Image: Dinosaur siege

A pack of aucasaurs, predators of Argentina's Auca Mahuevo badlands, attacks a group of startled titanosaurs in this artist's depiction. Scientists believe Aucasaurus probably attacked in packs, pushed past adult titanosaurs guarding nests, and picked off baby titanosaurs as they hatched.

Artwork by John Sibbick

Written by Joel Achenbach

Republished from the pages of National Geographic magazine

The bull gator lay in the sand under the oak trees. A few days earlier he had been hauled out of a murky lake in central Florida. Researchers instantly named him Mr. Big. He was sofa-size, with fat jowls framing his head like a couple of throw pillows. He would have measured 13.5 feet (4 meters) if a rival hadn't chomped the last foot off his tail.

Four people sat on his back. Excited alligators do more than thrash—they can spin like wound-up rubber bands. Yet Mr. Big, with his mouth taped shut and a towel over his eyes, was completely docile, as inert as luggage. He behaved like a gator basking in the sun rather than one in the middle of a science experiment.

Gregory Erickson, the scientist, stood a few paces away, grimly holding a plastic pole tipped with a little square plate called a force transducer. He intended to put this in the animal's mouth, to measure the force of its bite. Erickson also intended to retain all his body parts, which explained his serious countenance.

A man on the gator's back removed the towel and the tape. The animal opened its eyes and hissed. It was a factory noise, a steam pipe venting. The mouth opened as slowly as a drawbridge. The maw on Mr. Big was spacious enough to house a poodle. Erickson presented the force transducer to the largest tooth at the back of the right upper jaw—and the jaws snapped shut.

"Trouble, we got trouble!" Erickson said as the gator, pole firmly clamped, began to lurch in his direction. But then the animal calmed down. Erickson read some numbers off a meter. "Two point nine six—that's a lot!" he said.

The creature's jaws had come together with nearly 3,000 pounds (1,360 kilograms) of force.

The odd thing about this little experiment was that it was fundamentally about dinosaurs. Erickson, a paleobiologist at Florida State University, is an expert in the feeding behavior of tyrannosaurs, including the bite marks left on bones. That research spurred him to find out more about bites in general, which is why he's out here moonlighting with crocodilians.

We loaded Mr. Big on an airboat to be towed overland back home to Lake Griffin, about an hour to the south. We spent the night lakeside, testing ten more gators that had been freshly yanked from the water. All the while, we talked about dinosaurs.

Shortly before dawn—by which time we were thoroughly scuffed up and swampy, though still in possession of all our digits—Erickson turned to me and said, "It's not like diggin' bones, is it?"

Bone-diggin' is still essential, but an increasing number of vertebrate paleontologists are going beyond the bones, looking for novel ways to study dinosaurs.

Instead of spending the summer in a dusty badlands bone bed, they might spend it in a laboratory, analyzing the evolution of the flight stroke by tossing pigeons into a wind tunnel. Instead of scraping away the sandstone overburden on a nicely articulated ceratopsian, they might point and click on a computer screen, pivoting digital bones.

These paleontologists tend to be on the young and idealistic side, determined to intensify the scientific rigor of their profession. Their goal is to hunt not just for dinosaurs but for something even harder to reconstruct—how dinosaurs functioned and behaved.

They are tackling difficult questions:

Were dinosaurs fleet of foot or ponderous? What did they eat? Did they hunt or migrate in packs? Did they parent their young?

How fast did they grow? Did they get bigger and bigger even into old age? And how old did they get?

Did they use horns and frills and spikes in battle, like they do in the movies? Were these unusual anatomical structures part of the business of attracting mates?

How did one group of these creatures develop the ability to fly?

These new scientists are a diverse bunch, emerging from evolutionary biology, biomechanics, botany, physiology. Their tools include computers, CT scans, x-rays, and electron microscopes. They publish papers with titles like "Nostril Position in Dinosaurs and Other Vertebrates and Its Significance for Nasal Function" and "Caudofemoral Musculature and the Evolution of Theropod Locomotion." We might say they are geekier than the older generation of dinosaur researchers, and then quickly add that we mean this in the best sense of the word.

Make no mistake, the "field"—which is anywhere and everywhere bones can be found—still dominates dinosaur research. In recent years the field has produced feathered dinosaurs from China, egg-laying dinosaurs from Patagonia, and a host of new dinosaur species, such as the scale-breaking Argentinosaurus and the fearsome Giganotosaurus. In the field we find direct evidence of a lost world ruled by titanic creatures, thriving all over the globe from 230 to 65 million years ago, during the Mesozoic era.

And the field has charms that the laboratory can't match. The field is the staging ground for that whole Indiana Jones thing, for the type of charismatic, rock-star scientists who hang out in dinosaur graveyards with shovels, picks, plaster, graduate students, and personal documentary film crews.

But perhaps the very glamour of dinosaurs has spawned the backlash, the willful retreat to scientific basics by Greg Erickson and researchers like him. Most scientific disciplines aren't caught in the gravity well of public fascination. If you study fossil mollusks, for example, you aren't likely to be asked to become a scientific adviser for a Hollywood blockbuster. No one has snail fever. But dinosaur fans are insatiable for information. The new generation of scientists wants to put constraints on all the hypotheses flying around, and they think that the truth about dinosaurs—and dinosaur behavior—won't be uncovered with bones alone.

"For 20 years we've done what we call arm-waving," says Jack Horner, a legendary bone collector. "We've made hypotheses based on very little evidence. Now we're sitting down, we're saying, We've got all these ideas, are they real?"'

Horner can arm-wave like a champ, as he will admit. Since 1991 he's been arguing, for example, that Tyrannosaurus rex, the very emblem of predation, the killer of killers, was actually just a scavenger, an eater of the dead. An overgrown turkey vulture! Those banana-size teeth weren't for ripping live flesh, says Horner, they were for crushing the bones of a carcass. This is vintage contrarianism, and Horner so far has failed to persuade many of his peers, who point out that T. rex need not have been one thing or another. Hyenas, for example, are scavengers one day, predators the next.

But in any case this is precisely the kind of argument that can't be won by speaking louder than one's opponents. Science requires data. Science requires that ideas be subjected to tests. And paleontology—if the new generation has its way—will be seen as a no-nonsense field, a hard science, in addition to being a thrilling subject built around the bones of large, scary animals.

"This is where we have the rhino heads and the manatee heads," Lawrence Witmer is saying. "We've got a whole bin of ostrich heads and necks. We've got ducks and geese. Here's a bag of alligator parts."

We're in the deep freeze of his laboratory at Ohio University in Athens. Witmer has quite the collection of heads. They belonged to creatures that died, or were killed for some other reason, and were then obtained by Witmer for research. I keep thinking Witmer is about to produce the horse head from The Godfather.

Witmer reconstructs the soft tissues in dinosaur heads. His method exploits similarities among creatures across the vastness of time. It turns out that a dinosaur of the Triassic period, 248 to 206 million years ago, had anatomical features remarkably similar to those of a contemporary alligator or seagull.

Witmer recently caused a stir when he said that artists had long put the nostrils of dinosaurs too high on the head. He spent months studying the relative positions of noses and nostrils in modern animals. He wanted to see if there is a correlation—whether the bone of the nose reveals the location of the fleshy nostril. He found that as a rule there is such a correlation.

Witmer then examined fossils and discovered that in modern renditions of dinosaurs the nostrils had always been misplaced. They should be shown low on the nose, near the mouth. Nostrils in that location would heighten the animal's ability to nuzzle a potential food item and decide whether it was biteworthy.

Witmer investigated another paleontological presumption, the notion that Triceratops and other plant-eating dinosaurs had cheeks, like cows or horses or humans. Conventional wisdom said these cheeks were like feed bags, helping the animal chew and re-chew vegetation. Witmer, to his surprise, discovered that animals with cheeks have bone structures that are lacking in Triceratops and other herbivorous dinosaurs. Triceratops, he thinks, had something more like a bill or a beak.

The plant-eating dinosaurs may have clipped vegetation off plants with these beaks and then swallowed the material pretty much intact. "They probably actually chewed with their stomachs," Witmer says.

The day I visited, Witmer took maybe 15 animal heads out of the freezer and arranged them on a table, a buffet from a nightmare. He explained how he dissects them to examine soft tissues and how he uses his findings to flesh out model dinosaur heads. As we talked, the heads thawed. They got rather…drippy. Beyond ripe. The moose head seemed particularly malodorous. "Most of these guys are past their sell-by date," Witmer said, unfazed.

A few hours later, putting the heads back in the freezer and mopping up the mess, he said, "There's no real substitute for doing what we're doing—getting your hands dirty, rolling up your sleeves, getting out a scalpel, and seeing how these things are really put together.

Stephen Gatesy is another pioneer of the new dinosaur science and can spend days at his computer screen zeroed in on a single trochanter, the knobby protrusion on a bone where a tendon once attached. He might spend months or even years on a shoulder joint.

"I'm not ambitious enough to take on the whole animal," he told me when I visited him at Brown University.

That's a classic statement of the new science. Think of how dinosaur paleontology has been dominated by "the whole animal," by spectacular specimens, huge skeletons that can fill the entrance hall of a museum. This fellow Gatesy can get wrapped up in a single metatarsal.

A traditional dinosaur researcher might take a couple of loose dinosaur bones, stick them together at the joint, wiggle them, pivot them, move them around, and pronounce, "I think they went like this." Gatesy wants to do the hard labor of figuring out how these structures evolved and affected locomotion—how dinosaur ancestors, for example, went from walking on four legs to walking on two (and apparently back to walking on four in some cases). Thrown into the mix is the stunning fact that some dinosaurs lifted off the ground entirely.

How did flight develop?

Did the first airborne dinosaurs merely glide, or did they flap?

Did the flight stroke evolve from other types of motion, such as grabbing prey or trying to elude a predator? Were they flappers before they were fliers?

Or did flying emerge from climbing? The flight stroke might have given an animal increased traction on steep inclines. There's recent research at the University of Montana showing that baby birds, for example, start flapping when ascending an incline. They're not trying to fly, just trying to climb better.

Anatomy can be deceiving. Birds have hollow bones, feathers, wings, reduced tails, and wishbones, each characteristic designed for flight. And yet each of these traits or something like it appears in the fossil record before birds flew.

The dinosaur fossil record is actually rather poor. Intact, articulated, museum-quality skeletons are fairly rare. Fossils fall apart. A bone exposed to the elements may simply explode. In some bone beds there are so many tiny skeletal fragments you'd think the creatures had been dropped from a plane.

That's why dinosaur behavior is so difficult to fathom from just bones—why the task of understanding dinosaurs is truly like trying to squeeze blood from a stone. Some would argue that dinosaur behavior is a topic all too similar to extraterrestrial life—long on speculation and short on data.

Gatesy and other paleobiologists are struggling to ascend what Witmer calls the Inverted Pyramid of Inference. Imagine an upside-down pyramid with, at the pointed bottom, the word "bones." Bones are the known commodity, the solid evidence. They are aged; they may be broken, cracked, ambiguous. But you can at least hold them in your hand.

Above bones on the inverted pyramid are soft tissues. There aren't many of those because they rarely fossilize.

Above that is function, how the bones and tissues worked.

Above that—so very far from the hard evidence of bones—is behavior.

Above that is environmental interaction. The dream would be to know the behaviors of many different dinosaurs and to be able to put them in context so you'd know what dinosaurs ate and where they slept and what they feared and how they prowled the landscape.

And at the very top of the inverted pyramid, as far from hard science as you can get, is…well, probably the purple dinosaur known as Barney.

Dinosaur science was inherently flamboyant and mind-boggling from its very beginning. In 1853 paleontologist Richard Owen (who had given dinosaurs their name a little more than a decade earlier) staged a celebrated sit-down dinner in London. He and 21 other scientists dined at a table set up inside a model of an Iguanodon. An engraving of the scene created a national sensation in Great Britain.

Bone hunters scrambled to find ever more spectacular specimens. By the early 20th century the preeminent ambition in the field was to mount a skeleton dramatic enough to scare the bejabbers out of a schoolchild.

Roy Chapman Andrews's journeys to Mongolia's Gobi in the 1920s were worthy of a Cecil B. DeMille movie—great caravans of camels stretching into the wasteland, with Andrews packing a pistol and posing on bluffs with jaw thrust forward.

But just two decades later the heroic age of dinosaur collecting was over. Scientists began to view dinosaurs as an evolutionary dead end. They were tail-dragging losers in a Darwinian world, defeated by quicker, smarter mammals. "It is a tale of the triumph of brawn, a triumph that was long-lived, but which in the end gave way to the triumph of brain," wrote Edwin H. Colbert of the American Museum of Natural History in his 1945 publication, The Dinosaur Book.

The field was in the doldrums when in 1975 Robert Bakker, a maverick paleontologist at Harvard, published an article in Scientific American titled "Dinosaur Renaissance." It gave a shot of adrenaline to the entire discipline. Bakker, building on the work of his mentor, Yale's John Ostrom, said that dinosaurs were not cold-blooded, but rather warm-blooded, active, quick. They may have nurtured their young and hunted in packs. And they weren't even extinct! Birds, Bakker said (again, echoing Ostrom), are themselves the direct descendants of dinosaurs.

The new image carried the day. In the Jurassic Park movies the dinosaurs are fully Bakkerian. They sprint across meadows. They nurture their young. The "raptors" are so savvy they seem on the verge of inventing spaceflight.

"I'm a method paleontologist," Bakker said one day in Boulder, Colorado. He means like a method actor—like Robert De Niro or Marlon Brando. "I want to be Jurassic. I want to smell what the megalosaur smells, I want to see what he sees."

From a cigar box on the table he pulled a T. rex tooth. "This is a bullet," he said. A fossil site is a crime scene, he explained, and the teeth are the bullets. He thinks he's found evidence in the teeth of allosaurs, meat-eaters of the Jurassic, that those dinosaurs dragged huge prey to their nests to feed to their babies. As he puts it, "You're under care. Your first meal is given to you, and it's steak, and it's six feet [1.8 meters] thick."

Since Bakker's been theorizing about dinosaurs for more than a quarter century, I asked him if he thought dinosaur paleontology has become a more rigorous science with its new emphasis on lab work. He replied by citing an 1822 study of Ice Age hyenas by the Reverend William Buckland. Bakker says Buckland's work is as good as any modern paleontology. The profession looks at history, Bakker says—at the narrative of the rocks and bones. It can't possibly turn into a laboratory science.

"People who don't understand paleontology try to make it physics," he said. "Paleontology is history. It is made up of millions and millions of crimes. There are victims and there are perps."

Meanwhile, back at the lab....

John Hutchinson, a 30-year-old researcher at Stanford, wants to answer a big question: Could T. rex run? If so, how fast? Did it have the leg muscles to sprint 45 miles an hour (72 kilometers an hour) as some paleontologists contend?

Hutchinson doesn't think T. rex was that swift. He ponders T. rex through the prism of biomechanics. "The dream goal is to reconstruct exactly how an extinct dinosaur moved," he says. He uses a computer program that has digitized a number of T. rex bones.

To run that fast, Hutchinson figures, T. rex would have to have been almost all leg. Chickens run well, but a 13,000-pound (5,900-kilogram) chicken, Hutchinson has calculated, would need to have 62 percent of its mass in each leg.

Hutchinson also studies elephants and has made several trips to Thailand to analyze their locomotion. He paints white dots on elephants at crucial joints in the shoulders and legs. Then he chases the elephants, shouting "Bai, Bail" which means "Go, Go!" In videotapes he captures the movement of the white dots.

What Hutchinson sees in the tapes doesn't look like running. At least not exactly.

"The best definition of walking is that the body swings over the leg like a stiff, inverted pendulum. Running is very different. It's like a pogo stick, a bouncing ball. Instead of the leg being stiff, it compresses like a spring. So you're using that spring to keep running efficiently. The spring stores energy."

There are a couple of intermediate forms of locomotion, including what has been called the Groucho run, named after the bent-legged walking that Groucho Marx made famous.

Elephants are more on the Groucho side of things. They keep at least one leg on the ground at all times—like a walker—but the white dots move down then up, indicating a bouncing gait.

Hutchinson showed me how to use his computer program to move muscles around, to attach them at different places on the bones, altering the leverage. By playing around, I'm pretty sure I created a dinosaur that couldn't do much of anything but fall over backwards.

"I could spend all my life on this, analyzing every little data point," he said. "You have to have very well-defined questions, or else you'll just get submerged in data and never get anywhere"

There's another way to observe dinosaur behavior, and it doesn't involve bones or computers. Dinosaurs left tracks.

One summer day I checked out some dinosaur tracks at an abandoned mine in the Rocky Mountain foothills near Grand Cache, Alberta, Canada. I was with Rich McCrea, a 33-year-old doctoral candidate at the University of Alberta, who has scrambled over almost every square inch of exposed rock.

McCrea likes tracks. He says they're the closest he can come to live dinosaurs without using a time machine. When he presented his master's thesis, he jokingly told the professors he'd love to find a six-footed trackway. You know, two dinosaurs mating. Reptilian passion captured in stone. The professors were not visibly amused.

The fact is, most dinosaur footprints capture a mundane activity: walking. In one direction, usually. One of McCrea's associates jokes that, to judge by most dinosaur tracks, these creatures couldn't turn.

The mine is at the end of a dusty road that until recently was heavily used by coal trucks. The miners sliced off a chunk of a mountain, and there's a wall of stone more than two miles (three kilometers) long. At first you might not notice the prints. Then you see one or two, clearly outlined on the rock face. Then they gradually come into focus. The rock face is covered with footprints—"totally polluted," McCrea says admiringly.

Some go this way, some go that way. There are quadrupeds and bipeds, plant-eaters and meat-eaters. Some tracks strongly suggest herding behavior, and McCrea thinks there's evidence that meat-eaters stayed clear of the deep muck of coal-producing marshes. On some of the dark rock surfaces, remnants of swampy terrain, there are only plant-eater tracks. They were probably ankylosaurs, McCrea says. "They're like Humvees, four-wheel drives."

We climbed up a seam of broken rock, feet churning through coal fragments, and on a higher rock face found some theropod tracks, footprints that quite possibly had never been seen by a human being. The mine, after all, was a fairly recent operation, and the rock faces sheer off regularly, meaning there are always new exposures. Yet after a few hours of exploring, one also sees the limits of the trackway profession. Footprints are just footprints. Other scientists have eventually given up on this site, McCrea says. "They couldn't handle the ambiguities inherent in footprint research."

A while back Steve Gatesy decoded some dinosaur footprints. He'd gone with some colleagues to Greenland—yes, even the most dedicated digital bone manipulators spend time in the field—and found thousands of tracks. They varied greatly, as though made by different species. Some tracks had an odd, bulbous structure at the end of the third digit, like a miniature volcano had erupted. What kind of feet left such odd prints?

For help, Gatesy turned to a turkey. He and a student at Brown bought one from a nearby farm and coaxed it to walk across a variety of hard and soft surfaces, including thick mud. The turkey didn't much care for this, but the tracks it created offered a revelation: All those different dinosaur footprints could have been made by the same species. What varied was not the type of animal but the type of surface.

And that odd, volcanic shape at the end of the third digit? The turkey and the mud explained that too. As the foot goes into the goop with toes spread, it makes the initial footprint. It strikes the hard subsurface then lifts again, bunching like a closed fist. The entire foot emerges from the muck at the front of the track, creating a craterlike exit mark.

It's arcane, to be sure, but science is often nothing more nor less than deconstructing what we're staring at.

The ultimate dinosaur behavior was the act of going extinct. And the mystery of that event has hardly been solved.

So even before dinosaurs became extinct, they were disappearing in this part of the world. That is why it's so important for the discipline to go beyond the bones and truly understand these creatures and their environment. Something triggered a tremendous decline in biodiversity. The big impact may have been merely the final blow.

The end of the Cretaceous was a time when the global climate was changing and the sea level dropping. A shallow sea that covered the heart of North America drained. Lands that were formerly separated by water were now connected. New species arrived, perhaps carrying deadly microbes.

No wonder it's such a haunting scenario. Our world today is undergoing a climate change, a period of emerging pathogens, a rapid mixing of Earth's biota, a loss of biodiversity, and a virtual shrinking of the entire planet.

Currie and I passed the afternoon in a remote part of the park, looking for new bone beds. We came upon a hillside covered with fragments, including some preserved inside unusually large nodules of ironstone. "Weird and different," Currie declared as he took a satellite reading of our position. Bone bed 185, he named it.

It might yield some answers. Or it might yield nothing but shoulder bones—the kind you look at for a second, then toss over your shoulder. But it was still exciting, because what we don't know about dinosaurs is far more than what we know. No matter how you practice it—with shovels or computer programs, with fossils or rhino heads from a freezer—this is still a new and evolving science. We've just scratched the surface.

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