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Pigeons may not instill the same aura of fear as a Tyrannosaurus rex, but they inherited their sense of smell from such prehistoric killers.

Birds are known more for their flying abilities and their senses of vision and balance than for their sense of smell. According to conventional wisdom, the sense of smell declined during the transition from dinosaurs to birds as the senses of vision and balance were improved for flight. But new research published today by scientists at the University of Calgary, the Royal Tyrrell Museum and Ohio University suggests that millions of years ago, the winged critters also boasted a better sense for scents than their dinosaur ancestors.

"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 Dr. Darla Zelenitsky, Assistant Professor of Paleontology in the Department of Geoscience at the University of Calgary and lead author of the paper published in the journal Proceedings of the Royal Society B. "Surprisingly, our research shows that the sense of smell actually improved during the dinosaur-bird transition, just like vision and balance."

The research team used state-of-the-art CT scan technology to examine the skulls of dinosaurs and extinct birds to determine the size of the creatures' olfactory bulbs, a part of the brain involved in the sense of smell. Among modern-day birds and mammals, larger bulbs correspond to a heightened sense of smell.

"Of course the actual brain tissue is long gone from the fossil skulls," says study 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."

The study of fossils revealed interesting details about the evolution of the sense of smell among early birds.

"The oldest known bird, Archaeopteryx, inherited its sense of smell from small meat-eating dinosaurs about 150 million years ago," says co-author Dr. François Therrien, 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."

The combination of a keener sense of smell, good vision and coordination in early modern-day birds have may proved advantageous to orient themselves when flying and to look for food, mates, or suitable habitats.

The team was able to compare some ancient and modern-day animals under study. They discovered that ancient birds, like Archaeopteryx, had a sense of smell similar to pigeons. "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," says Zelenitsky. "Our discovery that small Velociraptor-like dinosaurs, such as Bambiraptor, had a sense of smell as developed as these birds suggests that smell may have played an important role while these dinosaurs hunted for food."

The notion that birds have a poor sense of smell may have been influenced by the birds we are most familiar with. The study found that among modern-day birds, the more primitive species, such as ducks and flamingos, have pretty large olfactory bulbs while the birds with the smallest olfactory bulbs are the ones we see every day—the perching birds (crows, finches)— at our feeders and the parrots in our bird cages. It may be no coincidence that the latter are also the cleverest birds, suggesting that enhanced smarts may decrease the need for a powerful sniffer.

Source : University of Calgary

April 14, 2011 12:22 AMBiology

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