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.”