Tuesday, November 16, 2010  
   Volume 80 - Issue 46 Website:www.passherald.ca   email: passherald@shaw.ca   $1.00   
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Looking Back - John Kinnear

I can’t believe it. I paid $100 to a fossil dealer in Jaffray for a 40 mm long specimen of a trilobite. What it the world would possess me to want to own this stone bug from the past?
I suspect my fascination with relics from the prehistoric led me to think that I needed to own a trilobite. And not just any old trilobite. This one comes from a place I first learned about when I researched the history of the Bull River, east of Cranbrook some years back. The Bull was at one time home to a CPR logging operation that had no less than 21 logging camps on it and in its heyday floated over a million railway ties a year down through the Bull River canyon. Part way up the Bull River a creek by the name of Tanglefoot ties into this remarkable river. In a small tributary of Tanglefoot in the late 1950’s a student of Stanford University working on his thesis discovered what is now known as the Tanglefoot Creek fossil locality.
This locality has yielded an astonishingly abundant and rich Upper Cambrian trilobite fauna. More than 3,600 specimens of largely complete trilobites record the presence of more than thirteen species. The trilobites of the Tanglefoot Creek locality are preserved in nodules composed of vertical encrustations of calcite crystals. Doesn’t that just make you want to head up that creek and find one!
A little internet research revealed a picture that identifies my prize possession as none other than “Wujiajiania sutherlandi”, one of the 13 different types of trilobites that are found at Tanglefoot. Sutherlandi, like most of the 17,000 known species of this remarkable little creatures, flourished throughout the lower Palaeozoic era. Trilobites first appeared about 526 million years ago and disappeared in a mass extinction about 250 million years ago. Good grief ! These critters were around for 276 million years. Imagine what evolutionary processes took place in that time. It is no wonder there are 17,000 different species. Try an internet search on trilobites and you will be overwhelmed at their diversity.
Trilobite means “three lobes” and these extinct marine arthropods had many life styles. Some moved over the sea-bed as predators, scavengers or filter feeders and some swam, feeding on plankton. New species of trilobites are unearthed and described every year. This makes trilobites the single most diverse class of extinct organisms, and within their body plan there was a great deal of diversity of size and form. The smallest known trilobite species is under a millimeter long, while the largest include species from 30 to over 70 cm in length (roughly a foot to over two feet long!).
Whatever their size, all trilobite fossils have a similar body plan, being made up of three main body parts: a cephalon (head), a segmented thorax, and a pygidium (tail piece).

 
However, the name "trilobite" is not in reference to those three body parts I mentioned but to the fact that all trilobites bear a long central axial lobe, flanked on each side by right and left pleural lobes (pleura = side, rib). These three lobes that run from the cephalon to the pygidium are what give trilobites their name, and are common to all trilobites despite their great diversity of size and form.
Work n Play
Greenhills Mine Rotary Dump
John Kinnear Photo
One usually only finds a preserved fossilized exoskeleton of the trilobite. They were moulters and their exoskeleton used to split between the head and thorax which is why most fossils are missing one or the other. Just like crabs and lobsters trilobites grew physically between the moult stage and the hardening of the new exoskeleton.
Trilobites developed one of the first sophisticated visual systems in the animal kingdom and had a pair of compound eyes. They were very sensitive to motion, like an insects are, and it is suggested that their closely spaced but separate eyes provided stereoscopic vision. Our eyes can change shape to focus but a trilobite’s were rigid, crystalline lenses. So they had two lens layers of different refractive indices which corrected for focusing problems. It probably gave them a remarkable depth of field with minimal distortion.
It is hard to imagine million of trilobites cruising in every ancient sea and body of water on earth back then. What a sight that must have been. When you get a close look at some of the wierdly diverse shapes they had you might be tempted to exclaim that: “In no way in hell would I have swum in any waters anywhere back then”
Looking for fossils comes naturally to those of us with Scottish ancestry. We are always walking around with our heads down looking for lost change. When I first moved back here I remembered my father talking to me about small black ammonite fossils in a bed just east of the municipal office in Coleman. I went walking one day with my wife and as I mentioned to her about the ammonites Dad had found she said:” You mean like that” and promptly pointed out a remnant of one in the ditch alongside the road that runs down to Blairmore Road. Go figure. And she’s not even Scottish.
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   Volume 80 - Issue 46 Website:www.passherald.ca   email: passherald@shaw.ca   $1.00   
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