Some dinosaurs ‘did most of their hunting at night’

April 15th, 2011 - 1:46 pm ICT by ANI  

Washington, April 15 (ANI): Stephen Spielberg’s ‘Jurassic Park’ may have been right in depicting that the dinosaurs hunted in the night too.

A new study on the eyes of fossil animals has found that velociraptors hunted by night while big plant-eating dinosaurs browsed around the clock.

The findings overturns the conventional wisdom that dinosaurs were active by day while early mammals scurried around at night, said Ryosuke Motani, geologist at the University of California at Davis, and a co-author of the paper.

It’s also providing insight into how ecology influences the evolution of animal shape and form over tens of millions of years, said Motani and collaborator Lars Schmitz, a postdoctoral researcher at UC Davis.

The researchers 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.

By looking at a 164 living species, they could confirm that the eye measurements were accurate in predicting whether animals were active by day, by night or around the clock.

Then they applied the technique to fossils, including plant-eating and carnivorous dinosaurs, flying reptiles called pterosaurs and ancestral birds.

The big plant-eating dinosaurs were active day and night, probably because they had to eat most of the time, except for the hottest hours of the day when they avoided overheating.

Modern megaherbivores like elephants show the same activity pattern, said Motani.

Velociraptors and other small carnivores were night hunters.

Flying creatures, including early birds and pterosaurs, were mostly day-active, although some of the pterosaurs–including a filter-feeding animal that probably lived like a duck, and a fish-eating pterosaur–were apparently night-active.

“This strongly suggests that ecology drives activity,” said Schmitz.

The study is published online this week in Science Express. (ANI)

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