Bird brains have a dinosaur source
A winsome dino called Bambiraptor has helped scientists determine that birds inherited a good sense of smell from dinosaurs-and then improved the faculty. Birds are long thought to have evolved from small two-footed dinosaurs that over a long period grew feathers, took to dwelling in trees and eventually started to fly.
Copyright Agence France-Presse, 2011
The first identifiable bird was Archaeopteryx, which lived around 150 million years ago.
A common assumption is that these early avians had a poor sense of smell, as evolutionary pressure would have shaped brain resources in favour of vision, balance and co-ordination rather than olfaction.
Not so, suggests new research published on Wednesday in a journal of Britain's Royal Society.
Researchers in Canada used computed tomography - the famous CT scan used in medical diagnosis - 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.
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, says the study, had about the same olfactory capacity as a modern pigeon - pretty good and certainly better than expected. Then, around 95 million years ago, birds that were the ancestor of modern birds, evolved an even better sense of smell.
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. Among modern birds, sense of smell varies widely, the study found.
Relatively primitive birds such as ducks and flamingos have relatively large olfactory bulbs, while birds that are considered smarter, such as crows, finches and parrots, have smaller ones, presumably to compensate for higher brainpower.