CHICAGO--Paul C. Sereno can't talk to me when I arrive on a Friday morning in early March. The University of Chicago paleontologist is busy preparing the lecture for a class that starts in 10 minutes. So I sit silently in a chair opposite him, taking in the ferocious-looking saber-toothed tiger skulls, dinosaur claws and other paleontological curiosities that perch atop the bookcases lining his spacious, sunlit office. Moments later he springs out of his seat, collecting the notes and transparencies. "It's been a hectic morning," he says hurriedly, explaining that he forgot his notes at home, as we head downstairs to pick up some slides. Realizing now that he's left something in his office, Sereno dashes back up the stairs two at a time. Within seconds he races down again, and we're off to class at a similarly aerobic pace.

Although it comes with a certain amount of chaos, such abundant energy has served the 42-year-old Sereno well in his prolific career as dinosaur hunter, scholar and popularizer. He has explored remote regions of South America and Africa and turned up numerous dinosaur skeletons (about a dozen of which represent new species)--discoveries that have elucidated such murky issues as the origins of dinosaurs and the effects of continental drift on their evolution.

There was a time, however, when such accomplishments seemed unlikely. Born and raised in Naperville, a western suburb of Chicago, to an artist and a civil engineer, Sereno was the second of six children. But unlike his siblings, he performed poorly in school. In fact, by sixth grade he was nearly flunking. "I couldn't imagine finishing high school," he says.

Fortunately, once Sereno actually entered high school he discovered something he loved, something he was good at: art. Driven by his newfound aspiration, he settled down. "I started studying during my lunch hours to make up the ground," he recounts. Eventually improving his entrance exam scores dramatically, he was accepted at Northern Illinois University, where he planned to become an artist.

He studied painting, favoring the detailed style of the 17th-century Dutch still-life artists. But during his junior year, on a trip to the American Museum of Natural History (AMNH) in New York City with his older brother, who was interviewing for graduate school, Sereno had an epiphany. At the end of their tour of the museum, he says, he knew he wanted to be a paleontologist, realizing he could combine his interests in art, science, travel and adventure. "I walked out of the museum and told them, 'You'll get my application next year.' "

Two years later, in 1979, Sereno entered Columbia University (which is affiliated with the AMNH), embarking on what would become a lifelong effort to understand the evolutionary relationships, or phylogeny, of the dinosaurs. The 1980s was an exciting time, he recalls. It marked the cusp of a revolution in systematics, and researchers were just beginning to sort out dinosaur anatomy and what it said about their family tree.

Then, in 1988, Sereno led his first expedition, to a remote Argentine valley in search of early dinosaurs. After three weeks of prospecting, their paltry research funds dwindling, he chanced on a skeleton that brought him to tears. Eroding out of the rock in a little corner that the team had nearly overlooked was a beautifully preserved specimen of one of the earliest dinosaurs ever discovered--a 228-million-year-old theropod dubbed Herrerasaurus. "I couldn't even look at it," Sereno remembers. "I thought it was going to disappear." A second field season at the site yielded an even more primitive beast, which they named Eoraptor.

Sereno gained some recognition for these early discoveries, but in recent years his has become one of the most recognizable names in the field. His approachable demeanor and youthful good looks have made him a media darling--even People magazine noticed, including the paleontologist in its "50 Most Beautiful People" issue in 1997. That same year Newsweek and Esquire put him on their own lists. Although he seems quite comfortable in the spotlight, Sereno acknowledges a downside. "Notoriety is a double-edged sword," he remarks, noting that it can convey what one is doing and so help research programs. But it can "engender a knee-jerk reaction on the part of other scientists," who suspect you have "sought every bit of attention that you are getting and are amplifying the importance of your work.