Coprolite chemistry – diet, digestion and methane emissions of extinct fauna

Coprolites (fossilised faeces) represent remarkable snapshots of the lives of extinct animals. This research aims to extend the utility of coprolites as repositories of palaeobiological information by analysing biomarker molecules preserved within them, which are derived from the diet, digestive processes or digestive tract microbes of the producer and can be recognised on the basis of their chemical structure, either intact or as a recognisable carbon skeleton.

In order to interpret biomarkers from coprolites, it is essential to perform a parallel analysis on faeces from modern animals in which diet parameters, digestive processes and gut microbial communities are already known, to enable these factors to be correlated with the organic compounds present in the faeces. Invoking the principle that “the present is the key to the past”, the results from the modern studies can be used to interpret the data from coprolites and determine what extinct animals ate and how they digested their food and lived in symbiosis with bacteria and other microbes. Faecal biomarkers can also provide insights into the wider ecosystem, e.g. comparisons of faecal biomarkers both within and between species, through time and space, may reveal differences in vegetation reflecting changing climate and evidence for resource partitioning between species.

Of particular interest is methane, an important greenhouse gas that contributes to global warming, in part because of emmissions from livestock. Methane is produced in the gut of modern animals by methanogenic archaea, which have cell membranes chemically different from those of bacteria, plants and animals. A key hypothesis to be tested is that the concentration of methanogen biomarkers in animal faeces correlates to the amount of methane emitted. If this is found to be the case, this would provide a brand new approach to quantifying methane emissions from modern animals (currently a poorly constrained variable in global methane estimates) and could also be applied to coprolites to estimate the contribution of extinct animals to methane levels during the Pleistocene.

This research is funded by the Royal Society.