I went to see the Field Museum's new bird fossil on Monday. They were still setting it up when I got there, so I waited around for a half an hour or so for the privilege of being one of the first to see it.
It was worth the wait. It is very tiny, of course. The living bird, I would guess, would have been about starling size. The legs are the easiest part of the fossil to see. The rest of the body is somewhat scrunched up and the rock surface over the rib cage is not as smooth as it is over the legs.
But, if you looked carefully, you could see the the stubby tail and the keel bone, two very birdish traits. You could also see the clawed fingers on the forelimbs, the teeth in the jaws, and the long extension on the ischium, one of the bones of the pelvis. These are characteristics of the dinosaurs that are now almost universally regarded as the ancestors of birds.
People have been fascinated with dinosaurs ever since the first specimens were dug up in the early 19th century. In 1852, a British sculptor named Waterhouse Hawkins even got a government grant to erect life-sized statues of dinosaurs and other ancient beasts in Sydenham, a London suburb. Richard Owen, the British naturalist--as biologists were then called--who coined the term "dinosaur" (It means "terrible lizard" in Greek), worked closely with him to ensure the authenticity of the recreations.
Of course, they got almost everything wrong. Specimens were few in those days. In some cases, Hawkins had nothing but a skull, so he had to imagine the rest of the body. He produced an amphibian called Labyrinthodon--which in life looked rather like a crocodile--as a giant frog. The largest dinosaur, the Iguanodon, came out looking like a rhino. We now know that this animal, like many other dinosaurs, was bipedal. It carried its weight on its huge hind legs, and its forelimbs were much reduced.
When the restorations were complete, Owen gave a celebratory dinner for 21 dignitaries. The dinner was held inside the Iguanadon model. The festivities went on for most of the night, becoming increasingly hilarious as toast after toast was raised to the glorious success of the models.
In the late 19th century, the major action in the dinosaur field shifted to the U.S. The Great Plains turned out to be one of the richest dinosaur beds in the world. Geologically, the rocks there were of just the right age, and the dry climate meant that the land wasn't all haired over with trees. There was, and is, a lot of exposed rock, so the fossils are much easier to see than they would be in a wetter climate.
As early as 1854, a geologist named Ferdinand Hayden accompanying a U.S. Army surveying expedition to the Judith River in Montana picked up some very large teeth. In 1854, the plains Indians were still very active and inclined to contest the passage of army surveyors. They gave Hayden a name of his own, "he who picks up stones while running," that suggests the conditions under which he had to work. However, he did gain protection because his actions seemed so bizarre that the Indians decided he was crazy. Lunatics were regarded as touched with divinity and were therefore left alone.
Hayden's finds aroused considerable interest, and by 1870--six years before Custer's defeat at Little Big Horn--there were paleontologists out on the plains of Kansas digging up fossils.
The two most notable paleontologists of the era were Edward Drinker Cope of Philadelphia and Othniel Charles Marsh of New Haven. They hated each other. I've been toying with the idea of writing a screenplay about their rivalry. The story has the romance of intrepid scientists in the Old West and the absolute silliness of otherwise sensible, intelligent men acting like three-year-olds.
Cope and Marsh set spies on each other. They tried to steal each others' fossils. They sent agents west under assumed names in order to avoid each others' spies. At the end of a field season, they--or their hired diggers--would destroy bones they didn't have time to remove to make sure they wouldn't fall into the hands of the hated rival.
Their battle culminated at the Como beds in eastern Wyoming, some of the richest fossiliferous rocks in the world. Both men had crews on the scene at the same time, and on some occasions, the two groups actually came to blows over the right to dig in particularly promising locations.
Fame was the spur to some of this rivalry. Then as now, dinosaurs made the headlines. Most paleontologists live lives of great obscurity. They chronicle the rise and fall of trilobites, molluscs, or flowering plants and nobody who is not in the same field ever hears of them.
Two kinds of paleontologists can get famous. Those who study the evolution of human beings and those who study dinosaurs. Our fascination with our own forebears is easy to understand, as is our almost equal interest in fierce animals as big as houses. Kids love dinosaurs. They are so wonderfully creepy and enormous.
In the past couple of decades, paleontologists have gotten even more interested in dinosaurs than they were before. Beginning in the sixties, a new conception of these huge old beasts began developing. The old interpretation, which dates back to Richard Owen, was that, in their behavior and physiology, dinosaurs were very much like the reptiles of today. Their body temperature fluctuated with the temperature of their surroundings, and they depended on the sun to get them warm enough to move around and be active.
The new interpretation says they were warm blooded, like birds and mammals. Their body temperature was controlled internally, remaining at a constant high level regardless of the air temperature around them.
The switch from cold-blooded to warm-blooded has lots of implications. Reptiles spend most of their lives sitting still and doing nothing. Their energy requirements are very low. A Komodo dragon, the enormous Indonesian lizard, eats the equivalent of its own weight every 60 days. A cheetah, on the other paw, needs to eat its own weight every nine days. Maintaining a constant, high body temperature uses up a tremendous amount of energy. It takes a lot of food to keep the furnace fed.
So warm-blooded dinosaurs would have been active animals. They would also have been fast growing. Reptiles grow slowly throughout their lives. They don't have the physiology to handle fast growth. Birds and mammals grow very fast until they reach adulthood. Then they stay the same size for the rest of their lives.
Warm-bloodedness would also make large size advantageous. When an animal gets bigger, its volume grows faster than its surface area. Small animals have lots of surface and very little volume. They lose heat rapidly from all that surface, so they have to eat furiously. Shrews, the smallest mammals, need to eat more than their own weight every day just to stay alive. Big animals, with more heat-generating volume and less heat-losing surface, can get by with less. We know from fossilized skins that dinosaurs had no hair or other insulating coverings, so large size would be especially helpful to them.
The newest famous paleontologist, a Montanan named John Horner, has added another new wrinkle to our view of dinosaurs. He has dug up strong evidence that at least one species of hadrosaur--a large herbivore--laid its eggs in nests, that the nests were grouped in colonies, and that the adults fed the young in the nests until they were big enough to fend for themselves. Parental care on this level is not a feature of reptilian life.
The connection between birds and dinosaurs has been known for over a century. One of history's most famous fossils, the Archeopteryx (ancient feather) was dug out of a limestone quarry in Germany in 1861. The bones of this creature were those of a small dinosaur. It had heavy jaws studded with teeth, claws on its forelimbs, and a long, bony tail. But on the fine-grained limestone, one could plainly see the outline of feathers. Depending on how you interpreted the fossil, this was either the first bird or a dinosaur on its way to becoming a bird.
Archeopteryx would have been too heavy to fly much. It might have glided some, but its hind feet are those of a terrestrial animal and wouldn't have been very useful for perching on a tree limb. If the feathers weren't so plainly visible, this fossil would be thought of as a small dinosaur.
The new fossil at the Field is ten million years younger than Archeopteryx, and much more birdlike. Its hind feet could fit a limb. It's tail vertebrae have been reduced to a stub, one of many changes in the direction of lighter weight that came with flight. It also has a keel bone on its breast where the heavy muscles needed to power the wings were attached.
If dinosaurs were truly warm-blooded and if some of them had evolved a high level of parental care, then the shift from dinosaur to bird would not be very large. In fact, two paleontologists have suggested that we need to reclassify these animals. Instead of a Class Aves and a Class Dinosauria, we need only a Class Dinosauria with birds as one of the groups within it.
In other words, dinoaurs didn't become extinct. They just changed with the times. If you want to see one, you don't need to go look at a skeleton in a museum. Just walk outside and look up and you can see the dinosaurs flying by.
The fossil now at the Field was found on a Chinese farm, and after November 15 it will be returned to the Beijing Natural History Museum. If you want to see it, don't delay.