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An amazing abundance of fossils 

in a bygone lake in Germany 

hints at the debt humans owe to animals 

that died out 48 million years ago

In the middle of a forest about 20 minutes from the city of Darmstadt in central Germany is a decommissioned strip mine half a mile wide. Today scrubby bushes cover the bottom, where dirt paths wind past rainwater ponds filled with bright-green algae. A gaping 200-foot-deep gouge in the forested countryside, the Messel Pit doesn’t at first glance seem worth preserving, never mind visiting, but since 1995 it has been a Unesco World Heritage site, thanks to a series of unfortunate events beginning some 48 million years ago.

The world was a very different place then, during the period known to scientists as the Eocene. The levels of carbon dioxide in the atmosphere were higher than today (at least, for the time being), producing a greenhouse effect of soaring temperatures. In the Arctic, giant crocodilians swam in warm waters among the ferns. A tropical rainforest covered Antarctica. The shapes of the continents would be mostly recognizable, though India was still on the collision course with Asia that would form the Himalayas. Sea levels were about 150 feet higher than today, so Europe wasn’t a largely continuous landmass but a vast archipelago.

The spot now occupied by the new, conspicuously sleek, concrete and glass Messel Pit visitor center—which includes a trip back in time through a virtual borehole—was, in the Eocene, near a deep lake that at its peak was around two miles across. The lake became a deathtrap for countless animals, and geochemistry in concert with millions of years of accumulating plant and mineral sediments would preserve features of the sunken carcasses to an astonishing degree.

Decaying animal and vegetable material buried and squeezed under tremendous pressure over millions of years yields, every school kid knows, fossil fuel, in this instance primarily oil shale—layers of soft gray stone impregnated with oil. Those deposits attracted miners from the late 1800s to the 1970s, when the open-pit mine closed down and was forgotten by all but a small group of people bent on extracting not the fuel but the fossils.

Then, in an instant, everything changed, apparently when an asteroid or comet struck Earth 66 million years ago and dramatically altered the climate, eventually wiping out the giant reptiles. The diversity of species found among the Messel Pit fossils reveals that mammals rushed to fill every empty ecological nook and cranny they could find. “They really tried everything—flying, jumping, running, tree-dwelling, ant-eating,” says Lehmann. “From the point of view of evolution, Messel is a fantastic laboratory to see what life might have given us.”

Might have, but in many cases didn’t.

Messel’s most fascinating specimens may be those species that have no living relatives, though they look jarringly familiar. In the visitor center, kids crowd around to watch as a conservator armed with toothbrushes, dental picks and scalpels cleans layers of oil shale away from a fossil unearthed just a few weeks earlier. To me, the skeleton of Ailuravus macrurus looks like that of a giant squirrel. It’s three feet long, including its bushy tail. Near the ribs a black stain traces the creature’s fossilized digestive tract. Despite its tail, Ailuravus is no squirrel ancestor. It’s an evolutionary dead end; Ailuravus and all of its relatives died out more than 37 million years ago. Why? Maybe they fell victim to climate changes, or a better-adapted competitor, or disappearing food sources, or simple bad luck.

Ailuravus’ resemblance to a modern squirrel is an example of evolutionary convergence. Given enough time, adaptations may lead to nearly identical solutions—bushy tails, say, or powerful, kangaroo-like hind legs—popping up in different species. “It’s like using the same Legos to build different forms,” says Lehmann.

And there are forms aplenty at the Messel Pit. The exquisitely preserved fossils have provided paleontologists with unprecedented insights into the adaptive strategies­—some successful, others not—adopted by mammals for feeding, movement and even reproduction. For instance, the contents of the tiny prehistoric horse’s stomach—fossilized leaves and grape seeds—indicate that the animal was not a grazer but a browser, eating what it found on the forest floor. The paleontologists also found eight fossilized specimens of pregnant mares, each carrying a single foal. That discovery suggests that the early horses had already adopted herd behavior, since joint care would be the best way to guarantee the survival of small numbers of offspring.

Such findings make the place feel less like a graveyard than a time capsule encompassing a 48 million-year-old ecosystem. “It’s not only paleontology, it’s biology,” says Jens Lorenz Franzen, a retired paleontologist who worked at the Senckenberg Research Institute and helped excavate some of Messel’s most remarkable finds. “We can reconstruct the living world of that era.”