Transylvanian Dinosaurs
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Our ability to identify serendipitous historical conjunctions—changes in features, resulting from a different interactive context—provides us with the means to suggest alternatives to explanations that involve immediate selection for biological features. Such momentary shifts in context can have huge consequences, some fatal, others with no effect at all, and still others that are spectacularly successful. Whatever the case, these shifts and their consequences cannot be predetermined, or even be strictly predictable; they can only be understood in a historical sense.63
CHAPTER 8
Alice and the End
Ancient Transylvania now makes sense as a land of contingency, a region where any number of unpredictable events provided the raw material for what would become the history of members of its dino-saurian fauna. Emerging from a synthesis of cladistics, paleogeography, heterochrony, and life-history strategies, the significance of the Transyl-vanian dinosaurs comes from what their evolution tells us about historical contingency. It’s even more exciting when studies like this transcend their intrinsic appeal to provide insights into larger issues in evolutionary biology. We think maybe this has happened here. To get there, however, we should probably first revisit one of the finest adventures to come from children’s literature. Enter Charles L. Dodgson, a British mathematician, deacon, and photographer, but better known throughout the world as Lewis Carroll, the author of Alice in Wonderland (1865) and Through the Looking Glass (1872).
Through the Looking Glass begins with Alice dreaming of being in a house where everything was in reverse, left to right, as if she had passed through a mirror. Outside was a beautiful garden, but she wanted to see it better from a nearby hill. However, as she followed what appeared to be a very straight path to the hill, she found that it led her back to the same house. When she tried to speed up, she instead immediately returned and crashed into the house. Eventually, Alice found herself in a patch of very vocal and opinionated flowers, telling her that someone (the Red Queen) often passed through this garden. When the Red Queen finally came into view, Alice tried to catch up with her, but to no avail; the Red Queen quickly disappeared. One of the roses in the garden advised Alice to walk in the opposite direction and, by this reversed action, she immediately came face-to-face with the Red Queen.
As the Red Queen led Alice directly to the top of the hill, she explained to her that in this world, hills can become valleys, valleys can become hills, straight can become curved, and progress can be made only by going in the opposite direction. At the top of the hill, the Red Queen began to run, faster and faster. Alice, following after the Red Queen, was further perplexed to find that neither one of them seemed to be moving. When they stopped running, they were still in exactly the same spot. Alice remarked on this, to which the Red Queen responded: “Now, here, you see, it takes all the running you can do to keep in the same place.”
We haven’t the slightest idea whether Lewis Carroll gave much thought to the evolutionary implications of Alice’s adventures with the Red Queen, although it might have been possible—Carroll lived no more than 45 km from Darwin’s Down House home in the neighboring county of Kent, and the two published their works just 13 years apart (On the Origin of Species was first released in 1859). Nevertheless, it took a century, and travel nearly 7,000 km to the west, for Carroll’s Red Queen to provide the moniker for a major shift in our understanding of evolutionary dynamics.
In 1973, Leigh Van Valen (figure 8.1), an evolutionary biologist and vertebrate paleontologist at the University of Chicago, published a paper that explored whether long-lived lineages were more resistant to extinction than short-lived groups. According to Darwin, natural selection weeds out the poorer- and promotes the better-designed organisms, thus improving the fit with their environment. If so, Van Valen then reasoned that a species should have less probability of becoming extinct in the future if it has already been around for a while. In other words, long-lived species are presumably the ones that have been finely tuned by natural selection. To test this proposition, he examined the rates of extinction for a large number of evolutionary lineages, compiling what amounts to life tables for a variety of organisms, from clams to mammals.1
To Van Valen’s surprise, his data showed that the probability of extinction remains constant, independent of whether the species has been in existence for a long or a short time. In order to explain this seeming paradox, he argued that a species’ state of adaptation must be under continual assault by an environment that itself is undergoing constant change. Van Valen likened this lack of staying power on the part of long-lived species to Carroll’s Red Queen. In the same way that the Red Queen must perpetually run in order to keep up with her literal place in the world, so, too, must organisms constantly evolve in order to simply maintain their state of adaptation. The Red Queen hypothesis (also referred to just as the Red Queen) should be especially applicable to cases with tightly coevolving species. In these instances, where the evolution of one species is directly related to its interactions with another (the biotic environment), the effect of these coevolutionary relationships is that as one species adapts to its environment and thus gains a competitive advantage over other species, the latter necessarily become less well adapted. The only way that a species in this the latter group can survive is by responding with its own improved design. From there on in, the emphasis on improvement becomes increasingly reciprocal; it can even go so far as to produce an evolutionary arms race. Caught in a zero-sum game of competition, the best a species can do is to keep producing evolutionary innovations (running) to try to tip the scale in its favor, just to maintain its existence (to stay in the same place), the whole time that its coevolutionary partner is trying to do the same. To win is to keep playing this game. Otherwise, that species is an evolutionary loser, having failed to keep up and therefore doomed to extinction.
Figure 8.1. Leigh Van Valen (b. 1935), portrayed as Alice being pulled through an ever-moving landscape by the Red Queen. (After the original by John Tenniel in Lewis Carroll’s 1871 Through the Looking Glass)
The Red Queen has been applied most successfully to the coevolution of hosts and parasites, predator-prey systems, and even to the persistence of sexual reproduction.2 The arms races between the red-backed shrike (Lanius collurio) and common cuckoo (Cuculus canorus), between the predator gastropod known as the whelk (Sinistrofulgur) and its dangerous bivalve prey (Mercenaria), and between bacteria and bacteriophages, all ensure that each individual species’ state of adaptation is a transient thing3—in a constantly changing environment, natural selection operates to enable organisms simply to maintain their state of adaptation, rather than improve it. The logical underpinning of the Red Queen hypothesis is a strict reliance on natural selection, which predicts that the best design/adaptation for one organism will be thwarted by tightly interlocked, interspecific competition with other organisms.4 Thus, because participants are a part of each other’s biotic environment, the feedback loop of selection between them produces the pattern of extinction documented by Van Valen—the probability of extinction is no different for old or young clades.
Our interest in identifying how chance events can influence evolutionary history grew as we developed our interpretation of the Transylva-nian dinosaurs, where we focused on the creative possibilities inherent in random events. We also began thinking about the original explanation of the Red Queen and its reliance on interspecific selection as the directing force in evolution, with predictable consequences. We wondered if, perhaps, the Red Queen curves may have an entirely different message, one going beyond elucidating the relationship between adaptation and extinction among coevolving lineages.
Let’s begin by looking at the sources of perturbations that keep organisms at suboptimal adaptation. For biotic systems, the Red Queen envisions a constant evolutionary arms race between species, with one, and then the other, temporarily holding sway in their coevolutionary competition. Perturbations come from the evolution of new features in one half of t
he arms-race pair, momentarily improving their fitness, which is subsequently overturned by their co-competing partner. This is all happening under the umbrella of a host of abiotic transformations—such as climate change, tectonic events, and meteoritic impacts (what Tony Barnosky of the University of California at Berkeley has called the Court Jester5)—that are also constantly acting to dampen the process of adaptation.
From an organism’s perspective, it is probably irrelevant whether the environmental alterations are biotic or physical; they have to be dealt with one way or the other in order to survive. If these two kinds of impacts are indistinguishable to a species, then perhaps what matters most in determining the Red Queen curves is that, wherever the disturbances come from, they should be random with respect to the organism’s current state of adaptation.6
Looked at from this different angle, the Red Queen can be seen as more than a theory about the relationships among coevolutionary selection, adaptation, and extinction. It now becomes a testimony to the ubiquity of random events of all kinds, as well as to their unpredictable consequences—both positive and negative—in evolutionary history. The bulk of this book has been dedicated to identifying the contingent opportunities derived from the unexpected European migration of the ancestors of several dinosaurs. Such unpredictability, in turn, may also have put an end to them individually—or, more strikingly, en masse—during the great Cretaceous-Tertiary extinction 65 million years ago.
Until recently, our explanations of why life is the way it is has been left in the hands of natural selection; because of their ahistorical and lawlike nature, adaptive hypotheses always trump alternatives. These explanations are most often couched as virtual pathways by which features evolve in a deterministic fashion under the constraints provided by physics, self-organization, and other constructional/developmental principles. These inferences may satisfy, but determining the potential track of natural selection is not necessarily equivalent to reading history. What do we do if an evolutionary pattern based on selection belies the homologies used to construct the history of these organisms? Clearly, we need a tool to separately assess the roles of contingency and natural selection during the unfolding of history, and, in this book, we have used phy-logenetic analyses to identify this historical context.
Identifying unpredictability in history, however, is a double-edged sword. By decoupling history from determinism, we alter our ability to rely solely on the laws of nature to test biological questions. We can’t do without this background of natural laws. Some boundaries of these laws are stringent, with very narrow channels that restrict the range of possible events, whereas others are vaguer and the pathway for potential events is broader. On the other hand, historical contingency—ultimately affecting this physical background—provides a role for both creativity and destruction in producing the extraordinary richness of nature.
To reconstruct and interpret the evolution of life on Earth, however, we need to set aside our reliance on selection for or against particular features as the sole explanation for their existence, and instead examine the role of contingent vagaries of history on our understanding of how evolution has worked. If, as Gould has suggested, evolutionary history is ruled by unpredictability, then nature may not be a zero-sum game eked out on a coevolutionary stage, as has often been proposed. Instead, it may be that odd, minor, unpredictable events of a physical kind that are faced by organisms are as effective as biological arms races in producing environmental decay with respect to the adaptive state of existing organisms. Such historical contingency—and not just coevolutionary selection—leads to the Red Queen, catapulting organisms on equally unpredictable pathways. In this way, the unpredictability of natural history can opportunistically soften or skirt the laws of nature, and thereby provide greater possibilities for further contingency.
C’EST FINI
Throughout our work on this project, we constantly asked ourselves why anyone should be interested in this stuff. After all, it’s a long leap from digging a bone or tooth out of the golden-brown rocks outside the village of Sânpetru on a hot day to historical unpredictability and Alice and the Red Queen, with many uncertain twists and turns from beginning to end. Perhaps because of this long (and, shall we say, contingent) jump, we became fixed on this self-reflexive question of ours, which, in the end, we thought was related to what might be called science as a game—not a game full of strict rules, but one of enjoyment.
We questioned why, in the first place, we indulged our penchant for these dinosaurs and the issues to which they have led us. Unabashedly, our initial motivation was that it would be fun and exciting. And why not? We obviously thought (and continue to think) that the prospects of our endeavor, ranging from fieldwork to aspects of evolutionary theory, looked fascinating. So we got on board to see where it would take us.
Beyond amusement, or perhaps as an extension of it, what we got out of playing this game fed back on itself, making the game more fascinating still. Our love of the subject and what it reveals about the ways of the world were the lynchpins that kept us participating in the project. This also led us in often novel and bizarre directions, forcing us into situations where we had to confront our ideas about a variety of scientific and philosophic matters. Some of these directions proved to be uninteresting, redundant, or barren, and they were subsequently dropped. Ultimately, though, whether the body of this work and its tangents are proven right or wrong, or declared insightful or misleading, are all irrelevant to our original decision to play the game we embarked on. Our goal was to try to make an honest effort at constructing a story about the dinosaurs of Transylvania, on as rich, to the point, and true to the details as we know them. Our intent was to expand our pursuit widely and delve deeply into bones, teeth, and rocks, applying parsimony to character evolution, using a host of ecosystem information, and following the choreography of continents through geologic time. As a result, you might think that we’ve arrived at the truth about the Transylvanian dinosaurs and their place in evolutionary history, but we cannot pretend that this is the case, nor that it was our goal or our motivation. Have we indeed found out what, exactly, happened to produce the Transylvanian dinosaurs? We doubt it. These dinosaurs sparked our efforts, which we took seriously as we progressed, but what we gleaned from all of this should not necessarily be taken as the truth. In other words, this game of science isn’t won by revealing what “really happened”; its purpose is as much as in providing the enjoyable possibility of allowing one to keep playing the game.
So why should anyone be interested in our prehistoric journey? From our own perspective, it ought to be because of its intrinsic fascination, leading to ever-increasing ripples in how one views the world. This is why we think that research such as what we’ve discussed here—abundantly evident in so many of the studies being conducted today—has great value to our understanding of and excitement about prehistory. It relies on the challenges of hard work, insight, imagination, and skepticism but, ultimately, rests on the availability of fossils, those meager resources that are also the only physical vestige we have of former life on this planet. Here we’ve tried to make the most of the extremely rare material that nature has provided, both to indulge ourselves and maybe to infuse you with some of our own fascination.
In 1964, Marcel Duchamp—one of the twentieth century’s most influential artists—spoke with his biographer, Calvin Tomkins, about his views of science:
We have to accept those so-called laws of science because it makes life more convenient, but that doesn’t mean anything so far as validity is concerned. Maybe it’s all just an illusion. We are so fond of ourselves, we think we are little gods of the earth—I have my doubts, that’s all. The word “law” is against my principles. Science is so evidently a closed circuit, but every fifty years or so a new “law” is discovered that changes everything. I just don’t see why we should have such reverence for science, and so I had to give another sort of pseudo-explanation. I’m a pseudo all in all, that’s my char
acteristic. I never could stand the seriousness of life, but when the serious is tinted with humor, it makes a nicer color.7
It is in Duchamp’s light that we view our contribution on the dinosaurs of Transylvania. Counterposing the capricious nature of history against what we call the “laws of nature” ultimately reduces the overarching command of the long arm of these laws in determining history. Our efforts have left sundry questions unanswered: many because we haven’t the ability to answer them, others because there’s just not enough time in the day. Yet the rewards we’ve received from the science we’ve described here lie in the possibility of continuing to play. Our efforts to construct a good, bad, or indifferent story about the dinosaurs of Transylvania now stand on the brink of the next phase of the game. Like the 1918 Dada Manifesto of Tristan Tzara, Romanian-born founder of the Zurich Dada movement, we have “throw[n] up ideas so that they can be shot down.”8