When Dinosaurs Roamed the Earth
Disney may have its dinosaurs speaking English, but that seems almost tame compared with the startling conclusions that scientists have reached about these Mesozoic reptiles lately. Finding vegetation balls in fossilized nests, paleontologists have concluded that dinosaurs piled plants atop their eggs so the rotting greenery would warm the little embryos. Unearthing nests in which the parent died with its arms outspread and its breastbone on the eggs, the researchers suggest that with its dying breath Mom or Dad tried to protect Junior. And in a move that will shock those to whom "Velociraptor" means those crafty homicidal beasts of "Jurassic Park," and to whom "bird" conjures up Tweetie, the American Museum of Natural History in New York has decked out its 'raptor in... feathers.
It's another dinosaur moment. Besides the premiere of the Disney film, May brings "Fighting Dinosaurs" to the American Museum. The exhibit of fossils from Mongolia includes the eponymous Velociraptor and Protoceratops, which, thanks to a collapsing sand dune that entombed them 80 million years ago like Pompeians in volcanic ash, are locked in an eternal death embrace. In Chicago, the Field Museum unveils Sue, the largest (at 13 feet tall) and most complete Tyrannosaurus rex skeleton ever discovered. Appearances to the contrary, though, dinosaurs are more than a marketing phenomenon. Excavating previously unexplored fossil beds, paleontologists "find at least five or six really great new species every year," says Mark Norell of the American Museum. In the past 30 years scientists have doubled the number of known dino species, and since 1997 they have discovered nesting sites that shed light on parenting behavior and CAT-scanned skulls to infer what kind of sounds the creatures' air passageways could have made. Answer: crested duckbills like Parasaurolophus probably squeaked when they were young, then bellowed in ultralow frequencies as adults. "When I began [in about 1980], we knew almost nothing. It was just piles of bones everywhere," says Paul Sereno of the University of Chicago. "But now dinosaur paleontology has advanced on all fronts."
In March, for instance, scientists unveiled the remains of what seems to be the largest meat-eating dino ever to shake the ground. At 45 feet long, the predator-to-be-named-later was four feet longer than Giganotosaurus, the eight-ton carnivore from South America that was the previous record holder. Six of the newly discovered needle-nosed beasts with razor-sharp choppers were found buried together, in Patagonia. At least three were juveniles. That suggests that although paleontologists "always think of these [carnivores] as solitary," says Philip Currie of the Royal Tyrrell Museum in Alberta, instead they might have lived and hunted in pairs or family packs. That's how the carnotaurs stalk our hero in "Dinosaur." "If you're a carnivore and you want to feed off herds, it makes sense to work cooperatively," says Currie. Fossils of a 30-foot-tall sauropod (long neck, four legs) that Sereno found in the Sahara last year add to the evidence that some dinos lived in mixed-age herds: an adult Jobaria tiguidensis was found atop a juvenile.
Footprints, too, support the idea of great herds composed of young, old and middle-aged. Norell even suspects that youngsters got corralled into the center of the herd, like baby elephants, for protection. But paleontologist Kenneth Carpenter of the Denver Museum of Natural History is struck by the apparent absence in herds of individuals smaller than half-grown. "They just never occur with the adults," he says. "I suspect the very small ones were segregated until they could keep up." Herds with more than one species, like those in the movie, were a rarity, too. Footprints offer evidence of who traveled with whom, and they argue against interspecies fraternizing.
The perennial nesting grounds in "Dinosaur" have a firmer basis in fact. At a nesting site discovered in Patagonia in 1997, says Luis Chiappe of the Natural History Museum of Los Angeles County, eggs are nestled in four distinct strata. That suggests that the titanosaurs, long-necked quadrupeds that grew 45 feet long, returned to the flood plain season after season, 80 million years ago. "There must have been hundreds of animals the size of school buses gathering at once," says Chiappe. At a nesting ground in Kazakhstan, "eggshells extend along a river for 200 meters vertically," says Carpenter. There, too, dinosaurs returned to the same hatchery year after year.
The parenting instinct probably did not extend to adopting babies of other species, as Disney has it, but at least some dinosaurs had progressed beyond the lay-'em-and-leave-'em school of reproduction. At Egg Mountain in Montana, says paleontologist Jack Horner of the Museum of the Rockies, little plant-eating dinos unearthed near the nests of carnivorous troodons "appear to be food brought back for the troodon babies. Their arms and legs are often missing, as if they'd been ripped apart" by the hungry hatchlings 75 million years ago. Finds from the American Museum's expeditions to Mongolia clearly show that some dinosaurs--like Troodon and Oviraptor--sat on their eggs and even died on them when sand dunes suddenly collapsed atop them. The titanosaurs of Argentina, in contrast, seem to have gone in for community day care: Chiappe says they may have raised the juveniles in a large group that different adults took turns guarding.
The young grew up fast. One of the perennial debates about dinosaurs is whether they were coldblooded (read: slow, sluggish) like reptiles today or warmblooded (quick, energetic) like birds. Today, warmblooded creatures grow fast, and coldblooded ones take their sweet time about it. Analyzing growth rings in the bones of Apatosaurus (once known as Brontosaurus), Kristina Curry of SUNY Stony Brook finds that this giant reached half-size in four or five years, and that reaching adult size took only eight to 11 years. High growth rates are characteristic of warmblooded beasts. Warmbloodedness conjures up a picture of dinosaurs very different from the sluggish beasts of "King Kong"-era movies. It also supports the notion that dinosaurs did not become extinct 65 million years ago. Rather, they evolved. Says Sereno, "If you look the evidence squarely in the face, there's no question that birds evolved from theropods," two-legged meat-eating dinos. Even more direct evidence of that evolution comes from "bio-molecules" preserved with some fossils. Using electron microscopy and antibody analysis, scientists have determined that the keratin preserved in a dinosaur from Mongolia is identical to the keratin in feathers, but not the keratin in reptilian scales. That's why "Fighting Dinosaurs" (which runs from May 19 to Oct. 29) depicts feathered Velociraptors (though Disney keeps all its dinosaurs scaly). "We would even predict that T. rex had protofeathers, what some people call dinofuzz," says Norell. (Everyone wants to knock T. rex off his throne: CAT scans of the big guy's skull show that its olfactory bulb is much larger than the brain's visual cortex. Since dead meat stinks more than the living kind, and since predators need sharp eyesight, the discovery supports the notion that T. rex was a mere scavenger, not a fierce predator, says Horner.)
Give Disney credit for shattering the myth that the asteroid impact at the end of the Cretaceous killed the dinos instantaneously. It didn't. Aladar and his real-world counterparts would have died of old age or predation long before the pall of dust and smoke veiling Earth brought on a plant-killing "nuclear winter." That took long enough that there should be no problem squeezing in a sequel or two.