Messel Pit: Germany's Eocene Fossil Treasure Trove

The Messel Pit is a former oil shale mine near Darmstadt in Germany that contains some of the best-preserved fossils of the Eocene Epoch, about 47 million years ago. Its finely layered shale holds complete skeletons of early mammals, birds, reptiles, fish and insects, often with traces of fur, feathers, skin and last meals. Nearly turned into a landfill in the 1970s and 1980s, it became Germany’s first natural UNESCO World Heritage Site in 1995.

A volcanic lake in a warm world

About 48 million years ago, rising magma met groundwater beneath what is now Hesse and caused a violent steam explosion. The blast left a deep, roughly circular crater known as a maar, which filled with water to form a lake perhaps 1 to 1.5 kilometres across.

The climate at that time was far warmer than today. Central Europe lay somewhat further south, and the period followed a long phase of global warmth that included the Paleocene-Eocene Thermal Maximum. Around the lake grew a subtropical forest with laurels, palms, vines and relatives of today’s walnuts and citrus.

Why the fossils are so complete

The lake was deep relative to its width, and its water rarely mixed. As a result, the bottom layers held little or no oxygen. Animals that sank there were not disturbed by scavengers, and decay was very slow.

Over several hundred thousand years, fine layers of algae and clay settled on the lake bed, eventually forming a soft, dark oil shale. Bodies were buried flat and whole. Some birds and bats may have been overcome by gases escaping from the lake, though this is still debated.

The result is a level of detail rarely seen in fossils. Messel specimens preserve outlines of fur and feathers, the contents of stomachs and intestines, and in beetles even the shimmering structural colours of their shells.

From mine to fossil site

Mining began at Messel in 1859, first for brown coal and later on a large scale for oil shale, which was heated to extract oil and paraffin. In 1875 workers found the first known fossil, a crocodile, and over the following decades more finds reached museums.

Industrial production ended in 1971. During the mining years and especially in the 1970s, private collectors also dug in the pit, and some important specimens left Germany. Fossils in oil shale are difficult to keep because the rock cracks as it dries, and a method developed in the 1960s and 1970s, which transfers the fossil onto a block of synthetic resin, made it possible to conserve them properly.

The landfill battle

In the early 1970s the regional authorities planned to use the empty pit as a large landfill for household waste. Scientists, especially from the Senckenberg Research Institute in Frankfurt, and local citizens’ groups opposed the plan, arguing that it would bury a unique scientific resource.

The dispute continued for nearly two decades through public campaigns and court cases. In 1991 the state of Hesse purchased the site and gave up the landfill plans. Scientific excavation, carried out mainly by Senckenberg and the Hessian State Museum in Darmstadt, has continued ever since.

In December 1995 UNESCO inscribed the Messel Pit on the World Heritage List, the first natural site in Germany to receive this status. A visitor centre opened beside the pit in 2010.

What has been found

Tens of thousands of fossils have been recovered, representing more than a thousand species of plants and animals. Some of the most celebrated include:

• Early horses such as Eurohippus, small forest animals about the size of a fox terrier with several toes on each foot. One specimen preserves a mare with an unborn foal.
• Bats with wing membranes and stomach contents still visible, showing that they already hunted moths and other insects much as bats do today.
• Mating turtles: several pairs of the freshwater turtle Allaeochelys were found joined, apparently having died during mating.
• Unusual mammals such as Eurotamandua, an animal with anteater-like features, an early pangolin, and small primates and insectivores.
• Birds, reptiles and fish, including snakes, crocodile relatives, lizards and gars, along with countless insects and leaves.

New ways of reading the fossils

Because Messel fossils are so complete, they have become a testing ground for new scientific techniques. X-ray imaging and CT scanning allow researchers to study bones still embedded in the shale without damaging them.

Microscopic studies have also revealed tiny pigment-bearing structures called melanosomes in feathers and fur. By comparing their shapes with those of living animals, scientists have suggested the original colours of some Messel birds and bats, which appear to have been largely brown. Fossil insects keep the metallic sheen of their wing cases, and their colours have been used to study how such structural colours change during fossilisation.

Stomach contents give equally direct evidence of behaviour. They show what early horses browsed on, what bats and birds hunted, and how food webs around the lake were organised.

Ida: the famous primate

In 2009 a team led by the Norwegian palaeontologist Jørn Hurum and the German palaeontologist Jens Lorenz Franzen unveiled a nearly complete fossil of a young primate from Messel. Named Darwinius masillae and nicknamed “Ida”, it had been discovered by a private collector in 1983 and kept in private hands before being bought for the Natural History Museum of the University of Oslo.

The launch was accompanied by a book, a television documentary and wide media claims that Ida was a “missing link” in human evolution. Many palaeontologists criticised this. Further studies placed Darwinius among the adapiforms, an extinct group most closely related to lemurs and lorises, rather than in the line leading to monkeys, apes and humans.

Even so, Ida remains scientifically valuable. It is one of the most complete early primate fossils ever found, with traces of fur and its final meal of fruit and leaves.

Myths and facts

A common myth is that Ida proved the origin of humans. In fact, its place in primate evolution is debated, and most researchers do not consider it a direct human ancestor. Like many fossils, it illustrates the broader evolutionary pattern described in Darwin’s On the Origin of Species, rather than being a single decisive link.

Another misconception is that Messel’s animals were killed in one catastrophe. The fossils actually accumulated over hundreds of thousands of years, layer by layer, as individual animals died in or fell into the lake.

Timeline

• c. 48 million years ago: A volcanic explosion creates the Messel maar crater, which fills with water.
• c. 48-47 million years ago: Oil shale and fossils accumulate on the bottom of the lake.
• 1859: Mining begins at Messel.
• 1875: Workers find the first recorded fossil, a crocodile.
• 1971: Oil shale production ends.
• 1983: A private collector discovers the fossil later known as Ida.
• 1991: The state of Hesse buys the pit, ending the landfill plans.
• 1995, December: UNESCO inscribes Messel Pit as a World Heritage Site.
• 2009: Darwinius masillae is unveiled to the public.
• 2010: The Messel Pit visitor centre opens.

Why it matters

Messel offers an unusually complete snapshot of a single ecosystem shortly after the rise of modern mammal groups. Along with sites such as the Burgess Shale, it shows how rare conditions can preserve soft tissues that normally vanish. Its rescue from a landfill also made it an early example of public campaigning to protect a fossil heritage site.