Researchers trust him; his publications are so extensive and his expertise so unusual that scientists don't worry about his stealing their thunder. As a result, he's done for paleopathology what the TV show Quincy did for medical examiners and what CSI has done for crime-scene investigators. He's helped popularize a field that looks past dry anatomical descriptions and recovers life histories from the bones of long-dead beasts.

"Paleopathology has had several areas of impact," says University of Kansas professor Larry Martin. "But the most useful is that it can give you direct access to behavior, and that's the hardest thing to reconstruct." Rothschild says, "I tend to look at pathologies and ask what they can teach us about the lifestyle and habitat of the animal."

Movies like Jurassic Park depict T.Rex as a storming terror chasing its prey. But was the mighty beast actually just a waddling scavenger?

Doctors often have the habit of quietly diagnosing the ailments of people they see walking down the street. Rothschild has raised his version of this tic to an art form. Zeroing in on a display case in a museum, he sees a prehistoric hospital ward full of 10-ton patients suffering from bone spurs, cysts, healed fractures, fusions, outgrowths, divots, unusual ossifications, noticeable asymmetries, or, in one notorious instance, a few cracks in a tyrannosaur's rib cage. In recent years, new discoveries about Tyrannosaurus rex have cast doubt on the traditional picture of the animal as a storming terror chasing its prey. Some anatomical studies indicated that T. rex could not run quickly, while an examination of the creature's braincase showed it had an outsize olfactory system. Together, these findings suggested that the mighty warrior was more like a waddling scavenger prowling, at best, for roadkill.

Rothschild is providing the old school with new evidence. In the late 1990s he showed that T. rex and other theropods had rib-cage fractures consistent with having made "a belly flop onto hard ground while running." His own recent review of T. rex's tiny forelimbs reveals a pattern of resistance fractures suggesting battles with living prey. Suddenly the shuffling vulture is looking more like his bad old self, although even newer evidence may change the picture yet again.

Last September, at the Tyrannosaur Symposium in Rockford, Illinois, Rothschild announced he is no longer convinced that all T. rex wounds are mouth bites. "Remember the fighting image of Deinonychus?" he asks. He is referring to a famous painting by Charles Knight that seems to capture in midaction a fight between two of these creatures, small but terrifying predators with sicklelike claws. Fossilized bones show that a deinonychus used its powerful hind limbs to gut a massive triceratops of its belly organs. "I think there may have been similar behavior in tyrannosaurs," Rothschild says. Among the numerous tyrannosaur bones he's reviewed were "many face-to-face interactions, and I can't account for some of the marks unless the T. rex was on his back."

By the time Rothschild reaches the T. rex exhibit hall, he has reimagined the world's most famous dinosaur as a kind of nimble, outsize, cannibalistic velociraptor. Up close with the tyrannosaur skeleton, Rothschild points to some healed bones in a skull and conjures up the sex life of the King of the Tyrant Lizards. "In many animals the females have to be overcome. But the female was larger, so the male T. rex had to be superaggressive in his sexual interactions," he says. "I don't think rough sex is new, but there's another aspect to it."

Sure enough, some tyrannosaur bones show signs of face bites, akin to the love bites that female lions get from their male suitors. The tyrannosaur known as Stan displays these marks, but some skeletal evidence hints that Stan was actually a male. "If Stan's a female, it all fits. But if Stan's a male," he says with a sly grin, "then another type of sexual behavior goes back 65 million years."

To Rothschild, bones shout out a multitude of questions. Sometimes, with the application of enough evidence and argument, they occasionally whisper an answer. Rothschild came to his specialty the way most boys begin their fascination with bones—at age 7, when he came across a big book full of evocative illustrations and huge Latinate dinosaur names. By the time he was a teenager growing up in New Jersey, he was a regular at the Museum of Natural History. His folks hoped he would become an engineer. Instead, he became a medical doctor with a specialty in rheumatology—and an interest in dinosaurs that kept him visiting museums around the world.

Ask Rothschild about his conspicuous last name and he'll wave off talk of the banking family; once, and once only, he admits, he tasted the expensive wine that bears his surname. For him, the real cachet of the Rothschild name traces to his great-uncle Walter: Lionel Walter, the second Baron Rothschild, a 19th-century naturalist whose vast private collection of specimens became the zoological wing of the Natural History Museum in London. No one knows where the stereotype of the eccentric scientist first arose, but it was certainly nursed along by Walter Rothschild, a famed adventurer and collector of birds and butterflies who also ended up selling part of his collection to the American Museum of Natural History because of a cash-flow problem. Walter was legendary for his oddities, including arriving once at Buckingham Palace in a stately brougham drawn by four zebras. Rothschild might lack his uncle's sense of Barnum publicity, but watching him barrel into an exhibit hall as excited as any of the 10-year-olds zooming around him suggests that the line from the baron to his nephew is direct. Suddenly, a corner is turned to reveal the plesiosaurs, long-necked aquatic reptiles that lived alongside the dinosaurs.

"Look at the bilateral depression at the humeral head where it articulates with the pectoral girdle," Rothschild says. Regular museumgoers quickly glance up, curious to figure out what the rumpus is all about. "You know what that is?"

I grin gamely, as if to tell him that I wouldn't rob him of the pleasure of observing something so obvious, although the truth is that I have no idea. "Manifestation of decompression disorder," he says. "The bends!" He points to a nearby ichthyosaur and notes the absence of any similar skeletal deformation. "So the plesiosaur is a deep-diving, repetitive-diving animal. We didn't really know that before. There are a lot of questions about the habitat of these critters." Needless to say, Rothschild wrote a paper about it, recently published in the Journal of Vertebrate Paleontology.

Today Rothschild is intrigued by the fact that for any given marine species, getting the bends was an all-or-nothing proposition. "Every single Mosasaurus shows evidence of the bends, but every single Clidastes lacks it. Every single Tylosaurus has it, but every single Halisaurus lacks it." In fact, he has tracked the bends in marine critters from the Triassic through the age of mammals and up to our own time as a way to study how certain animals evolved a resistance to the disorder.

"All I would need is a day," he says wistfully. "A day to do the whales in Brussels and one to do the whales in New Zealand. If we track that through to the Eocene era—the Ambulocetus and Pachycetus—we might figure out what modifications allowed them to avoid the bends. Then we'll have some way of understanding it in humans. Keep in mind, there isn't a naval diver still who doesn't have this problem." This is typical Rothschild: considering the bends not as a human ailment, first documented by a miner in 1841, but as a vertebrate's disease, one that can be tracked backward through more than 200 million years of mammalian evolution.

Rothschild darts among the crowds of the museum, never letting up on his improvisational lecture. Over here, a suggestion that T. rex suffered from gout; there, some dinosaur knees that prompt a discussion of the evolution of an inflammatory joint disease called spondyloarthropathy. Check out the cancerous tumors on this duck-billed dinosaur, he exclaims.

Minutes later—while Rothschild is cooing over the toes of a triceratops, finding stress fractures that indicate that the animal followed much heavier migration schedules than commonly thought—a museum official interrupts to tell him he can now visit the museum's bird skeleton collection in the basement. Rothschild never schedules a trip without getting some scut work done on one of his giant trans-epoch metastudies.  

The ligaments in the spine of a 20-ton diplodocus, seen here in an X-ray, had hardened into bone, fusing two vertebrae together. Rothschild's diagnosis: diffuse idiopathic skeletal hyperostosis—that is, arthritis.

It's easy to be misled by Rothschild's many highly focused observations and forget that his idea of the big picture is about as big as such pictures come. His latest research involves collecting data on the ankles of 50,000 modern birds in order to compare them with ankles he's observed in other animals dating back to Iguanodon, a Jurassic dinosaur. He is studying one of the most common complaints of his modern-era human patients—osteoarthritis—and projecting it far into the past.

"What Rothschild has done is greatly increase the confidence of the diagnosis," says Larry Martin, who has been dragooned by Rothschild into various collaborations. Some paleopathologists draw limited conclusions after studying a single bone; Rothschild channels his frantic energy toward compiling overwhelming evidence. "If you have too much ambiguity about what disease you're talking about," Martin says, "it's hard to be confident about your conclusions. Rothschild has expanded the entire scope of what paleopathology can do."

Rothschild's latest, massive bird experiment is one of his most ambitious efforts yet. "One of the challenges in humans is that osteoarthritis is the most common form of arthritis," he explains. Most physicians believe that excess weight—that is, contemporary obesity—has a lot to do with the outbreak of this problem. But after examining 10,000 dinosaur bones all over the world, Rothschild is not so sure.

"There are two known examples of osteoarthritis in dinosaurs, and that's in a herd of 39 found a mile under Brussels in a coal mine. That was an Iguanodon bernissartensis." The near-complete absence of the disease in dinosaurs makes it hard to argue that weight is a cause. So Rothschild is scouring the eons for other evidence. His dinosaurs have persuaded him to set aside the fashionable diagnosis of obesity. Modern birds, he thinks, may hold a more convincing clue.

Amid cramped towers of specimen cabinets, Rothschild moves with the antic pace of a silent-screen comedian. The long, shallow drawers slide open with a squeaky roar. At each one, he shuffles the boxes of specimens—some the size of shoeboxes, others no bigger than a pack of cards. He separates out the ones that fit his study. All the while he talks nonstop—not exactly to me, not exactly to the bones, but somehow to both.

He pops open a lid, and his forefinger fishes around until he finds the bird's anklebone. He touches the tiny joint ball. In many cases the bone is thinner than a straight pin, yet Rothschild can feel a bony spur no bigger than half a salt grain: the telltale sign of osteoarthritis. He mutters his findings (no spurs) and marks his sheet. His finger spends no more than two or three seconds in each box until . . . "Bingo!" He hands me an African bee eater captured by J. P. Chapin in the Belgian Congo on February 21, 1911. He invites me to feel the bird's osteoarthritis. It's hard to believe than he can really feel this tiny protuberance, yet there it is under a magnifying glass.

"I've gone through about 45,000 birds, so I'm pretty good at this," he says. Already he is flicking his way through a half dozen other boxes and soon finds another victim: a specimen of Coracias caudatus that died in the New York Zoological Society in 1932. It's like watching a Renaissance musician strike at the keys of an early clavichord. Before long I find myself coerced out of my job as a journalist and holding check sheets instead, taking Rothschild's commands as he confirms the data.

"Bruce isn't happy unless everyone is busy," Martin says. "I've often been handed busywork so I don't look unoccupied. I remember one trip, looking at him and realizing, 'Hey, you've got a full professor writing down your data for you.'"

What's good for the dinosaurs is also good for people. After journeying back in time to apply his knowledge of human bone disease to Jurassic animals, Rothschild returns to Ohio with dinosaur data that can benefit the living H. sapiens bones he heals during the workweek. With the lessons learned from dinosaurs, Rothschild refers fewer osteoarthritis patients to surgery and hopes to prove through his work that the proper treatment may instead be exercise therapy that rebuilds muscle control.

Dinosaurs, Rothschild notes, had joints whose movements were highly constricted; they could swing back and forth on a very narrow track. Human knee joints have much more rotational maneuverability. "The problem is that nature's design for humans didn't include exuberances of youth, like football and sports, that stretch out and damage ligaments; these don't repair, so muscles have to take over," he says. "As we get older and aren't as active, we slowly lose the muscles that sustain that stability." Because older ligaments are no longer strong enough to do that work, we contract osteoarthritis.

Sports, though, are just one contributing factor. There are many more, which is why Rothschild is turning to birds for help. "If you want to understand the disease, you want to take out the variables," he says. Birds are a helpful model; they are partway between people and dinosaurs in the design of their knees. By correlating osteoarthritis in living birds with their known behaviors, Rothschild hopes to learn more about the causal factors than he ever could from his human patients.

To a doctor whose arc of interest flits across the epochs, the differences between Iguanodon, the toothpicklike skeleton of a bird from the Belgian Congo, and that slouching teenager in the museum cafeteria are few but revealing. Nothing collapses the entire history of vertebrate evolution into a cozy family reunion quite like paleopathology.

"It's amazing when you look at a bird's ankle," Rothschild calls out while wiggling the frail joint of a flycatcher he's found in a specimen drawer. "Look how much it resembles a human knee."