Wonderful Life: The Burgess Shale and the Nature of History (23 page)

I cannot imagine a greater contrast (and, therefore, better seeds of drama) than the disparate styles of Whittington and Conway Morris—Harry, the older conservative systematist, about to start the greatest project of a full life, versus Simon, the radical beginner, consciously seeking to overturn established opinion. Their working procedures could not have been more different. Harry began with greatest caution, choosing the most common animal in the Burgess. He proceeded with a series of monographs on individual genera, each taking years of preparation:
Marrella
(1971),
Yohoia
(1974), trilobite limbs (1975b),
Opabinia
(1975a), and as we shall see,
Naraoia
(1977) and
Aysheaia
(1978). He confined his work (or so he thought when he began) to the arthropods, the group that he knew best. He started with conventional views about the taxonomy of Burgess organisms, changing his mind only when unexpected evidence forced itself upon his consciousness. Simon, by contrast—with the innocence of Pearl Pureheart and the proven skill of Alvin Allthumbs, but armed with the sublime confidence of Muhammad Ali as his youthful avatar Cassius Clay—began with an explicit search for embodiments of the most radical interpretation of Burgess anatomy. The rarer the better; several of Simon’s weird wonders are reconstructions based upon single specimens. In two years, 1976 and 1977, Conway Morris initiated his career by publishing five short papers, on five creatures with the anatomical uniqueness of new phyla.
*

Such differences should breed dissension and open conflict. Nothing of the kind occurred—intellectual drama of the highest order, yes, but no juicy stories of overt battle. Oh, Derek does remember Harry mumbling a bit about people running before they learned to walk, and some private feelings may be left unsaid to this day. But when I asked Harry how he felt about a student who published five short papers before his Ph.D., sometimes basing new phyla upon single specimens, he replied: “I stood by and smiled. I wouldn’t dream of discouraging a research student.”

I know that the following comment is trite, but the foundation of banality is often evident truth: The final coalescence of the Burgess transformation emerged from a lovely synergism between these two disparate approaches. Perhaps the process of interpretation would have led to the final outcome in any case. Perhaps either the slow sequence of descriptive monographs or the rapid succession of short papers with radical claims would eventually have compelled assent by itself. But nothing can beat the one-two punch of laborious description so careful that it cannot be gainsaid combined with overt claims so sparsely documented and so divergent from tradition that they can only inspire fury—and attention. I know that this combination “just happened” along one of the odd and unpredictable pathways of human affairs, but if anyone is up there regulating the progress of knowledge, he could not have acted with better or more deliberate purpose than by arranging this synergism of youth and experience, caution and daring.

I stopped the narrative once before (with
Opabinia
) to announce a key moment meriting special type for emphasis, and I shall do so just once again (for
Anomalocaris
); but Simon’s field season in the cabinets of the Smithsonian marks the second of three major transitions, as I read the story of the Burgess. When Simon began,
Opabinia
was hinting at something strange, but no one knew either the extent or the nature of the phenomenon; I believe that Harry was still favoring an interpretation of oddballs as stem groups, primitive combinations of characters that would later sort themselves into discrete phyla living today, rather than as uniquely specialized experiments in multicellular design, separate lineages without later issue. When Simon completed his initial sequence of five papers on curiosities, the tentative and peculiar had become a Burgess norm, and the notion of separate lineages beyond the realm of modern anatomy had displaced the conventional fallback to “primitive” and “precursor.” Whittington recalled his gradually dawning reaction to Simon’s discoveries: “The whole atmosphere changed. We were not just dealing with predecessors of known groups. The whole thing was beginning to make a picture.”

Simon’s five oddballs span a remarkable range of anatomy and life style. Their only common theme is peculiarity.

1.
Nectocaris
. Walcott did single out this peculiar animal, represented by only one specimen lacking a counterpart—for Conway Morris found a photo, retouched as usual, next to the well-prepared specimen. But Walcott had published nothing, and left no notes. Conway Morris justified his decision to publish on such scant information: “The fine preservation and unusual anatomy warrant notice being taken of this unique specimen” (1976a, p. 705).

From the “neck” forward,
Nectocaris
looks mostly like an arthropod (figure 3.28). The head bears one or two pairs of short, forward-projecting, but apparently unjointed (and therefore not arthropod-like) appendages. A pair of large eyes, probably borne on stalks, lies just behind. The back part of the head is enclosed by a flattened oval shield, perhaps bivalved. But the rest of the body evokes no particular hint of arthropod, and gives off more than an intriguing whiff of chordate—our own phylum. The body is laterally compressed and built of some forty segments (a common characteristic of arthropods and several other phyla, including our own). Conway Morris found no hint of the defining arthropod character—jointed appendages. Instead, both the dorsal and ventral (top and bottom) surfaces bear continuous structures that, at least superficially, look like chordate fins supported by fin rays! (With a single specimen, one cannot proceed much beyond the superficial, so this crucial issue remains tantalizingly unresolved.)

Three features of these fins and fin rays deny arthropod affinities and hint chordate: First, a thin and continuous structure, preserved as a dark film on the rock, seems to connect the parallel series of short, stiffening rays into a coherent fin; arthropod limbs, by contrast, are discrete. Second, the fins run along the top and bottom edges of the animal, as in early chordates; arthropod appendages generally attach to the sides of the body. Third, the fins of
Nectocaris
have about three stiffening rays per body division; one pair of appendages per original segment is a defining character of arthropods. (Tagmosis, or coalescence of arthropod segments, is identified by the presence of more than one appendage per division. The segments of
Nectocaris
are too narrow and too numerous for interpretation as amalgamations of several ancestral divisions.)

3.28. The enigmatic
Nectocaris
, looking mostly like an arthropod in front and like a chordate with a tail fin behind. Drawn by Marianne Collins.

What can be done with such a chimaera—a creature that looks mostly like an arthropod up front (with possibly unjointed appendages casting some doubt), and mostly like a chordate (or a creature of unknown design) behind? Not much more, when you have but one specimen. So Conway Morris wrote a short, provocative paper and dropped
Nectocaris
into the great holding bin of taxonomy—phylum Uncertain. The title of a taxonomic paper traditionally lists the broad affiliation of the animal being described, but Conway Morris chose a conspicuously noncommittal approach: “
Nectocaris pteryx
, a new organism from the Middle Cambrian Burgess Shale of British Columbia.” His final words express no surprise at such a peculiar beast, but hint instead at an emerging generality: “The failure to resolve definitely the affinities of this creature need not be a source of surprise. Current research is showing that a number of species from the Burgess Shale cannot reasonably be accommodated in any extant phylum” (1976a, p. 712).

2.
Odontogriphus
. Conway Morris mounted one rung higher on the ladder of evidence with his second treasure of 1976. He still had only a single specimen, but this time he found both part and counterpart. Walcott had at least set
Nectocaris
aside and supplied a photograph to signal its importance. But
Odontogriphus
—appropriately endowed by Conway Morris with a name meaning “toothed riddle”—was a true discovery, an entirely unnoted specimen, with part and counterpart in separate sections of Walcott’s collection. Conway Morris began his paper in the conventional passive voice, but his personal pride and passion come through beneath the stylistic cover-up:

The fossil of
Odontogriphus
is not well preserved and few structures can be distinguished, but these few are strange indeed. This highly flattened, elongated, oval animal is about two and a half inches long, and marked behind its frontal region with a series of fine, transverse parallel lines, spaced about a millimeter apart. Conway Morris regards these marks as annulations, not separations between true segments. He found no appendages or indications of hardened areas, and assumes that
Odontogriphus
was gelatinous.

The body includes only two resolvable structures, both on the ventral surface at the head end (figure 3.29). A pair of “palps” (probably sensory organs) occupies the corners of the animal’s front end. These are shallow rounded depressions formed by up to six platelike layers of tissue parallel to the body surface. The more interesting feature, presumably a mouth surrounded by a feeding apparatus of some kind, lies just forward of the palps, but right in the midline. The structure has the form of a shallow, squashed U, opening toward the front. Along the trackway of this U, Conway Morris found some twenty-five “teeth”—tiny pointed, conical structures less than half a millimeter in length. Since these teeth were far too small and fragile to rasp or bite, Conway Morris made the reasonable conjecture that they acted as supports for the bases of tentacles, and that the tentacles, serving as food-gathering devices, surrounded the mouth in a ring.

Such a ring of tentacles would strongly resemble a lophophore—the feeding structure of several modern phyla, notably the bryozoans and brachiopods. Hence, Conway Morris tentatively placed
Odontogriphus
among the so-called lophophorate phyla. But no modern lophophores grow internal teeth to support their tentacles, and nothing else about
Odontogriphus
recalls the form or structure of any other lophophorate animal. “Toothed riddle” remains a fine designation.

Those who follow high-risk strategies must accept the embarrassment of error with the joys of chancy victory. Simon’s decision to publish on the rarest and oddest specimens, and to range widely in his interpretations, almost guaranteed some significant mistakes. These come with the territory, and are not badges of dishonor. Simon “made a beauty,” as we Yanks used to say, in trying to judge the wider implications of
Odontogriphus
. He couldn’t help noticing that its “teeth” bore a vague resemblance to conodonts, then the most enigmatic objects of the fossil record. Conodonts are toothlike structures, often quite complex, that occur abundantly in rocks spanning the great geological range from Cambrian to Triassic (see figure 2.1). They are among the most important of all fossils for geological correlation, but their zoological affinities had long remained mysterious, thus fueling the most famous and long-standing of all paleontological puzzles. Obviously, conodonts are the only hard parts of a soft-bodied animal. But the creature itself had never been found—and what can you tell from some disarticulated teeth?

3.29. The flattened swimming animal
Odontogriphus
. The mouth surrounded by tentacles and the pair of palps are shown on the underside of the head. Drawn by Marianne Collins.

Conway Morris thought that the “teeth” of
Odontogriphus
might be conodonts, and that, perhaps, he had discovered the elusive conodont animal. He even took a chance and placed his toothed riddle in the class Conodontophorida. What a potential coup for a beginner—to discover the secret of secrets, and resolve a century of debate! But Simon was wrong. The soft-bodied conodont animal has since been found—with undeniable conodonts lying just in the right place at the forward end of the gut. This creature was also discovered in a museum drawer—in a collection made during the 1920s from a Carboniferous
Lagerstätte
in Scotland known as the Granton Sandstone. The conodont animal, now ranking as one of the few post-Burgess oddballs, looks nothing at all like
Odontogriphus
. Derek Briggs participated in the original description and thinks (though I am not convinced) that the conodont animal may be a chordate, or member of our own phylum (Briggs, Clarkson, and Aldridge, 1983).