![Geological Survey of Canada Geological Survey of Canada](/web/20061103020410im_/http://www.gsc.nrcan.gc.ca/esst_images/gsc_e.jpeg) Natural Resources Canada > Earth Sciences Sector > Geological Survey of Canada > Past lives: Chronicles of Canadian Paleontology
Past lives: Chronicles of Canadian Paleontology The Hallucigenia flip
Its name is suggestive of a past age of psychochemical
experimentation -- this fossil cautions against overweening confidence of
paleontologists who think they know how ancient animals lived
![Conway Morris' reconstruction of Hallucigenia Conway Morris' reconstruction of Hallucigenia](/web/20061103020410im_/http://www.gsc.nrcan.gc.ca/paleochron/images/conwaymorris.jpg) Conway Morris' reconstruction of Hallucigenia |
![Ramskold's photograph Ramskold's photograph](/web/20061103020410im_/http://www.gsc.nrcan.gc.ca/paleochron/images/halluci1.jpg) Ramskold's photograph |
![Ramskold's reconstruction Ramskold's reconstruction](/web/20061103020410im_/http://www.gsc.nrcan.gc.ca/paleochron/images/halluci3.gif) Ramskold's reconstruction |
Hallucigenia, one of the weirdest and rarest of the fossils from
Walcott's Quarry, has probably received more column space in the
scientific and popular press than any of the other Burgess Shale fossils.
In 1977, it was the subject of one of Simon Conway Morris' first papers
in his revision of the worm-like Burgess Shale fossils. He named this
small fossil Hallucigenia and reconstructed it as a cylindrical
trunk balanced on seven pairs of slender spikes with a single row of seven
tentacles along its back. The head is ill-defined and the anus is located
at the tip of a long flexible tail. Other paleontologists and biologists
immediately questioned the orientation of this reconstruction, pointing
out that no other animal has ever been known to walk on rigid spines. The
critics suggested that the tentacles made more sense as legs than did the
spikes, but Conway Morris effectively responded that a single row
was simply not plausible as legs. Because only a few specimens were
available for study, no more data was available and the discussion came to
an impasse. Conway Morris' interpretation of Hallucigenia
remained -- a bizarre animal without fossil or living relatives.
Then in the late 1980s, Lars Ramsköld, a Swedish dentist turned
paleontologist who was studying similar fossils from China, examined most
of the available museum specimens of Hallucigenia and proposed that
the spines were dorsal and protective in function. If these spines were
indeed located along the back of the animal, then the single row of
tentacles must be legs, and if they were legs, they must be paired. To
test his idea, Ramsköld asked the curator of the Walcott Collection in
Washington to let him prepare the type specimen of Hallucigenia sparsa
-- that is, to excavate into the shale around the fossil. This was an
audacious request. To put it in perspective, it is comparable to an art
historian asking the curator of Rembrandt paintings at the Riiksmuseum in
Amsterdam to allow him to flake away some of the paint of "The Night
Watch" to determine if Rembrandt had painted over the face of the
original captain of the company. To his surprise, Ramsköld got permission.
After he cautiously removed a few shale chips he discovered that a second
row of tentacles lay beneath the first row. By this simple and boldly
executed test, Ramsköld's scientific intuition had been confirmed.
Virtually all paleontologists now view Hallucigenia as a small
animal that walked on seven pairs of slender flexible legs and protected
by seven pairs of long thin spines along its back.
By flipping this animal and providing it with legs, Ramsköld also gave
it a home. The Onychophora, a phylum of caterpillar-looking animals now
living in tropical rainforests, was represented by a single Burgess Shale
fossil -- the stumpy-legged Aysheaia which had just been
redescribed by Harry Whittington. Aysheaia lacks dorsal spines. It
is now joined by Hallucigenia with its long slender spines. Other
Cambrian onychophorans with short spines provide a link between the two.
Further reading:
Conway Morris, S. |
1998: |
The Crucible of Creation: The Burgess Shale and the Rise of Animals. Oxford University Press, 242 p. |
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