Excerpt. © Reprinted by permission. All rights reserved.
CHAPTER 1
Birds: The Dinosaurs
That Made It
What good is half a wing?
—St. George Jackson Mivart
Where did the first flying bird come from? Did it spring, fully formed, with perfect wings, from the mind of God? Or was the first act of flying carried out by a small dinosaur with feathers who leaped out of a tree, glided gently through the air, and landed on the ground like a child’s balsa airplane? Did a galloping feathered dinosaur chase so fast after a buzzing insect, leaping to gobble it, that it found itself airborne? How flight first happened is a mystery, but in the birds that surround us today, which are the only surviving dinosaur lineage, some have found a look back at how dinosaurs might have gone airborne and what these creatures from long ago were like.
The governing theories about how the first animal evolved the ability to fly—first proposed in the nineteenth century and still operable today—are divided into two main camps, the arboreal and the cursorial. Derived from the Latin word for “tree,” the arboreal theory holds that around 125 million years ago, small reptilelike creatures with four limbs were covered with something like feathers. The featherlike covering was used not for flying but as a cloak to keep the creatures warm or as a way to look sexy and attract partners, or as camouflage, or all three. Perhaps these creatures leaped from tree to tree in a dense rainforest, the way a flying squirrel travels—not really flying, but gliding.
Then one day, arborealists imagine, with its forelimbs stretched in front of it and its feather coverings spread out to the side, the first flying animal glided from a tree to the ground, and as it went on it added flapping to increase thrust. Perhaps the critter had a random genetic mutation that gave it larger forelimbs than others, which helped propel the animal forward. There are some sticky problems, however, that some argue shoot down the trees-to-ground theory, one of which is that there are no gliding animals today that flap for thrust.
The cursorial, or ground-up, theory of the origin of flight refers to the animal’s ability to run. In this scenario, the first fliers were track stars with a yearning to take to the skies and soar. After zooming along the ground and making a series of leaps, to chase a dragonfly perhaps, or cross a creek, they somehow found themselves soaring with feathery forelimbs that had, perhaps through random mutations, grown large and light enough to keep them aloft. Left unexplained is where a heavy dinosaur would get the energy to run three times faster than modern birds in order to break the bonds of gravity and flap its way through the air, all with a developing wing. Perhaps, some have thought, they were half wings on a bipedal, or two-legged, creature, but why would an animal have a half wing if only a full wing would allow it to fly?
It’s a good question, and one that’s often asked when it comes to the evolution of flight. “What good is half a wing?” was first asked in 1871 by St. George Jackson Mivart, an English biologist. Mivart was at first devoted to Darwin’s theory of natural selection—the idea that as creatures evolved, only those who were most fit survived. He turned against his mentor, though, and later became one of the theory’s most vehement critics—largely over the bird wing. There is no reason on God’s green earth for an animal to have half wings, because they are useless, he claimed. Ergo, the theory of evolution doesn’t make sense; God must have created birds fully formed. To this day, creationists hold fast to the argument that half a bird wing refutes evolution.
This is where the first-flying-creature debate has stood for quite a while—two main schools of thought arguing about their respective ideas, with a separate school believing that a bird’s wing is a result of the act of divine creation, rather than meticulous and persistent shaping by eons of evolution.
A new perspective that combined aspects of both evolutionary theories arose when Ken Dial weighed in in the early 2000s. While his distinguished career has been about studying bird flight mechanics, he found that his approach could also be uniquely applied to the evolution of flight. “Study the dinosaurs that made it—the birds,” he says. Understanding more about the evolution of flight by studying living animals provides a new perspective on the ecology and biology of birds and dinosaurs, information that can’t be gotten elsewhere. “These are things you would never get from studying fossils,” he says.
With his shaved head, goatee, and glistening aviator sunglasses, the guitar-playing, jet-piloting Dial is perfect for the role of a renegade. He’s a bird nut, as many people who investigate birds are, energetic and excited when talking about his research. The fact that he’s an interloper on the subject, wading as a biologist into a field occupied largely by paleontologists, doesn’t bother him. The origin-of-flight theorists base their respective arguments on the study of fossilized dinosaur bones. This necessarily involves a lot of conjecture because the beasts are so long gone, and their bodies are very unbirdlike at this point because they are fossils frozen in stone. Dial’s work is based on videos of hundreds of live birds performing in his lab, doing things that no one knew birds did, as well as his study of their muscles, limbs, and other mechanics. I watched several of these films with Dial in his office at the Flight Laboratory in Missoula, part of the University of Montana, and I asked him how he thinks bird flight first took off. His is a fascinating idea, based, in part, he told me, on something called “recapitulation theory,” a theory that is largely rejected by science but that Dial has resurrected.
Recapitulation theory is a notion that goes back to ancient Egypt, though it was formalized in the nineteenth century by the German biologist Ernst Haeckel. It holds that the early development of a single animal mirrors the evolutionary history of the species. Very young human embryos look like fish, for example, as the theory poses that our human ancestors did long ago. Dial doesn’t agree that this is true all of the time, but he believes it sometimes appears to be true.
Students in a graduate seminar he was teaching in the late 1990s, Dial tells me, helped set him on his path to investigate how flight may have first developed. As part of their assignment, they studied the origin of flight and interviewed published researchers in both the arboreal and cursorial schools. They concluded that there wasn’t a lot of good data for either theory. So at the end of the seminar, the students issued Dial a challenge. Why didn’t he, the functional morphologist, do some research and come up with a new take on this question of the origin of flight? Dial thought that was a fine idea, since the study of the subject is indeed “very limited by the fact that the animal has been replaced by stone. It’s not moving, just an anatomy left for us to try and interpret.” The two theories, based on fossils and very little concrete evidence, “constitute a lot of arm waving and little data,” according to Dial. “It’s easy to come up with a hypothesis with a simple dead structure you want to fit into your story. That’s just storytelling. My feeling was that we need to understand broadly and in depth the anatomy and physiology of the living.” Dial believed he could use his high-speed cameras and other sophisticated instrumentation to come up with some new ideas about the origin of flight.
Dial is well suited to take on the subject from a new angle. He’s observed hundreds of species of wild birds for decades and taught field courses on birds across Africa. As a researcher, he has long and meticulously studied the physiology of birds, every component part, muscle, nerve, and bone, and how this equipment determines how birds fly and run. As the host of the acclaimed series All Bird TV on the Discovery Channel, he has also traveled across North and Central America, filming birds in the field and interviewing a wide range of other bird experts.
It was in an unlikely source that Dial found a glimpse into the likely origins of flight: baby birds, who, in those first few weeks of their existence, he believes, provide a detailed look at the millions of years it took for the ability to fly to evolve. It’s just one example of how modern-day birds inform our knowledge about the very distant past.
It’s hard to fathom the notion that the feathery little creatures that flock to our feeders are modern-day dinosaurs, but it’s true. All birds are, though chickens and turkeys are genetically the closest dinosaur relatives. Researchers, in fact, have manipulated chicken genetics so chicks grow dinosaurlike beaks, feet, and legs. It took a scientific revolution to overthrow the notion that dinosaurs were reptiles, an idea that purportedly arose in 1868, when the biologist Thomas Henry Huxley, so fierce an adherent to the idea of natural selection that he was known as Darwin’s bulldog, was eating dinner one evening while thinking about a dinosaur bone he had earlier been working with in the lab. As he nibbled on the bottom of a turkey drumstick, he was struck by its similarity to the anklebone of the dinosaur.
There was also a peculiar fossil find in 1861 in Germany that fueled such thinking, the discovery of the archaeopteryx. About the size of a raven, the strange creature had broad wings and long feathers, and could fly, or at least glide, but actually had more in common with small dinosaurs than birds, including sharp teeth and a long bony tail. Archaeopteryx was a theropod—Greek for “beast feet”—a group that includes small to gigantic dinosaurs, including Tyrannosaurus rex, with feet similar to birds. Theropods had numerous other birdlike features: They brooded their eggs, had bones filled with air pockets to make them lighter, and in many cases had feathers and a wishbone, or furcula.
Birds and dinosaurs, Huxley thought, had to be related. It was a marked departure from the prevailing idea in the nineteenth century that birds were descended from a predinosaur reptile. It also implied that they had been warm-blooded, not cold. Huxley’s idea got little traction, and the notion of a bird-dinosaur connection was largely forgotten. In the 1960s, though, Yale University’s John Ostrom found twenty-two features in the skeletons of dinosaurs that were also found in birds, and he refloated the hypothesis. The “dinosaur wars” were under way, reaching a fever pitch in the 1980s as experts battled over whether dinosaurs were birdlike or reptilelike. By the 1990s, though, the matter was largely settled science.
Because they are related to dinosaurs, birds have been enlisted by scientists to tell us something about their ancestors. Dial turned to an unlikely subject—a baby chukar partridge. “I’ve worked in the lab with everything from pigeons and starlings, parakeets, magpies, finches, ducks, geese, and swans,” he says, “but chukars fit the bill.”
There are two forms in which birds are born into the world. One is altricial, which means “requires nourishment.” Altricial birds, such as the robin, are feeble, naked, and helpless after they burst through their eggshell, and they need days of doting care from parents who keep them warm and stuff food into their perpetually wide-open mouths as they develop feathers and the ability to fly. The other radically different way birds arrive is precocial, mind-bogglingly mature at birth, able to walk or run, evade predators, and forage for food on their own. Precocialism occurs along a spectrum and is especially pronounced in ground birds, who are most susceptible to predators. Some unusual birds, such as the megapodes—“large foot”—of Australia and New Zealand, are superprecocial, which means they are the most mature birds at birth of all. And Australian brush turkeys are the champions of superprecocial behavior.
Brush turkeys are bold, with no fear whatsoever of people. These days, they hang out in parks, near malls, and in other suburban settings. They look something like the wild turkeys found in North America—a deep blue-black color, with a bright head and flat tail. They forage through leaves and grass on the forest floor for seeds, fruit, mice, frogs, and other small animals, and they build unusual giant communal nests out of leaves and twigs that can be as large as twelve feet wide and six feet tall. They are known as incubator birds, because when the hens lay their customary eighteen to twenty-four large white eggs, the heat from a compost pile they build beneath the nest radiates up to keep the eggs warm. The males tend the eggs carefully, sticking their beaks into the compost to monitor its temperature and adjusting the mix to make it warmer or cool it down.
As soon as the babies peck their way out of the shell they are ready to roll. At one day old—one day!—the fully feathered chick’s eyes are wide open, and it literally hits the ground running. With extremely powerful legs and feet, these little chicks are able to fly and climb vertically up trees and rocks, abilities that allow them to evade snakes, dingoes, and other predators. “The hatchlings are very comfortable on extraordinary slopes, with no panting or stress, doing it over and over again,” says Dial. On that magical first day, a baby brush turkey can fly and run up steep and rocky cliffs better than an adult, though that ability eventually diminishes.
The chukar partridges that Dial studies are also precocial—though not superprecocial—ground birds. Chukar partridges are small and stocky, a member of the Galliform family, which also includes chickens and pheasants. They have a distinctive white face with a black gorget, or collar, of dark feathers. They favor dry, harsh terrain, and they eat a mixed diet, a buffet of insects, grass seed, roots, and whatever else they can scrounge. They were introduced to the United States from the deserts and mountains of their native Pakistan because they are fast and flap furiously when they take flight, which makes them an appealing quarry for bird hunters.
Chukars, like the pheasant and ostrich, lay their eggs in a depression in the ground. After a couple of weeks, the young hatch, and within twelve hours they run and start foraging for food, though they are still occasionally tended to by parents. There was something in the chukars, Dial thought, that was very dinosaur-like—it was the way they used their four appendages, something he calls “wing and leg cooperative use.” They also maintained a wildness about them when he brought them into the lab. The Japanese quail he was using, on the other hand, which are commonly used as lab animals, were docile and sat quietly in his hand as he stroked them. Chukars could be raised and handled, yet they remained skittish and fled when he came near them—a perfect combination of traits, he says, for studying how they learn to fly as a window into how the dinosaurs might first have learned to take to the air.
