Alan V. Morgan
Figure 1: A very large Isotelus trilobite crawls through soft sediments near the Ordovician shoreline of 445 million years ago. The location at that time was near the equator, today it is at Churchill, Manitoba. A specimen of Isotelus from this locality is currently the world's largest known trilobite.
Students and members of the public visiting the Earth Sciences museum (soon to be relocated in the new atrium in the Centre for Environmental Information Technology in Fall, 2003) have the opportunity of looking at casts of two very large trilobites. One of these has been in the museum since 1989, the second was purchased far more recently in 2002, and both originated from Churchill, Manitoba. So how is there a connection with Waterloo?
I suppose the connection started very indirectly on the 3rd of August 1973, when my wife Anne and I visited Diane and Bill Erickson at their home in Churchill. We were on our second Arctic beetle collecting trip through the Barren Lands of northern Manitoba and Keewatin (now Nunavut). Diane had been one of the first Introductory Geology Distance Education students at the University of Waterloo and had taken my course. It was a wonderful opportunity to stop in, chat and see the start of what was to be their Boreal Projects gardening operation. This early contact led to a third beetle collecting visit in July 1988 when, in a visit to their home, Bill revealed a very large trilobite (genus Isotelus) that had been found in the September of 1986 in the limestone beds on the foreshore of Hudson Bay below their home. The original discoverer was a visiting American professor. Bill had eventually retrieved the fossil by dint of a lot of crowbar, hammer and chisel work, managing to rescue it before the winter freeze-up threatened to destroy it. The specimen was eventually sent to the National Museum in Ottawa, but was ultimately accessed as Geological Survey of Canada Type Specimen 85292. The late Tom Bolton of the GSC prepared several casts that were sent to Diane and Bill Erickson and to the University of Waterloo.
Late
that
July
evening
Bill
and
I
wandered
along
the
foreshore
and
I
saw
a
huge
trilobite
track,
illuminated
by
the
light
of
a
swiftly
setting
sun.
I
was
able
to
take
one
photograph
before
poor
light
and
a
huge
cloud
of
mosquitoes
drove
us
back
from
the
Ordovician
(and
modern)
shoreline
to
the
safety
of
the
house.
We
discussed
the
setting
over
a
few
after-dinner
drinks.
The
Ordovician
sea
had
lapped
against
the
Precambrian
rocks
that
formed
the
small
rise
on
which
Diane
and
Bill's
home
is
located.
In
the
near-
and
off-shore
environments
several
very
large
trilobites
had
trundled
through
the
soft
lime-rich
sediments
leaving
a
series
of
corrugated
and
raised
trackways
.
Fortuitously
these
had
finally
been
exposed
that
year
on
the
modern
Churchill
shore
some
445
million
or
more
years
later.
Whatever
these
trilobites
were,
they
obviously
were
very
large
to
leave
tracks
this
size
behind.
The
original
specimen
found
two
years
earlier
was
big
,
but
the
exposed
tracks
were
far
larger,
dwarfing
the
usual
trace
trackways,
known
as
Cruziana,
that
one
normally
finds
in
the
Paleozoic
record.
There
was
little
doubt
that
some
very
large
trilobites
were
resident
in
the
area
at
the
time
these
sediments
were
laid
down,
but
unfortunately
there
was
no
time
left
for
a
search
of
the
shoreline
outcrops
and
I
left
the
following
day.
A decade later Graham Young and Bob Elias of the Manitoba Museum of Man and Nature commenced their 1998 field season. They were accompanied by Dave Rudkin (a trilobite specialist from the Royal Ontario Museum), Janis Klapecki (collections manager at the Manitoba Museum of Man and Nature), Ed Dobrzanski and David Wright (volunteers, MMMN), and Curtis Moffat (a student at the University of Manitoba).
On the third day of the fieldwork David Rudkin discovered part of an extremely large trilobite projecting from the thinly bedded limestones along the foreshore. Rising tide and poor light prevented the excavation of the overlying strata until the following day. However, the specimen was finally exposed and retrieved. It turned out to be substantially larger than the 1986 specimen, measuring 72 cm from the front of the headshield to the end of the fused tail segments. This is the largest known trilobite.
The genus Isotelus is confined to the Ordovician Period. The specimens from Churchill illustrate the common characteristics of the genus, with a large, smooth headshield, a number of articulating segments in the central part of the body (in the case of the large specimen eight can be clearly seen), and then a large smooth tail shield that consists of a number of fused segments. Trilobites are interesting animals, confined to the Paleozoic Era (the time of ancient life) and are distantly related to the lobsters, crabs and shrimps that we see in our oceans today. If you want to see the original specimen you will have to travel to the Manitoba Museum of Man and Nature in Winnipeg. However, our casts are a little closer for those of you who live in southwestern Ontario. I hope that when you visit the museum or future atrium at the University of Waterloo, you will remember that these ancient animals have a distinct, "Waterloo connection"!
Acknowledgments:
My sincere thanks to Diane and Bill Erickson (Boreal Projects), Manitoba, for jogging some very old memories! (Photographs are all copyright of the author).
Alan Morgan
Figure 4. Detail of the headshield (cephalon) of the largest Isotelus. To give some impression of the immense size of this specimen, a complete more normal-sized trilobite, (Pseudogytes sp.), also Ordovican in age from Collingwood, Ontario, has been superimposed. The lenscap is 5cm.