Eyes fossilized

Fossilized insects are normally two-dimensional, because the exoskeleton tends to collapse during decay. The remarkable specimens shown above have been preserved in three dimensions because of the unusual conditions under which they formed. The images are scanning electron micrographs of the eyes of fossilized beetles from the Tertiary period, found in limestone at a site in northwest Queensland, Australia. The beetles probably fed on the carcasses of vertebrates — colonizing them before they sank to the bed of a pool, where the accumulation of bones would have generated high concentrations of calcium phosphate. Fossilisation of easily degraded tissues is more rapid in calcium phosphate than in other minerals, so the eyes became mineralized before they decayed and collapsed. The partially fractured surface of a whole compound eye is shown at top left. In some cases the corneas are intact (top right), whereas in others the surface has been fractured to reveal the rhabdomal framework underlying the corneas and lenses (bottom left). Bacterial activity mobilizes phosphate for mineralization, as well as causing decay. Here, the balance was tipped towards mineralization rather than decay and the bacteria themselves were also fossilized. They can be seen lining the walls in the interior of a rhabdom (bottom right), where the pigment cells have decayed. The photographs were kindly provided