Some new answers to old questions about dinosaurs

Edwin Colbert is likely to bristle when someone says today's big gas-guzzling cars are going the way of the dinosaurs. Dr. Colbert has no soft spot for Continentals or Dodge trucks - but he does care about the reputation of the dinosaurs.

Using them as a symbol for something big and short-lived, contends the noted paleontologist and veteran fossil hunter, is simply inaccurate. For one thing, not all dinosaurs were big: Some were as small as bantam roosters. For another, they roamed the earth for more than 100 million years - an enduring stay by anyone's standards.

Yet the paleontologist's pet peeve also raises a point: There are many gaps in the knowledge of both scientists and the public about one of the more intriguing life forms on earth.

''Hard evidence [about dinosaurs] eludes us,'' said Dr. Colbert in an interview during a stopover here. ''It is like trying to determine if there is life in other parts of the universe. There is a lot of speculation. But it remains just that, speculation.''

Dr. Colbert should know. He has been chiseling bones out of locations ranging from icy Antarctica to steamy South America for more than 50 years. The curator emeritus of the American Museum of Natural History's department of vertebrate paleontology, he is now with the Museum of Northern Arizona in Flagstaff. But he still finds time to pull on worn trousers, clip on a canteen, and, toting pick and perseverance, head out to do fossil fieldwork.

Much of his time, however, is taken up behind podiums, lecturing and assessing the state of 130-odd years of dinosaur research (capsulized in his book, ''Dinosaurs: An Illustrated History'').

What he sees is a field in transition. The study of dinosaurs used to be a simple affair: paleontologists piecing together the past from femurs and footprints. But today the study encompasses many disciplines, with ecologists, biologists, geologists, and even astronomers contributing theories.

The thrust is also less on finding bones and more on piecing together a picture of the world in which the dinosaur lived - climate and food supply, for instance. All of this is producing new knowledge but also breeding more disputes among scientists - the most heated of which is the museumful of theories surrounding dinosaur extinction.

At one time, paleontologists considered the study of dinosaurs intriguing but somewhat irrelevant, since they seemingly had no evolutionary links to the modern day.

Now, says Dr. Colbert, it is recognized that special lessons can be gleaned from these ancient behemoths, over and above the normal insights an animal species can provide. Evidence of the distribution of dinosaurs around the world, for instance, is unraveling mysteries about the early arrangement of continents. New thoughts are also emerging about the ways animals adapt to varied environments.

''They were (once) considered gee-whiz reptiles,'' he says. ''Now they're considered important in their own right.''

That new ideas are surfacing is fine with almost everybody. Dinosaurs, after all, have long fascinated people. Dr. Colbert sees three reasons for this: (1) throughout history, giants have been a popular subject in literature and legend; (2) nothing in the animal kingdom resembles them today; and (3) dinosaurs are one of the Agatha Christie stories of the reptile world: Their existence remains shrouded in mystery, and most people like a good mystery.

But slowly the dinosaur plot is evolving. Among areas of study:

* Dinosaur speed. By studying footprints (some as large as washtubs), as well as the locomotion of such extant animals as horses and elephants, scientists are piecing together how fast the creatures moved about. Not all were sluggards. Some of the smaller reptiles, for example, scampered around at 12 mph. The big dinosaurs, such as the familiar goose-necked brontosaurus, lumbered about, moving probably at just a few miles per hour. A few dinosaurs had so much girth that they preferred to rest in water - where, in effect, they were practically weightless.

* Life span. Pinpointing how long the dinosaurs lived remains largely guesswork. The largest ones probably lived at least 200 years, judging from some modern reptiles (a few turtles have lived that long), and the length of time required for creatures to grow to such size. But whether any of them saw a 500th birthday, as some scientists have suggested, remains uncertain, according to Dr. Colbert.

* Hot vs. cold. Paleontologists continue to puzzle over whether these early animals were cold-blooded, like modern reptiles, or warm-blooded, like today's birds and mammals. An answer would provide clues to such things as how dinosaurs could have wandered so widely (fossils have been found on every continent but Antarctica) and how such vertebrates could have dominated the land for so long.

To simplify, evidence supporting the idea that dinosaurs were warm-blooded is based on their posture (usually erect like modern mammals), the length of their limbs (long in contrast to early cold-blooded Permian reptiles), brain size (some later dinosaurs had large brains, a mammalian trait), and bone structure. Yet reasons abound to doubt every theory.

Dr. Colbert leans toward the idea that some big dinosaurs were cold-blooded. Any animal that weighed 40 tons, if warm-blooded, would have had to eat huge amounts of food - perhaps a ton per day - to maintain its body temperature.

* Extinction. The most vociferous debate still swirls around the cause of the dinosaurs' demise some 65 million years ago. Dozens of plausible ideas exist. But the most fervently pressed, of late, among geologists is the ''catastrophe theory'' - that a massive asteroid careened into the earth at about the time the dinosaurs vanished, kicking up an earth-circling dust cloud that choked off sunlight for three to four years. This killed plant life and, in short order, led to the destruction of half the life on earth, dinosaurs included, the theory posits.

Paleontologists working at a remote site in Montana have recently unearthed evidence that casts new doubts on the theory. They have found fossils suggesting dinosaurs were disappearing well before the planetoid hit. Other remains indicate many creatures survived the disaster without ill effects - lending credence to the argument that the mass extinction was a gradual, complex process.

The debate, in other words, seems to be back at Square 1. This was evident at a recent symposium on the ''dynamics of extinction'' at Northern Arizona University, where the asteroid-impact theory was a central theme. According to a report in the journal Science, many paleontologists and geologists alike have now come to accept the theory as a partial - but still incomplete - explanation of the mass extinction.

It isn't surprising that uncertainties about dinosaurs remain: Our view across 65 million years is murky. But it is partly the mystery that keeps detectives like Dr. Colbert searching.

''If we didn't have anything to look forward to, it would get pretty dull,'' he says. ''It's like looking for gold - there is always something to be found.''