Messor barbarus ants as soil bioturbators: Implications for granulometry, mineralogical composition and fossil remains extraction in Somosaguas site (Madrid basin, Spain)

Abstract

Few studies have inquired about the relationship between myrmecological activity and the granulometry and mineralogy of sediments of a palaeontological site. The objectives of this article are to determine the sedimentological or mineralogical distinctions produced by ants of the species Messor barbarus when excavating their nests and extracting grains and vertebrate fossil remains from the Miocene palaeontological site of Somosaguas (Madrid, Spain), to evaluate the degree of taphonomic influence this myrmecological activity has on the fossil remains, and to decide whether or not it can be used as a tool for palaeontological prospection. Results show that Messor barbarus does not alter fossil remains when examined under a 10× binocular magnifying glass. Ants preferentially extract from the ant nest grains of medium sizes (0.25–2 mm) compared to the non-ant-modified soils, and also extract a higher quantity of feldspars. These significant granulometric and mineralogical modifications should be considered when carrying out compositional, sedimentological or stratigraphical studies, since these can become biased and alter geological interpretations as provenance or palaeoclimatic signal. Grain size selection could be due to Messor barbarus' physical capacities or the use of clay particles as cementing elements in nests. Mineralogical distinction may be related to feldspars' embayments and pits filled with finer material (mainly smectites), making transportation and pheromone impregnation easier.

Results show that the ant mounds had increasing concentrations of fossil remains the nearer they were from the main excavation area, therefore the study of ant mounds in potentially fossiliferous zones can indeed be used as a new method of palaeontological prospection.