New Theories And Old Bones Reveal The Lifestyle Of The Dinosaur

On the undulating plains of Montana and Wyoming, where the barren terrain stretches as far as the eye can see and hawks ride the thermals overhead, you can't walk 10 feet without kicking the taupe-colored stones that litter the ground. Pick one up and you will see soft ridges. They are the ripples left in the sand as the Jurassic seas dried up. Listen closely and you can almost hear the ebbing surf... and the hooting, honking of dinosaurs that lived beside a sea that stretched from Canada to Louisiana 75 million years ago. Among them were 25-foot-long maiasaurs--duckbilled dinosaurs that trekked en masse to this high coastal plain where dogwoods, evergreens and berry bushes grew amid languorous streams. This was their rookery. Every spring females scooped out nests, carefully placing them exactly as far from neighbors as the mothers were long. They each laid a clutch of eggs, in two circular layers, and covered it snugly with vegetation. As the plants rotted, the heat warmed the eggs. After a few weeks the hatchlings began chirping in unison, as crocodiles do today, to alert Mom to dig them out. She did. Then she and her mate chewed and swallowed berries, seeds and leaves growing nearby, and regurgitated this repast into the gaping little mouths-the ultimate in fast food.

It was a great time for dinosaurs. Almost as good as today--save for the inconvenience of being extinct. A mere 150 years after English anatomist Richard Owen named them (from the Greek words deinos, or terrible, and sauros, lizard), these ancient reptiles are finally getting some respect. From mute bones and enigmatic footprints, paleontologists are inferring dinosaurs' family life and social structure, their mating rituals and their wanderlust. "We're like coroners," says paleontologist Michael Brett-Surman of the Smithsonian Institution, "except with us the crime occurred more than 65 million years ago, all the witnesses are dead and all the evidence has been left out in the rain."

The clues come in sizes large and larger. New species are still being found-about six each year. This year alone dinosaur prospectors have announced the discovery of the first dinosaurs from the Arabian Peninsula and from Antarctica and may be on the verge of identifying the fourth brontosaurus species. As fast as the diggers dig up mineralized corpses and petrified footprints, theorists boldly extract dinosaurs' behavior from them. Trackways found this year in South Korea show the marks of scores of tiny, milling brontosaurs, the size of calves. The find belies these giants' image as dumb adherents of the lay-'em-and-leave-'em school of motherhood: yearlings stayed near their birthplace and were cared for by herds of 20 to 40. Stress fractures in the toe bones of horned ceratopsians found in Alberta, Canada, suggest that these four-legged tanks stomped their big feet often-perhaps to catch the attention of a prospective mate. Footprints from Montana show that medium-size bipeds such as Deinonychus hunted in ferocious gangs of four, ripping the entrails out of prey 10 times their size. And this week in San Diego, at the meeting of the Society for Vertebrate Paleontology, one researcher will announce new calculations showing that lumbering, plated stegosaurs and long-necked brachiosaurs did not have the reptilian equivalent of an IQ of 20: they were at least a 50. So there.

The discoveries reveal how wildly diverse dinosaurs were, and add up to "a golden age of dinosaur paleontology," says Peter Dodson of the University of Pennsylvania. From the discovery of great graveyards of 10,000 duckbills in Montana, they deduce that the beasts formed herds that stretched to the horizon 80 million years ago. (The herds were occupational hazards, though. Duckbills' broken-but-healed vertebrae show that these dinosaurs were not very good in crowds; they were trampling each other's tails.) From backbone injuries in long-necked sauropods, which probably occurred during copulation and appear no more than once in each animal, paleontologists figure that these beasts got it right the next time--or swore off sex for life. "These bones are like Michelangelo's slaves, trying to wrestle free of the rock " says Robert Bakker of the University of Colorado. For a discipline that considers the Ziploc plastic bag the greatest technological innovation in fossil hunting, paleontology is finally making bold strides into the, oh, 1970s. Andrew Leitch of Dynasaurium Corp. in Toronto is peering into dinosaurs' heads with CAT scans. He recently found that the smallest tyrannosaur, Nanotyrannus, had a brain twice the expected size, with a large vision center that would have resolved minute detail. Sensory glands in the snout may have enabled Nano to sniff out dinner as efficiently as today's wolf.

David Gillette, the Utah state paleontologist, has teamed up with researchers from Los Alamos National Laboratory who, in their spare time, use ground-penetrating radar to find buried fossils. Yet Gillette can thank dumb luck--in the form of hikers-for the discovery of the largest dinosaur ever. Named Seismosaurus ("earth-shaker"), it lived in New Mexico and grew to 140 feet in length and weighed 60 to 90 tons. But its head and teeth were probably no bigger than a horse's. Staying well fed was like trying to fill a reservoir with a funnel. Gillette thinks he knows how Seismo managed, He has found 230 plum-size stomach stones in its skeleton, which the beast used instead of teeth to grind food. Gillette has also found, near Seismo's ribs, a stomach stone the size of a grapefruit. He thinks Seismo may have choked on it; Dr. Heimlich would not show up for another 154 million years.

In Montana, Jack Horner of the Museum of the Rockies has discovered scores of dinosaur nests. The eggshells in the fossilized mudstone nests were totally mashed. Conclusion: hatchlings stayed in the nest, lying around on the shells. The tips of the babies' bones had large masses of cartilage, like some baby birds. Says Horner: "It means they couldn't walk, so someone had to bring them food." Horner found fossilized berries and seeds that had been regurgitated. In nearby strata, he uncovered nests, eggs and unhatched babies of smaller, graceful biped dinosaurs called hypsilophodonts. The fetuses had smooth, hard bone ends; they could have been up and out of the nest right after birth, like turtles and crocodiles. There was no single right way to be a dinosaur parent.

The dozens of nests clustered in the coastal upland raise the intriguing possibility of Mesozoic day care. By nesting together, only a few parents would have had to baby-sit, freeing others to gather food. In Mongolia, for instance, nests of little one-horned Protoceratops were filled with eggs whose volume exceeded that of an entire adult. "Many females laid their eggs together in a communal nest," says Brett-Surman. "Such efficient use of nests indicates a degree of intelligence in dinosaurs that exceeds that of all other reptiles." Even long-necked sauropods, which as every child can tell you had brains no bigger than walnuts in bodies 10 Buicks long, had enough gray matter to protect their progeny. When that mecca of dinosaur lovers, the American Museum of Natural History in New York, unveils its Barosaurus display on Dec. 4, the long-necked behemoth will no longer be planted in the floor like a dining table. Instead, mother Barosaurus will be rearing back and preparing to bring her front legs crashing down. Her target: an Allosaurus threatening to make lunch out of the baby desperately trying to hide behind Mama's tail.

Other bones speak of an intricate social structure. Skulls of crested duckbills called lambeosaurs show that their budding cranial crests didn't grow until they entered adulthood, and then only slowly. "It's a pattern we see in modern herding animals," says Horner. "It's related to hierarchy. An animal with smaller horns won't challenge one with larger horns." That would mean fewer intergenerational battles. The headgear, long believed to have been used to fight off predators, more likely had a different purpose: showing off for the opposite sex. "Sexual display comes once a year no matter what," says Horner.

Lambeosaurs' crests are so elaborate that "it's as if their nasal cavities were plucked out of their faces and put on their heads," says anatomist David Weishampel of Johns Hopkins University Lambeosaurs thundered forth with loud calls 75 million years ago that carried for miles. How does Weishampel know? He built an exact replica of the crest, down to the internal passageways, and blew it. Perhaps the calls summoned juveniles; perhaps they warned of a lurking Deinonychus pack. (Low frequencies travel long distances and also hide the location of the caller.) Since the hollow adornments grew when the animals were sexually mature, they might have been lures for mates, too. Weishampel envisions mating as a hooting, honking affair punctuated by courtship dances and aggressive displays. ("Look, honey, my horn's bigger than his!")

Some products of these matings produced dinosaurs that grew like weeds. Duckbills measured 14 inches long when they cracked open the shell, but grew to 9 feet as yearlings and 20 feet by the age of 4. To achieve such growth, Horner and others contend, these dinosaurs would have needed to keep their internal temperature constant and high, through internal processes. Does that mean that dinosaurs were warmblooded? In 1968, Bakker ignited a scholarly bonfire by asserting they were. He argued that coldblooded creatures could not have been so energetic and fast; sunning oneself on a rock is no way to rev up the metabolism quickly enough to escape a carnivore.

Bakker was probably right about small two-legged dinosaurs. But otherwise his theory has more critics than partisans. Penn's Dodson, for one, argues that if the big sauropods were warmblooded, "they would have had to stay out of the midday sun to keep from suffering meltdown": sunshine plus its huge internal furnace would have given the beast heat prostration. In fact, choosing between warm-and coldblooded schemes may be underselling dinosaurs' ingenuity. Last year James Farlow of Indiana University-Purdue suggested that dinosaurs' metabolism may have varied by season: warmblooded in winter and coldblooded in summer. His evidence: growth rings on juveniles' bones that he interprets as seasonal markers. Call them reptilian tree rings. Jack Horner will suggest in an upcoming paper that dinosaurs, though warmblooded, "were specialized to grow real fast. But after they reached sexual maturity, or a particular size, their metabolism slowed way down so they didn't require so much to eat."

How ever they kept warm, dinosaurs needed efficient metabolisms, for they made treks that would exhaust Ol' Yeller. Since 1988 Martin Lockley of the University of Colorado has been finding "megatracksites," footprints that may mark dinosaur migrations of hundreds or thousands of miles, such as one made by 20-foot-long iguanodons from Denver to New Mexico 100 million years ago. "We call it the dinosaur freeway," says Lockley, one that may have been a seasonal route for herbivores seeking greener pastures. They may have visited the same nesting grounds every year, too: some of Horner's nests in Montana were built only one year apart.

Why did the dinosaur cross the continent? To get to the safety on the other side, according to fossils from the Arctic. The remains of horned ceratopsians and duckbilled hadrosaurs lie north of the Arctic Circle; fossils of long-necked plesiosaurs and the birdlike Hesperornis have been found 1,400 miles north of the Canadian border. Since all four are also found in more southerly climes, these dinosaurs were evidently migrants. They walked north, speculates Brett-Surman, because of the "explosion of plant life during the arctic summer--and because the only predators around would be those that followed them north." Not many did. A large proportion of the plesiosaurs found in the far north are juveniles, suggesting that the migrants found the peace and safety of the tundra a good place to breed.

Such discoveries about how dinosaurs lived has made them the darlings of stage, screen (silver and small) and pasta shelf. Dinamation International Corp., of Irvine, Calif., builds life-size dinosaurian robots that roar, swing their tails and nuzzle their hatchlings. It runs 120 shows a year, attracting 10 million viewers last year. There are dino sitcoms ("Dinosaurs," on ABC) and dino films (Universal Pictures' "Jurassic Park," about dinosaurs that are cloned back to life, is due in summer 1993) dino macaroni and soup, dino socks and sheets. And now there's The Dinosaur Society to keep droopy tails off brontosaurus-shaped macaroni. Formed last year, the nonprofit society will vet books, toys and other products in exchange for a contribution to field research, says the society's Don Lessem. For $15.95 a year beginning in January, the society will send kids the monthly broadsheet Dino Times,* chronicling the latest finds and theories.

A support group is just what paleontologists need. On a budget of $1 million a year, the 55 dino researchers worldwide (most of whom make their living doing something else) are seeing data whisked out from under them. Commercial collectors, who typically pay landowners $1,000 for the privilege of digging and $10,000 if they find something, offer such trophies as Triceratops skulls for $150,000. Every fossil that winds up in a private home is one less bit of data for reconstructing the glory of the dinosaur age. Last month, though, science won one. Employees of the Bureau of Land Management noticed someone digging on public land in Wyoming. It was a Swiss collector, Kirby Siber, who had permission to excavate on a private parcel but inadvertently wandered onto BLM turf. He found an 18-foot-long, nearly complete, young allosaur, an ancestor of T. rex that lived 135 million years ago. Siber figured he could get $500,000 for it. Instead, BLM dispatched a crew from Montana State University, which will house the fossil.

How did dinosaurs manage to dominate every corner of the planet and every climatic condition longer than any other land animal? Dinosaurs were born in death, 248 million years ago, when some cataclysm caused the extinction of many small mammals and 98 percent of the marine animals. Two-legged carnivores--the first dinosaurs--moved into the vacated niches. In 1989 Jose Bonaparte of the Buenos Aires Museum and Paul Sereno of the University of Chicago found, in 220 million-year-old sediments in Argentina, remains of what seems to be the oldest dinosaur. Named Herrerasaurus, it was a fierce and nimble carnivore, nine feet long and two feet high.

Life in the Mesozoic, 240 million to 65 million years ago, was no picnic, however, what with meteorites slamming into your backyard every few million years. Yet for dinosaurs, the cataclysms opened the door to some glorious evolution. The end of the Triassic period, 201 million years ago, saw a wave of extinctions. Likely triggered by the impact of extraterrestrial missiles, they wiped out dinosaurs' larger competitors, especially mammals. Paul Olsen of Columbia University has seen the survivors. In strata in Nova Scotia deposited just before and just after the extinction, he finds unnamed carnivores smaller than a pigeon and diminutive sauropods that resemble Lilliputian brontosaurs. Why did the small survive? Olsen speculates that they required less food or reached sexual maturity sooner. Whatever the reason, the survivors quickly diversified into giant four-legged sauropods, biped carnivores and iguanodons. "Dinosaurs were really good at evolving," says Kevin Padian of the University of California, Berkeley. "They replaced themselves constantly."

And that ushered in the pinnacle of dinosaur evolution. The late Cretaceous era, 90 million to 65 million years ago, saw the debut of sophisticated, graceful bodies, a brain-to-body ratio greater than modern reptiles and advanced physiologies and behaviors. And it dramatized what forces shape new species. As the great inland sea from the Arctic to the Gulf of Mexico rose, spreading 200 miles in a million years, dinosaurs living on the coastal plain squeezed onto less land. Many died. In the smaller, more stressed populations left behind, any unusual gene-for a faster gait, a more efficient internal furnace, a sexier nose horn-had a better chance of becoming established and producing new forms. This was the era of crested lambeosaurs and the extravagantly horned and frilled styracosaurus.

Of 300 known dinosaurs, fewer than a dozen faced the final extinction 65 million years ago. A minority of paleontologists believe that an asteroid smashing into Earth threw up enough dust and dirt to blot out the sun, dooming plants and the animals that ate them. It was the Mesozoic's nuclear winter, But perhaps dinosaurs did not go extinct. More and more evidence suggests that the Cretaceous extinction wiped out only the earthbound dinosaurs, flying species, descendants of small meat eaters, evolved into modern birds. Trackways found this year in South Korea show that small waders and shorebirds lived 30 million years before the end of the age of dinosaurs: dinosaurs shared the planet for thousands of millenniums with birds, just as Neanderthals once lived beside modern Homo sapiens in Europe. "Dinosaurs are not extinct," says the Smithsonian's Brett-Surman. "They're looking down on us."Be kind to your fine-feathered friends, for they might be your favorite dragon's younger brothers and sisters.

*The Dinosaur Society, P.O. Box 171, Newton Lower Falls, Mass 02162.

For 140 million years dinosaurs dominated Earth. One reason for their success was their ability to evolve a dazzling array of shapes, sizes and behaviors. They thought it would never end.

The first known dinosaur, 9 feet long, found in Argentina. Lived 220 million years ago.

The largest dinosaur known, was 140 feet long and weighed up to 90 tons. This herbivore, found in New Mexico, lived 154 million years ago.

A.ka. Apotosauras. Weighed as Much as 30 tons and measured 80 to 110 feet in length. At least three different species have been found in the Americas, South Africa and Europe. Lived 150 million years ago.

The deadliest dinosaur; hunted in packs. The 3 to 5-foot-tall, 9-foot-long carnivore used sickle-shaped claws to kill. Found in western United States. Lived 140 million years ago.

The smartest dinosaur, with huge eyes and a brain comparable to contemporary birds and mammals. Its 3-fingered hands could grasp objects; the clawed third toe slashed prey Found only in North America. Lived 75 million years ago.

The smallest tyrannosaur, had a large brain, sharp binocular vision and acute sense of smell "the better to eat you with." Found in Montana. Lived 65 million ears a o.

A large herbivore, 30 feet long and up to 4 tons. Evolved into duckbills. Found on every continent except Antartica. Lived 144 million years ago.

Horned herbivores up to 27 feet long; tipped the scales at 20,000 pounds. Formed herds of hundreds in North America and Asia. Lived 90 million years ago.

Or duckbills, 21 to 50 feet long. Some formed nesting colonies, cared for young and used elaborate crests to toot out warning and mating calls. Found in North America, Europe and Central Asia. Lived 75 million years ago.

The largest terrestrial carnivore, 50 feet long with 8-inch razor-sharp teeth. Lived in North America and Eastern Asia 67 million years ago.






What color is a dinosaur? The few pieces of fossilized skin that have been recovered don't tell us, of course, so scientists have to reason by analogy to existing creatures. Old-fashioned dinosaurs were assumed to be as dull in appearance as in intellect, and artists generally rendered them in a muted reptile green, with slimy highlights. But today's improved dinosaurs come in a wider range of colors, appropriate to the ancestors of parrots and warblers. The size and configuration of dinosaurs' brains, says Robert Bakker, make it "scientifically certain that these were color-sighted animals who used colors a lot." Presumably they used colors as animals do today, for protection, sexual attraction and aggressive display to warn-away predators or rivals. What skin has been found suggests that dinosaurs were not unconscious of appearance: Stephen Czerkas describes it as highly ornamental, with spikes or scales in rosette patterns that would be visible from some distance, Presumably, though, this was true mostly of carnivores, or heavily armored species with few enemies. As Czerkas cautions: "A plant eater, no matter how large, does not want to advertise itself"

Artists walk a fine line in striving for maximal scientific accuracy without sacrificing their drawings. Mark Hallett, a leading "paleo-illustrator," allows himself to imagine that the crests in Allosaurus were brightly colored, or that the iguanodon could have sported a bright skin flap "like a coxcomb." Eleanor Kish, who specializes in dinosaur books and museum murals, is so scrupulous that she duplicated the precise color of the sand in which a skeleton of Tenontosaurus was found for the dappled camouflage pattern of its skin. Still, as a museum curator said when she turned in her first dinosaur paintings: "Your guess is as good as mine."