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Fossil Threads in the Web of Life
By Scott D. Sampson
UNIVERSITY OF CALIFORNIA PRESSCopyright © 2009 the Regents of the University of California
All rights reserved.
A SPONTANEOUS BARRAGE OF EXPLETIVES rang through the air, bringing my coworkers scrambling over the hill. Madagascar's sweltering midday heat no longer mattered. There before me, beneath a clod of freshly dislodged sediment, were four shining teeth, exposed to the light of day for the first time in more than 65 million years. Most kids could have confirmed that these sharp, recurved, chocolate brown objects, each topped with fine serrations, once lined the mouth of a meat-eating dinosaur, a theropod. Best of all, these teeth were still attached to a jawbone. Further digging revealed a complete and undistorted jaw, with every tooth in place. over the next couple of days we found more bones of the same, exceptionally preserved skull—part of the eye socket, another jaw with teeth, a gnarly bone from the nose region. Soon it became clear that most of the skull was buried here, although the individual bones had fallen apart and now lay strewn over several square meters. We could barely contain our excitement. Field paleontology relies as much on serendipity as on know-how and hard work, and the fates had smiled down upon us. Yet, as more and more bones of the ancient predator were unearthed, we began to get nervous. A key portion of the skull remained missing, leaving a mystery unsolved.
In Lewis Carroll's classic tale, Through the Looking-Glass and What Alice Found There, Alice gazes into a mirror to find a world similar to her own yet distinctly different. Her view of this reflected world varies dramatically depending on where she stands and how she holds the mirror. And Alice dreams of actually stepping through the looking glass to experience firsthand the wonders beyond. Like Alice, paleontologists attempt to gaze through the looking glass of time in order to catch glimpses of other, distant worlds. We, too, find that our perspective is always limited, changing considerably depending on how we hold the mirror and indeed which mirror we choose. And we, too, dream of witnessing these worlds firsthand. The ongoing efforts to open windows into ancient landscapes and their inhabitants comprise the science of PALEONTOLOGY, the study of ancient life.
Dinosaur paleontology, my particular specialty, is a peculiar profession. After all, how many people can claim to have a job that is the envy of most 6-year-olds? Telling others that you're a dinosaur paleontologist often results in the usual questions. "How do you know where to dig for them? What was the biggest dinosaur? Why do you think dinosaurs went extinct?" Of the most common queries, the one that I find most amazing and dismaying is "Don't we already know everything about dinosaurs?"
People tend to think of science as the gradual, steady accumulation of facts that has been ongoing for centuries. So it's often imagined that today we scientists are merely adding insignificant grains to an enormous, established mountain of knowledge. This view could hardly be further from the truth. The vast majority of nature's secrets have yet to be revealed. In the evocative words of biologist and environmentalist David Suzuki: "It is as if we are standing in a cave holding a candle; the flame barely penetrates the darkness, and we have no idea where the cave walls are, let alone how many caves there are beyond. Standing in the dark, cut off from time, and place, and from the rest of the universe, we struggle to understand what we are doing here alone." Rather than being daunted by our overwhelming ignorance, I am inspired by the multitude of new discoveries that patiently await us, entombed within the earth, carefully preserved in museum drawers, and tucked away in the corners of our imaginations. It's an exciting time to be a paleontologist.
If the overriding aim of science is to understand and describe as accurately as possible the workings of nature, certainty turns out to be a scarce commodity. To speak of "scientific facts" is to border on using an oxymoron. Most scientists would agree that there is a single, physical reality to comprehend. To borrow the slogan of a recent popular television show, "the truth is out there." Yet the best we can offer are successive approximations of that truth, formulated as alternative explanations, or HYPOTHESES. The scientific method involves sorting among these various alternatives. Consequently, testability is an integral part of the process, and only the strongest THEORIES, like gravity and EVOLUTION, withstand decades of testing and become accepted as fact.
But how can paleontologists test ideas? Like geology, paleontology is a historical science, concerned predominantly with understanding and interpreting past events. Historical sciences differ in at least one fundamental way from nonhistorical fields such as physics and chemistry. Paleontologists cannot test a hypothesis through direct experimentation for the simple reason that it is impossible to reproduce past events. For example, barring the highly unlikely cloning of a dinosaur from its DNA or the invention of a time machine (even less likely), we clearly can't investigate the metabolism of Tyrannosaurus rex directly. Similarly, geologists cannot observe the rifting and collisions of ancient continents. Given the strong emphasis on reproducibility—the ability to run the same experiment multiple times in order to test for similar results—some have even argued that the inability of historical sciences to reproduce results should disqualify them as scientific disciplines.
Yet the historical sciences are able to circumvent the conundrum of time's arrow, at least to some degree, through an elegant loophole. Although the inexorable march of time prohibits actual reproduction of past events, it's possible to observe multiple examples of such events. If these examples are consistent with a stated hypothesis, it gains support. If not, the hypothesis is falsified or at least brought under closer scrutiny.
Take evolution, for example. Darwin's theory states that all organisms past and present share common ancestry and that life evolved from simple, single-celled beginnings. Thus, we predict that the order of appearance of particular groups of organisms should mimic the branching pattern of evolution, with a trend toward increasing complexity through time. Convincing evidence against evolution would be the discovery of any animal that lived long before its supposed time of its origin—say, for example, the fossilized remains of a rabbit (or human or dinosaur, for that matter) dating to 400 million years ago. With hundreds of paleontologists working around the globe in rocks that span most of Earth history, this amounts to hundreds of thousands of opportunities annually to discredit evolutionary theory. Yet, invariably, we continue to find groups of organisms restricted to rocks of a specific age range. In all the years I have been hunting for dinosaurs in Mesozoic-aged deposits, I have never found any indication of advanced mammals such as cats, whales, or aardvarks, let alone humans. And the same is true for all of my paleontological colleagues, because such a find would be headlined in the media worldwide and bring with it the potential for all forms of academic accolades, as well as research funding. In short, through study of multiple examples of past phenomena, paleontology and geology are anchored on testability.
Science grows in fits and starts. Research occurs within a particular theoretical framework, or paradigm, that guides scientific thinking. Occasionally, a new overarching theory, sometimes triggered by a dramatic discovery, causes an entire scientific field to reassess its assumptions and ask new kinds of questions. A fundamental breakthrough of such magnitude is called a PARADIGM SHIFT, because it requires restructuring or even wholesale replacement of an old theoretical framework. Prime examples of paradigm shifts in the history of science include the Copernican and Darwinian revolutions. The first of these devastated the then-current worldview of a fixed and finite universe with Earth presiding at the core, forcing humans to regard their planetary home as being far removed from the celestial center stage. The second knocked us further off the pedestal of centrality, relegating Homo sapiens as one of millions of species that together represent merely the latest wave in an unfathomably deep ocean of evolutionary change. Importantly, with rare exceptions like the Copernican revolution, paradigm shifts do not entail the wholesale tossing out of previous ideas. Science proceeds by building on what has come before, and many ideas within science are known with great confidence, unlikely ever to change. As the architecture of the building is modified, however, occasional large-scale renovations are necessary.
Beginning in the late 1960s, dinosaur paleontology experienced its own, humbler paradigm shift. As a child of the baby boom generation, my first exposure to paleontology occurred just prior to this shift, when dinosaurs were regarded as sluggish, dimwitted behemoths. I fondly remember flipping the pages of large dinosaur books with awe-inspiring illustrations of long-necked sauropods (aka "brontosaurs") fully submerged in lakes except for the tops of their heads. Prevailing thinking viewed these animals as simply too gargantuan to support themselves on land. Those dinosaurs that did walk on terra firma were generally depicted as slow and awkward. Giant bipedal CARNIVORES such as Tyrannosaurus were reconstructed as Godzilla-like, with upright bodies and massive tails dragging behind. Four-footed plant eaters like Stegosaurus were portrayed with sprawled, lizardlike front limbs, low-slung bodies, and dragging tails. The overall impression was one of awkward giants lumbering across ancient landscapes, with brains barely capable of carrying them from day to day.
Then, virtually overnight it seemed, dinosaurs received a stunning makeover. Sauropods emerged from the water to strut on land with elephantine limbs, and scientists came to argue that an aquatic lifestyle would have been impossible for these behemoths because of water pressure compressing the chest cavity. Meanwhile, T. rex pivoted to a sleeker, horizontal body posture. No longer trailing uselessly behind, its rigid tail projected rearward to counterbalance the head and trunk. Stegosaurus and its armored, four-footed kin were also transformed, bestowed with upright limbs and nimble, airborne, potentially lethal tails. Reconstructions like these signaled much more active, agile animals. In addition to their redesigned bodies, these freshly envisioned dinosaurs were considered more intelligent, engaging in such behaviors as pack hunting, herding, and parental care.
What caused this fundamental change in our conception of dinosaurs? The answer is a paradigm shift triggered by a combination of discovery and insight. The pivotal FOSSIL discovery was a sickle-clawed "raptor" theropod, recovered in Montana in 1964 by an expedition from Yale University. The revolutionary insights came from Yale paleontologist John Ostrom. In his 1969 description of this extraordinary predator, which he called Deinonychus ("terrible claw"), Ostrom argued that at least some dinosaurs were considerably more active than previously assumed. Shortly thereafter, noting a large number of birdlike features on the skeleton of Deinonychus and related predators, Ostrom revived the nineteenth-century idea that birds evolved from dinosaurs. He catalogued numerous bony characteristics linking theropod dinosaurs with birds, and subsequent workers have added many more, bringing the total number of shared, specialized features to greater than one hundred. Today, most experts agree that birds are the direct descendants of dinosaurs and thus are, in a very real sense, dinosaurs themselves.
Faced with this new evidence and a fresh perspective, paleontologists quickly began to view all dinosaurs as more like birds than lizards. Investigators returned to existing museum collections and began to reassess long-held views and biases. Soon, the mounted skeletons of bipedal carnivores and HERBIVORES were reengineered to assume a more horizontal posture. Further support for the revised stance came from the discovery of dinosaur trackways that showed no signs of dragging tails.
This paradigm shift spawned novel research programs and heated debates. Were dinosaurs warm-blooded? Did some forms exhibit parental care? What were the intellectual and behavioral capacities of the different dinosaur groups? In an attempt to address these questions, paleontologists have applied a range of analytical tools old and new, from detailed anatomical comparisons with living animals to computed tomographic (CT) scanning of fossils. Several decades of extremely active research have led to numerous insights, many of which are discussed in this book.
As is often true of cultural and scientific trends, once in motion, the pendulum of a paradigm shift tends to swing in a wide arc. This has certainly been the case with dinosaurs. If John Ostrom ignited the paradigm shift, the fuel for the subsequent explosion was Robert Bakker, Ostrom's flamboyant, iconoclastic student and avid champion of the dinosaur renaissance. Not long after Ostrom's original argument for more active, potentially warm-blooded dinosaurs, Bakker rescued sauropods from their aquatic torpor and even had them rearing up on their hind legs to battle marauding theropods. Similarly, Tyrannosaurus and its large carnivorous kin, no longer awkward and lumbering behemoths, were depicted as agile predatory machines capable of running speeds in excess of 65 kilometers (40 miles) per hour. Then there were the small raptorlike, sickle-clawed theropods such as Deinonychus and Velociraptor, traveling in packs and utilizing a combination of cunning and cooperative behavior to take down prey of much greater body sizes. The Jurassic Park movie series brought these new ideas to popular audiences via the big screen and stretched science to the breaking point.
Today, the pendulum is swinging back toward the middle, as paleontologists generate more rigorous, tempered, yet undoubtedly richer reconstructions of dinosaurs and their worlds. One example is the recent work indicating that Tyrannosaurus and other large theropods could not attain the remarkable, jeep-pursuing speeds previously reported and that they were likely incapable of true running. It has even been suggested that T. rex was not the predatory tyrant-king long depicted but rather a lowly scavenger, eking out a living from remains of the dead. The same type of scrutiny is being applied to plant eaters as well. Not only have investigators questioned whether sauropods could rear up on their hind legs. Some have also argued that these successful giants could not elevate their elongate necks much above the horizontal because of, among other things, the difficulty of pumping blood up to the head.
On July 16, 2005, John Ostrom passed away at the age of 77. A few years before, Ostrom confessed to me that he would give just about anything to be back near the beginning of his career. He talked about the new age of discovery in dinosaur paleontology and the exciting work yet to be done. Yet, unlike the great majority of us, John leaves behind a deep and lasting legacy. His discoveries and vision triggered a revolution in our perception of dinosaurs, a true paradigm shift has enabled us to see these long-dead animals with new eyes, and to explore questions never previously conceived. Many of Ostrom's students went on to become leaders in the field, and the dinosaur renaissance he initiated has ushered in new generations of scientists eager to conduct research on these long-dead yet suddenly more fascinating beasts. Today there are about 100 dinosaur paleontologists worldwide, more than ever before. And the number of new dinosaur species named in the past 25 years exceeds that found in all prior history, with no end in sight.
Excerpted from Dinosaur Odyssey by Scott D. Sampson. Copyright © 2009 the Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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Table of Contents
1 Treasure Island 1
2 Stardust Saurians 19
3 Dramatis Dinosaurae 35
4 Drifting Continents and Globe-Trotting Dinosaurs 53
5 Solar Eating 71
6 The River of Life 87
7 The Green Gradient 103
8 Panoply of Predators 123
9 Hidden Strands 143
10 Of Horn-Heads and Duck-Bills 157
11 The Goldilocks Hypothesis 175
12 Cinderellasaurus 193
13 Jurassic Park Dreams 213
14 West Side Story 233
15 The Way of All Creatures 255
Epilogue: Whispers from the Grave 273
Notes and References 283
Art and Photograph Credits 317
What People are Saying About This
"A wonderful book, crammed with information that will surprise you."Truthdig
"This thought-provoking book is a must read not only for dinosaur enthusiasts and science educators but anyone interested in the larger context of life."Magill's Literary Annual / Salem Press
"Sampson is right on target. . . . There is no better overview available than 'Dinosaur Odyssey.'"Earth Magazine
"A great in-depth read for those seriously interested in the history of dinosaurs."Dig