Article: A Miocene rodent nut cache in coastal dunes of the Lower Rhine Embayment, Germany

A fossil burrow system containing a food cache was discovered in coastal facies in the Lower Rhine Embayment near Cologne, Germany, in the lignite sequences of the Garzweiler open-pit mine. Because these sediments are of Burdigalian age (late Early Miocene), this cache appears to be the geologically oldest food cache to date. The burrow occurs in the Morken Sand beds (horizon 5D), and it is hypothesized here that it was excavated by a Miocene burrowing animal from the surface of a palaeosol into the underlying dune sand in an interdune area. Based on the morphology of the burrow system and the size of the galleries, the burrow was made by a rodent, most likely a large hamster (e.g. Lartetomys or Karydomys) or, conceivably, a large ground squirrel. The chambers, and sometimes the galleries, of the burrow were filled with a monospecific cache of considerable size, estimated here as a minimum of 1800 nuts, although it was probably much larger. This food cache, a larder hoard, consisted of the three-dimensionally preserved nuts of Castanopsis pyramidata (Fagaceae). Because many extant rodents are long-term larder hoarders in regions experiencing seasonal food shortages (e.g. those with cold winter conditions or a dry season), the occurrence of this type of food cache in the Early Miocene implies an acute or chronic scarcity of food resources which, in turn, may be linked to either seasonal cycles in food availability in the backbeach environment or, plausibly, may possibly foretell the onset of climatic seasonality in the entire region.