In Hinduism’s Vedic mythos, the deity Indra does battle with a dragon that swallows Indra whole. Now, scientists have found a strikingly similar tale captured in the fossil record: a newly recognized species of lizard that met its end in the belly of a glimmering dinosaur.
Named Indrasaurus wangi as a nod to the mythical encounter, the unfortunate reptile was found within the abdomen of a feathered dinosaur known as Microraptor. The fossil of this four-winged dinosaur was itself unearthed from the 130-million-year-old Jehol biota, a treasure trove of Cretaceous-period fossils in what’s now northeastern China.
The find—described today in the journal Current Biology—is the fourth Microraptor fossil to preserve stomach contents, but it’s the first to show that Microraptor ate lizards. Previous fossils captured it eating small mammals, fish, or birds. The specimen also reveals that, like some predatory birds today, Microraptor had a taste for swallowing lizards whole and head-first.
The small dinosaur “really seems to have been a generalist, going after anything that would fit in its mouth,” says paleontologist Scott Persons, a postdoctoral researcher at the University of Alberta who was not involved in the new study.
Now that the fossil and its last meal have been identified, the specimen is already helping to improve reconstructions of the ancient Jehol food web. As part of their work describing Indrasaurus, lead study author Jingmai O’Connor, a paleontologist at China’s Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), and her colleagues pieced together the most detailed look yet at what ate what in this long lost world.
At least six types of plants form the base of the food chains in this tangled web, with seeds that fueled local herbivores. Lizards and dinosaurs alike fed on the lake ecosystem’s abundant fish, and small mammals played the part of both predator and prey. Sinocalliopteryx, an eight-foot-long carnivore, seems to have been an apex predator, while Microraptor sat in the middle, picking off whatever it could.
The Jehol biota “is the best record we have anywhere of what dinosaurs were eating which other dinosaurs, and other things too,” Persons says.
Found sometime before 2003, the Microraptor fossil went years without giving up its secret. After Xiaoting Zheng, the former head of a Chinese state gold-mining company, bought it from a local farmer, the fossil ended up at the sprawling Tianyu Museum of Nature, which Zheng later founded. The fossil collection there numbers in the thousands, and navigating its riches can border on overwhelming.
“At this point, we’ve seen everything, [but] the thing is, when you have five hours to look at 3,000 specimens, you can’t process everything,” O’Connor says. “I know that I’ve seen that specimen before, but I missed the stomach contents, even though they’re super-obvious.”
Once the team noticed the lizard, they were able to identify it because its bones are so well-preserved. And this exceptional preservation raises questions about how dinosaurs—including birds—evolved to digest their food.
To power flight, modern birds have evolved an extremely efficient, specialized digestive system. Instead of chewing their food with teeth, they swallow it whole down an enlarged esophagus, which in many birds forms a kind of pouch called the crop. The food then makes its way through a gauntlet of two stomachs. The first secretes digestive enzymes that chemically break down the food. The second, a thunderdome of muscle called the gizzard, grinds up the food with the help of small stones.
Some predatory birds such as owls take an additional step and spit back up pellets of undigested bone, feathers, and hair. This behavior appears to go way back: The feathered dinosaur Anchiornis, an ancient cousin of modern birds, seems to have also spat up pellets of bone, based on analysis of six 160-million-year-old fossils.
“I like the idea of imagining a little Anchiornis in a tree and chucking up a ball of early-mammal fur,” Persons says.
Some paleontologists had interpreted the Anchiornis evidence as a sign that forming gastric pellets was a necessary adaptation on the road to avian flight. By spitting up bone and feathers, the thinking goes, some flying birds wouldn’t have to lug around unnecessary weight. (Find out more about another feathered dinosaur that had four “wings” but couldn’t fly.)
But Microraptor’s flight-ready feathers seem to suggest that it could fly under its own power—and judging by the more intact state of Indrasaurus and other Microraptor meals, not all flying dinosaurs vomited up pellets. Of the four Microraptor specimens that have fossilized stomach contents, all four prey items appear to be whole, not jumbled-up bits of bone.
Though their sample size is small, O’Connor and her colleagues suspect that Microraptor kept its meals in its stomach for longer than Anchiornis and modern birds, ultimately passing bone in their feces like other dinosaurs such as Tyrannosaurus rex.
This difference may be surprising, given how closely Microraptor and Anchiornis are thought to be related. Perhaps the Anchiornis pellets suggest that its lineage lies closer to the ancestors of modern birds than the dromaeosaurs, the dinosaur group to which Microraptor belongs.
But as O’Connor points out, it’s also possible that pellets simply evolved more than once. After all, hacking up indigestible bits of food is hardly unique to birds; living creatures from crocodiles to sperm whales do it, too. Like other traits, such as feathers, perhaps birds’ presently unique digestive tract wasn’t so evolutionarily unique, after all.
“You can’t point to one change, one thing that evolved, and say that’s what contributed to [birds’] success,” O’Connor says. The ancestors of modern birds “survived the end-Cretaceous extinction probably because they were the only lineage that had all these adaptations that had evolved numerous times ... they were the ones that had them all together in one package.”