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by William Speed Weed, DISCOVER MAG, Sept. 2000
Yet it is precisely that experience with which a growing number of scientists have a big problem: There is precious little data about dinosaurs to transcend. What the museum scientists know about Indians, whales, and elephants is more than enough to mimic real life. But when it comes to dinosaurs, all they really have to work with is an incomplete jumble of bones. Indeed, if the exhibits department were limited to just skeletal data for its dioramas and reconstructions, these halls would take on a most unromantic flavor. For instance, the Indians in the canoe would lack noses, ears, and breasts, and the diorama artists (ignoring for the moment that they are humans themselves) would be at a loss for what to cover them in-slick skin like a dolphin? Monkey fur? Horse pelt? As for the blue whale, no one would know to make it blue. And the elephants are a special case. There's a running joke among professional dinosaur artists that goes like this: Given just an elephant skeleton, they'd probably render a titanic hamster.
Does anyone know what dinosaurs really looked like? Sure we do. We see them everywhere, not just in the museums, but in magazines, movies, even in value meals at McDonald's. But all of these lifelike renderings are mostly artistic interpretations based on very sparse scientific evidence. To begin with, dinosaur skeletons are rarely found intact, and figuring out how scattered bones fit together is not always clear. Then, making the leap of placing tissue and skin on those bones is a process fraught with unknowns. Some paleontologists trained in comparative anatomy are beginning to analyze microscopic marks that soft tissues make on bones in search of clues to what dinosaurs actually looked like. But taking a pile of bones and conjuring up what snarling dinosaurs about to battle each other really looked like involves at best equal parts educated guesswork and complete artistic fancy. As Mark Norell, curator of vertebrate paleontology at the museum, puts it, dinosaur artwork "is a fantastic leap from what we know." And most scientists say we may never know a lot more than we do now.
If that seems discouraging, it's good to know that scientists are also quick to say that asking what dinosaurs looked like is asking the wrong question anyway. Paleontology is a much broader endeavor than worrying about outward appearances. Those who study dinosaurs are more eager to know the life histories of the beasts: what particular adaptations they had, how they ate, how they raised their young, and what evolutionary relationships they might have had with one another and with modern-day animals. Time-traveling visual imagery grabs the public's attention, but it's not the point. "Dinosaur entertainment is healthy, sure," says Luis Chiappe, a paleontologist with the Natural History Museum of Los Angeles County. "But we don't look at Batman and think it's a documentary about the LAPD."
Further, to blame the artist is also to blame the messenger. Dinosaur art pervades our culture because we want it to. As fantastic creatures that really did exist, dinosaurs excite our imaginations. We want to explore their size and power and weirdness-and be glad they're no longer around. Biologist Stephen Jay Gould describes dinosaurs as "big, fierce, extinct-in other words, alluringly scary, but sufficiently safe." Randall Osborne, a social psychologist, contends that our need to imagine creatures vastly more powerful than we are is so strong that, "if we hadn't discovered dinos yet, we would have invented them ourselves. We would have made them in our movies." Or in our mythology: The Loch Ness Monster, Chessie the Monster of Chesapeake Bay, and the various fire-breathing dragons that cropped up millennia ago in both Eastern and Western mythology are hardly accidental.
Our attraction to dinosaurs doesn't spring from a scientific source, so the paleontological inability to say what they really looked like has no real power to drive dinosaur icons from our world. In fact, rather than wholly dismiss dinosaur art, many scientists use its popularity to their advantage. After all, it does win money for museums and field research. Some of the more media-savvy, like Paul Sereno at the University of Chicago, will wait to publicize a dinosaur discovery until they have a commissioned painting of the creature to show. By working with artists, scientists can at least inform them about what is known. "It's great when [artists] try to be scientifically accurate," says Scott Sampson, an officer of the Society of Vertebrate Paleontology. Thanks in part to efforts by his group to encourage relationships between professional dinosaur artists and scientists, most dinosaur images produced today, whether for movies or magazines or museums, are grounded in hard data, even though hard data can only be a starting point.
Jason Brougham, a senior preparator at the American Museum of Natural History, sculpted the Fighting Dinosaurs' protoceratops in the new diorama. To start with the science, Brougham studied protoceratops bones under the direction of paleontologist Norell. Brougham had a lot to go on because some 120 protoceratops skeletons have been found. For some dinosaur species, the fossil record contains only one skeleton, which is, more often than not, incomplete. Many dinosaur artists have faced the challenge of rendering a creature on the basis of half a skeleton. Mark Hallett, who has drawn and painted dinosaurs for museums, scientific publications, National Geographic, and movie studios, recently rendered a newly discovered dinosaur, Seismosaurus, on the basis of only 40 percent of its skeleton: "A few neck vertebrae, a complete pelvis, about a third of the tail, and no skull," he says. To help get a better idea of what the creature looked like, Hallett studied its closest known relatives and made a plausible guess.
Even with complete skeletons, there is lots of room for interpretation on how the bones go together. One major controversy with ceratopsians (the family of Triceratops and Protoceratops) is whether they stood on straight legs like rhinos or crouched crook-legged like crocodiles. In most dinosaur art before the 1980s, ceratopsians dragged their bellies under legs crooked out to the sides. Since then, it has been more popular to render them straight up, as on rhinos. That is the way Brougham sculpted his protoceratops. But Peter Dodson, a ceratopsian expert at the University of Pennsylvania, argues the proper pose is crook-legged, not necessarily in the "extreme push-ups" pose of modern crocodiles, but certainly not in the straight pillar fashion of modern rhinos either. According to Dodson's reading of bones, all straight-legged ceratopsian reconstructions suffer from painful shoulder dislocations.
With a working model of the skeleton, artists like Brougham must first think about muscles. The bones help in this regard. Muscle attachment points are sometimes obvious as scars on fossils, and the relationship between muscles and bone is fairly consistent for most vertebrates.
The process of laying muscles over the skeletal frame was vital to the success of Disney's Dinosaur movie. Hallett put together some of the initial working illustrations of these imaginary dinosaurs. He sketched detailed skeletons of iguanodons, the herding, four-legged, long-necked, long-tailed dinosaurs that serve as the main characters in the movie. Over each skeleton, he drew a full set of muscles adapted from crocodile anatomy and complete with Latin names. Then, at the behest of Disney, Hallett modified the overall look of the creatures to be reminiscent, in a Mesozoic way, of horses. The muscle drawings became the basic set of instructions the animators used to move the dinosaurs around in a believable way.
Applying muscles to a skeleton can be error prone. While the upper arm bone and elbow of a human strongly suggest biceps, the abdominal cavity of a skeleton provides no information-in humans or dinosaurs. "There's a lot of extrapolations involved," says Hallett, but if you are a careful student of comparative anatomy, "you can be reasonably assured of the major groups." If the artists render the muscles the way dinosaurs actually wore them, then their accuracy approaches that of, say, the musculature page in a human anatomy book: not a bad indication of what we look like on the outside, but still missing breasts, ears, noses, pot bellies, and all the other soft-tissue structures that define a creature's shape but make no large marks on the bone.
Brougham respects these limitations. A thoughtful 30-year-old with dexterous artist hands that he doesn't use when he's talking, Brougham mentions elephant trunks and ears' tapir snouts, and toucans as examples of creatures whose appearance one could never guess from their skeletons alone. "A toucan is preposterous," he says. Its head seems too big to hold up and "it's too extreme to be true." Still, Brougham believes that reminders of nature's whimsy do not give him license to speculate as many illustrators have done, putting, for example, proboscises or caruncles on a variety of dinosaur body parts. If Brougham doesn't have good information on soft tissues, he won't add any-no hump on the protoceratops's back, nor droopy wattles under its chin, nor a peacocky frill about its crest, even though all are as likely as the trunk on an elephant.
Brougham covered his protoceratops model with an ochre skin embossed with a scaly pattern suggested by fossilized skin impressions. What dinosaur skins actually looked like is one of the least-known elements of reconstruction. Brougham had to guess how the scales might have differed over the various parts of the body. He chose ochre as a neutral tone that might have blended well with the arid sands of the area, subtly camouflaging the creature from the eyes of a velociraptor. Most dinosaur colorations in recent years-and every year brings a wider range of patterns and pigments-are based on guesses about the landscape the creature lived in and its need for camouflage. By necessity, this reasoning makes unscientific assumptions about the ability of dinosaur eyes to distinguish colors and shapes. Eyes are a soft tissue that we will likely never have direct evidence for, paleontologists say. We do not know what dinosaurs saw, or if they saw in color, so we cannot know how they evolved to hide from one another.
We also can't know what the eyes themselves looked like, although they are major contributors to the appearance of a dinosaur face presented to the public. The slit pupils of reptiles and the round pupils of birds are good guesses, but artists have tended to go with slits only when they want the dinosaur to look mean. Brougham's protoceratops has nondescript beads with round pupils.
The rest of the face of Brougham's protoceratops is the same shape as the fossil skull. There are no extra flourishes, folds, or fringes except around the mouth, where he pulled the flesh over the sides of the jaw to make cowlike cheeks. Cheeks "look right," he says, but there's no conclusive evidence for them. The Disney dinosaurs also have cheeks, as well as fringes that look like eyebrows and lips for speaking English. Brougham put the nostrils on his protoceratops far forward, near its beak, following the example of most living creatures. Think of alligators, lizards' dogs, and donkeys: The nostrils go as close to the mouth as the nasal cavity will allow. Vertebrates like to lead with their noses. Disney's dinosaurs follow a different example, quite popular in dinosaur art. Their nostrils are farther back on the snout, halfway between the eyes and the mouth.
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The most conservative answer, which many give, is that we just don't know. Paleontology is the study of fossils; fossils are limited in the information they provide, so we will always run the risk of drawing a titanic hamster instead of an elephant, and we'll never know if we're doing it. Artists give a curiously different answer. In a sense, they know better than the scientists how far off they might be because they are the ones who must constantly do the guesswork. Many artists agree we'll never know whether a particular drawing accurately represents a creature that's been dead for 80 million years, but they also say it is possible to get a sense of how far off dinosaur art could be by exposing the process of layered guesswork. Hallett puts it this way: If he took a set of scientific evidence about a dinosaur and allowed himself to explore all the possible muscle placements, soft-tissue structures, facial variations and skin tones and patterns and folds and frills, he says he could draw a series of solutions and "come up with very different-looking dinosaurs." To scientists, of course, they'd all be the same, based on the same evidence. But to museumgoers, they'd be different creatures. The Society for Vertebrate Paleontology's Scott Sampson thinks such a varied lineup would be a great way for the science to peer through the art, because the only constant across the range of pictures would be hard facts: "Don't just illustrate [a few options] with a given set of evidence, but do the whole range. Vary everything and get 17 different things. It underscores our ignorance about these animals."
Museums and moviemakers seem not likely to offer that approach soon. You can't have a movie dinosaur looking entirely different from one scene to the next. The art is supposed to convince the viewer of the image, not of the science behind it. "I want to suspend the disbelief as much as I can," says Michael Skrepnick, a Canadian paleo-artist who has done dinosaur illustrations for National Geographic and various museums.
"I want you to believe in the animals you're looking at. I want you to think they're real." It is also uncommon for differing interpretations to crop up among illustrators. Because illustrators know how much hard work goes into reconstructing a dinosaur for the first time, they respect one another's original interpretations. Once a species is painted or sculpted, later illustrators generally honor the speculations of the original artist.
There is yet another take on dinosaur art, one that comes from a small but growing circle of young paleontologists who say that many of the decisions currently guessed at by artists might someday be based on real evidence from scientists. Larry Witmer, a professor of anatomy at Ohio University's College of Osteopathic Medicine, maintains that scientists can increase the yield of data from the bones they've got. All they have to do is look closer. His idea sounds simple enough: Look hard at the bones of modern animals to study the tiny marks that soft tissues make on bones, and see if such subtle marks can be found on dinosaur fossils as well. This growing field of soft-tissue research is a radical departure for paleontologists, most of whom were trained in geology (fossils are rocks found in rocks). Their soft-tissue analysis of bones has been largely limited to the muscle scars that can be seen with the naked eye. "People thought that soft-tissue stuff was just truly out of reach-that there was no rigorous way to know, so they just let the illustrators do it," Witmer says.
As a full-time teacher of anatomy, Witmer cuts up more animals in a year than most paleontologists do in a lifetime. He is a tall man with young features and a frame that would have no problem flipping over a walrus cadaver on a dissection table. Curious as he is about the relationships between soft tissues and bone, most of his work is delicate, requiring a dental pick, a magnifying glass, and a hefty amount of patience.
When colleagues suggested that the dinosaur Diplodocus might have a tapirlike snout, Witmer methodically dissected three tapirs (as many as he could get his hands on) looking for what he calls "osteological correlates" of the snout. We often think of bones as a stiff scaffold that everything else hangs on, but anatomists know that soft tissues actually morph bones as an animal grows, and over the course of evolution. "Soft tissues evolve, bones respond" is Witmer's working slogan.
In the case of tapirs, Witmer found that their skulls have various characteristics such as nerve passages, blood ducts, and small muscle attachments that are caused by the snoutlike structure, and therefore necessary for the snout's existence. When he searched for these characteristics on diplodocus skulls, he found none. His inference that Diplodocus did not have a tapirlike snout now has some scientific basis. Witmer did a similar study of the mooselike jaw muscles that some illustrators put on duck-billed dinosaurs and found that duck-bills do not have the hefty bone structure moose need to support such prominent jowls. He understands why the artists put them on in the first place. The big muscles "look great in reconstruction." Most renderings of duck-billed dinosaurs have that same familiar look of Iguanodons-they are great lizards reminiscent of horses. "If you make a duck-billed dinosaur look like a horse, which so many illustrators do, well, it looks right. But we have reconstructed it in modern guise," Witmer says. We live in an era of mammals, so dinosaur art is heavy with mammal flesh that is simply out of place. Dinosaurs are more closely related to snakes than they are to mammals. Moreover, moose and horses are no better guides to what dinosaurs looked like than manatees, humans, or voles.
Commenting on the series of choices illustrators have to make, from muscle reconstruction to soft tissues and facial features, Witmer suggests that any time an artist makes a decision because it "looks right," he risks falling into the mammal trap. Artists could do a better job by stealing soft tissues from crocodiles and birds to flesh out their dinosaurs he says, and science-minded artists like Hallett, Skrepnick, and Brougham have already begun to do so. Witmer does not expect the approach to satisfy our expectations. "If you go back and do it right, then it'll look totally weird. But it'll be right," he says. "We've missed a lot of their bizarreness by using these false analogues."
Witmer continues to dissect modern animals, looking for tiny, signature bone structures that they might share with fossil dinosaurs. He just obtained "a wonderful huge head of a rhino," which required a bigger freezer in his lab. Many paleontologists have maintained that the horns of ceratopsians were rhinolike, and Witmer can now test that hypothesis. He's on the lookout for crocodiles and birds, too, because they hold the best clues to dinosaur soft tissues. The ideal find for him is a set of soft-tissue marks on the bones of both crocodiles and birds. If he can find those same marks on dinosaur fossils, he has strong evidence that the dinosaur had the same soft tissue. He has already used this technique to establish that dinosaurs had an air sac housed in a skull cavity between the eye socket and the nasal opening. For more than a century, paleontologists kicked around hypotheses as to the cavity's function: It was a muscle, it was a gland for salt. Crocodiles and birds have air sacs in that cavity, and those air sacs leave the same characteristic microscopic marks Witmer found on fossil skulls.
This subcutaneous soft-tissue discovery doesn't dramatically change the outside look of dinosaur art. And Witmer's goal isn't to improve dinosaur art. His purpose is to learn more about questions like: What organs did dinosaurs have and what were they used for? But Witmer's work, and the work of a handful of other young paleontologists who are approaching the soft-tissue questions with scientific methods, may ultimately allow artists to flesh out dinosaurs with more hard data. "Anything that increases the chances of a paleo-artist [rendering] something more accurate would be welcomed with open arms," says Hallett. He says he and his colleagues aren't in this business to make guesses. They want to know the truth.
And what about all the paleontologists who say anyone trying to figure out what dinosaurs really looked like is asking the wrong question? Deep down inside, suspects Hallett, they want to know too.
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