We’ve researched
fossil beds that included depictions of ‘soft parts’ before. One of the most
famous places for finding this type of fossil is the Burgess Shale found in the
Rocky Mountains of British Columbia, Canada. It is a large deposit of shale,
with at least 2 known outcrops, one near the town of Field in Yoho National
Park, and another 42 km south, in the Kootenay National Park. This shale bed is
508 million years old, so it contains some of the earliest known soft-part fossils.
Charles Walcott
discovered one of the Burgess Shale beds late in August 1909, just as the
season for such work in Canada was drawing to a close for the year. He returned
in 1910 with his wife and children to the area of Fossil Ridge. In fact, he returned
almost every year until 1924, when he was 74 years old. In that quarter
century, he had collected over 65,000 specimens.
He recognized
that a huge number of these organisms were unknown to science, and he continued
to describe them and attempted to categorise all of them into living taxa until
his death in 1927. Unfortunately, most scientists of the time saw the fossils
as mere curiosities.
In 1962, Alberto
Simonetta started a first-hand reinvestigation of these shale fossils and
realized that Walcott had barely scratched the surface, so to speak, because it
was clear the fossils did not fit into modern groups.
The Geological
Survey of Canada resumed excavations at the Walcott site, as well as
established another side 10 metres high on Fossil Ridge. Trilobite expert Harry
Blackmore Whittington and his helpers began a thorough reassessment of the
Burgess Shale, discovering that the fauna were much more diverse and unusual
than Walcott had recognized. Some had bizarre anatomy, including the Opabinia,
which had 5 eyes and a snout like a vacuum cleaner hose, and the Hallucigenia,
which was originally reconstructed upside down.
Collecting
Burgess Shale fossils became more difficult - politically - after the
mid-1970’s, when Parks Canada and UNESCO recognized the shale’s significance.
Other outcrops have been discovered, and yield new organisms continuously.
One thing I
reported previously was that soft tissues are fossilized in anoxic conditions,
meaning very little oxygen was present. However, mounting research has shown
that oxygen was continually present Burgess Shale was deposited. An alternative
hypothesis involves brine, rather than a lack of oxygen.
Of the organism
discovered in Burgess Shale, about 14% have hard parts that are more typically
fossilized. It is assumed that the organisms without hard parts are typical for
the time and location. Free-swimming creatures are relatively rare, while the
majority were bottom dwellers, either moving about in some way or attached to
the sea floor. About 2/3 of them fed on organic content of the muddy sea floor,
while the rest filtered fine particles from the water. Less than 10% were
predators or scavengers, but these were larger than the organisms they ate.
If I ever write
a story about people who find themselves on a planet during its Cambrian-type
age, I’ll have to remember to give my imagination free reign when dreaming up
local inhabitants! 5 eyes! A vacuum cleaner nose! Spines on the back that could
easily be mistaken for legs. Reality can be so much stranger than fiction!
No comments:
Post a Comment