New in paleoclimatology: pseudo-rodent piss as climate proxy

image: Wikipedia 

The Rock Hyrax is a remarkable animal. Native to dry, rocky environments throughout Africa, you would be forgiven for assuming that it is a large rodent, with its short legs, short neck, rounded ears and overall resemblance to a particularly large guinea pig or a coypu minus a tail.

And yet, in defiance of expectations, the creature’s nearest living relatives are elephants and manatees. This in itself should be enough to make any research involving Rock Hyraxes worth reading.

But these furry fellows have a distinctive behaviour which, by good fortune, enables climatologists to study the environmental history of rocky areas where traditional techniques – such as taking a core – are not viable. Rock Hyraxes, it seems, are very particular about where they urinate and defecate. They like specific locations underneath rocky overhangs and generation after generation of Hyraxes will use that same spot – called a midden – over and over again. For literally thousands of years.

Some of these middens can date back 30,000 years or more. That’s the Stone Age. That’s actually the Upper Palaeolithic period!

The urine crystallises and what you end up with is a block of solid, stratified material which provides the sort of historical record that is otherwise impossible to find in these dry, rocky parts of the world. Within the midden is a record of Hyrax metabolytes as well as particles which have passed undigested through their systems (and the occasional bit of organic material that just happened to get blown there). These can be accurately dated, giving an indication of how the vegetation – and hence the climate – has changed over the millenia. And that’s what some researchers in our Department of Geography are looking into.

Just to be completely unambiguous about this:

Geographers at the University of Leicester are studying the prehistoric climate of southern Africa by examining lumps of thousand-year-old crystallised wee from something that looks like a rat but is actually more closely related to the dugong.

How brilliant is that?

Dr Andrew Carr and Dr Arnoud Boom from Leicester are part of an international team led by Dr Brian Chase from the Institut des Sciences de l’Evolution de Montpellier. Funding for the research has been provided by the Leverhulme Trust and the European Research Council and papers on the topic have so far been published in Quaternary Research, in Geology and in the snappily named journal Palaeogeography Palaeoclimatology Palaeoecology.

Hyrax middens were first used by a South African palynologist named Louis Scott who naturally concentrated on their pollen content. The current team are the first scientists to study this extraordinary resource on a molecular level, examining animal metabolytes and plant biomarkers. Equipment at Leicester is being used to measure the bulk nitrogen and carbon isotope contents, and to identify individual plant and animal biomarkers. Colleagues in Belfast are able to accurately peg the age of a given sample using radiocarbon-dating techniques.

Hyraxes are common creatures; indeed in some areas they are considered pests. Their middens are however pretty smelly, and these ancient urinary deposits can be tricky to reach. Fortunately, Dr Chase is an experienced rock climber – that’s him in the picture equipped with angle-grinder and gas mask (cutting this stuff kicks up a lot of dust that you really don’t want to breathe in). Initially samples were knocked off with a hammer and chisel but once it was realised that cut and polished middens were finely laminated, more care was taken to extract neat samples using a micro-drill.

Paleaoenvironmental knowledge of southern Africa, which encompasses countries such as Botswana and Namibia, has always been very fragmentary and largely reliant on ocean core records. The data from the Hyrax middens open up a whole new realm of research into how some of these dynamic environments have changed over 30,000 years or so. The next step is to compare this data with established models of climate change.

Rock Hyraxes have always been interesting to anyone with a fascination for zoology, not least because of their elephantine link which is a staple of ‘interesting animal facts’-type books. But their excretory habits, or rather the potential use of what they excrete, is now raising them to a whole new level of interest.

• University press release
• The potential of plant biomarker evidence derived from rock hyrax middens as an indicator of palaeoenvironmental change. doi:10.1016/j.palaeo.2009.11.029