The Geological Survey of Canada expedition had discovered an odd specimen in the Raymond quarry, just above Walcott’s phyllopod bed. Whittington had taken this large, ill-defined, and virtually featureless fossil and placed it in a drawer—hoping, I think, to bury it by the old cliché: Out of sight, out of mind. But he kept thinking about this peculiar fossil of a creature so much larger than anything else in the Burgess Shale. “I used to open the drawer and then close it,” Harry explained to me. One day in 1981, he decided to excavate the fossil in the hope that some details of structure might be resolved. He dug into one end of the creature and, to his astonishment, found a specimen of Anomalocaris apparently attached and in place (figure 3.63). Harry told Derek Briggs about his discovery, and Derek simply couldn’t believe it. The excavated object was surely Anomalocaris, but, like Simon’s interpretation of the jellyfish Peytoia on the sponge Laggania, perhaps this specimen of Anomalocaris had been accidentally entangled with a large sheet of something else as the mudslide coalesced.
Soon afterward, Whittington and Briggs were studying a suite of specimens borrowed from the Walcott collections. These slabs showed relatively featureless blobs and sheets that had never attracted much attention, including the body of Laggania with Peytoia on top. On a single momentous day—the positive counterpart (in the vernacular, not technical, sense) of another key Burgess moment, nearly a decade before, when Whittington had cut through the head and sides of Opabinia and found nothing underneath—they excavated and found both Peytoia and appendage F as organs of a larger creature.
As they assimilated this greatest of all Burgess surprises, and kept finding Peytoia and appendage F in the same association on other slabs, Harry and Derek realized that they had resolved a forest of problems into one creature. Peytoia was no jellyfish, but the mouth of the large beast, attached to the ventral surface near the front. Appendage F was not one member of a large sequence of repeated limbs on an arthropod; rather, two appendage F’s formed a single pair of feeding organs attached, in front of the mouth, to the bottom end of the new animal.
3.63. The specimen dissected by Harry Whittington that revealed the true nature of Anomalocaris. In this camera lucida drawing, the mouth misidentified by Walcott as the jellyfish Peytoia is at top center (labeled Pp); the oblique line (ve) just above it represents a crack in the rock. The structure originally named Anomalocaris is the curved feeding appendage just to the left of the mouth with its middle segment labeled j5. Also visible is the trace of the central gut, or alimentary canal (al).
But Whittington’s specimen back in England bore Anomalocaris, not appendage F, in this frontal position (see figure 3.63). When he dissected this specimen more fully, he found traces of both the Peytoia mouth and a second Anomalocaris, forming a pair of feeding organs in the same position as the appendage-F pairs on the specimens in Washington (figure 3.64).
3.64. The key specimen of Anomalocaris further dissected to reveal parts of both feeding appendages. This is the other slab, and therefore a mirror image, of part of the specimen represented in figure 3.63. Note the mouth (labeled p) and the first discovered appendage (j1–j14). But now a trace of the second feeding appendage has been excavated at the lower left, just below the oblique line representing the crack in the rock.
All the pieces had finally come together. From four anomalies—a crustacean without a head, a feeding appendage that didn’t fit, a jellyfish with a hole in the middle, and a squashed sheet that had bounced from one phylum to another—Whittington and Briggs had reconstructed two separate species of the single genus Anomalocaris. Laggania was a squashed and distorted part of the body; Peytoia, the mouth surrounded by a circlet of toothed plates, not a series of lobes with hooks; Anomalocaris the pair of feeding organs in one species (Anomalocaris canadensis); appendage F a feeding organ in the second species (Anomalocaris nathorsti, borrowing the old trivial name of Peytoia). The uncompromising rules of nomenclature, honoring oldest first, required that the entire genus be called Anomalocaris, to recognize Whiteaves’s original publication of 1892. But what a happy and appropriate imposition in this case—an “odd shrimp” indeed!
Since the organ originally named Anomalocaris can be up to seven inches in length when extended, the entire animal must have dwarfed nearly everything else in the Burgess Shale. Whittington and Briggs estimated the biggest specimens as nearly two feet in length, by far the largest of all Cambrian animals! A recent reconstruction of the whole fauna (Conway Morris and Whittington, 1985), basically an update of the 1979 Scientific American version, has replaced the pineapple-slice Peytoia that used to angle in from the west (see figure 3.62) with a large and menacing Anomalocaris, purposefully advancing from the east (figure 3.65).
Whittington and Briggs published their monograph on Anomalocaris in 1985, a fitting triumph to cap what may be the most distinguished and important series of monographs in twentieth-century paleontology. The long oval head of Anomalocaris bears, on the side and rear portion of its dorsal surface, a large pair of eyes on short stalks (figure 3.66). On the ventral surface, the pair of feeding appendages attaches near the front, with the circlet of the mouth behind and in the midline (figure 3.67). The plates of the circlet could substantially constrict the area of the mouth but not fully come together (in any orientation that Whittington or Briggs could reconstruct), so the mouth probably remained permanently open, at least partially. Whittington and Briggs conjecture that the mouth may have worked like a nutcracker, with Anomalocaris using its appendages to bring prey to the opening (figure 3.68), and then crushing its food by constriction. The inner borders of the plates in the Peytoia circlet all bear teeth. In one specimen, Whittington and Briggs found three additional rows of teeth, stacked one above the other parallel to the circlet of mouth plates. The teeth in these rows may have been attached to the circlet, but they probably extended from the walls of the gullet—thus providing Anomalocaris with a formidable array of weapons both in the mouth itself and in the front end of the gut (figure 3.69).
3.65. A recent reconstruction of the Burgess Shale fauna (Conway Morris and Whittington, 1985), showing the new interpretation of Anomalocaris (24), and the great size of this creature compared to the others. Note the weird wonders Opabinia (8), Dinomischus (9), and Wiwaxia (23); and the arthropods Aysheaia (5), Leanchoilia (6), Yohoia (11), Canadaspis (12), Marrella (15), and Burgessia (19).
3.66. The two known species of Anomalocaris: top, Anomalocaris nathorsti as seen from below, showing the circular mouth, misidentified by Walcott as a jellyfish, and the pair of feeding appendages; bottom, Anomalocaris canadensis as seen from the side, in swimming position. Drawn by Marianne Collins.
Behind the mouth at the ventral surface, the head carries three pairs of strongly overlapping lobes (see figure 3.67). The trunk behind the head is divided into eleven lobes, each triangular in basic shape, with the apex pointed back in the midline. The lobes are widest at the middle of the trunk, evenly tapering both in front and behind. These lobes, like the three at the rear of the head, strongly overlap. The termination of the trunk is short and blunt, without any projecting spine or lobe. A multilayered structure of stacked lamellae, presumably a gill, attaches to the top surface of each lobe.
3.67. Anomalocaris as seen from below, showing how the feeding appendages could bring food to the mouth (Whittington and Briggs, 1985). Just behind the mouth at the left, part of the ventral surface of the animal has been omitted, to show the gills lying above the three posterior segments of the head.
3.68. The probable mode of feeding of Anomalocaris. (A) The head of Anomalocaris nathorsti seen from the side, with the feeding appendage extended (top) and coiled up to bring food to the mouth (bottom). (B) The same operation viewed from the front. (C) As seen from below, the feeding appendage coiled to bring food to the mouth, in Anomalocaris nathorsti (top) and in Anomalocaris canadensis (bottom).
3.69. The mouth of Anomalocaris, mistaken by Walcott for the jellyfish Peytoia. Several rows of teeth can be seen extendi
ng down from the central space; these tooth rows may be projecting from the gullet of the animal. (A) A photograph of the specimen. (B) A camera lucida drawing of the same specimen.
Since Anomalocaris has no body appendages, it presumably did not walk or crawl along the substrate. Whittington and Briggs reconstruct Anomalocaris as a capable swimmer, though no speed demon, propelled by wavelike motions of the body lobes in coordinated sequences (figure 3.70). The overlapping lateral lobes would therefore work much like the single lateral fin flap of some fishes. An Anomalocaris in motion may have resembled a modern manta ray, undulating through the water by generating waves within the broad and continuous fin.
Again, as with Wiwaxia and Opabinia, one can make reasonable conjectures about the biological operation of Anomalocaris—a creature can, after all, only eat and move in so many ways. But what could such an odd animal be in genealogical terms? The feeding appendages had been read as arthropod parts for a century—and their segmented character does recall the great phylum of joint-footed creatures. But repetition and segmentation, shown by the sequence of lobes as well as the feeding appendages, are not restricted to arthropods—think of annelids, vertebrates, and even the molluscan “living fossil,” Neopilina. Nothing else about Anomalocaris suggests a linkage with arthropods. The body bears no jointed appendages, and the mouth, with its perpetual gape and circlet of plates, is unique, utterly unlike anything in the phylum Arthropoda. Even the pair of feeding appendages, though segmented, strays far from any arthropod prototype as soon as we attempt any comparison in detail. Whittington and Briggs concluded that Anomalocaris “was a metameric animal, and had one pair of jointed appendages and a unique circlet of jaw plates. We do not consider it an arthropod, but the representative of a hitherto unknown phylum” (1985, p. 571).
3.70. Reconstruction of Anomalocaris as seen from the side, in the act of swimming (Whittington and Briggs, 1985).
CODA
The Burgess work will continue, for many genera remain ripe for restudy (the bulk of the arthropods have been monographed, but only about half of the known weird wonders). However, Harry, Derek, and Simon are moving on, for various reasons. The Lord gives us so little time for a career—forty years if we start early as graduate students and remain in good health, fifty if fortune smiles. The Devil takes so much away—primarily in administrative burdens that fall upon all but the most resistant and singularly purposeful of SOBs. (The earthly rewards of scholarship are higher offices that extinguish the possibility of future scholarship.) You can’t spend an entire career on one project, no matter how important or exciting. Harry, in his seventies, has returned to his first love, and is spearheading a revision of the trilobite volume for the Treatise on Invertebrate Paleontology. Simon’s burgeoning career includes a Burgess Shale project or two, but his main interests have moved backward in time to the Cambrian explosion itself. Derek’s expanding concerns center on weird wonders and soft-bodied faunas of post-Burgess times.
Others will finish this generation’s run at the Burgess Shale. And then the next generation will arrive with new ideas and new techniques. But science is cumulative, despite all its backings and forthings, ups and downs. The work of Briggs, Conway Morris, and Whittington will be honored for its elegance and for the power of its transforming ideas as long as we maintain that most precious of human continuities—an unbroken skein of intellectual genealogy.
No organism or interpretation can have the last word in such a drama, but we must respect the closure of a man’s work. The epilogue to this play belongs to Harry Whittington, who in his typically succinct and direct words, wrote to me about his Burgess monographs: “Perhaps these necessarily dry papers conveyed a little of the excitement of discovery—it certainly was an intriguing investigation which had its moments of great joy when a new and unexpected structure was revealed by preparation” (March 1, 1988). “It has been the most exciting and intriguing project that I have been associated with” (April 22, 1987).
SUMMARY STATEMENT ON THE BESTIARY OF THE BURGESS SHALE
DISPARITY FOLLOWED BY DECIMATION: A GENERAL STATEMENT
If the soft-bodied components had never been found, the Burgess Shale would be an entirely unremarkable Middle Cambrian fauna of about thirty-three genera. It contains a rich assemblage of sponges (Rigby, 1986) and algae, seven species of brachiopods, nineteen species of ordinary trilobites with hard parts, four of echinoderms, and a mollusk and coelenterate or two (Whittington, 1985b, pp. 133–39, presents a complete list). Among the soft-bodied organisms, bringing the total biota to about 120 genera, some are legitimate members of major groups. Whittington lists five certain and two probable species of priapulid worms, six species of polychaetes, and three soft-bodied trilobites (Tegopelte and two species of Naraoia).
My five-act drama, just concluded, emphasizes a different theme, taught to me by the soft-bodied components alone. The Burgess Shale includes a range of disparity in anatomical design never again equaled, and not matched today by all the creatures in all the world’s oceans. The history of multicellular life has been dominated by decimation of a large initial stock, quickly generated in the Cambrian explosion. The story of the last 500 million years has featured restriction followed by proliferation within a few stereotyped designs, not general expansion of range and increase in complexity as our favored iconography, the cone of increasing diversity, implies. Moreover, the new iconography of rapid establishment and later decimation dominates all scales, and seems to have the generality of a fractal pattern. The Burgess revisions of Whittington and colleagues have specified three ascending levels.
1. Major groups of a phylum. No group of invertebrate fossils has received more study, or stands higher in general popularity, than trilobites. The mineralized skeletons of conventional fossils show extraordinary diversity, but all conform to a basic design. One would hardly have anticipated, after all this study, that the total anatomical range of the group could have been far broader in its early days. Yet soft-bodied Naraoia is undoubtedly a trilobite in its distinctive series of head appendages (one pair of antennae and three post-oral biramous pairs), and its conventional body appendages of the “right” form and number of segments. Yet the exoskeleton of Naraoia, with its two valves, stands far outside the anatomical range of the group as seen in conventional fossils.
2. Phyla. We can completely grasp the extent of a surprise only when we also know the full range of conventional possibilities—for we need a baseline of calibration. I find the story of Burgess arthropods particularly satisfying because the baseline has “no vacancy,” and all additional disparity truly supplements a full range of membership in major groups. The orphaned arthropods of the Burgess are spectacular, but the representatives of conventional groups are just as important for documenting the first phrase of the primary theme—“all we could expect and then a great deal more.” The recent discovery of Sanctacaris brings the conventional roster to completion. All four great groups of arthropods have representatives in the Burgess Shale:
Trilobita—nineteen ordinary species plus three soft-bodied
Crustacea—Canadaspis and perhaps Perspicaris
Uniramia—Aysheaia, if correctly identified as an onychophoran
Chelicerata—Sanctacaris
But the Burgess Shale contains an even greater range of anatomical experiments, equally distinct in design and functionally able, but not leading to subsequent diversity. A few of these orphans may show relationships among themselves—Actaeus and Leanchoilia, perhaps, on the basis of their distinctive frontal appendages—but most are unique, with defining features shared by no other species.
The monographic work of Whittington and colleagues has identified thirteen unique designs (table 3.3), all discussed in the preceding chronology. But how many more have yet to be described? Whittington lists twenty-two species (and inadvertently omits Marrella) in his category “not placed in any phylum or class of Arthropoda” (1985b, p. 138). Therefore, by best estimate, the Burgess Shale contains at le
ast twenty unique designs of arthropods, in addition to the documented representatives of all four great groups within the phylum.*
3. Multicellular animal life as a whole. The weird wonders of the Burgess Shale excite our greatest fascination, though the arthropod story is every bit as satisfying intellectually, especially for its completion of the baseline and consequently firm estimate for the relative frequency of oddballs. Still, whereas Marrella and Leanchoilia may be beautiful and surprising, Opabinia, Wiwaxia, and Anomalocaris are awesome—deeply disturbing and thrilling at the same time.
The Burgess revision has identified eight anatomical designs that do not fit into any known animal phylum: in order of publication, Opabinia, Nectocaris, Odontogriphus, Dinomischus, Amiskwia, Hallucigenia, Wiwaxia, and Anomalocaris. But this list is nowhere near complete—surely less exhaustive than the account of documented oddballs among arthropods. The best estimates indicate that only about half the weird wonders of the Burgess Shale have been described. Two recent sources have provided lists of all potential creatures in this category of ultimate strangeness. Whittington counts seventeen species of “miscellaneous animals” (1985b, p. 139), and I would add Eldonia to his total. Briggs and Conway Morris count nineteen “Problematica from the Middle Cambrian Burgess Shale of British Columbia” (1986). Finding no basis for genealogical or anatomical arrangement among the weird wonders, they simply list their nineteen creatures in alphabetical order.
What may the future bring us in further surprises from the Burgess Shale? Consider Banffia, namesake of the more famous national park adjoining Yoho and the Burgess Shale. Walcott’s “worm”—with an annulated front portion separated from a saclike posterior—is almost surely a weird wonder. Or Portalia, an elongate animal with bifurcating tentacles arrayed along the body axis. Or Pollingeria, a scalelike object with a meandering tubelike structure on top. Walcott interpreted Pollingeria as a covering plate from a larger organism, akin to the sclerites of Wiwaxia, and explained the meandering tube as a commensal worm, but Briggs and Conway Morris think that the object could be an entire organism. The general form of the Burgess story may now be well in hand, but Walcott’s quarry has not yet yielded all its particular treasures.