Wonderful Life: The Burgess Shale and the Nature of History (33 page)

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 extending 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).

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).