Misadventures in the Burgess Shale
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Misadventures in the Burgess Shale One hundred years after Charles Doolittle Walcott found a wealth of Cambrian fossils in the Rocky Mountains of British Columbia, Desmond Collins reflects on the bumpy road of their classification. T his August marks the centenary of Charles Doolittle Walcott’s discovery of the Burgess Shale — the fossil bed in the Canadian Rockies that first opened mankind’s eyes to the wealth of animals living in Cam- brian seas 505 million years ago. The fossil bed itself is famous; for decades ‘Burgess Shale life’ was synonymous with ‘Cambrian life’. Less well known is the full story leading to Walcott’s dis- covery in 1909. The finding of Burgess Shale fossils in Yoho National Park, British Columbia, was inevita- ble once the Canadian Pacific Railway ran its track through Kicking Horse Valley, between Mount Stephen and Mount Field in the 1880s. The first fossils were found on Mount Stephen by a carpenter helping to build a railway hotel, attracting the attention of Richard McConnell from the Geological Survey of Canada (GSC). In September 1886, 23 years before Walcott’s more famous find, McConnell hit on the Mount Stephen trilobite beds: the first Burgess Shale fossil site. McConnell collected a host of trilobites, a now extinct marine arthropod that is the trade- mark creature of the Cambrian. He also found two unusual specimens. Joseph Whiteaves, the GSC chief palaeontologist, described these in 1892 as the headless body of some sort of shrimp, noting that the appendages of the segmented body were not jointed, making it a sort of non-arthropod arthropod. He called it Anomalocaris, after this anomaly. Whiteaves unwittingly set the pattern for much misiden- tification and misclassification in Burgess Shale fossil research. The true nature of these fossils would not be revealed for 90 years. The Darwin connection Walcott first visited Mount Stephen in 1907 — the year that he was appointed secretary of the Smithsonian Institution in Washington DC — to study the Cambrian stratigraphy of the area. Two years later the Darwin centennial seems to have provided the serendipitous stimulus for his discovery of the Burgess Shale. Walcott was given an honorary doctorate at the University of Cambridge, UK, in June, as part of the 1909 celebrations. Afterwards he visited the British Museum (Natural History) in London. The keeper of geology there, Henry Woodward, had observed in a 1902 paper that Mount Field is part of the same massif as Mount Stephen and “will no doubt yield the same Cambrian fossils”. Presumably Woodward repeated this observation during Walcott’s visit, because, on Walcott’s return to the Rockies nine weeks later, he made straight for Mount Field. On Saturday 28 August 1909, Walcott went up to Burgess Pass, next to Mount Field, to take photographs, and, according to his diary, “found the Stephen formation trilobite bed”. His family followed him up to the site on 30 August. The story often told is that Mrs Walcott’s horse stumbled on the important ‘discovery slab’. Instead, it seems that the man leading the packhorse train crossed over a rock that had slid onto the trail, and Walcott, concerned that his wife’s horse might trip, moved it away. The next day, he and Mrs Wal- cott broke up the offending slab and found “a remarkable group of Phyllopod crustaceans”. Walcott sketched three in his diary. Walcott did not immediately realize the significance of what he had discovered. He spent just five days collecting at the site. But he returned to find the source of the discovery slab in 1910, excavating the source rock layer and making a large collection of fossils. In 1911, Walcott began to describe his finds. This was an unprecedented challenge. How to classify fossilized animals for which there is no known comparative material? This did not seem to bother Walcott. As a long-time trilo- bite expert, he began with the arthropods. One of these he named Sidneyia inexpectans, after his son Sidney, who had found the first speci- men. Walcott portrayed it in a 1911 National Geographic article along with giant claws that had also been found at the site, with the cap- tion: The King of the Cambrian World. Walcott never found such claws attached to Sidneyia; it seems that he simply associated the large, obviously arthropodan claws with the largest arthropod present. Like Whiteaves before him, Walcott got it wrong. Stab in the dark Walcott’s next two papers, also published in 1911, were on four sea cucumbers, one jellyfish and some annelid worms. These descriptions revealed the exquisite preservation of Burgess Shale fossils. These were all soft-bodied ani- mals, with no hard parts. Preservation of such creatures is extremely rare in the fossil record, and was unknown for the Cambrian. Walcott’s identifications did not fare well. Only one of the sea cucumbers is still thought to be a sea cucumber, and the jellyfish is now known to be part of an extraordinary arthropod. Of the 12 annelid worms, only one is still recognized as such. Walcott was on more familiar ground with his publication of arthropods in 1912 but, even here, many of the 18 genera he described are now known to belong to classes different to those to which he assigned them. By the end of Walcott’s final excavation in 1917, he had collected some 65,000 fossils, and observed: “This practically exhausts a quarry which has given the finest and largest series of Middle Cambrian fossils yet discovered in any formation in any country.” Despite his obvi- ous pride in making such a fabulous collection, Walcott’s main goal continued to be to study the Lower Palaeozoic stratigraphy of the Cana- dian Rockies. Of his 18 seasons in the area, he spent 15 studying this, and only 3 (spread over 5 years) on the Burgess Shale fossils. Charles Dolittle Walcott discovered the most important, if not the first, Burgess Shale fossil beds. SMITHSONIAN INSTITUTION ARCHIVES 952 NATURE|Vol 460|20 August 2009 OPINION © 2009 Macmillan Publishers Limited. All rights reserved
Transcript of Misadventures in the Burgess Shale
Misadventures in the Burgess ShaleOne hundred years after Charles Doolittle Walcott found a wealth of Cambrian fossils in the Rocky
Mountains of British Columbia, Desmond Collins reflects on the bumpy road of their classification.
This August marks the centenary of Charles Doolittle Walcott’s discovery of the Burgess Shale — the fossil bed in the
Canadian Rockies that first opened mankind’s eyes to the wealth of animals living in Cam-brian seas 505 million years ago. The fossil bed itself is famous; for decades ‘Burgess Shale life’ was synonymous with ‘Cambrian life’. Less well known is the full story leading to Walcott’s dis-covery in 1909.
The finding of Burgess Shale fossils in Yoho National Park, British Columbia, was inevita-ble once the Canadian Pacific Railway ran its track through Kicking Horse Valley, between Mount Stephen and Mount Field in the 1880s. The first fossils were found on Mount Stephen by a carpenter helping to build a railway hotel, attracting the attention of Richard McConnell from the Geological Survey of Canada (GSC). In September 1886, 23 years before Walcott’s more famous find, McConnell hit on the Mount Stephen trilobite beds: the first Burgess Shale fossil site.
McConnell collected a host of trilobites, a now extinct marine arthropod that is the trade-mark creature of the Cambrian. He also found two unusual specimens. Joseph Whiteaves, the GSC chief palaeontologist, described these in 1892 as the headless body of some sort of shrimp, noting that the appendages of the segmented body were not jointed, making it a sort of non-arthropod arthropod. He called it Anomalocaris, after this anomaly. Whiteaves unwittingly set the pattern for much misiden-tification and misclassification in Burgess Shale fossil research. The true nature of these fossils would not be revealed for 90 years.
The Darwin connectionWalcott first visited Mount Stephen in 1907 — the year that he was appointed secretary of the Smithsonian Institution in Washington DC — to study the Cambrian stratigraphy of the area. Two years later the Darwin centennial seems to have provided the serendipitous stimulus for his discovery of the Burgess Shale. Walcott was given an honorary doctorate at the University of Cambridge, UK, in June, as part of the 1909 celebrations. Afterwards he visited the British Museum (Natural History) in London. The keeper of geology there, Henry Woodward, had observed in a 1902 paper that Mount Field is part of the same massif as Mount Stephen
and “will no doubt yield the same Cambrian fossils”. Presumably Woodward repeated this observation during Walcott’s visit, because, on Walcott’s return to the Rockies nine weeks later, he made straight for Mount Field.
On Saturday 28 August 1909, Walcott went up to Burgess Pass, next to Mount Field, to take photographs, and, according to his diary, “found the Stephen formation trilobite bed”. His family followed him up to the site on 30 August. The story often told is that Mrs
Walcott’s horse stumbled on the important ‘discovery slab’. Instead, it seems that the man leading the packhorse train crossed over a rock that had slid onto the trail, and Walcott, concerned that his wife’s horse might trip, moved it away. The next day, he and Mrs Wal-cott broke up the offending slab and found “a remarkable group of Phyllopod crustaceans”. Walcott sketched three in his diary.
Walcott did not immediately realize the significance of what he had discovered. He spent just five days collecting at the site. But
he returned to find the source of the discovery slab in 1910, excavating the source rock layer and making a large collection of fossils.
In 1911, Walcott began to describe his finds. This was an unprecedented challenge. How to classify fossilized animals for which there is no known comparative material? This did not seem to bother Walcott. As a long-time trilo-bite expert, he began with the arthropods. One of these he named Sidneyia inexpectans, after his son Sidney, who had found the first speci-men. Walcott portrayed it in a 1911 National Geographic article along with giant claws that had also been found at the site, with the cap-tion: The King of the Cambrian World. Walcott never found such claws attached to Sidneyia; it seems that he simply associated the large, obviously arthropodan claws with the largest arthropod present. Like Whiteaves before him, Walcott got it wrong.
Stab in the darkWalcott’s next two papers, also published in 1911, were on four sea cucumbers, one jellyfish and some annelid worms. These descriptions revealed the exquisite preservation of Burgess Shale fossils. These were all soft-bodied ani-mals, with no hard parts. Preservation of such creatures is extremely rare in the fossil record, and was unknown for the Cambrian.
Walcott’s identifications did not fare well. Only one of the sea cucumbers is still thought to be a sea cucumber, and the jellyfish is now known to be part of an extraordinary arthropod. Of the 12 annelid worms, only one is still recognized as such. Walcott was on more familiar ground with his publication of arthropods in 1912 but, even here, many of the 18 genera he described are now known to belong to classes different to those to which he assigned them.
By the end of Walcott’s final excavation in 1917, he had collected some 65,000 fossils, and observed: “This practically exhausts a quarry which has given the finest and largest series of Middle Cambrian fossils yet discovered in any formation in any country.” Despite his obvi-ous pride in making such a fabulous collection, Walcott’s main goal continued to be to study the Lower Palaeozoic stratigraphy of the Cana-dian Rockies. Of his 18 seasons in the area, he spent 15 studying this, and only 3 (spread over 5 years) on the Burgess Shale fossils.
Charles Dolittle Walcott discovered the most important, if not the first, Burgess Shale fossil beds.
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After Walcott’s death in 1927, his Burgess Shale fossils languished on the upper shelves of the Smithsonian collections. His third wife, Mary Vaux, was unwilling to have oth-ers rifling through them. This hiatus ended in the late 1960s when Harry Whittington of the University of Cambridge and his colleagues began a restudy of Burgess Shale animals, based mainly on Walcott’s collections.
Whittington changed the world’s perception of Cambrian life when he redescribed Opab-inia, a bizarre looking animal with a frontal nozzle and five eyes. Walcott had classified it as an arthropod, but Whitting-ton could find no appendages, jointed or not, so labelled it of “unknown affinities”. This was the first time that anyone had questioned Walcott’s implicit assumption that Cambrian animals belonged to groups alive today.
Weird wondersAs for the Anomalocaris ‘shrimp’ first described by Whiteaves, Whittington’s student Derek Briggs recognized in 1979 that it was more likely to be an appendage of some larger crea-ture. Soon after this, Whittington began to excavate from the enclosing rock what seemed to be part of one of these appendages in an unknown fossil. To his amazement, his prepa-ration revealed two Anomalocaris appendages as frontal claws. Moreover, what Walcott had called a jellyfish in 1911 was revealed to be radiating jaws in a circular mouth at the front. This animal was like nothing ever seen before — “unlike other shrimps”, as Whiteaves had written, was an understatement.
Whittington’s work left Anomalocaris,
Opabinia and six others, mostly described by another of Whittington’s students, Simon Conway Morris, unclassifiable in any known animal group. Stephen Jay Gould, in his 1989 book, Wonderful Life: The Burgess Shale and the Nature of History, took the next logical step: he suggested that the eight unclassifiable “weird wonders” belonged to animal groups that had become extinct.
Gould criticized Walcott for “shoehorning” his animals into known groups, so delay-
ing the true understanding of the Burgess Shale animals. He attributed this to Walcott’s conservatism and Presbyte-rian upbringing. To me, this is nonsense. None of Walcott’s contemporaries, nor indeed
the scientists who followed him, questioned Walcott’s assumption that the Burgess Shale animals belonged to living animal groups; not until Whittington. True, many of Walcott’s zoological assignments were wrong, but this led others to attempt to correct his mistakes. In effect, Walcott’s misadventures provided the incentive for later revelations.
Since 1975, I have led 18 seasons of field-work and excavation in the Burgess Shale by Royal Ontario Museum parties. We greatly expanded the existing quarries, and discovered and excavated three new faunas, each with its own distinct composition. In 1991, we found the first complete Anomalocaris. For the first time, we could see what it actually looked like: a metre-long, fierce predator with large claws and radiating jaws. Two forms were described and assigned to a new class of arthropods, the Dinocarida — the ‘terrible crabs’. The dino-carids preyed on animals in Cambrian seas
much as dinosaurs preyed on Mesozoic land animals. They change, radically, our view of the Cambrian way of life.
With a flood of new specimens coming from 12 seasons of excavation between 1983 and 2000, new forms are being described and old forms redescribed. Today, we have returned mostly to Walcott’s practice of classifying Burgess Shale animals in living animal groups, but the groups are different. There are some extinct classes, such as the Dinocarida, but very few extinct phyla. Five of Gould’s weird wonders have been classified, only one in a new phylum. This year, one of the conundrums from Walcott’s time was solved — the claws of The King of the Cambrian World are now known to belong to Hurdia, a ‘terrible crab’.
Additional Cambrian material is now coming from the Chengjiang fauna in China (particularly new chordates, the group that includes humans), and the Sirius Passet fauna in Greenland. Along with the Burgess Shale animals, they demonstrate that virtually all animal groups alive today were present in Cambrian seas.
Walcott’s 1909 discovery was not the first, but the best Burgess Shale site. By his collec-tions and publications, Walcott contributed more than anyone, before or since, to draw-ing back the curtain obscuring our view of the life of the Cambrian world. For this alone, he deserves the glory of this month’s centennial celebrations. ■
Desmond Collins served as curator of
invertebrate palaeontology and head of
palaeobiology at the Royal Ontario Museum from
1968 to 2004. He is now retired.
e-mail: [email protected]
Further reading online at http://tinyurl.com/oxgo9k.
Anomalocaris, once described as a shrimp, was revealed by Desmond Collins’s Burgess Shale fossil find in 1991 (above) as a ‘terrible crab’ (reconstruction inset).
“Virtually all animal groups alive today
were present in Cambrian seas.”
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