Four-winged dinosaur raptor feasted on fish

Microraptor probably was as big as a hawk, had teeth like a crocodile and could spear fish like a kingfisher -- when the diminutive, four-winged dinosaur wasn’t busy plucking squirrel-like animals and other birds from trees.

That’s the conclusion drawn by scientists who found fish remains preserved in the stomach of a Microraptor gui fossil in the Jehol area of northeastern China, known as the Pompeii of the Cretaceous period. Their work was published this week in the journal Evolution.

“Prior to this specimen, we actually thought it was a candidate for the title of the world’s tiniest dinosaur,” said Scott Persons, a paleontologist at the University of Alberta in Canada. “Our new specimen punches that size up. It’s actually the size of a hawk. Previous specimens were the size of a pigeon. We believe those were juveniles.”

The discovery suggests it’s too early to hold up Microraptor as conclusive evidence that birds evolved from dinosaurs in a “tree-down” fashion – dwelling in branches and dining on other mammals rather than employing flight in its efforts to capture prey.

“If it caught the fish, it was not doing it like a stork,” Persons said. “It was more like a kingfisher.”

Microraptors also had teeth that pointed outward like those of a crocodile, with serrations only on one side, Persons said. That latter evolutionary development is common in piscivores, and probably helped Microraptor become an efficient fisherman in a forested area surrounding a large lake about 120 million years ago.

“If you want to grab ahold of fish, you don’t want to slice and dice it,” Persons said. “You want to spear it and swallow it and not have it squirm and thrash around and go swimming off.”

The fish remains could not be fully identified, although the researchers believed it was a ray-finned species whose fossilized remains are abundant in that area.

“Fish are the most common vertebrate fossil found in that part of China, and the most common dinosaur found there was Microraptor,” Persons said.

Microraptor has been at the center of a controversy over two theories of how flight developed among feathered dinosaurs. One holds that they were land-based, and extended their extremities while running from predators, giving those that could briefly take flight a distinct survival advantage. The “arboreal” theory holds that these bird ancestors glided to the ground from trees, and that those that could flap to stay aloft longer proved more adaptive.

The paper does not resolve the debate, although it strongly suggests that Microraptors were opportunistic, dining on a wide variety of prey and were not limited to the trees.