April 13, 2011

Birds Evolved Sense Of Smell From Dinosaurs

Birds are known in present time more for their vision and hearing than their sense of smell. However, a new study reveals that millions of years ago, their ancestors had a better sense for scents.

Scientists at the University of Calgary, the Royal Tyrrell Museum and the Ohio University College of Osteopathic Medicine tested a long-standing view that the sense of smell for birds declined as they developed heightened senses of vision, hearing and balance for flight during evolution.

The olfactory bulbs in the brains of 157 species of dinosaurs and ancient and modern-day birds were compared by the team.

Despite what we know today, the study found that the sense of smell increased rather than decreased in early bird evolution and peaked millions of years ago as the modern-day birds' ancestors competed with other dinosaurs and more ancient branches of the bird family for survival.

"It was previously believed that birds were so busy developing vision, balance and coordination for flight that their sense of smell was scaled way back," says Darla Zelenitsky, assistant professor of paleontology at the University of Calgary and lead author of the research.

She says, "Surprisingly, our research shows that the sense of smell actually improved during dinosaur-bird evolution, like vision and balance."

CT scans of dinosaurs and extinct bird skulls were used to reconstruct the brains. The scans helped the researchers determine the size of the creatures' olfactory bulbs.

"Of course the actual brain tissue is long gone from the fossil skulls," says co-author Lawrence Witmer, Chang Professor of Paleontology at the Ohio University College of Osteopathic Medicine, "but we can use CT scanning to visualize the cavity that the brain once occupied and then generate 3D computer renderings of the olfactory bulbs and other brain parts."

Olfactory bulbs are a part of the brain that is involved in the sense of smell. A larger olfactory bulb equates to a better sense of smell for modern-day birds and mammals.

The study also revealed how modern-day birds inherited their sense of smell from dinosaurs.

"The oldest known bird, Archaeopteryx, inherited its sense of smell from small meat-eating dinosaurs about 150 million years ago," says co-author of the study François Therrien, a curator of dinosaur palaeoecology at the Royal Tyrrell Museum.

"Later, around 95 million years ago, the ancestor of all modern birds evolved even better olfactory capabilities," he says.

Scientists have not been able to make a complete comparison, but it is believed that dinosaurs had a wide range of olfactory abilities, notes Witmar.

For example, the T. rex probably had large olfactory bulbs that helped it to track prey, find carcasses and maybe even aided in territorial behaviors. On the other hand, for Triceratops dinosaurs, the sense of smell was probably less important.

As for comparisons between ancient and modern-day birds, scientists were better able to make a better evaluation.

For example, Archaeopteryx had a sense of smell that is similar to our pigeons today, who rely on odors for a number of behaviors.

Zelenitsky says, "Turkey vultures and albatrosses are birds well known for their keen sense of smell, which they use to search for food or navigate over large areas."

"Our discovery that small Velociraptor-like dinosaurs, like Bambiraptor, had a sense of smell as developed as turkey vultures and albatrosses suggests that smell may have played an important role while these dinosaurs hunted for food."

The sense of smell among modern-day birds varies widely, according to the study.

Smarter birds such as crows, finches and parrots have smaller olfactory bulbs, which are believed to help compensate for higher brain power; whereas primitive birds such as ducks and flamingos have large olfactory bulbs.

The published study can be found in Proceedings of the Royal Society B: Biological Sciences.


Image 1: This is the dinosaur Bambiraptor in a turkey vulture's colors. Credit: Courtesy of Julius Csotonyi

Image 2: Evolution in birds of the olfactory bulb, the part of the brain where smell information is processed, passing from a dinosaur (Bambiraptor) through early birds (Lithornis, Presbyornis) to a modern-day bird (pigeon). Credit: Courtesy of WitmerLab at Ohio University


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