UC Davis dinosaur eye bone study offers new view

SFGate: UC Davis dinosaur eye bone study offers new view

In the long-ago age of the dinosaurs, the smaller, fierce and predatory beasts were night hunters, stalking and seizing their unwary prey in the dark, while giant plant eaters of the same era browsed both day and night in order to fill the energy needs of their huge bodies.

This new picture of dinosaur behavior - based on studies of the fossil bony structures of their eyes - has been drawn by paleontologists at UC Davis, and it challenges some long-held ideas about the way dinosaurs lived.

Lars Schmitz, a postdoctoral researcher, and Ryosuke Motani, an evolutionary biologist at Davis, developed an ingenious approach to their study.

They measured the fossil eye bones of 33 varied dinosaurs, including those that lived on land like velociraptor of movie fame and archaeopteryx, the first flying bird, as well as diplodocus, the long-necked land giant that gorged on leaves and ferns and all sorts of other vegetation.

They also examined the eye bones of 164 modern birds, because the birds - as dinosaur experts now maintain - are, in fact, living dinosaurs.

Within the bony eye sockets of all those animals is a circular bone called the scleral ring; the ring is larger around large eyes and smaller when eyes are smaller. Big eyes let in more light allowing animals to see in the dark; smaller eyes are all that's needed to see clearly in daylight.

So Schmitz and Motani measured the scleral rings in all the fossil beasts they could find, and in the modern birds, too, and they concluded that the bony rings are excellent clues to the feeding habits of the dinosaurs.

In the movie "Jurassic Park," the savage velociraptors were pictured as hunting their prey only at night, but that image annoyed many scientists, for conventional wisdom held that the carnivorous beasts only attacked by day.

But velociraptor fossils show large scleral rings in their skulls - suggesting their large eyes helped them to prey on the small mammals for food at night. So, it seems, the makers of "Jurassic Park" were right.

And diplodocus, the huge plant eaters with the long, snake-like necks, had smaller scleral rings, indicating they must have been actively feeding most of the day and evening - except for the hottest sunshine hours when their bodies needed to avoid overheating, the scientists concluded.

Flying dinosaurs like archaeopteryx were daylight hunters, the analysis showed, although some modern birds that hunt at night have large scleral rings, Schmitz said.

Mark Goodwin, assistant director of the Museum of Paleontology at UC Berkeley and an expert on dinosaur bone growth, said the Davis scientists developed "a creative and innovative technique" to infer the activity patterns and behavior of the dinosaurs.

The researchers also have shown that earlier notions of dinosaurs as daylight hunters "may be, at best, very simplistic and most likely not entirely accurate," Goodwin said.

"I like the study," he said.

Schmitz and Motani published two reports of their study last week, in Science Express and in the journal Evolution.