Geoscience Reference
In-Depth Information
Needless to say, there is active scientific debate on this issue. Despite
their unusual forms, until the late 1980s, the Ediacaran Fauna were usu-
ally thought to represent ancient, primitive animal forms. Debate was
sparked when leading paleontologist Dolf Seilacher from Tubingen,
Germany, reinterpreted these fossils as something completely different.
He argued that, instead of animals, they were long extinct varieties of
living organisms, a result of failed lineages with no successors. In Dolf's
view, they had nothing to do with animals at all. Dolf has a special eye
for how animals, long extinct, dug, crawled, and fed in the muds of the
ancient world, and what Dolf said was therefore taken very seriously.
Seriously, yes, but not all, and perhaps not even most, have been con-
vinced by his reinterpretations.
Indeed, recent thinking has returned to animal interpretations for
most of these organisms, albeit not animal groups that are necessarily
represented today. For example, let's take a weird one. An Ediacaran
faunal type called
Charniodiscus
is found on the Avalon Peninsula among
the very rocks that Simon and I went to explore (
ig. 10.2)
. In life, it was
10 or more centimeters in length and was firmly rooted on the seafloor.
It was constructed of a holdfast and stem connected to a frond that
gently swayed in the ocean currents, presumably collecting small parti-
cles or dissolved organic material from the water. The water was quite
deep where these organisms lived, so they lived well out of reach of any
sunlight. In summary, these organisms were large, they exhibited com-
plex morphology constructed from many different cell types, as animals
do, and they fed like animals. According to Andy Knoll, it is difficult
to imagine how such organisms could have grown without an epithelial
covering of cells,
2
another attribute of animals. Finally, because of the
deep, light-free water depths where they grew, any plant or algal affilia-
tion is out of the question. So there you have it, many animal-like attri-
butes, but not much like any animal you or I might know. And so it
goes with many of the Ediacaran Fauna.
3
So, what brought Simon and me to the Avalon Peninsula? As it turns
out, rocks on the Avalon Peninsula house the oldest known representa-
tives of the Ediacaran Fauna. These so-called rangeomorphs (
ig. 10.2
)
date back to 575 million ago and appear relatively soon after the end of
the Gaskiers glaciation some 580 million years ago.
4
Was this a coinci-
dence? Could we identify any geochemical triggers that might correlate
