Rendered skulls and brains (in blue) from CT scans of small theropod dinosaur Bambiraptor (top), extinct bird Presbyornis, and modern-day pigeon (bottom). Rendered brain in lower left belongs to the extinct bird Lithornis. Credit: WitmerLab, Ohio University.
Artist's rendering of the dinosaur Bambiraptor in a turkey vulture's colours. While the colours are speculative, Bambiraptor had a keen sniffer similar to that of a modern-day turkey vulture. Credit: Julius Csotonyi
PARIS: Modern birds inherited a good sense of smell from dinosaurs – and then improved the faculty, according to new research. Combined with good vision and coordination, this may have helped the birds survive the Cretaceous-Tertiary extinction event 65 million years ago.
A common assumption is that early avians had a poor sense of smell, as evolutionary pressure would have shaped brain resources in favour of vision, balance and coordination rather than olfaction.
But a new study by Canadian scientists 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,” said lead author Darla Zelenitsky, palaeontologist at the University of Calgary. “Surprisingly, our research shows that the sense of smell actually improved during the dinosaur-bird transition, just like vision and balance.
Visualising the brain cavity
Publishing their results in the Proceedings of the Royal Society B: Biological Sciences. the researchers used computed tomography (CT) to get a 3D image of the skulls of dinosaurs, extinct birds and modern birds.
They measured the likely size of the olfactory bulb, a part of the brain that is used in smell. Among modern-day birds and mammals, a larger olfactory bulb means that the sense of smell is better. 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,” said study co-author Lawrence Witmer, from the Ohio University College of Osteopathic Medicine in the U.S. “But we can use CT scanning to visualise the cavity that the brain once occupied and then generate 3D computer renderings of the olfactory bulbs and other brain parts.”
Evolving better olfactory capabilities
The 157 samples traced the olfactory lineage of modern birds to a group of small carnivores called theropods whose larger family also included the Tyrannosaurus rex. Early birds, said the study, had about the same olfactory capacity as a modern pigeon – pretty good and certainly better than expected.
“The oldest known bird, Archaeopteryx, inherited its sense of smell from small meat-eating dinosaurs about 150 million years ago,” said co-author François Therrien, curator of dinosaur palaeoecology at the Royal Tyrrell Museum in Canada.
“Later, around 95 million years ago, the ancestor of all modern birds evolved even better olfactory capabilities.”
Using smell for hunting
Included in the fossils from this time was Bambiraptor, one of the key pieces of evidence for bird evolution. A fast-moving critter about the size of a dog, Bambiraptor was unable to fly, but its body was probably covered in feathers and its skeleton was astonishingly similar to fleet-footed birds like roadrunner.
It had roughly the smell capacity as turkey vultures and albatrosses today, which rely on smell to forage or navigate over long distances, the researchers found.
“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,” said Darla Zelenitsky, a University of Calgary palaeontologist in Canada.
Surviving the dinosaur extinction
Modern birds survived the mass extinction that wiped out dinosaurs and archaic birds. The combination of a keener sense of smell, good vision and coordination in early modern birds have may been advantageous when orienting themselves during flight or when looking for food or suitable habitats.
“Although there are no clear answers explaining why some groups of animals survived the extinction when so many others died out, maybe the keener sense of smell in of modern birds could have been a factor that helped them survive the Cretaceous extinction,” said Zelenitsky.
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 their enhanced smarts may have decreased the need for a powerful sniffer.
