Stephen Spielberg's movie Jurassic Park got one thing right.
Velociraptors hunted by night while big plant-eating dinosaurs browsed around the clock, according to a paper on the eyes of fossil animals published on-line this week in Science Express.
That overturns the conventional wisdom that dinosaurs were active by day while early mammals scurried around at night, said Ryosuke Motani, a geologist at the University of California at Davis, and a co-author of the paper.
"It was a surprise, but it makes sense," Motani said.
It's also providing insight into how ecology influences the evolution of animal shape and form over tens of millions of years, according to Motani and collaborator Lars Schmitz, a postdoctoral researcher at UC Davis.
"These authors' conclusion that these dinosaurs were active diurnally and nocturnally challenges a general dogma--that nocturnality in that time was mostly restricted to mammals," says H. Richard Lane, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.
Motani and Schmitz worked out the dinosaurs' daily habits by studying their eyes.
Dinosaurs, lizards and birds all have a bony ring called the "scleral ring" in their eyes, although this is lacking in mammals and crocodiles.
Schmitz and Motani measured the inner and outer dimensions of this ring, plus the size of the eye socket, in 33 fossils of dinosaurs, ancestral birds and pterosaurs--and in 164 living species.
Day-active, or diurnal animals have a small opening in the middle of the ring while the opening is much larger in nocturnal animals.
Cathemeral animals--active in both day and night--tend to be in between.
But the size of these features is also affected by ancestry.
For example, two closely related animals might have similar eye shape even if one is active by day and the other by night: the shape o
|Contact: Cheryl Dybas|
National Science Foundation