Lens to the Natural World. Kenneth H. Olson
to do with new information about them that has emerged in the last twenty years. Approximately every six or eight weeks, a new dinosaur species is described and named; there are now more than a thousand. No longer is their image that of the painfully obsolescent, slow, cold-blooded, stupid, green tail-draggers in the swamp that were simply too outmoded to survive. That image is humorously portrayed in The Far Side cartoon by Gary Larson that shows a Stegosaurus standing at the podium during a dinosaur convention. Speaking gravely to his “dino” audience, he says, “The picture’s pretty bleak, gentlemen . . . The world’s climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut!” In fact, dinosaurs dominated the world scene for at least 150 million years, indicating they were masters of survival. Active and dynamic creatures they were, and many of them, particularly the meat-eating “theropods,” are likely to have been warm-blooded.
In 1964, John Ostrom and his crew from Yale University were working in the badlands of Montana when they struck paleontological gold. In the resulting scientific paper, he wrote, “Among the important discoveries made was that of the spectacular little carnivorous dinosaur described here—an animal so unusual in its adaptations that it undoubtedly will be the subject of great interest and debate for many years among students of organic evolution.” It was Deinonychus—the name means “terrible claw”—a creature similar to Velociraptor, those fierce, if rather enlarged, killers portrayed in the kitchen-scene in Jurassic Park. Ostrom was right: the specimen ignited a wide-ranging debate on several aspects of dinosaur relationships, including that of their relationship to birds.
In addition to laying eggs and having three-toed feet, some dinosaurs had hollow bird-like bones. There is evidence that they had air-sacs, which, as in birds, extended from the lungs into much of the rest of the body and into some of the bones of the skeleton. Some even had clavicles (to become wishbones). Fossils of small dinosaurs found in China clearly show feathers, which may have been brightly colored. These are just a few of numerous characteristics shared with birds.
In fact, most paleontologists now regard the system of animal classification developed by Linnaeus, which served well for more than two hundred years, to be in need of revision, and they go so far as to say that recent discoveries strongly support the idea that dinosaurs are birds. If this is true, then we can say that at least some of the dinosaurs are still with us. In biologic nomenclature, Aves is the Class occupied by birds. Not only the scientific literature but now almost every new dinosaur book talks about “avian” dinosaurs (i.e. birds) and “non-avian” (traditional) dinosaurs. As an example, the popular book, Discovering Dinosaurs in the American Museum of Natural History, has a chapter entitled, “Why Did Non-Avian Dinosaurs Become Extinct?” Another chapter includes a photo of the world’s smallest bird perched on a penny (and about the same size). Below is this caption: “The smallest dinosaur is the bee hummingbird, Mellisuga helenae, found only on Cuba.”
Robert Bakker, as long ago as 1975, published a lengthy Scientific American article titled “Dinosaur Renaissance,” in which he detailed several aspects of the anatomy of a number of prehistoric creatures and concluded with the statement, “The dinosaurs are not extinct. The colorful and successful diversity of the living birds is a continuing expression of basic dinosaur biology.”
Therefore, when V-shaped flocks of Canadian geese are seen coursing through the skies in the month of March, some of us are prone to think, “The dinosaurs are migrating. Spring cannot be far behind.”
The bird-dinosaur connection became vivid for me over the course of a recent springtime that found me making an 800-foot ascent in the foothills of a nearby mountain range. It is a climb upward through time. There, each step may span thousands of years of strata, in this case of marine shale and limestone that was laid down in the Jurassic Period some 150 million years ago. Oyster shells are exposed in the rocks and have weathered out in profusion. This was also the time, elsewhere, of Archaeopterix, the primitive bird with a bony tail, teeth set in sockets in its jaws, and claws on its wings. Now, millions of years after those ancient oceans left behind their telltale fossils, my path leads near a large ponderosa pine tree where a pair of golden eagles has built a huge nest. My heart is beating faster from carrying the needed equipment up the steep slope but also in anticipation of seeing the wild creature that, to me, holds a fascination above all others.
I enter the small portable blind, which had been staked down almost two months before and camouflaged with pine branches in order not to disturb the birds. In a few minutes, my equipment is in place: tripod, camera, and an extreme telephoto lens that magnifies approximately twenty-four times and enables detailed images of what would otherwise be indiscernible. Soon, an eagle chick, in a white, downy covering perches on the edge of the nest. The chick has a large head and stubby wings and looks like—a dinosaur. (Many researchers now imagine the young of even the large meat-eating dinosaurs, such as T. rex, to have had downy feathers for insulation.)
Several weeks later, the bird has grown to be nearly as large as an adult eagle. The parents have fed it well. (On one occasion, I photograph it feeding upon half the carcass of a whitetail deer fawn that had been carried into the tree.) A small airplane passes overhead, and the young eagle’s eyes follow it with intense interest, as if thinking, “You can do that?”
Now, with a full set of feathers, the dark brown raptor often faces the wind and flaps its wings, even rising a bit from that platform of sticks in the sky. Then comes the day when it works its way out onto the far end of the branches that support the nest. There, it flaps a bit more, then stands motionless, gazing far outward and beyond. Not quite ready yet to catapult into empty space, an awkward turn-around is executed, and it moves back to the safety of the only world it has ever known. That scene, repeated several times, was reminiscent of a youngster edging out on the diving board at the local swimming pool: hesitating, wondering whether to take that first plunge, wanting it, yet fearing it. The next day, when I came back, the young eagle was nowhere to be seen. The thin air would now be its home for much of its life. The dinosaur had flown. Paleontologists say birds are dinosaurs, and I believe it.
Among the pieces of information contributing to a renewed interest in the prehistoric world are some that we never thought could be obtained, such as the presence of a so-called “medullary” bone layer found in a Tyrannosaurus rex femur that confirms the beast’s gender. Such bone, rich in calcium, is deposited in the skeletons of female birds (more connection) during the egg-laying cycle. So, it seems this rex, (first named “Bob” after Bob Harmon of the Museum of the Rockies, who found it) is really a female. The discovery was described by Mary Schweitzer, Horner, and others, in the journal Science in 2005. In that same year, they detailed still another remarkable find having to do with the same specimen. Following an acid-bath process to dissolve away hard, fossilized bone, some soft tissue remained behind: elastic, vessel-like material with cell-like structures within. This was a first-of-its-kind revelation, and the preservation astonished dinosaur researchers around the world. More work was done on the specimen in 2007, using mass spectrometry to find proteins, and they were found to be most closely linked to—you guessed it—birds. New techniques are leading to new discoveries.
Some phenomena are less subtle and the bones speak quite graphically, which is the case with a unique Triceratops dinosaur pelvis I excavated some years ago. It shows fifty-eight bite-marks made by the teeth of Tyrannosaurus rex. The specimen consists of one of the hip-bones plus the ten fused vertebrae in between the hips called the sacrum. The left hip-bone has had some 15 percent of it bitten off, and the other one is gone completely. Bite-marks of every size and description abound. In a sense, it is fossilized feeding activity of Tyrannosaurus. Based on this fossil, paleontologist Greg Erickson and I described such behavior in The Journal of Vertebrate Paleontology in 1996. The specimen has also been featured in a number of television documentaries, books, and magazines, and Erickson referred to it in a cover article in Scientific American that sought to depict the lifestyle of this largest of dinosaurian carnivores.
One bite-mark shows that a tooth entered at an angle, dragged backwards, making a long groove, then splintered off bone. Numerous other marks are of various depths. A Tyrannosaurus tooth can fit in many of the holes, leaving no doubt about the source. Sometimes, such teeth are compared to steak knives, but that is misleading; the teeth are not narrow, for slicing. Instead, they are round/oval in cross-section,