Libellule fossile (positif et négatif)

Fossil Dragonfly Positive/Negative Preservation
Tharsophlebia exima
Upper Jurassic, Tithonian stage
Solnhofen Formation, Eichsätt, Germany
The delicate features of insects such as dragonflies are seldom seen in the fossil record. Dragonflies are one of the most delightful types of fossils found in the famed sediments of Solnhofen. This dragonfly has been preserved in the fine-grained Solnhofen limestone matrix by a lithographic process, the outline of the insect chemically transferred to the stone over millions of years due to the anoxic conditions of the thick oxygen-free mud silt that remained when the lagoons of the area dried out towards the end of the Jurassic period. This is an exceptional example, with perfect symmetry and remarkable three-dimensionality, including a most unusual amount of detail to the wing membranes. Most impressive is that it has been preserved in the rare form of a positive and negative fossil. A slab was here split in two to reveal not only the fossilized body of the delicate Dragonfly, but also a cast of the body, the negative impression. A rare occurrence in its own right, the slabs are further enhanced by the presence of a small ammonite, also captured in positive/negative form. The well-defined wingspan measures 12 cm. Each half of the limestone matrix measures 28.5 x 30 cm (2)