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Photo courtesy of Lars Schmitz

Skull of a planting eating Diplodocus longusshows scleral ring.

Jurassic after dark: Did dinosaurs love the nightlife?

by Anna Gaynor
April 14, 2011


Photo courtesy of Lars Schmitz

 Skull of a Protoceratops andrewsi showsscleral ring.


Photo courtesy of Lars Schmitz

 Skull of a dinosaur shows scleral ring.


Photo courtesy of Lars Schmitz

Skeleton of a Ctenochasma elegans shows scleral ring.

Dinosaurs might have had a later bedtime than previously believed, University of California, Davis researchers reported on the online edition the journal of Science.

The study questions the belief that dinosaurs were diurnal, or active in the day, while the evening hours belonged to mammals.

Researchers find their answers by peering into fossilized dinosaur.

"We knew that there was something happening to eye shape," said co-author Lars Schmitz, a post doctoral researcher in evolution and ecology

Schmitz and Ryosuke Motani at UC Davis compared the eye structure of modern-day animals to the structure in dinosaur fossils. They concluded that many dinosaurs went out at night. Next, they recommend that researchers study the dinosaurs' surroundings and the effects diet and size had on when dinosaurs were active.

In 2004, Schmitz became interested researching dinosaurs while studying a marine reptile, which had a scleral ring. The scleral ring is a wheel-like bone located in the white of the eye surrounding the iris, he said. All birds and most lizards have scleral rings.

As do dinosaur fossils.

“That was a turning point,” Schmitz said, “and then I realized, wait a second, this could actually tell us something about dinosaurs, too.”

After studying modern animals' eye structure, the two traveled across North American, Germany and China to look at various museum collections of dinosaur fossils. They examined the eye sockets, scleral rings and the rest of the eye area.

“The eyes are known to be closely related to their environment,” Schmitz said. “They can tell us a lot about what kind of physical characteristics they are exposed to.”

The two researchers created a large family tree to help their analysis. According to Schmitz, two closely related species can have similar eye shapes because they have the same ancestry. However one could be diurnal and the other nocturnal. The researchers used those relationships to shape how they analyzed the data.

Peter Makovicky, associate curator of dinosaurs and the chair of the department of geology at the Field Museum said, Schmitz and Motani’s research is an example of a new trend in paleontology that started in the early to mid-‘90s.

Especially in the last few years, researchers have adapted the methodology to “use modern animals as a guide to see activity patterns,” he said.

While older studies made more linear connections, these studies use more data in their analysis, such as examining close species relatives.

“We started to address paleontological issues with a new toolkit,” Makovicky said.

For him, the paper adds another dimension to the field. Dinosaurs are no longer lumped together in one group with the same lifestyle habits.

Schmitz believes the strength of the paleontological field is that it takes such a comparative approach to research.

“If you just look at the standing diversity that we see today, you’re missing a whole chunk of information,” Schmitz said. “That way we can better understand how the diversity that we see today how that actually came to be.”