Wonderful Life: The Burgess Shale and the Nature of History (9 page)

The basic answer is unambiguous: the broad anatomical disparity of the Burgess is an exclusive feature of the first explosion of multicellular life. No later
Lagerstätten
approach the Burgess in breadth of designs for life. Rather, proceeding forward from the Burgess, we can trace a rapid stabilization of the decimated survivors. The magnificently preserved, three-dimensional arthropods from the Upper Cambrian of Sweden (Müller, 1983; Müller and Walossek, 1984) may all be members of the crustacean line. (As a result of oddities in preservation, only tiny arthropods, less than two millimeters in length, have been recovered from this fauna, so we can’t really compare the disparity in these deposits with the story of larger-bodied Burgess forms.) The Lower Silurian Brandon Bridge fauna from Wisconsin, described by Mikulic, Briggs, and Kluessendorf (1985a and 1985b), contains (like the Burgess) all four major groups of arthropods. It also includes a few oddballs—some unclassifiable arthropods (including one creature with bizarre winglike extensions at its sides) and four wormlike animals, but none so peculiar as the great Burgess enigmas like
Opabinia, Anomalocaris
, or
Wiwaxia
.

The celebrated Devonian Hunsrückschiefer, so beautifully preserved that fine details emerge in X-ray photos of solid rock (Stürmer and Bergström, 1976 and 1978), contains one or two unclassifiable arthropods, including
Mimetaster
, a probable relative of
Marrella
, the most common animal in the Burgess. But life had already stabilized. The prolific Mazon Creek fauna, housed in concretions that legions of collectors have split by the millions over the past several decades, does include a bizarre wormlike animal known as the Tully Monster (officially honored in formal Latin doggerel as
Tullimonstrum
). But the Burgess motor of invention had been shut off by then, and nearly all the beautiful fossils of Mazon Creek fit comfortably into modern phyla.

When we pass through the Permo-Triassic extinction and come to the most famous of all
Lagerstätten
—the Jurassic Solnhofen limestone of Germany—we gain enough evidence to state with confidence that the Burgess game is truly over. No fauna on earth has been better studied. Quarrymen and amateur collectors have been splitting these limestone blocks for more than a century. (These uniform, fine-grained stones are the mainstay of lithography, and have been used, almost exclusively, for all fine prints in this medium ever since the technique was invented at the end of the eighteenth century.) Many of the world’s most famous fossils come from these quarries, including all six specimens of
Archaeopteryx
, the first bird, preserved with feathers intact to the last barbule. But the Solnhofen contains nothing, not a single animal, falling outside well-known and well-documented taxonomic groups.

Clearly, the Burgess pattern of stunning disparity in anatomical design is not characteristic of well-preserved fossil faunas in general. Rather, good preservation has permitted us to identify a particular and immensely puzzling aspect of the Cambrian explosion and its immediate aftermath. In a geological moment near the beginning of the Cambrian, nearly all modern phyla made their first appearance, along with an even greater array of anatomical experiments that did not survive very long thereafter. The 500 million subsequent years have produced no new phyla, only twists and turns upon established designs—even if some variations, like human consciousness, manage to impact the world in curious ways. What established the Burgess motor? What turned it off so quickly? What, if anything, favored the small set of surviving designs over other possibilities that flourished in the Burgess Shale? What is this pattern of decimation and stabilization trying to tell us about history and evolution?

WHERE

On July 11, 1911, C. D. Walcott’s wife, Helena, was killed in a railway accident at Bridgeport, Connecticut. Following a custom of his time and social class, Charles kept his sons close to home, but sent his grieving daughter Helen on a grand tour of Europe, accompanied by a chaperone with the improbable name of Anna Horsey, there to assuage grief and regain composure. Helen, with the enthusiasm of late teen-aged years, did thrill to the monuments of Western history, but she saw nothing to match the beauty of a different West—the setting of the Burgess Shale, where she had accompanied her father both during the discovery of 1909 and the first collecting season of 1910. From Europe, Helen wrote to her brother Stuart in March 1912:

The legends of fieldwork locate all important sites deep in inaccessible jungles inhabited by fierce beasts and restless natives, and surrounded by miasmas of putrefaction and swarms of tsetse flies. (Alternative models include the hundredth dune after the death of all camels, or the thousandth crevasse following the demise of all sled dogs.) But in fact, many of the finest discoveries, as we shall soon see, are made in museum drawers. Some of the most important natural sites require no more than a pleasant stroll or a leisurely drive; you can almost walk to Mazon Creek from down-town Chicago.

The Burgess Shale occupies one of the most majestic settings that I have ever visited—high in the Canadian Rockies at the eastern border of British Columbia. Walcott’s quarry lies at an elevation of almost eight thousand feet on the western slope of the ridge connecting Mount Field and Mount Wapta. Before visiting in August 1987, I had seen many photos of Walcott’s quarry; I took several more in the conventional orientation (literally east, looking into the quarry, figure 2.2). But I had not realized the power and beauty of a simple about-face. Turn around to the west, and you confront one of the finest sights on our continent—Emerald Lake below, and the snow-capped President range beyond (figure 2.3), all lit, in late afternoon, by the falling sun. Walcott found some wonderful fossils on the Burgess ridge, but I now have a visceral appreciation of why, well into his seventies, he rode the transcontinental trains year after year, to spend long summers in tents and on horseback. I also understand the appeal of Walcott’s principal avocation—landscape photography, including pioneering work in the technology of wide-angle, panoramic shots (figure 2.4).

But the Burgess Shale does not hide in an inaccessible wilderness. It resides in Yoho National Park, near the tourist centers of Banff and Lake Louise. Thanks to the Canadian Pacific Railway, whose hundred-car freights still thunder through the mountains almost continuously, the Burgess Shale lies on the border of civilization. The railroad town of Field (population about 3,000, and probably smaller today than in Walcott’s time, especially since the Railway hotel burned down) lies just a few miles from the site, and you can still board the great transcontinental train from its tiny station.

Today you can drive to the Takakkaw Falls campground, near the Whiskey Jack Hostel (named after a bird, not an inebriated hero of the old West), and then climb the three thousand feet up to Burgess Ridge by way of a four-mile trail around the northwest flank of Mount Wapta. The climb has some steep moments, but it qualifies as little more than a pleasant stroll, even for yours truly, overweight, out of shape, and used to life at sea level. A more serious field effort can now employ helicopters to fly supplies in and out (as did the Geological Survey of Canada expeditions of the 1960s and the Royal Ontario Museum parties of the 1970s and 1980s). Walcott had to rely upon pack horses, but no one could brand the effort as overly strenuous or logistically challenging, as field work goes. Walcott himself (1912) provided a lovely description of his methods during the first field season of 1910—a verbal snapshot that folds an older technology and social structure into its narrative, with active sons scouring the hillside and a dutiful wife trimming the specimens back at camp:

2.2. Three views of the Burgess Shale quarries taken during my visit in August 1987. (A) The northern end of Walcott’s quarry, with Mount Wapta in the background. Note the quarry wall with cores drilled for the insertion of dynamite charges, and the debris from blasting on the quarry floor. (B) A similar view of the quarry opened by Percy Raymond in 1930, with yours truly and three avid geologists. This much smaller quarry lies above Walcott’s original site. (C) My son Ethan sitting on the floor of Walcott’s quarry as seen at the southern end.

2.3. The view from Walcott’s quarry. A geologist searches for fossils on the talus slope in the foreground. Emerald Lake lies beyond.

2.4. This reduced version of one of Walcott’s famous panoramic photographs gives a good impression of the technique, but lacks the grandeur of the original, which is several feet long. Walcott took this photograph in 1913. The right-hand side shows the Burgess quarry, with Mount Wapta to the left. Note some collectors and collecting tools within the quarry.

A year before he discovered the Burgess Shale, Walcott (1908) described an equally charming, rustic technology for collecting from the famous
Ogygopsis
trilobite bed of Mount Stephen, a locality similar in age to the Burgess, and just around the next bend:

The romance of the Burgess has had at least one permanent effect upon all future study of its fossils—the setting of their peculiar names. The formal Greek and Latin names of organisms can sometimes rise to the notable or the mellifluous, as in my favorite moniker, for a fossil snail—
Pharkidonotus percarinatus
(say it a few times for style). But most designations are dry and literal: the common rat is, for overkill,
Rattus rattus rattus
; the two-horned rhino is
Diceros;
the periwinkle, an inhabitant of near-shore, or littoral, waters, is
Littorina littorea
.

Burgess names, by contrast, are a strange-sounding lot. Decidedly not Latin in their roots, they are sometimes melodious, as in
Opabinia
, but other times nearly unpronounceable for their run of vowels, as in
Aysheaia, Odaraia
, and
Naraoia
, or their unusual consonants, as in
Wiwaxia, Takakkawia
, and
Amiskwia
. Walcott, who loved the Canadian Rockies and spent a quarter century of summers in its field camps, labeled his fossils with the names of local peaks and lakes,
*
themselves derived from Indian words for weather and topography.
Odaray
means “cone-shaped”;
opabin
is “rocky”;
wiwaxy
, “windy.”