The research published Thursday in the journal Science represents a fundamental change in the way scientists view dinosaurs - not only in their outward appearance but in several important traits.
The determination of the correct placement of the nostrils helps explain how dinosaurs smelled, found food, detected predators and mates and regulated brain and body temperature, Ohio University paleontologist Lawrence Witmer said.
The study could also help scientists nail down whether dinosaurs were cold-blooded like other reptiles or warm-blooded like birds.
"The nose is a remarkable multipurpose organ," said Witmer, a dinosaur researcher at the College of Osteopathic Medicine of Ohio University. "It is involved in a whole range of physiological functions. ... It just makes more sense" for it to be at the tip of the snout, just above the mouth.
Since the 1800s, said Witmer, dinosaur scientists have assumed that the noses of the extinct animals were up just below the eyes. This was where the nasal passage dips into the skull, and most experts assumed the outside opening to this breathing airway would be nearby.
Since the tissue and cartilage of a nose are too soft to fossilize and never have been part of recovered dinosaur remains studied by scientists, said Witmer, researchers made an educated guess about where the dino nose belonged.
After some of the first dinosaur fossils were found in the late 19th century, he said, "experts thought they were so large that these animals couldn't have supported themselves on land and had to be aquatic so the water would support their bulk."
Since they lived in water, the reasoning went, and since the nasal opening in the skull was near the top of the head, then the nose must have been there, too.
"It seemed reasonable that (the nose) would serve as a kind of snorkel," Witmer said.
Later, scientists realized the huge dinosaurs were perfectly capable of living on land, "but we never thought about the nose again," Witmer said. "We left it on top of the head and never moved it."
Witmer is now proposing that the dino nose in pictures and models be moved to where he thinks nature actually put it - on the end of the snout.
"Even though it's a radical change in how we view the appearance of these animals, basically it makes them much more consistent with what we see in animals today. From a scientific point of view, it's much more conservative. To put the nostril on the back (of the snout) is sort of an off-the-wall sort of notion," Witmer said.
The researcher said he studied 62 animals from 45 species of crocodiles, birds and lizards, documenting the placement of soft tissues through dissection and hundreds of -rays. He found that nearly always the nose is on the very front of the face.
A forward-facing nostril can capture information right in front of an animal, while a nostril atop the head makes less sense, Witmer said.
Witmer also closely examined the bony skulls of many dinosaur specimens. On the long snouts, he found channels and tunnels that suggested the presence of delicate nasal passages filled with nerves and blood vessels and covered with cartilage and flesh.
The only reasonable explanation, said Witmer, is that dinosaurs had fine, long noses that extended in a fleshy tunnel from the nasal passageway near the top of the skull down to nostrils just above the mouth.
That is the most common type of nose in modern animals, said Witmer, and it seems most likely that dinosaurs would have the same arrangement.
If he is right, Witmer said, the airway for many of the larger dinosaurs was six to eight inches longer than previously believed. This could be important to the animal because a long nose does important things, he said.
"When we think of a nose we think of this thing that our glasses perch on," he said. But noses aren't made only to support specs or to smell the roses.
The moist airway of a nose filters and conditions air as an animal breathes. Warm air is cooled, cold air heated by the nose. Witmer said a nose can even condense some moisture from the air, helping an animal preserve fluids, which is important in dry regions. The longer the nose, the more effective it performs these functions, he said.
"This is a solid piece of work," Paul Sereno, a University of Chicago dinosaur expert.
Sereno said when he and others reconstruct dinosaurs from bony fossils, there is always a problem of where to put fleshy openings, such as the nose. Putting the nose farther front, he said, makes sense.
"If Larry Witmer says the nostrils are forward on dinosaurs, he's probably right," said Jack Horner, a dinosaur researcher at the Museum of the Rockies and Montana State in Bozeman. "He is definitely an expert on dinosaur noses."
"It's a powerful example of how our underlying assumptions may not fit with the actual evidence if simply looked at through the glasses of common sense and hypothesis testing," said University of Iowa paleontologist Christopher Brochu.
"We're now looking at these animals differently. So we're pulling new information from the same old bones," added University of Utah paleontologist Scott Sampson.
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