Science Spin September 2009

Germany's amazing fossil pit

By Tom Kennedy

About 47 million years ago a volcanic crater filled with water and became a lake surrounded by dense forests. The climate was warm, an annual average of 25ºC, and while the ancestors of today's birds flew over the lake, the air was alive with insects, and reptiles basked in the sunshine. At that time, the lake, now known as Messel in Germany, was situated far to the south, where Sicily lies now.

In time the lake disappeared, but not without trace. The Messel Pit, Grube Messel, southeast of Frankfurt is so rich in fossil remains that in 1995 it was declared a World Heritage site. Although geologists had been aware of these fossil treasures since the beginning of the 20th century, the area with its abandoned coal and oil shale workings, came to be regarded as a wasteland.

COLLECTORS

In the 1970s, just twenty years before that declaration, local planners had been thinking of turning the site into a dump, and collectors scrambled over the Pit in a bid to recover fossils before they were covered up by rubbish.

Many of the collectors were amateurs, and later, when the importance of the Pit was recognised internationally, an amnesty was declared, so that important fossils could go back into the public domain and become available for scientific study.

The Messel Pit is about 60 metres below the surrounding area, and the fossil-rich oil shale was formed as an accumulation of mud and dead vegetation became compressed into a deposit over 100 metres in depth. This build up of material was quite slow, estimated to have been just 0.1mm a year, and with little oxygen or disturbance, the probability of anything that fell to the bottom of the lake being preserved was high.

Sometimes nature gave some assistance, and given that the Earth was more active then, volcanic events are likely to have been frequent. Geologists believe that the sudden release of gases, such as carbon dioxide or sulphur dioxide, would have overwhelmed many animals, so birds and bats, for example, would have fallen into the lake, sinking down to be preserved in the mud.

Scientists also think that the richness and diversity of fossils preserved in the Messel Pit is due to the frequency of volcanic venting of gases.

FINDS

Among the fossils more than 10,000 fishes of various species have been catalogued, and thousands of insects, some with colours, have been found. Among the mammals are pigmy horses, giant mice, and eight different types of bats. About 60 near complete horses have been recovered, but compared to their descendants, they were tiny.

On average they were just 20 cm high. Crocodiles, frogs, turtles, and salamanders are also abundant, and over 30 plant species have been identified.
Every year when scientists from the Senckenberg Research Institute carry out a dig in the Messel Pit, they recover about 3,000 fossils.

Researchers come from the world to see the results, and among them this year was Dr Krister Smith from the US. His particular interest is in the beaded lizards and gila monsters that occur now in the southwest of the US and Canada.

One of the recent finds at the Messel Pit is an 80 centrimetre long reptile, an early representative of that family, and like the descendants, it appears to have been venomous. Teeth in the fossilised skull had what appear to be venom carrying canals.

Another recent find was a metallically gleaming jewel beetle, and Dr Sonja Wedmann, a specialist in insects, commented how amazing it is that the colouration, created by refraction of light within the chitin, still shows after 47 million years. One of the most remarkable fossils is that of a rat-like mammal, Masillamys. Not only do we see the animal from nose to tip of its tail, but the outline of the skin can be seen, and darkening around the gut area are the remains of the animal's last meal.

PRESERVATION

Although the fossils are abundant and of exceptional quality, even preserving traces of colour and the detail in insect wings, they are extremely delicate, and as soon as they are exposed they begin to deteriorate because the shale in which they are embedded starts to dry out and crack.

On drying out, the oil bearing shale which can consist of 40 per cent water just crumbles into dust. To solve that problem, geologists in the 1970s developed a special 'transfer' technique. At first the specimen is kept damp, and the fossil is cleaned up.

Then with the help of a blow-drier, the fossil is dried off, and as soon as this begins to happen, a water-based lacquer is applied. Because the lacquer only penetrates the fossil, and not the rock, separation of the two parts can begin. The fossil is further strengthened by the application of epoxy, and finally the specimen is turned over so that the shale backing can be carefully scraped and brushed away.