"The question of whether dinosaurs were warm- or cold-blooded is no longer the focus it once was," said Thomas Holtz, a dinosaur paleontologist and director of the Earth, Life, and Time program at the University of Maryland. "The majority of scientists would consider that dinosaurs certainly had elevated temperatures relative to living crocodiles, snakes, and turtles. Whether extinct dinosaurs had the same physiology as living mammals and birds remains uncertain. We haven't found the evidence yet to totally resolve it."
The warm-blooded/cold-blooded argument is now inextricably tied to the scientific tug of war over whether birds are descended from dinosaurs. Feathered dinosaur fossils found in extraordinarily rich fossil beds in northeastern China have brought the debate much closer to resolution. Only a handful of scientists oppose the birds-descended-from-dinosaurs point of view.
Having feathers does not mean dinosaurs could fly. Primitive feathers or a downy coat probably developed initially as a way to keep them warm.
Another long-standing and perhaps somewhat less vitriolic debateWhat wiped out the dinosaurs 65 million years ago?has evolved over the years, said Dale Russell, the senior curator of paleontology at the North Carolina State Museum of Natural Sciences. "The extinction of the dinosaurs by an extraterrestrial cause has become the most popular theory," he said.
Defining the Family Tree
Early ideas of what dinosaurs looked like were based almost entirely on specimens found in North America and western Europe. Paleontologists looking in South America, Africa, and China, in deserts and the Arctic, have rewritten the book.
"Paleontology has really gone international," said Norell. "It's not that we'd never seen fossils from Australia, South America, Africa, and Antarctica. But the increased amount of research has given us an entirely different, more globalized picture."
One of the big tasks of biologists is to describe the history of life, said Holtz. Paleontologists and biologists are interested in the evolutionary relationships between the different groups of dinosaurs, patterns of common ancestry, the sequence of adaptations acquired, whether changes occur independently within different groups, and the sequence in which diversity took place.
"We can't resolve those things without knowing what the family tree of dinosaurs looks like," Holtz said. "The increased number of fossils from the southern continents and increased computing speed have contributed to great strides being made in fleshing out that tree."
Technology's Day in the Sun
Breakthroughs in scientific applications and techniquesscanning, computer modeling, and the application of biomechanicsare also changing how we picture dinosaurs.
Scientists can tell a lot by studying soft-tissue anatomybody coverings, early feathers, muscles, veins, arteries, cartilage, respiratory systems, air sacs. Of course, the problem is that soft tissue is not fossilized.
One advance that has made a better understanding of dinosaur biomechanics possible is the leap forward in computer modeling of living systems.
"We know a lot less about the biomechanics of living creatures than people realize," said Holtz. "A lot of assumptions being made in the past were just that, assumptions, not tested in living forms. Only in the last five years have we had a detailed understanding of things like bird flight, running mechanics, what it takes to be a fast swimmer."
Larry Witmer, an associate professor of biomedical science at Ohio University and pioneer in this field, published a paper in 2001 on the correct placement of dinosaur nostrilsthey belong closer to the mouth rather than on the top of the head. What difference does it make if the dinosaur's nostrils were closer to his mouth than the top of his head? Nostril placement is key to the organization of the entire respiratory system, and has implications for how the creatures breathed, found food, ate, detected predators, reproduced, and regulated brain and body temperature.
The Smithsonian's National Museum of Natural History recently spent U.S. $1 million to remount their Triceratops horridusone of the first dinosaurs ever to go on displaybased on bone scans and computer modeling.
And the running speed of Tyrannosaurus rex?
John Hutchinson, a postdoctoral research fellow in the Biomechanical Engineering Division at Stanford University and a colleague developed a computer model of the fallen king, and determined that the dinosaur just didn't have the leg muscle to be all that fast. Their model placed its top speed at the lower end of 10 to 25 miles (16 to 40 kilometers) per hour; not completely lumbering, but also not likely to beat a car traveling at 45 miles (72 kilometers per hour) as depicted in the movie Jurassic Park.
Not everyone agrees with Hutchinson's interpretation, of course. "That's ridiculous," said Gregory Paul, an independent paleontologist based in Baltimore, Maryland. "There's plenty of evidence that Tyrannosaurus rex was a fast runner."
Leonardo, a 77-million-year-old mummified duck billed dinosaur (Brachylophosaurus) found in northern Montana may provide much-needed soft tissue clues to researchers. Only four mummified dinosaurs have ever been found, and three of them were discovered in the early 20th century when excavating and preservation techniques were relatively rudimentary. Patches of Leonardo's skin, scales, muscle, throat tissue, nail material, a beak, and foot pads were all preserved.
Clues to Life as a Dinosaur
Leonardo's stomach contents are so well preserved researchers can tell what he had for his last supper. His stomach contained pollen from 40 different plants, which will help determine the diet and paleo-environment of the Late Cretaceous (98.9 to 65 million years ago) in that part of the world.
Paleontologists are not proud; they use everything they can find to learn more about dinosaurs.
Dino poop, known more technically as coprolite, and dinosaur vomitboth of which would look like rocks to most of usprovide information not available from fossils, information about whator whoma particular dinosaur ate, how it digested its food, and how the food was processed.
There is tantalizing evidence from such widely diverse areas as Montana and the Gobi desert that some dinosaur species practiced parental care, much as birds do, tending and feeding their young. Recent nesting grounds found in Spain and France have yielded embryonic fossils. Trackways found in Oxford, England, that look to be made by different types of sauropodsbig, long-necked plant-eatershave lead researchers to consider the possibility that dinosaurs may have traveled in mixed-herds.
"We have slight snippets of evidence that indicate some herding behavior, and some snippets that suggest some parental care," said Norell. "But you have to remember that dinosaurs were an incredibly diverse group of animals, so we're not talking about these behaviors in all dinosaurs."
To know "a lot of this stuff takes discovery of fantastic fossils, and you just never know what you'll find," he said.
The fossil record gives us only a minute fraction of what existed, and much remains unknown.
"Say there are 5,000 species of mammals today; if we go back a million years ago and look worldwide, we find just a tiny tiny percentage of that in the fossil record," said Norell. "And the fossil record a million years ago is going to be better than 65 million years ago."
"What makes the Liaoning Province in China so interesting is we're finding all these small theropod dinosaurs, and there's no reason to believe they didn't live worldwide," he said. "But there's no evidence of them; small things with delicate bones don't preserve well."
More National Geographic News Stories on Dinosaurs:
Dino Hoax Was Mainly Made of Ancient Bird, Study Says
"Mummified" Dinosaur Discovered In Montana
"Weird" Bucktoothed Dino Found in China
Dinosaur Tracks Shed Light on Sauropod Evolution
New Find: Pterosaur Had Strange Crest, Fishing Style
Fossil Leaves Suggest Asteroid Killed Dinosaurs
New Study Supports Idea That Primates, Dinosaurs Coexisted
Mass Extinction That Led to Age of Dinosaurs Was Swift, Study Shows
Dinosaur Tracks Preserved on Scottish Island
Comets May Have Led to Birth and Death of Dinosaur Era
Fossil of Dog-Size Horned Dinosaur Unearthed in China
Tyrannosaurus rex Was a Slowpoke
Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out
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