A new study on the fossilized remains of a flightless dinosaur has shed light on their diet.

Researchers from the University of Alberta studied the abdominal contents of two raptor-like predators known as Sinocalliopteryx at the Liaoning province in China. The dinosaur species was about six feet long (two metres) and was about the size of a modern-day wolf. Sinocalliopteryx is identified as a flightless dinosaur, but had feathers or hair-like fuzz covering its body to maintain a warm body temperature.

When the researchers analyzed the contents of the specimens' gut, they found that one of the Sinocalliopteryx had fossil remains of three flying bird-like dinosaurs known as the ConfuciusornisConfuciusornis are known be one of the earliest birds which have a basic resemblance to modern-day birds.

They found the birds in undigested state, suggesting that the Sinocalliopteryx might have consumed its prey one after the other in rapid succession.

The study shows evidence to the diet of the extinct vertebrates such as the Sinocalliopteryx. This species is said to have lived some 120 million years ago when the region was warm and filled with diverse fauna including bird-like dinosaurs, crocodiles and other vertebrates.   

According to the researchers, the evidence of three fossilized remains of flying bird-like dinosaurs in the stomach suggests that the raptor was once an avid eater.  "Stomach remains are evidence of actual interactions between animals, which is extremely rare in the fossil record," researcher Phil Bell, a vertebrate paleontologist at the Pipestone Creek Dinosaur Initiative in Canada, told LiveScience.

"We're lucky to find one or two bones of anything; to get a specimen with the remains of its last meal or meals is pretty cool," he said.

When the other specimen of Sinocalliopteryx was examined, the dinosaur species had remains of a small feathered bird known as Sinornithosaurus , a house cat-sized meat-eater that were able to fly shorter distances.

The fact that the ground-dwelling dinosaurs fed on flying bird-like creatures suggests that the SinocalliopteryxI might possibly be good hunters of prey, according to researchers.

The findings of the study published in the Aug. 29 issue of the journal PLoS ONE also give first direct evidence of a raptor falling prey to another dinosaur.