Wonderful Life: The Burgess Shale and the Nature of History (20 page)

Laughter is the most ambiguous of human expressions, for it can embody two contradictory meanings. Harry recognized the laughter of his colleagues at Oxford as the sound of puzzlement, not derision—but it really shook him up nonetheless. Both Simon Conway Morris and Derek Briggs, his two superb students, agree that this Oxford reaction marked a turning point in Harry’s work on the Burgess Shale. He simply had to resolve and diffuse that unanticipated and incongruous laughter. He had to overwhelm his colleagues with a reconstruction of
Opabinia
so incontrovertible that all its peculiarities could pass into the realm of simple fact, and never again disturb the courts of science with the spirit of Milton’s
L’Allegro:

Although
Opabinia
is a rare animal with only ten good specimens (Walcott found nine, and the Geological Survey of Canada added another in the 1960s), Walcott established its importance as a centerpiece in interpreting the Burgess fauna. He awarded
Opabinia
pride of place, describing this genus first among the Burgess arthropods (see table 3.1). Walcott put
Opabinia
at the head of his classification because he regarded the elongate body, composed of many segments without prominent and complex appendages, as “very suggestive of an annelidan ancestor” (1912, p. 163). Since the Annelida, or segmented worms (including terrestrial earthworms and marine polychaetes), are the presumed sister-group of the Arthropoda, an animal that combined characters of the two phyla might stand close to the ancestry of both and act as a link between these great invertebrate groups. To Walcott,
Opabinia
was the most primitive Burgess arthropod, the closest model for a true ancestor of all later groups.

But what arthropod features did Walcott discern in
Opabinia
? He had little to offer for the head, since he could find no appendages. The frontal “nozzle” might be interpreted as a pair of fused antennae, and the eyes were consistent with arthropod design (Walcott noted only two eyes, but Whittington found five—two paired and one central). Walcott admitted that “none of the heads … show traces of antennules, antennae, mandibles or maxillae. If these appendages were large they have been broken off; if small they may be concealed beneath the crushed and flattened large posterior section of the head” (1912, p. 168). I regard this statement as a lovely example of apparently unconscious bias in science. Walcott “knew” that
Opabinia
was an arthropod, so the animal had to have appendages on its head. Since he didn’t find any, he provided explanations for their absence—either they were so large that they always broke off, or they were so small that they became hidden beneath the head. He never even mentioned the obvious third alternative—that you don’t see them because they didn’t exist.

(Walcott, by the way, also made another error—see the next paragraph—that may seem merely amusing or tangential but underscores the serious point that we observe according to preset categories, and often cannot “see” what stares us in the face. A set of empirical anomalies may have instigated the Burgess revision by Whittington and colleagues, but as we shall see, the conceptual framework of the new view, coalescing between 1975 and 1978, established a novel context that allowed further observations to be made. I preach no relativism; the Burgess animals are what they are. But conceptual blinders can preclude observation, while more accurate generalities guarantee no proper resolution of specific anatomies, but can certainly guide perceptions along fruitful paths.)

Walcott, following our primal biases of gender, found two specimens that appeared to lack the frontal nozzle. (Walcott thought that the nozzles were truly absent on these specimens, but Whittington later proved, by dissecting one of the specimens and finding the jagged edge of the break point, that the nozzles had been broken off.) On one specimen, Walcott found a slender, two-pronged structure in the same location as the nozzle. (This turned out to be a fragment from an unrelated worm, but Walcott interpreted it as a genuine part of
Opabinia
, in the same position as the nozzle of other specimens.) Walcott therefore concluded that he had discovered sexual dimorphism in
Opabinia:
the strong and stout nozzle belonging to the male (naturally), and the slender structure to the more delicate female. He wrote that these supposed females “differ from the male … in having a slender, bifid frontal appendage instead of the strong appendage of the male.” He even foisted the stereotypes of active and passive upon his fictitious distinctions, arguing that the nozzle “was probably used by the male to seize the female” (1912, p. 169).

Walcott’s main justification for regarding
Opabinia
as an arthropod lay in his interpretation of the paired body segments. He read these flaps as the gill branches of ancestrally biramous appendages. He thought that he had observed two or three “rather strong, short joints” (1912, p. 168) at the base of each flap, followed by the broad lobe bearing the gills. He hoped to find the inner leg branches as well, but he could never fully persuade himself, and eventually concluded that the walking legs probably existed in an “insignificant or rudimentary” form (1912, p. 163).

Walcott was clearly troubled by the failure of
Opabinia
to preserve any smoking gun of arthropod affinity. He even took some modern anostracans and crushed them between plates of glass, trying to simulate the conditions of Burgess fossilization. This mayhem provided some solace, because such treatment often destroyed all evidence of the delicate appendages. He wrote: “After flattening specimens of
Brachinecta
and
Branchipus
between plates of glass and studying them, I am greatly surprised that any distinct characters of the appendages are preserved in the fossils in a recognizable condition” (1912, p. 169). Walcott had shown the cardinal skill of his adopted profession—administration. He had put the best face upon adversity.
Opabinia
would remain an arthropod.

But Walcott had been downright circumspect compared with later reconstructions that added more and more arthropod features with less and less compunction. In 1931, the great ecologist G. Evelyn Hutchinson, driven to paleontology by the fascinating problem of how anostracans could change their environmental preferences from Cambrian oceans to modern freshwater ponds, reconstructed
Opabinia
in the standard upside-down position of a swimming anostracan (figure 3.22). He turned the lateral flaps into long bladelike appendages neatly fitted to the side of an arthropod carapace.

The climax of this imaginative tradition arrived with the aesthetically lovely but fanciful reconstruction of Simonetta (1970).
*
Opabinia
has become an ideal arthropod (figure 3.23). The frontal nozzle is shown with a longitudinal suture (entirely imaginary), indicating its origin as a pair of antennae, now fused. Simonetta “found” two additional pairs of short arthropod appendages on the head—one constructed from a pair of eyes, the other from a bump on the carapace. On each segment of the body itself, Simonetta drew a strong and fully biramous appendage—a bladelike gill branch above a small but firm leg branch. Whittington faced this unchallenged tradition when he began his work on the ten precious specimens of
Opabinia
.

I now come to the fulcrum of this book. I have half a mind to switch to upper case, or to some snazzy font, or to red type, for the next page or two—but I desist out of respect for the aesthetic traditions of bookmaking. I also refrain because I do not wish to fall into the lap of legend (having already dispersed one for the discovery of the Burgess Shale). My emotions and desires are mixed. I am about to describe the key moment in this drama, but I am also committed to the historical principle that such moments do not exist, at least not as our legends proclaim.

Key moments are kid stuff. How can such a story as this, involving so many people engaged in complex intellectual struggles, proclaim any moment as a single focus, or even as most important? I have labored to master all the details and to arrange them in proper order. How can I now blow all this effort on the myth of eureka? I suppose that one can discover a single object—say, the Hope diamond—at a particular moment, but even such a pristine event has a tangle of inevitable antecedents in geological training, political intrigue, personal relations, and good luck. But I am talking about an abstract and far-reaching transformation in our view of life’s pattern and the meaning of history. How can such a complex change possess a moment before, when it wasn’t, and a moment after, when it was? Does natural selection, or laissez-faire economics, or structuralism, or the rationale for the Immaculate Conception of Mary, or any other complex moral or intellectual position, owe its formulation to a single person, place, or day?
*

3.22. Hutchinson’s reconstruction of
Opabinia
as an anostracan swimming upside down in the modern position (1931).

Still, as Orwell said about his metaphorical Russia in a farmyard, some animals are more equal than others. We need heroic items and moments to focus our attention—the apple that hit Newton and the objects that Galileo did not drop from the Leaning Tower. The beat goes on, but we may discern a high spot in the continuity.

I believe that the transformation of the Burgess Shale did have a Rubicon of sorts, at least symbolically—a key discovery that can separate a before and an after.

So we return to Harry Whittington, facing the entire world’s supply of
Opabinia
. Everyone had always identified this animal as an arthropod, but no one had found the smoking gun, the segmented appendages that define the group. But then, no one before Whittington had possessed the techniques needed to seek out small appendages hidden under an external carapace. A few years before, Harry had made the central methodological discovery that the Burgess Shale fossils are three-dimensional objects (however crushed), with top layers that one can dissect away, to reveal the structures underneath. Harry had already resolved
Marrella, Yohoia
, and the Burgess trilobites with this method.

Opabinia
virtually clamored for its crucial experiment under the new techniques: dissect through the carapace to find the body appendages and their attachments, dissect through the head shield to find the frontal appendages. So Harry dissected, in full confidence that he would find the jointed appendages of an arthropod. Harry dissected—
and he found nothing under the carapace
.

Opabinia
was not an arthropod. And it sure as hell wasn’t anything else that anyone could specify either. On close inspection, nothing from the Burgess Shale seemed to fit into any modern group.
Marrella
and
Yohoia
at least were arthropods, even if orphaned within this giant phylum. But what was
Opabinia
?

3.23. Attractive but fallacious restoration of
Opabinia
as an arthropod by Simonetta (1970). (A) Top view. (B) Side view. Simonetta showed the frontal nozzle as formed by fused antennae, and drew biramous appendages on each supposed body segment.

Whittington’s conclusion may have been confusing, but it was also liberating.
Opabinia
did not have to conform to the demands of arthropod, or any other, design. Whittington could come as close as any paleontologist ever had to the unattainable ideal of Parsifal—the perfect fool, with no preconceptions. He could simply describe what he saw, however strange.

Opabinia
is peculiar indeed, but not inscrutable. It works like most animals.
Opabinia
is bilaterally symmetrical. It has a head and a tail, eyes, and a gut running from front to back. It is an ideal creature for any eager scientist—not so crazy as to be intractable, but weird enough to thrill any curious person.

Whittington began his monograph by chiding his predecessors for their unquestioning allegiance to the arthropod model, and for their consequent tendency to rely more on expectations of the model than on observation of the specimens: “Continuous interest in
Opabinia
has not been accompanied by critical study of the specimens, so that fancy has not been inhibited by facts. The present work aims to provide a sounder basis upon which to speculate” (1975a, p. 3). With characteristic understatement (his personal tendency added to the British norm), Whittington then wrote: “My conclusions on morphology have led to a reconstruction which differs in many important respects from all earlier ones” (1975a, p. 3).