The oldest known fossils of the predatory snakes were found at a German site, changing the snake family tree.

From 20-foot anacondas to species that can comfortably fit on a quarter, snakes slither across much of the world today. That’s in part because they’re remarkably good at adapting to new environments — for instance, the Burmese python, native to Southeast Asia, is thriving in Florida’s Everglades National Park. Now, researchers have analyzed four fossilized python skeletons unearthed in Germany — part of a region that’s currently free of the scaly creatures — and rewritten the snake family trees.

These results were published last week in Biology Letters.

Last year during a sabbatical at the French National Museum of Natural History, Hussam Zaher, a paleontologist, pored over a 52-page manuscript written in German that contained an illustration of a skull of an unnamed snake species. Dr. Zaher was intrigued — he was studying ancient snakes, and this skull had some but not all of the characteristics of modern pythons.

Dr. Zaher tracked down the specimen, which measured just over 38 inches long, in the State Museum of Natural History Karlsruhe in southwestern Germany. With the help of Krister T. Smith, a vertebrate paleontologist at the Senckenberg Research Institute in Frankfurt, he set off looking for more like it.

Dr. Zaher and Dr. Smith located four similar skeletons in the collections of history museums and paleontological institutions across Germany. The skeletons, all remarkably intact, had been excavated from the country’s Messel Pit, a UNESCO World Heritage Site.

“The fossils there are exquisite,” said Dr. Zaher, who is now at the University of São Paulo in Brazil.

Based on where the fossils were excavated relative to volcanic rock of a known age, the researchers estimated that the skeletons were at least 47 million years old. That places them squarely in the geological epoch known as the Eocene.

A second specimen, with the skull only partly preserved; the snout is mostly just an impression. Credit...Senckenberg Gesellschaft für Naturforschung

The researchers compared the four unidentified skeletons with fossils from collections across the globe representing 90 different species of snakes and lizards. They examined the specimens using microscopes and CT scanning and made measurements of bones and other features.

“Counting vertebrae is a pain in the butt,” Dr. Smith said.

Dr. Zaher tabulated 785 characteristics about the animals’ skeletons, such as the presence, placement and shape of certain bones and teeth.

“We go deep into the anatomy,” Dr. Smith said.

Based on anatomical differences and similarities, the researchers assembled a snake family tree. They found that the four skeletons excavated from the Messel Pit belonged to a new species of python, which they named Messelopython freyi, after both the geographic location of the discovery as well as Eberhard “Dino” Frey, the chief curator of the State Museum of Natural History Karlsruhe.

Messelopython freyi died out during the Eocene, the researchers believe. It’s an evolutionary dead end, a “stem” in the parlance of paleontologists. But this discovery is important, said R. Graham Reynolds, a biologist at the University of North Carolina, Asheville, who was not involved in the research. It’s the oldest known species of python, and pushes the snake’s origins back 20 million years. “That helps us contextualize the amount of diversity we see in the pythons today,” he said.

Finding this species also sheds light on the geographic origin of pythons, Dr. Smith said. Until now, a compelling case could be made that these snakes originated in Gondwana, an ancient supercontinent that included South America, Africa, India, Australia and Antarctica. But the discovery of Messelopython freyi flips that idea on its head — it now looks like pythons originated instead in the supercontinent known as Laurasia, which was composed of North America, Europe and Asia.

That’s a bit of a surprise, Dr. Smith said, given that pythons aren’t currently found in Europe. “Pythons today are mostly found in the southern continents.”

In the future, Dr. Zaher and Dr. Smith plan to dig even deeper into Messelopython freyi’s past — they hope to determine where its ancestors came from. “One of the big questions for us will be to see if we can trace this lineage beyond Europe,” Dr. Smith said.