Fossil hamster’s food cache

It is uncommon to find fossilised nuts, so imagine the fervour that has greeted an actual cache of them, clearly secreted by some hoarding animal.  The Garzweiler lignite pit near Cologne in Germany has long been a treasure house for Miocene terrestrial fossils, thanks largely to the keen eyes of miners who work there.  In 1992 they came across 1800 nuts in one of the sand horizons that divides the lignite deposit.  They were in a burrow through probable dune sands.  Its dimensions give a clue to the hoarder, which was about 25 cm long and weighed in at 225 grams (Gee, C.T., Sander, P.M & Petzelberger, B.E.M. 2003. A Miocene rodent nut cache in coastal dunes of the Lower Rhine Embayment, Germany.  Palaeontology, v. 46, p. 1133-1149).  This is about the size of an extinct hamster, remains of which have been found at a similar level in the lignites.  Evidently, hamsters have always worried about their future, especially when food is likely to be scarce, but are also dim-wittedly forgetful.  The hazel-like nuts are the earliest-known example of a lost food cache (about 17 Ma), and have been suggested to represent the onset of seasonality in Europe during the late Early Miocene.

The selectivity of mass extinctions

Every mass extinction, whatever its magnitude, was selective; there always were surviving organisms, otherwise we wouldn’t be here.  However, selectivity according to the lifestyles of animals that became extinct can give important clues to the causes of extinctions.  Die-off across the ecological board strongly suggests a cause that was all encompassing, such as a major impact or geochemical stress that reached into every corner, as might occur with massive flood-basalt volcanism.  At the end of the Pliensbachian Epoch of the Early Jurassic there was a significant mass extinction.  Its victims were mainly marine organisms, especially molluscs.  Study of the disappearances of bivalve species shows that those which lived in burrows suffered more than ones inhabiting open sea floor (Aberhan, M. & Baumiller, T.K. 2003.  selective extinction among Early Jurassic bivalves: A consequence of anoxia.  Geology, v. 31, p. 1077-1080).  A likely cause is loss of oxygen from the upper layer of sea-floor sediments, but a less reducing environment immediately above the sediment surface

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