Some
510 million years ago during a shadowy, Cambrian time, what
we now call Wisconsin was way south, some 10 degrees below the
equator. The diversity of life then was still expanding, with
new forms radiating, with the new forms themselves exerting
new types of selective pressures to further drive evolutionary
processes. The Krukowski quarry of Central Wisconsin near Mosinee
(outcrops of the Mount Simon and Wonewoc Sandstone, Elk Mound
Group), was then beachfront property, with the burgeoning life
forms of the pelagic environment lying just offshore. Hagadorn
posits an ancient environment comprising inter-fingering shallow
marine, fluvial and eolian facies.
Paleobiology
has many mysteries, and of these, the early venturing of life
onto land is one of the most mysterious. Many clues to these
mysteries are buried in the Krakowski quarry. Recently, many
Ichnofossils, as well as body fossil impressions, are being
exposed in its various horizons and studied by a number of paleontologists.
No
shelly animals are found in the Krukowski quarry, only trackways
(Ichnofossils) and body impressions of Jellyfish
and arthropods. Apparently,
hard body parts such as trilobite exoskeletons never underwent
mineralization, but were instead dissolved back into the sea.
Besides a few mysterious trackways that can not be named, one
finds Diplichnites, Protichnites
and Climactichnites, and most
recently a putative trackmaker arthropod from the enigmatic
Euthycarcinoid or Aglaspid
groups. These fossils are only now being interpreted paleontologists.
But ichnofossils in many ways are more revealing than body preservation,
because they can give hints about animal behavior and interaction
in the ecosystem, and in the case of the Krokowski quarry fossils,
possibly the first footprints on land in the fossil record.
Thus, hopefully, the result will be some shedding of more light
on this shadowy period of geological history.
The
ichnofossils of the Mount Elk Group possibly encode an early
step toward colonization of the land, an evolutionary trend
that would gain tremendous momentum during the Paleozoic. It
is likely that these earliest of terrestrial footprints were
made by animals that could leave the water to the intertidal
areas for brief periods. In so doing, they had a brief reprieve
from marine predators while grazing on abundant microbial biofilms.
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