My Trilobite Fossils: 1 Man`s Treasure

My Trilobite Fossils: One Man`s Treasure Is Another's Trash

g reached the watershed age of 70, you may (or just might if you are lucky) Shale from Craigleith area, Southwestern Ontario, showing Trilobite fossil (tail section only) of Pseudogygites latimarginatus. (Photo by FC Yue)  

expect wave upon wave of purges sweeping through your already down-sized home. Your "Boss" -- the spouse, usually the wife -- wants to forcibly de-clutter, time and again, the "unwanted and useless accumulated items" you spent some time and efforts in collecting. Any unfamiliar objects taking up valuable spaces in the home are, to her anyway, just garbage that must be thrown out and buried in a landfill.

One of the unfortunate victims here is the piles of "rocks" I dug up with some friends some twenty years ago from the Craigleith area, about 10 km west-northwest of Collingwood, Ontario, on the southern shore of Georgian Bay in Canada. (See the photo above and the two photos below.)(Collingwood, a popular resort town, is located just 148 km NW of Toronto.) There, the exposed bedrock consists of slightly-tilted layers (strata) of limestone and shale deposited around 450 million years ago in the then existing warm, shallow, subtropical sea.

 You can see the cut-out layers of shale in this sample inside a lump of sedimentary rock (formed by compaction, under immense water pressure over the long years, of fine practicles of silt, sand, clay or limy oozes at the bottom of a body of water).

​I was rather sad at the prospect of having to throw out my collection of trilobite fossils. Luckily, the property manager at my condo apartment was quite sympathetic; she was glad to take over the "organic rocks" and give them a home.

 Most of the material in this article is based on the Ontario Ministry of Natural Resources guidebook "GEOLOGY AND FOSSILS -- Craigleith Area Ontario" by Harish M. Verma. (OMNR-OGS 1979 )

 Latex cast of young individual of trilobite Pseudogygites latimarginatus (by Dr. Rolf Ludvigsen, Dept. of Geology, University of Toronto.) (See page ii of guidebook) 

Trilobites found in the Craigleith area. Left: Triarthrus eatnoi (ROM 34505)  Right: Triarthrus eatoni, Restoration showing appendages. (Page 26, ibid)

 A rare slab of shale (shown in part) from Craigleith showing a cluster of Pseudogygites latimarginatus (specimen coutesy Royal Ontario Museum). (Page 18, ibid) 

  A rare slab of shale (shown in part) from Craigleith showing a cluster of Triarthrus eatoni (specimen courtesy Royal Ontario Museum). (Page 20, ibid)

 Geological Time Chart (left) showing the position and geological ages of the different rock formations of southwestern Ontario. (Page 15, ibid)

There were no land animals and plants during the Ordovician Period (500-440 million years ago). In the seas, however, life was dominated by invertebrates (animals without backbones) similar to the present day corals, clams, lobsters, snails, sea lilies and squids.

Cephalapods -- straight, conical molluscs (or hard shelled animals) -- are the largest fossil in the Craigleith area. One of the Craigleith cephalapods, Endocerus portiforne,  measuring about 5 m in length and 25 cm in diameter, was the largest sea creature known in Ontario's early Paleozoic world!

What are tribobites?

Trilobites were an extinct group of tiny sea-bottom dwelling animals in the warm seas. They were the dominant form of life during the Cambrian and Ordovician Periods. Of all known Cambrian fossils, 60% are trilobites.

As the name suggests, the trilobite's body consists of three part: the head shield (cephalon), the segmented body (thorax) and the tail shield (pygidium). The eyes vary in size, shape and location on the head. During growth, the animal shed its external skeleton by moulting periodically. Broken into the three segments, the moults litter the sea floor. Trilobites were both scavengers and predators. They fed on organic debris, crawling or swimming close to the sea floor.

Of the ten different species of trilobites found in the Craigleith area, the two extremely abundant are Pseudogygites latimarginatus and the smaller Triarthrus eatoni (both shown in the photos above).​

Fossils are rather hard to come by since only a small fraction of any animal population in a particular area ever gets fossilized. Then an even smaller number of the remaining fossils may become available for observation or collection. Many centuries must also elapsed before the mineral of the hard parts of the dead animal is replaced by a more stable mineral. Therefore, fossils are great survivors, before formation they survive by not being eaten by predators, they then survive being uplifted by geological forces to the surface by not breaking up in tiny fragments, they survive by not being eroded by the actions of wind and water, they finally survive by being found and collected by knowledgeable and appreciative humans. (Well, my wife is probably not one of them.)

Like the trilobites, from star dust we come, back to star dust we will return... Unlike the trilobites,we human beings are still in the on-going process of evolution in the face of challenging changing global environments.

The day after tomorrow humans will be living on Mars! As Stephen Hawkins has pointed out -- interplanetary travel and colonisation would ensure the continuation of the human species Homo sapiens.