This Fossil Is A Bug Inside A Lizard Inside A Snake!

Forty-eight million years ago, a snake ate a lizard with a bug in its belly, and all three fossilized—capturing an ancient food chain.

Forty-eight million years ago, an iguana relative living in what’s now Germany scarfed down an insect with a shimmering exoskeleton. Soon thereafter the lizard’s luck changed—when a juvenile snake gulped it down headfirst.

We know this happened because the snake had the spectacularly bad luck to end up in a death trap: the nearby Messel Pit, a volcanic lake with toxic deep waters and a possible knack for belching out asphyxiating clouds of carbon dioxide.

It’s unclear if the lake poisoned or suffocated the snake, fates that more often befell the area’s aquatic and flying creatures. Most likely, it somehow died near the lake and was washed in. But no more than two days after eating the lizard, the snake lay dead on the lake floor, entombed in sediments that impeccably preserved it, its meal, and its meal’s meal.

And that’s a very good thing. That fossil, recently described in Palaeobiodiversity and Palaeoenvironments, is only the second of its kind ever found, revealing three levels of an ancient food chain nested one inside the other in paleontology’s version of Russian nesting dolls—or its culinary equivalent, a turducken.

“It’s probably the kind of fossil that I will go the rest of my professional life without ever encountering again, such is the rarity of these things,” says Krister Smith, the paleontologist at Germany’s Senckenberg Institute who led the analysis and a National Geographic/Waitt Grant recipient. “It was pure astonishment.”

“To see this kind of trophic scale recorded within the gut of a snake is a very cool thing,” says Jason Head, the University of Cambridge’s curator of vertebrate paleontology and an expert on ancient reptiles. He wasn’t involved with the study.

Tracking Snakes’ Tastes

For Smith and his colleagues, the recently excavated fossil is more than an oddity. In fact, the CT scans that revealed the meal-within-a-meal confirm a longstanding dietary trend among boids, a snake group that includes neotropical boas, Madagascar boas, and Asian and African sand boas.

Agustín Scanferla, a study co-author and ancient-snake expert at Argentina’s National Council of Scientific and Technical Research (CONICET), says that boids’ food preferences change as they age. When they’re young, they tend to spring for small lizards and amphibians, but once they reach adulthood, they shift to larger-bodied prey, including mammals, birds, and large reptiles such as crocodiles.

Interpretive drawing of the fossil, overlaid on a photograph. The lizard,Geiseltaliellus maarius (orange), is preserved in the stomach of the snake (white). The insect rests in the abdominal cavity of the lizard (blue) [Illustration: Krister T. Smith]

“This specimen shows us the earliest evidence of this dietary shift, [since] this beautiful boid, Palaeopython, is a juvenile,” says Scanferla, with a clear craving for small lizards—much like today’s young boas, but 48 million years earlier.
Head also notes that the fossil helps define the range of Palaeopython, which isn’t closely related to modern pythons, despite its name.

“[The fossil] tells us something new about the biogeography of this group, which is interesting,” he says. “And once the evolutionary relationships of Palaeopython are figured out, I think [the species] is actually going to change a lot of what we know about the history of dispersal of these snakes.”

A Many-Layered Find

Despite the specimen’s novelty, it’s not the first vertebrate fossil to show three levels of a food chain at once. In 2008, researchers led by the University of Vienna’s Jürgen Kriwet described the fossil of a shark that gobbled up an amphibian with a spiny fish in its stomach.

That fossil, more than 250 million years old, even suggests that the amphibian had been digesting the fish for quite some time before becoming a meal itself.

“Finding gut contents provides a direct view million years back on who was eating whom,” Kriwet wrote in an email. “But normally, these records only cover two trophic levels. Finding a fossil preserved as gut content that itself still contains remains of its last meal provides even deeper insights.”

And the specimen is hardly the first astounding find from the Messel Pit, a UNESCO World Heritage Site that’s home to some of the best-preserved fossils from the Eocene epoch, about 56 to 34 million years ago.

Fossilized bat stomachs from the site, for instance, contain tiny fragments of moth. Messel horses show clear signs of having eaten leaves and grapes. And the Messel Pit also preserved animals’ less literal appetites. One fossil contains two turtles that seemingly died in the middle of mating.

“Messel fossils are well known and have had much press and popular coverage because of their extraordinary preservation,” wrote Ken Rose, a paleontologist at the Johns Hopkins University School of Medicine and a National Geographic grantee. “This factor certainly played a role in this unusual preservation.”

Smith and Scanferla aren’t done probing the Messel Pit for treasures. The team is working through other fossils right now, in the hope of finding similarly spectacular evidence of adult Palaeopython meals.

But for Scanferla, there will always be something special about the young snake that died 48 million years ago with a full belly.

“This fossil is amazing,” he says. “We were lucky men to study this kind of specimen.”

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