Olenellus are a genus of trilobites — extinct arthropods — common in but restricted to Early Cambrian rocks some 542 million to 521 million years old and thus a useful guide fossil for the Early Cambrian. Olenellus had a well-developed head, large and crescentic eyes, and a poorly developed, small tail. The fellow you see had a bit of his tail crushed as he turned to stone.
This specimen of Olenellus is from the Lower Cambrian Eager Formation of British Columbia and is typical of the group. He's from the Rifle Range outcrop near Cranbrook.
The site — which is literally on a Rifle Range where folks go to shoot at things — is just a shade older than the Burgess Shale. Burgess is Middle Cambrian and the deposits there have similar species to the ones found here are the Eager fauna is much less varied. Trilobites were amongst the earliest fossils with hard skeletons. While they are extinct today, they were the dominant life form at the beginning of the Cambrian and it is what we find as the primary fossil fauna in the Eager Formation. The Eager Formation has produced many beautifully preserved Wanneria, abundant Olellenus and a handful of rare and treasured Tuzoia. The shale matrix lends itself to amazing preservation. The specimens of Wanneria from here are large. Some are up to thirteen centimetres long and ten centimetres wide. You find a mixture of complete specimens and head impressions from years of perfectly preserved moults.