Adventures in Ichnoarchaeology
Ichnology is the branch of palaeontology that deals with trace fossils – dinosaur footprints for example. Ichnoarchaeology, then, involves looking at similar traces of living things in archaeological contexts. The term was introduced in a stimulating call to arms by Baucon et al. (2008) (on academia.edu – you can read it for free online but will need to sign in to download it). They review past work on archaeologically preserved footprints and handprints, on animal burrows, on invertebrate borings (such as woodworm), on trepanation of human skulls, and also suggest that coprolites (preserved faeces) and gnaw marks are also of ichnoarchaeological interest.
They state that the lack of a consistent ichnoarchaeological approach in all these cases means that “archaeologists are not taking full advantage of traces”. I’m not wholly convinced that this is the case. I think that these different trace remains are rightly the preserve of different experts. Interpreting the preserved footprints of humans living beside the Severn Estuary 7000 years ago requires a very different expertise (more akin to biological anthropology) to interpreting the borings of a beetle in wood from the same site (more akin to entomology). Indeed, some specialisms have sprung up that are more specific than ichnoarchaeology – palaeodermatoglyphics (archaeologists and their long words…) for example, is the study of preserved fingerprints (such as those of a potter in the clay of ancient pots).
Coprolites, archaeologically speaking, are deposits and so positive contexts, unlike (e.g) animal burrows or footprints which are negative contexts because they do not add a new deposit to the stratigraphic record, so I think they are a different class of thing (in fact, Baucon et al. do say they are a grey area for ichnoarchaeology). As for trepanation, it requires a tool so is more like analysing toolmarks on worked wood than the direct evidence of a biological organism.
I probably won’t be using the term ichnoarchaeology very often (although I do recommend Baucon et al‘s paper), but I do think the concept provides quite a useful framework for looking at some classes of remains that aren’t often talked about when people talk about archaeology. Here then, are photographs some of my brushes with the ichnoarchaeological record.
Footprints (from humans and other animals) and handprints can be preserved in deposits which are very quickly sealed by another deposit. The classic example of this is in intertidal silts where the subsequent tide lays new sediment in the footprints. Such prints abound in the Severn Estuary, and have been well-studied on the Welsh side, forming the basis of a PhD by Rachel Scales and a number of papers by her and her colleagues at Reading John Allen and Martin Bell. Windblown sand can also preserve footprints, and hoofprints preserved this way have been excavated at Cladh Hallan on South Uist in the Western Isles. Where a sediment is artificially hardened, by firing for example, prints may be preserved, such as the pawprint in the first picture.
Quite a few different invertebrates on land, in the sea and in freshwater bore into substances. Just yesterday I was talking to colleague in Poland about snails boring into rocks for calcium to build their shells (see this paper by Daniel Quettier for more details – with thanks to Aldona Kurzawska). Another burrowing mollusc, shipworm, can be a serious problem for wooden ships. Other molluscs and some insects prey on molluscs by making holes in their shells, while yet other invertebrates use mollusc shells as a substrate in which they live (Jessica Winder gives some great information about this with relation to oysters, for example here about sponge borings). On land, wood may be attacked by the larvae of a number of insects, perhaps most famously woodworm.
Rhizocretions are mineral tubes that form around plant roots due to ion exchange in carbonate rich sediments. They occur in some waterlogged estuarine and intertidal clays and look a bit like long streaks of rust.