Scientists investigated two specimens of a carnivorous dinosaur from Liaoning, China, known as Sinocalliopteryx gigas, shown here feeding on the dromaeosaur Sinornithosaurus.
[Read more about the predatory dinosaur]
One of the specimens held the remains of a crow-size, flight-capable, bird called Confuciusornis, suggesting the species might have been a stealthy, capable hunter, the researchers said.
The predator Sinocalliopteryx gigas was about 6 feet (2 meters) long, roughly the size of a wolf, and had feathers or hairlike fuzz covering its body to help keep it warm.
A tiny bird skeleton within the stomach of the dinosaur Sinocalliopteryx.
Possible scapula bone from the tiny bird found in the abdomen of Sinocalliopteryx gigas. The bone's texture suggests it was corroded by gastric juices, the researchers said.
Abdominal contents of Sinocalliopteryx gigas, which include undigested featherlike structures (blue), the hindlimb of a dromaeosaurid (red), and gastroliths, or stones in the gastrointestinal tract that help with the mechanical breakdown of food (yellow).
A close-up of the right hind limb of the dromaeosaur Sinornithosaurus inside the stomach of one of the specimens of Sinocalliopteryx gigas found in Liaoning, China.