Wonderful Life: The Burgess Shale and the Nature of History (21 page)

These “many important respects” led to an animal that might grace the set of a science-fiction film, if considerably enlarged beyond its actual length of 43–70 mm (less than three inches at most). Consider the major features of Whittington’s reconstruction:

1.
Opabinia
does not have two eyes, but, count ’em, five! These are arranged as two pairs on short stalks, with a fifth eye, probably unstalked, mounted on the midline (see figure 3.20).

2. The frontal nozzle is not a retractable proboscis or a product of fused antennae (the two favorite interpretations consistent with arthropod design). It is attached to the bottom front border of the head and extends forward. It is a flexible organ, built as a cylindrical striated tube—literally like the hose of a vacuum cleaner, and perhaps bendable by the same principles. Its end is divided longitudinally into two halves, each with a group of long spines directed inward and forward. The tube may have contained a central, fluid-filled canal—a good device for requisite stiffness with enough flexibility.

3. The gut is a single tube running straight along the center of the animal for most of the body’s length (see figure 3.24). However, at the head, the gut makes a U-shaped bend, and turns sharply around to produce a backward-facing mouth. Interestingly, the frontal nozzle has just the right length to reach, and appropriate flexibility to bend around and pass food to, the mouth. Whittington suggests that
Opabinia
fed primarily by capturing food in the “pincers” formed by the spiny parts at the front of the nozzle, and then bending the nozzle around to the mouth.

4. The main portion of the trunk has fifteen segments, each segment bearing a pair of thin lateral lobes, one on each side of the central axis. These lobes overlap, and are directed downward and outward (see figure 3.20).

5. Each lobe except the first bears on its dorsal surface a paddle-shaped gill attached near the base of the lobe. Although the bottom surface of the gill is flat, the upper surface consists of a set of thin lamellae, overlapping like a deck of cards spread out.

6. The last three segments of the trunk form a “tail” built by three pairs of thin, lobate blades directed upward and outward (see figure 3.20).

Whittington needed all his special methods of dissection, varied orientations, and part–counterpart to resolve the morphology of so peculiar a beast. He also discovered that a failure to appreciate these methods had provided a major argument to support the arthropod model. Walcott had confused part and counterpart in one important specimen. He thought that he was viewing the bottom surface of the animal; in fact, he was looking down upon the upper surface. Raymond, accepting this upside-down interpretation, had made the perfectly reasonable claim that the gills of
Opabinia
lay
below
the outer carapace—as in the standard arthropod arrangement, with gill branches as the upper limbs of biramous appendages located just under the carapace. But in the correct orientation, the gills lie above the body lobes in a most unarthropod-like orientation.

Figures 3.24–3.26 provide a striking illustration of the power of Whittington’s methods. These are his camera lucida drawings of three specimens, in varying orientations, each combining features from the part and counterpart of the same specimen. Figure 3.24 provides a view from above (dorsal). We see the position of the eyes and nozzle, the full sequence of lateral lobes, and the gills lying above the lobes. The gut runs as a straight tube down the middle of the body. Figure 3.25 is a side view and reveals several features that could not be seen from the top. We now discern the point of attachment for the nozzle, and we note that the gut bends in a U to form the rearward-facing mouth. (In top view, the bend and rearward section collapse upon the straight portion and cannot be distinguished at all.) The top view also tells us nothing about the relative positions of lateral lobes and tail fins, for these are collapsed into the same plane. But the side view of figure 3.25 shows the lateral lobes pointing downward and away from the body, while the tail fins stand high and point upward—in good positions, respectively, for oars and rudders.

3.24. Camera lucida drawing for a specimen of
Opabinia
in the conventional position, viewed from the top. On each side, gills (labeled
g
) and lobes (
l
) are clearly distinguishable; the trace of the gut runs along the midline. Two pairs of eyes are visible, and the nozzle extends forward from the front end.

Figures 3.24 and 3.25 provide the two basic orientations, but they still leave several questions unanswered—and further specimens are needed. For example, neither shows the full complement of five eyes (they are delicate, and often collapse together into a jumble). Figure 3.26 fills some crucial gaps: five separate eyes are visible, and the frontal nozzle bends around to the area of the mouth.

Marrella
and
Yohoia
had challenged Walcott’s shoehorn, but these genera were only orphaned within the Arthropoda. With
Opabinia
, the game cranked up to another level, and changed unalterably and forever.
Opabinia
belonged nowhere among the known animals of this or any former earth. If Whittington had chosen to place it within a formal classification at all (he wisely declined), he would have been forced to erect a new phylum for this single genus. Five eyes, a frontal nozzle, and gills above lateral flaps! Walcott’s shoehorn had fractured. Whittington wrote with characteristic brevity in the passive voice: “
Opabinia regalis
is not considered to have been a trilobitomorph arthropod, nor is it regarded as an annelid” (1975, p. 2). Harry may be a measured man, but he knew what
Opabinia
implied for the rest of the Burgess fauna. “The Burgess Shale,” he remarked laconically, “contains other undescribed segmented animals of uncertain affinities” (1975, p. 41).

3.25. A specimen of
Opabinia
preserved in a more unusual orientation, on its side. Here lobes and gills of the right and left sides are jumbled together and difficult to distinguish. But many features not visible in the conventionally positioned specimen of figure 3.24 can now be understood: the orientation of the tail fins (labeled fins relative to the side lobes, the point of insertion for the nozzle, and the rearward bending of the front end of the gut.

3.26. A third specimen of
Opabinia
, again in the conventional position. Several features not apparent in the other specimens can be distinguished: the fifth eye (labeled
m
, for “middle eye”) is visible at the upper right, and we note that the nozzle can bend around to the level of the mouth.

I believe that Whittington’s reconstruction of
Opabinia
in 1975 will stand as one of the great documents in the history of human knowledge. How many other empirical studies have led directly on to a fundamentally revised view about the history of life? We are awestruck by
Tyrannosaurus
; we marvel at the feathers of
Archaeopteryx;
we revel in every scrap of fossil human bone from Africa. But none of these has taught us anywhere near so much about the nature of evolution as a little two-inch Cambrian oddball invertebrate named
Opabinia
.

Think of all the accumulation songs in the English folk tradition. The first item never amounts to much—a partridge in a pear tree, or a paper of pins. “Green Grow the Rushes, Ho” puts it best: “One is one and all alone and ever more shall be so.”

Opabinia
carries the full weight of the Burgess message for a new view of life. It is as bizarre, as different from all living creatures, as anything else in the Burgess Shale. But one is all alone and ever more shall be so. The fossil record contains other oddities here and there—like the Tully Monster of Mazon Creek (see page 63).
Opabinia
, just one case, is a shrug of the shoulders, not a discovery about life in general. This example did not establish an incontrovertible new interpretation. Quite the opposite; it only hinted at a possibility worth exploring—especially with
Marrella
and
Yohoia
indicating that something similar, at a lower level, was running rampant among the Burgess arthropods.

All interesting issues in natural history are questions of relative frequency, not single examples. Everything happens once amidst the richness of nature. But when an unanticipated phenomenon occurs again and again—finally turning into an expectation—then theories are overturned.
Opabinia
would not earn its status as primer and flagship for a new view of life until its message of taxonomic uniqueness became ordinary within the Burgess Shale, however exquisitely rare for later times.

This need for numbers of examples—for an assessment of the relative frequency of oddballs within the entire Burgess fauna—makes the myth of the hero, grade B Western movie style, inapplicable to this story in principle. Harry Whittington could not be a lone lawman subduing saloonful after saloonful of reprobates.
Marrella
had taken more than four years. The Burgess arthropods alone would require several lifetimes. Whittington could either intone the lament of the frustrated Mercedes—“So many pedestrians, so little time”—or he could enlist a fleet to help. He chose the second alternative. Science is a collective enterprise in any case.

After selecting the genera that would provide a focus for his personal studies, Whittington divided the remaining arthropods into three groups, each suitable for an extensive research project by a collaborator. In addition, and growing both more troubling and crucial since the identification of
Opabinia
as an oddball outside any established phylum, stood the many genera that Walcott had classified as annelid worms (191lc). If Walcott’s shoehorn had hidden a general theme, of taxonomic uniqueness, the story would probably emerge (if not explode) even more clearly from the annelids than from the arthropods. Arthropods have clear and complex defining characters. Walcott might have wrongly shoehorned his arthropods into conventional groups within the phylum, but most were genuine arthropods at least (with
Opabinia
and, later,
Anomalocaris
as exceptions). But anything soft, segmented, and bilaterally symmetrical might be called a worm. The potential for oddballs loomed largest among Walcott’s “annelids.”

Whittington doubted that the three arthropod groups were coherent taxonomic assemblages. Each shared some features of superficially similar appearance, but
Marrella
and
Yohoia
had already taught caution about such externalities. Still, the three groups formed convenient divisions for research efforts, and the postulate of coherence could become a focal question for testing. (All three groups turned out to be heterogeneous—an important conclusion that confirmed the status of Burgess arthropods as spectacularly disparate compared with all later faunas.)

The three groups, all generally recognized in Burgess classifications from Walcott to Størmer, were (1) the large assemblage of arthropods with bivalved carapaces, always assumed to be true malacostracan crustaceans; (2) the “merostomoid” species, generally oval in shape and with a large discrete head shield that seemed to recall the great group of fossil eurypterids and their cousins the horseshoe crabs; and (3) apparent crustaceans with simple carapaces not divided into two parts, or valves.