Messel Pit

Why does Messel have such extraordinary fossils?

Today, Messel is known as the world's richest treasure trove of Eocene fossils, and is a UNESCO World Heritage site. The secret to the remarkable preservation of Messel's fossils lies in its formation. 47 million years ago, Lake Messel was created when magma beneath the earth's surface came into contact with groundwater, causing a series of volcanic explosions.

The resulting crater quickly filled with groundwater and rain but with no rivers or major streams to drain it, the water in the lake was not only very deep but also very still. While the top sixty-five feet contained some oxygen and could have been rich in life, below that, the still water contained very little oxygen, and very few bacteria.

The rainforest surrounding the lake teemed with life, and whenever an unfortunate animal in the vicinity died, their corpse would be washed into the lake. There, the corpse would slowly sink into the ooze where it would lie undisturbed, decaying very slowly, and compressed by the weight of the water for millions of years.

These conditions were perfect for fossilisation - not just of bones but also of the animals' finest details. Typically, the shape of a Messel animal's flesh remains in the shale as an outline, which paleontologists call the “skin shadow.” We can tell, for instance, whether the animals had long ears or short ears, and often even the gut contents have remained in situ, allowing us to see the animal's last meal. Ida's last meal, which included fruits, seeds and leaves, can be seen in her stomach, pictured below.

Even more incredibly, we can often see the fine detail of the animal's hair or feathers. This was made possible by the few bacteria that survived in the depths of the lake, which covered the entire surface of any corpse that came their way, including every hair and every feather. As the bacteria fed upon the protein of the hairs and feathers, they respired, producing carbon dioxide. The dark shape surrounding the skeleton of Ida's fossil, seen below, is the outline of her soft body tissue.

The carbon dioxide then reacted with iron in the lake to form iron carbonate, also known as siderite. The siderite formed a thin layer over the bacteria coating the hair and feathers. Finally, the surface layer of siderite killed the bacteria, encasing each hair and feather in its own individual covering of black iron-based salt.

It was because of these unique conditions that animals like Ida have been preserved in such remarkable conditions for millions of years.