The Messel Pit

In 2012 a team led by Walter Joyce reported something no one had found in the fossil record before: pairs of turtles that died while mating. Numerous couples of Allaeochelys crassesculpta, preserved together in the Messel shale.

The finding is not a curiosity, it is evidence about the lake. Turtles would not begin mating in poisonous water, so the couples must have started at the surface where conditions were survivable, then sunk, absorbing toxins through their skin as they went down. That makes Messel a stratified volcanic maar lake: a habitable top and a deadly abyss below it. The same structure explains why everything else here is so complete.

What came out of that abyss is 47 million years old and astonishing. Over 1,400 taxa of plants, fungi and animals have been documented, among them Darwinius masillae, and the oil shale preserves not just bones but outlines, stomach contents and colour patterning.

The pit itself very nearly became a rubbish dump. Brown coal and then oil shale were mined from 1859. Commercial mining stopped in 1971 when oil prices fell, a cement works built in the quarry failed the year after, and the land was earmarked for landfill. Local resistance killed that plan, the state of Hesse bought the site in 1991 to guarantee scientific access, and on 9 December 1995 it became a UNESCO World Heritage Site.

The best part of the story belongs to the amateurs. In the few years between the end of mining and 1974, when the state started preparing the pit for garbage, amateur collectors were allowed in. Oil shale dries and crumbles once exposed, so they invented the transfer technique to lift and stabilise small fossils, and that method is still how Messel specimens are preserved today. Many known specimens came from those collectors, and in 1996 an amnesty was declared on previously collected material to bring private collections back into public hands.