be tested.
The goal of this project is to develop a methodological pipeline to test the EDM in inland archaeological settings, and apply it to a study area in the Kasitu Valley of Malawi.
I used intra-tooth measurements of radiogenic strontium ratios (87Sr/86Sr) and oxygen isotope ratios (δ18O) in ungulate prey that was hunted by humans and recovered from archaeological sites in Malawi to infer the location of herds in the landscape. Then, I analyzed the faunal assemblage from one of these sites (Hora 1) and used a series of classic zooarchaeological tests derived from behavioral ecology to estimate the distance of the archaeological site from the hunting grounds and the abundance of high-return game (read the paper here). The results suggest that ungulate prey was highly predictable, but likely was not abundant enough to favor the establishment of controlled territories.
Research has demonstrated that both Neanderthals and H. sapiens had very diverse diets during the Late Pleistocene. The drivers of this variability remain debated and include changes in mobility, resource intensification in response to demographic pressure or resource depression, and technological innovations, among others. Our ability to disentangle these competing possibilities is limited by some areas remaining understudied compared to others.
The goal of this group of projects is to investigate Late Pleistocene human subsistence, with a focus on hunting of vertebrates, in areas for which there is little available information or available information was obtained without modern taphonomic controls.
1) In the Swabian Jura of southwestern Germany, Upper Paleolithic humans hunted a variety of small game including birds, hares, and fish (read the paper here). Previously, it was believed that in this region people hunted almost exclusively large ungulates such as reindeer and wild horse, but that was likely due to a bias in the recovery, curation and selection of samples for study.
2) In the Armenian highlands, Upper Paleolithic humans hunted adult equids and wild goats, but not small game. Selective carcass transport strategies indicate that foragers exploited relatively large territories, in contrast to sites elsewhere in the southern Caucasus that were likely established in the vicinity of the prey herds (read the paper here).
3) In the miombo woodlands of Malawi, Late Glacial foragers hunted a large variety of mammalian prey, with up to half of the fossil assemblages representing animals <24 kg. Carcasses belong to individuals of all ages (juveniles to old adults) and were likely introduced into the site relatively complete, suggesting a broad spectrum subsistence strategy (read the paper here). Previously, there was no information on Pleistocene human subsistence in Malawi.