Past lives: Chronicles of Canadian Paleontology |
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Past lives: Chronicles of Canadian Paleontology Eozoon canadense: the false dawn animal
When he established Eozoon canadense, Sir William Dawson
hailed this fossil as "one of the brightest gems in the scientific
crown of the Geological Survey of Canada". Soon tarnished, this gem
later turned to dross
![Polished specimen of Eozoon canadense from the Cote St. Pierre locality north of Papineauville, Quebec. Green mineral is serpentine; white mineral is calcite. GSC specimen is 26 cm long. (Photo by BDEC (c)) Polished specimen of Eozoon canadense from the Cote St. Pierre locality north of Papineauville, Quebec. Green mineral is serpentine; white mineral is calcite. GSC specimen is 26 cm long. (Photo by BDEC (c))](/web/20061103040447im_/http://www.gsc.nrcan.gc.ca/paleochron/images/eozoon1.jpg) Polished specimen of Eozoon canadense from the Cote St. Pierre locality north of Papineauville, Quebec. Green mineral is serpentine; white mineral is calcite. GSC specimen is 26 cm long.
(Photo by BDEC (c)) |
To many mid-Victorian geologists and paleontologists these laminated
green and grey rock specimens from altered limestones of the Canadian
Shield of Ontario and Quebec were the most important fossils ever found
because they constituted evidence of the existence of complex life
forms deep in the Precambrian. J. William Dawson, the Principal of McGill
University and one of the foremost geologists in Canada, named the fossil Eozoon
canadense -- the Canadian dawn animal. In his presidential address to
the British Association for the Advancement of Science in 1864, Sir
Charles Lyell singled out this fossil as "one of the greatest
geological discoveries of his time". Charles Darwin, in the fourth
edition of Origin of Species in 1866, was relieved to be able to
cite the first fossil evidence that the succession of life on earth
proceeded from simple unicellular organisms to complex multicellular
animals and plants.
Dawson concluded that Eozoon was the shell of a foraminiferan, a
single-celled protistan complete with chambers and canal systems, but one
hundreds of times larger than any of the living forms which are all
microscopic. This view was almost immediately challenged by a pair of
Irish geologists who claimed that Eozoon was not organic, but a
metamorphic feature formed from the segregation of minerals in marble
through the influence of great heat and pressure. For the next ten years,
increasingly acrimonious debates on the nature of Eozoon appeared
in British and American journals. An exhaustive analysis by a German
professor of zoology, Karl Möbius in 1879 demonstrated that Eozoon displayed
not a single characteristic trait of foraminiferans. This settled the
matter for virtually all geologists and paleontologists, but not Dawson.
![A drawer of thin sections and polished specimens of Eozoon prepared for Sir William Logan by GSC geologist H.G. Vennor in 1867 (Photo by BDEC (c)) A drawer of thin sections and polished specimens of Eozoon prepared for Sir William Logan by GSC geologist H.G. Vennor in 1867 (Photo by BDEC (c))](/web/20061103040447im_/http://www.gsc.nrcan.gc.ca/paleochron/images/eozslides.jpg) A drawer of thin sections and polished specimens of Eozoon prepared for Sir William Logan by GSC geologist H.G. Vennor in 1867
(Photo by BDEC (c)) |
Compelling evidence came from an unlikely source in 1894 when two
geologists reported Eozoon in limestone blocks ejected from the
volcano Mount Vesuvius. Precambrian fossils shot out of an Italian volcano
was something few paleontologists were prepared to accept. Undeterred, but
virtually alone in the geological community, Sir William continued to
defend the organic nature of Eozoon. When he died in 1899 he was
working on yet another Eozoon paper.
![J. William Dawson, the Principal of McGill University and chief Eozoon promoter. J. William Dawson, the Principal of McGill University and chief Eozoon promoter.](/web/20061103040447im_/http://www.gsc.nrcan.gc.ca/paleochron/images/dawson2.jpg) J. William Dawson, the Principal of McGill University and chief Eozoon promoter. |
Further reading:
Hofmann, H.J. |
1971: |
Precambrian fossils, pseudofossils, and problematica in Canada. Geological Survey of Canada Bulletin 189. |
O'Brien, C.F. |
1970: |
Eozoon canadense "The dawn animal of Canada". Isis, vol. 61, p. 206-223. |
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