Is small beautiful? A review of the advantages and limitations of using small mammal teeth and the direct laser fluorination analysis technique in the isotope reconstruction of past continental climate change

Oxygen isotopes in mammalian tooth enamel have become a widely used proxy for reconstructing past continental climate change. However, owing to sample size constraints in the chemical separation and precipitation of the phosphate prior to oxygen isotope analysis, this technique has been, until recently, limited to relatively large mammal teeth. As the result of recent developments in chemical and analytical techniques, including the development of a novel pre-treatment technique and a direct laser fluorination methodology of analysis, small mammal teeth (rodents), which are relatively more abundant in the fossil record than large mammal teeth, can now be used. Published examples from the recent literature are provided with the aim of examining the advantages and limitations of using small mammal teeth in palaeoclimate reconstruction studies. Issues that are addressed include 1) the rationale behind the calculation of the mean oxygen isotope composition of local water and the problems associated with the intake of 18O enriched water from plant food and from small water bodies fractionated as a result of evaporation; 2) the methodology, justification and limitations in determining mean annual temperatures (MATs) from calculated δ18O local water values and also combining the δ18O local water values with δ18O values from freshwater biota to calculate, using established thermometry equations, multiple palaeotemperatures of differing climatic significance; 3) specific published examples of how the phosphate oxygen isotope composition of small mammal teeth are being used in studies of continental climate change.