A snake that had swallowed a lizard that had swallowed an insect. It is the unusual fossilized predation scene for 48 million years that have just highlighted Krister Smith of the Senckenberg Institute in Frankfurt am Main and Agustín Scanferla of CONICET (the Argentine equivalent of the CNRS ), In the oil shale of Grube Messel, a disused quarry located 35 kilometers from Frankfurt am Main. This extraordinary site has delivered so many exceptionally preserved fossils that in 1995 it was classified as a UNESCO World Heritage Site.

This ancient volcanic lake formed during the Eocene (56 to 33.9 million years ago) when the ascent of a volcanic vein brought lava into contact with the water table. The resulting explosion dug a „funnel“ 700 meters deep. After the volcano had cooled, a lake 200 to 300 meters deep was formed. It had to emit deadly gases because the many organisms buried there appeared to have died suddenly as they swam on the surface or stood on the shore.

The absence of oxygen at the bottom of the lake explains the exceptional state of conservation of fossilized animals and plants, which were sealed in a vessel saturated with organic matter before decomposing. Germany was then at the present latitude of Sicily in a tropical climate, as evidenced by the tropical nature of the 150 species of plants, 8 species of fish, several hundred species of insects, 70 species of birds, 30 species of reptiles, amphibians and 45 species of small mammals that paleontologists identified in Messel. Among them, pygmy horses with paws with fingers, including those of a bearing mare preserved with her uterus!

The stomach of many fossilized animals of Messel has been preserved with its contents. Paleontologists have thus revealed grape and leaf remains in the stomach of pygmy horses, fragments of insects in the bat, or a crocodile inside a constricting snake. In addition, a coprolith of a carnivorous mammal contained remains of the jaw of a small primate, and those of fish, the remains of many arthropods. All these discoveries have informed us about the food webs of Lake Messel, but this is the first time that three levels of the food chain are found fossilized together.

The remains of the lizard are not visible in those of the snake: they have been demonstrated by tomography. Certain traits of the vertebrae allowed to identify a lizard of the species Geiseltaliellus maarius, about twenty centimeters long. On his bones, no trace of digestion by the gastric juices of the snake is visible, which testifies that the snake died very shortly after his last meal. The latter, about one meter long, was a young Palaeopython Fischeri. As its name indicates, it is a small species of constrictor related to the current boas.

In the stomach area of ​​the lizard, researchers also discovered the decomposed remains of a green insect (a structural color, that is, not produced by a pigment, but by the structure of the area).

According to the researchers, this snake containing an iguana containing an insect is the second known case of simultaneous fossilisation of three levels of the food chain. In 2008, a team led by Jürgen Kriwet of the University of Vienna described the case of a Permian shark that ingested two amphibians, one of which had ingested an acanthodian fish. It seems to be necessary to add the case of a carnivorous fish that has seized a pterosaur in the process of ingesting a fish and trained by its prey in the oxygen-free depths of a lake in Bavaria …