TRILOBITES are a subphylum belonging to the ARTHROPODS. An exception to all of the fossils being described, no trilobite fossils were seen from Magwood Park to the Bloor Street West bridge on the east side of the Humber River. A complete fossil has three segments, head-thorax-tail, and three lobes formed by two long grooves running from the head to the tail of the animal. They reached a maximum of over 70 mm, but many fossils are less than a tenth that size. Trilobites became extinct about 185 million years ago at the end of the Permian Period, after attaining their greatest development from the early Cambrian to the late Ordovician times.
Samples photographed for the next page were collected at Collingwood and the Scarborough Bluffs. They are typical of the incomplete trilobites associated with shale in Southern Ontario. A specimen of approximately 40 cm in length was discovered in a limestone quarry which once existed at point "X" on the accompanying map (some time before the construction of the Don Valley Parkway). I saw it displayed during the mid-1960's at a science fair held at the Toronto Education Centre 155 College Street; a class of students had assisted in cleaning away some of the surrounding limestone matrix so that an almost complete fossil of the animal was revealed. The nearest quarry to my collection sites was once located where Smythe Park now stands (bounded by Jane Street and Scarlett Road and half-way between Eglinton Avenue and St. Clair Avenue where Black Creek, a tributary of the Humber River, passes through it); to the best of my knowledge, no-one found any trilobite fossils or even thought of looking for them at that location.
Other Arthropods include the scorpions, spiders, ticks, mites, horseshoe crabs and extinct eurypterids of the Chelicerata Subphylum. The Subphylum Crustacea is comprised of ostracods, barnacles, lobsters, crabs, shrimps, sow bugs, and crayfish. A very large subphylum of insects are the most numerous representatives of the Arthropod Group.