Lifting the Veil
Deep inside the rabbit-warren basement of the Museum of the Rockies in Montana, past the fierce-looking pet lizard that devours live mice and fish heads, sits a room that is not your father's paleontology lab. There's not a dusty old bone in sight. Instead, Sun Microsystems computers and Silicon Graphics workstations blink away, pushing the envelope of dinosaur knowledge. Curator Jack Horner recently sent the skull of a Hypacrosaurus, a four-legged herbivore dug up in Montana, to San Diego Children's Hospital. The hospital CT-scanned it, gratis. Now, scan in hand, Horner boots up software to create a three-dimensional color picture of the skull. He scrutinizes it from every angle, and then he morphs it: the computer shows how the skull grew and changed shape throughout the hypacrosaur's life. Next he'll build a model of the skull, complete with an over-the-top crest that Horner thinks acted as a horn. Then he'll blow it. He expects to hear nothing less than "the wailing of a hypacrosaurus," says Horner (whose scientific achievements are dwarfed by his fame as the model for the paleontologist in "Jurassic Park"). Some 75 million years after extinction silenced this dinosaur, Horner will have made its Mesozoic music blare again, and will have taken a giant step toward resolving one of the most annoying dinosaur enigmas: what they sounded like.
Martin Lockley steers his four-wheel drive into a ditch at Dinosaur Ridge, in the foothills of the Becky Mountains just outside Denver. Shaking the dust off his T shirt, the University of Colorado paleontologist points to a set of cookie-cutter footprints that dot a fiat rock, They are the tracks of a Cretaceous beach bum called Iguanodon, who waded along the shores era 1,000-mile-wide inland sea 100 million years ago. Lokley is the Daniel Boone of paleontology, a master tracker who can infer from what he calls "seemingly ephemeral traces in the sands and muds of time" that a two-legged carnivorous dinosaur hunted alone, traveled hundreds of miles tracking migrating herbivores and "occasionally ran as fast as [an] Olympic sprint champion."
Horner and Lockley are two of a tiny band of scientific sleuths using techniques from CT scans to common sense to pry open a window on the 165 million-year reign of the dinosaurs. For reign they did. From little Compsognathus, no bigger than a Perdue Oven Stuffer, to the earthshaking Seismosaurus, the long-necked quadruped that could have seen eye to pane with a sixth-floor window, dinosaurs conquered every continent on earth. They didn't do too badly after they went extinct, either. Starting in the 1970s, paleontologists, apparently figuring that no one could disprove their conclusions and egged on by the media, went wild with brash assertions about this lost world. Dinosaurs had day care and fast food; their young were born alive rather than hatched, some said. Now the rethinking has set in. Examining the slim evidence on which some researchers based conclusions about everything from dino sex to dino family values, paleontologists are reassessing what they know, and what they can know, about these extinct animals. Now, says paleontologist Michael Novacek, provost of New York's American Museum of Natural History, it's all about "how we know what we know." That humility is reflected in a powerful new dinosaur exhibit opening this week at the museum (page 58).
Sometimes the evidence is as solid as a videotaped confession. Finding the bones of a baby Coelophysis inside the rib cage of an adult leaves no doubt that these 220 million-year-old carnivores, among the first dinosaurs to evolve, were cannibals. An Edmontosaurus, a duckbill that lived at the end of the dinos' reign, has a stomachful of fossilized cone, bark and needles; no guesswork is needed to deduce his favorite cuisine. In 1981, paleontologists found in Mongolia a fight-to-the-death still life: the right arm of a Velociraptor, a lithe meat eater of "Jurassic Park" fame, is caught in the mouth of a Protoceratops. The raptor's hand is grabbing the clunky plant eater's face; its large slashing foot claw is stuck in its prey's neck, at the carotid artery. Both died in midfight. "It's rare for the bones to tell us about the interaction between dinosaurs," says Philip Currie of the Royal Tyrrell Museum in Alberta, but there's no doubt about this food chain. Sometimes the bones tell almost poignant stories about dinosaurs as individuals, not merely as representatives of their species. At the April meeting of the Geological Society of America, William Hammer of Augustana College in Rock Island, Ill., described a large, crested carnivore from Antarctica. In its mouth were two long, thin rib bones from an unidentified species. This creature apparently choked to death on its last meal.
But those are the easy ones. The vast majority of dinosaur puzzles--which color they were and how smart, how they sounded and whether they brought up Baby or abandoned it at hatching--remain hidden by the veil of time. "Short of building a time machine, we will never be sure about these things," says Lowell Dingus of the American Museum. But by applying anatomy, neuroscience and new techniques of inferring evolutionary relationships, paleontologists can "go to the scene of the crime, gather the clues and try to make a story out of it," says the balding, root-beer-quaffing Horner.
What better to find at a crime scene than footprints? For Lockley, identifying who made the prints is just the first step. (Each group of dinosaurs--four-footed sauropods, birdlike theropods--has a distinctive print.) He can also tell how fast the beast was traveling. Studies of modern animals reveal a relationship between the length of a stride and speed. Applying the formula to dinosaurs, Lockley finds that medium-size carnivores zipped along as fast as 27 miles an hour, for instance. In contrast, "the huge sauropods, plated stegosaurs and armored ankylosaurs . . . ambled most of the time," he says.
Trackways also offer the strongest evidence that some dinosaurs were as social as the great herds of wildebeest, zebra and elephants that cover Tanzania's Serengeti Plain. A trackway from Davenport Ranch in Texas, made 107 million years ago, has 23 sets of footprints. All but two overlap. That indicates "that the sauropods were crossing the area in a line, not spread out on a broad front," says Lockley, "with larger sauropods leading the way." At a New Mexico site, Lockley's team has mapped the tracks of 55 small herbivores heading north and 25 larger ones going south. (One little guy was limping, as Lockley can tell from the pattern of short then long strides, but kept up.) This pattern of segregation by size is common in sauropod tracks, too. It's easy to envision yearlings cavorting with yearlings while adults kept to themselves. To test his theories, Lockley can't ask Apatosaurs to amble across some nice wet concrete to see if the prints they make match the herd structure he has inferred. So he lugs equipment to Africa, where he sets up time-lapse photography. He compares what the lens sees--milling zebras, migrating wildebeests--to the tracks the animals leave. If his inference that dinos in a line made tracks like this, but elephants in a line made tracks like that, he revises his conclusions.
Paleontologists measuring bones take living animals as their benchmark, too. Sometimes this is straightforward, as when researchers deduce that a dinosaur with a set of sharp, serrated teeth ate meat, while one with flat, grinding surfaces on its pearly whites crushed and pulverized plants. It's also clear what the marks that dinosaurs' muscles left on the fossil bones mean. Big muscle attachments at the base of the tails of armored Ankylosaurus imply that anky very likely wielded its tail like a deadly medieval mace.
Robert Bakker reads even more into muscle attachments. Bakker made his name in the 1970s with the then crazy idea that dinosaurs were warmblooded, which meant they could be as active as birds and mammals rather than as sluggish as turtles. It's more or less accepted now that at least some dinosaurs were warm-blooded, but Bakker is still considered the wild man of paleontology. Lately he's spent a lot of time over his kitchen sink in Wyoming, dissecting pickled chicken feet and crocodile hand muscles. Then he matches each tendon to the wrist bone and claw core. That lets him link every attachment point he sees on the fossils of Allosaurus (a scaled-down Tyrannosaurus rex), Acrocanthosaurs (a bipedal carnivore) and raptors to a muscle or ligament. From his map, Bakker, whose novel (yes, novel: "Raptor Red") about a raptor is due out in September, reads differences in how the predators killed. Holding down prey, acro pulled its claw over its meal in a careful evisceration, Bakker says; raptors had less leverage and so were ruthless slashers.
Anatomy can also shed light on dinosaurs' IQ and sensory abilities. The brain, conveniently, often leaves its mark on the inside of the skull in a pattern of squiggles. The braincases of maniraptors, the bipedal meat eaters that included Troodons and Dromaeosaurs, show relatively large and complex cerebrums, the region that regulates sensory functions and memory. "In these advanced dinosaurs, you begin to get the same brain characteristics as in birds," says Mark Norell of the American Museum. Velociraptors and Deinonychus were probably about as smart as ostriches, but not as bright as hawks. The cerebrum, which processes vision, is most developed in raptors. At the front of a brain, protrusions called the olfactory bulbs process smell. Most dinos had small olfactory bulbs, suggesting they couldn't smell very well. Velociraptor and T.rex appear to be exceptions, says Horner: in both, a larger chunk of the brain is given over to the olfactory bulb.
Horner takes this as evidence that T.rex did not hunt, but scavenged--a theory as controversial as calling Jaws a vegetarian. The size of its eye sockets shows that rex had small eyes, Homer explains. Poor vision is ill suited to spotting moving prey. Rex's short calf bones would have made the big fellow rather slow. But the huge olfactory bulbs in rex's skull, says Horner, could catch the scent of decaying flesh miles away. "There's nothing more important to a scavenger than the ability to smell for a long, long way," Horner says. This is plausible, but to many paleontologists it is squeezing more out of the fossils than they can reasonably give.
In fact, even inferring something as basic as dinosaurs' weight can divide the detectives. In one approach, paleontologists use the skeleton to build a model of what the fleshed-out, living creature looked like. All flesh has the density of water, more or less. So one can calculate weight from volume (volume x density = weight). This method says that Brachiosaurus, a long-necked, four-legged plant eater, weighed 87 tons. But there's a competing approach. In living animals, a formula relates the length and width of the bones to the creature's weight. By this method brachiosaur weighed 31.6 tons.
Oddly, the evidence for dinosaur communication is less ambiguous. The duckbill Corythosaurus had a bony helmet reminiscent of a gladiator's. It was hollow, so it could have made bellows and honks. Since crests differed from species to species, the pitch--a wail or a moan--would have been unique to a breed and thus could have served as an identifying call. Of course, showing something could make noise is not equivalent to showing that it did. For more evidence, paleontologists look to dinos' genealogy. Both crocodiles and birds, which bracket dinosaurs on the family tree, vocalize. If one believes that advanced traits such as talking usually appear only once in evolution, then crocs' and birds' common ancestor talked, too. Dinosaurs share that common ancestor, so it's likely they communicated, too. But it's not definite.
The golden ring of paleontology is how the animals behaved. It's a truism that behavior does not fossilize, but in fact sometimes it does. A velociraptor from Mongolia has two parallel rows of small punctures--a pattern of marks that matches exactly a raptor's upper teeth. It was killed by its own kind. But the victim was not scavenged, suggesting it was not killed for food. Was it for territory? or over a mate? On that, the bones are mute.
Even without such an easy-to-read fossil, paleontologists can make educated guesses about behavior. Anatomist Scott Sampson of the New York Institute of Technology has examined scores of horned dinosaurs such as Einiosaurus, young and mature. Horns appeared late in an animal's life, he finds, suggesting they did not serve to keep away predators. If they did, "one would expect early rather than late development, so they could be put to use as soon as possible," says Sampson. In living animals, like bighorn sheep, such features "permit animals of different ages and strengths to assess one another['s strength] without resorting to physical contact," Sampson writes in the June issue of Natural History. "The result is a . . . pecking order." There is a possibility, then, that "horned dinosaurs lived in complex, hierarchical herds."
And at least some abjured the lay 'em and leave 'em school of motherhood. In nests of Oviraptor, an ostrichlike meat eater, fossilized eggs are "arranged in a circular pattern, with the large end of the eggs facing inward," reports Mark Norell. This isn't how eggs come out naturally, and so indicates that "oviraptorids manipulated their eggs in the nest," says Norell. But after this interior decorating, did Mom hang around? Bakker has been studying "predator lairs" in Wyoming, where the masticated bones of herbivores are piled up with tooth crowns of predators, evidently broken off during the meal. In each lair, Bakker has found crowns of both adults and babies of the same carnivores. Since dinner was a multiton herbivore, adults were evidently lugging dinner home.
But were dinosaurs green? A very few fossils show skin impressions. None shows color. There is no way to tell which dinosaur might have been a drab olive and which a bright tangerine. None, presumably, was purple. Paleontologists may be hot on the trail of dinosaurs' talents and behaviors, but with their new humility, though, they readily concede that the magnificent creatures have carried at least some of their secrets to their eternal graves.
Applying new theories of evolution, anatomy and neuroscience, paleontologists deduce all sorts of details about how dinosaurs lived. They start with fossil bones, teeth and footprints.
The gray matter leaves impressions on the bone. From them, scientists infer which sensory regions were developed, and even how smart the dinosaur was.
Muscles leave marks where they attach to bones. Big attachment marks on Ankylosaurus's hip suggest it wielded the flexible tail and bulbous end like a mace.
Large bumps, where muscles ached to the base of Deinony-chus's daws, indicate the claws were powerful slashing weapons, capable of eviscerating prey.