Fishwich
To a fossil-fish hunter, the geological map of southern Ellesmere
Island must look like a treasure map. At one time, the terrain was
part of the Gondwana super-continent and sat just north of the equator
in subtropical conditions where marine life flourished. Similar to today's
Mississippi River, some areas were run through by great rivers,
including the region where the fossilized transition between fish
and land animals known as Tiktaalik roseae was recently
uncovered. The sediment-laden waters of
the river deltas shrouded recently deceased critters in sand and silt, creating
the
ideal conditions for preservation. The sediment solidified into
rock and was overlain by more sediment, sandwiching the fossil-fish
between rock layers and burying the story of the Devonian landscape
deep within the Earth. Three-hundred million-odd years later, the
fossils' cover was blown when glaciers eroded deep fjords
in the Arctic coastline, revealing a storybook in the steep cliffs
where layers of sandstones and siltstones from the Devonian era – the
age of the fish – were exposed. Today, the sparse vegetation
of the Arctic environment means there are no forests to conceal
the mineralized gems and the isolation of the region means it's
not covered over with pavement. With minimal snow and rain in the
Arctic desert conditions, the rocks are protected from erosion by
the elements and even glaciers have worn away the rock to just the
right level to expose the treasures.
"There are great places to look for fossilized fish all over
Canada," says Steve Cumbaa, a fossil fish expert at the Canadian
Museum of Nature in Ottawa. "This part of Ellesmere was a
good spot to look [for the transitional fossil] because it has lots
of rocks of the right age exposed." The crew that found Tiktaalik
roseae was looking at rocks from the period just prior to when
fish grew legs and became amphibians, around 375 million years ago.
With the new discovery, Cumbaa expects there will be an increase
in interest in the area, because the fossils are almost perfectly
preserved in three dimensions. "The Arctic," he says, "has
preserved some great fossils."
— Jodi Di Menna
What the fish looked like 375 million years ago.
Credit: Kalliope Monoyios
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