About 140 million years ago a microraptor—a bird-like dinosaur with four feathered wings—was zipping around in what is today northeastern China when it found a snack. The little dino grabbed a lizard and swallowed it whole, head first. Then, soon after, it died, likely on the edge of a mucky lake, which preserved the creature and its last meal for eons.
The intertwined fossils were discovered in the Jehol biota, a fossil bed from the Cretaceous era with some of the best-preserved records of species interacting and gobbling one another up. The hapless lizard that the Microraptor zhaoianus snacked on has paleontologists particularly excited; a new species, called Indrasaurus wangi, after the goddess Indra who was swallowed by a dragon, has teeth different from any other Cretaceous lizard, meaning it likely had a unique diet. The fossil is analyzed in the journal Current Biology.
Both diner and dinner are helping researchers piece together the complex food web of Jehol, reports Michael Greshko at National Geographic. Over the last two decades, 20 similar finds of animals with their stomach contents still intact have helped researchers begin to understand exactly who was nomming on whom around the ancient lake.
At the base are six types of plants whose seeds nourished herbivores. In the middle were smaller mammals, early birds and fish that acted as both predator and prey. Then there was the apex predator, Sinocalliopteryx, an 8-foot-long carnivorous theropod dinosaur that ate what it wanted.
M. zhaoianus was likely a step down from that, eating all sorts of creatures. Scott Persons of the University of Alberta, not involved in the study, explains the specimen was a generalist that fed on anything it could get in its mouth. So far, he says, the Jehota biota “is the best record we have anywhere of what dinosaurs were eating which other dinosaurs, and other things too.”
The lizard lunch also brings up another possibility. Modern birds eat in a very specialized way, some researchers believe, to help them fly. They typically swallow their prey whole, digest them in their gut, then hork up a pellet of bone, cartilage and fur. Getting rid of these heavy elements, the researchers believe, cuts down on weight and allows the birds to get airborne.
There is evidence that Anchiornis, a genus of dinosaur that’s a cousin to modern birds, digested food in this way. While microraptors and Anchiornis are thought to be closely related, the new find suggests that one may be more closely related to modern birds than the other. That’s because this is the fourth microraptor discovered with its stomach contents intact (the others had mammals, birds and fish in their tummies). That suggests the animals ate their prey whole, but didn’t digest them into pellets, instead keeping them in their stomachs longer and passing the bones in feces.
But it’s possible, too, that the pellet-vomiting strategy may have evolved multiple times. “You can’t point to one change, one thing that evolved, and say that’s what contributed to [birds’] success,” first author Jingmai O’Connor from China’s Institute of Vertebrate Paleontology and Paleoanthropology tells Greshko. The species that evolved into 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.”
Researchers may flesh out the Jehol food web even more in coming years. Thousands of fossils have been unearthed from around the ancient lake that still await analysis. In fact, this M. zhaoianus was dug up in 2003, but on first glance researchers didn’t see the lizard inside of it. Who knows what revelations lie in the tummies of other ancient beasts?