Dinosaurs are a bit like the city of Paris: If you aren't interested in them, you aren't interested in life.

That may seem wild and arbitrary, but it can be justified literally. Thanks to a convergence of ancient accidents and modern discoveries, dinosaurs at present stand near the very center of evolutionary biology. The mysteries of their rise and fall are linked closely with the largest questions of how life has evolved.

The whole story is populated by exotic creatures of the human as well as the reptilian variety, and John Noble Wilford has done justice to both by casting "The Riddle of the Dinosaurs" as a historical narrative that is also an essay on the subject of wonder.

That process began around 1825, in the days when even Charles Darwin was still a creationist. Wilford describes the work of Gideon Algernon Mantell, a hobbyist fossil-collector who made sense of the earliest iguanodon fragments, which he scavenged from a quarry in Sussex.

The book documents the role of Georges Cuvier in opening 19th-century science to the radical idea that animals once alive might now be extinct. The roster of characters also includes: Richard Owen, an arrogant British anatomist who presented the first comprehensive report on dinosaurs and coined their common name, but who cited them as evidence that evolution had not occurred; O.C. Marsh and E.D. Cope, the two preeminent American paleontologists of the last century, who were so fiercely competitive that their collecting expeditions to the Rocky Mountains were conducted almost in a spirit of war and pillage; and Franz von Nopcsa, a Transylvanian nobleman who made serious contributions to the understanding of dinosaur phylogeny, but whose real ambition was to be appointed king of Albania.

Those wild tales, though, can also be found in earlier books. The great merit of Wilford's volume (which has spectacular illustrations by Douglas Henderson) is that it brings the long, crazy pageant of humankind's fascination with dinosaurs up to date -- and into its modern scientific perspective.

This new generation of dinosaur experts, as Wilford says, have no longer measured their success by "the tonnage of their haul or the number of new species they could identify." Instead, he writes, they have asked "the big questions. Were the dinosaurs examples of evolutionary misdirection, anomalous creatures plodding toward a dead end? How did their success and ultimate extinction shape the course of life thereafter?" Three members of the new generation stand out: John Ostrom, Robert Bakker and Jack Horner. Wilford has focused on each.

Ostrom is the man who unearthed a small creature now known as Deinonychus and thereby was set on a trail of thought toward the notion that perhaps dinosaurs were not sluggish, coldblooded animals like the reptiles of today. Deinonychus, according to Wilford, is "one of the most remarkable dinosaurs ever discovered. Nearly everything about the animal, its arms and legs, its terrible claws and stiff tail, was soon to be introduced as Exhibit A in the case for the swift, agile, dynamic Bakkerian dinosaurs."

Those Bakkerian dinosaurs were postulated by Robert Bakker. In a series of provocative papers, published mainly during the 1970s, he argued that dinosaurs had been warmblooded, lively and more closely related to modern birds than to modern reptiles. Then Jack Horner came along and, on a bare hillside in central Montana, found the first dinosaur nest ever discovered containing the remains of hatchlings. The find suggested that some dinosaurs fed and protected their own offspring -- another bit of evidence for their having been warmblooded and birdlike.

And finally, over just the last five years, an intriguing conjecture known as the "death-star" hypothesis has arisen.

The notion is that the Cretaceous extinction 65 million years ago was triggered by a dim companion star that circles our own sun on a huge orbit, dragging a shower of comets and death down onto Earth every 26 million years.

The evidence is compelling, although not conclusive. And the death-star hypothesis, right or wrong, now is inextricably linked with the study of dinosaurs.

"The wonder of dinosaurs also," Wilford writes, "is that they are an enigma seemingly beyond solution. Science has explained so much: the divisibility of atoms and the nature of subatomic particles; the decipherable code of heredity contained in DNA; the earth's restless crust; gravity, electromagnetism, and the age of the solar system . . . It is reassuringly human of scientists that, when it comes to dinosaurs, they can be just as stricken with puzzlement as the next person and find themselves with little more to work with than their imaginations. Yet they persist in their search for solutions to the riddle, knowing they will never fully succeed but believing they will learn something about the greater mysteries of life."

This is also, in Wilford's view, the wondrous riddle of humans.