A splayed-out corpse of Marrella is fragile evidence of the passage of the life of a single animal -- a life briefly lived and abruptly terminated more than half a billion years ago. Marella splendens, the "lace crab" from Walcott's quarry, is the most abundant fossil in the Burgess Shale. GSC specimen is 1 cm long. (Photo by BDEC (c).)

On the last day of August, 1909, Charles Walcott and his family and field crew were wrapping up work for the season. Traveling by horseback along a well-established trail across the ridge between Mount Wapta and Mount Field above Emerald Lake, they were on their way to the comfort of Mount Stephen House in the village of Field. The lead horse was halted by a slab of shale that had fallen across the narrow trail and, before the crew could dislodge it, Walcott caught sight of some faint and shiny, but well-defined outlines of fossils. He knew Cambrian fossils better than anyone in the world and immediately recognized that these were unknown types of arthropods. The non-mineralized cuticle of these animals was clearly evident, but they also displayed, in astonishing detail, their soft-bodied anatomy -- spindly legs, antennae, comb-like gills, even guts and muscles. Walcott also spotted segmented worms and sponges among the fossils as well as a few familiar trilobites establishing that these strange fossils were of Middle Cambrian age.

Hurrying before the onset of winter in this high alpine setting, the crew scoured the slope above until the source of the fossil-bearing talus block was identified. Walcott made preliminary fossil collections, including many specimens of the "Lace Crab", his field name for the arthropod he later named Marrella splendens after his friend John Marr of Cambridge University.

Seen for the first time, a Burgess Shale fossil is a bit of a disappointment. It's hard to believe that this bit of wispy film can really be part of the most important fossil assemblage in the world. The common Marrella is a case in point. Small, without relief, and difficult to see, this fossil is certainly not as impressive as a dinosaur bone or even an ammonite, but because it is the entire body of an animal, it is packed with much more anatomical information. When examined closely with a hand-lens or under a microscope, the details that become visible are truly astonishing. Two pairs of long horns can be seen to extend back from the blunt head and two pairs of annulated antennae sweep in front. The triangular body consists of more than twenty segments; each with a pair of spindly jointed walking legs and a pair of feathery gills. The multiple legs lie akimbo on the shale surface -- a frozen frame of its unsuccessful struggle to escape death when caught up and buried by a rapidly moving slurry of mud. The tiny corpse, entombed in firm mud, escaped the depredations of bacteria to be preserved intact, effectively for eternity. Adjacent to many specimens of Marrella are dark blotches -- the squeezed out body fluids of the animals; a few even include an expelled intestine. All of these anatomical (and forensic) details are visible on a fossil not much larger than a house fly.

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