Sidneyia's an extinct arthropod known from fossils found in the Cambrian-age Burgess Shale formation of British Columbia. General description Sidneyia ranged from 2 to 5 inches in length and's one of the largest arthropods found at the site. It's thought to have been a benthic carnivore that walked along the sea floor in search of hard-shelled prey. Gut contents have revealed that Sidneyia fed on hyolithids (molluscs) and other small crustaceans and trilobites. Sidneyia was discovered in 1910 d… (More on Sidneyia)