The world's largest trilobite; the Waterloo Connection!

Saturday, March 1, 2003

Alan V. Morgan

A very large Isotelus trilobite crawls through soft sediments near the Ordovician shoreline

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

Detail of the headshield (cephalon) of the largest Isotelus

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.

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