BOOK REVIEW : A Grown-Up Look at Earth’s Big Lizards : DINOSAURS, SPITFIRES, AND SEA DRAGONS <i> by Christopher McGowan</i> ; Harvard University Press : $29.95, 365 pages

At last, a grown-up’s book about dinosaurs.

“Dinosaurs, Spitfires, and Sea Dragons” reawakens and even intensifies the awe we felt as kids when we learned about the giant lizards that roamed the Earth long ago. This beautifully illustrated work, written by a literate scientist for an educated lay audience, shines a bright new light into the darkness of the 150-million-year reign of the dinosaurs--the biggest, most biologically successful and most mysterious land animals that ever lived.

The study of ancient life has produced an explosion of new research in the last 20 years, sparked by a rash of new fossil discoveries and by radical new ideas of two controversial scientists.

One, paleontologist Robert Bakker of the University of Colorado, began claiming in the 1970s that dinosaurs were warm-blooded and far more lively than had been thought possible. The other spark plug in the debate, the late UC Berkeley physicist and Nobel laureate Luis Alvarez, proposed in 1980 that the dinosaurs were wiped out by a giant asteroid that crashed into the Earth, raising a worldwide dust cloud and bringing on a long, artificial winter.

In “Dinosaurs,” author Christopher McGowan, curator of vertebrate paleontology at the Royal Ontario Museum in Toronto and professor of zoology at the University of Toronto, takes a careful look at the new discoveries and the controversial hypotheses and--equally important--shows the reader how to evaluate the scientists’ claims.

To appreciate what a paleontologist’s investigative job involves, consider the biggest dinosaur yet discovered. It’s the so-called ultrasaurus: 98 feet long, 180 tons (twice the weight of a Boeing 727), tall enough to allow the biggest African bull elephant to walk under its rib cage with plenty of room to spare.

How did this monster make a living? We know from studying modern animals that large beasts are much harder to “engineer” than small ones, for their bioenergetic problems quadruple in magnitude as the animals double in size.

Elephants, the author says, have to eat 18 hours a day just to stay alive. They can’t run or even trot. They can’t lie down for long without their enormous weight suffocating them. Like other large animals, they have trouble maintaining a comfortable body temperature. How did the dinosaurs, most of which weighed many times as much as elephants, even survive, let alone flourish?

McGowan addresses this perplexing question and many others. Among them: how did the flying dinosaurs, some with a wingspan equal to that of an executive jet, take off and land?

Did the sea-dwelling icthyosaurs (the author’s specialty) give birth to their young alive, or cannibalize them or both? The fossil record, he says, is tantalizingly meager and the temptation is strong to invent scenarios beyond what the evidence can support.

McGowan describes himself as conservative in interpreting the evidence, remarking archly of a more liberal colleague: “I have even read of the possible diet of an animal that was represented only by its footprints.”

McGowan shows, though, that “conservative” needn’t mean “dull.” Rather than offer a brief and superficial update on the lifestyles of all the many species of dinosaurs, McGowan looks closely at a few representative species of the three main types as determined by where they lived--on land, in the sea and in the air.

And instead of trying to reconstruct his chosen species’ natural history, he approaches the animals as a problem-solving engineer would, working out the optimum design for an animal of a certain size living in a certain environment.

McGowan begins these discussions at a reassuringly simple level. The level of complexity ramps up from there, but his prose is so clear and logical that the reader can follow him anywhere. We learn, in a typical example, that the flying dinosaur’s wings were made of skin attached to enormously elongated fingers, somewhat like those of a modern bat.

Then, after absorbing a lesson on the effects of air flowing over surfaces and an examination of the performance of various wing shapes, we sideslip into a discourse on the World War II British Spitfire, the underpowered fighter plane that through superior maneuverability won the battle of Britain.

And we discover that--surprise!--the Spitfire’s wings looked remarkably like the pterosaur’s--hence the title. “Dinosaurs, Spitfires, and Sea Dragons,” in brief, is an altogether captivating book.

Next: Jonathan Kirsch reviews “Rainmaker: The Saga of Jeff Beck, Wall Street’s Mad Dog” by Anthony Bianco (Random House).