In prehistoric times there was a species of sea scorpion that grew to over seven feet in length. The Discovery Channel ran a documentary several years ago about that and other horrors of the late Cambrian era. Mosquitos the size of sparrows, dragonflies as big as a hawk, snakes that could crush a rhinoceros, armor-plated fish, large spiders everywhere, and much of the land was covered with swamps. Fascinating from a biologist's perspective but I don't think the world smelled very good at the time. 
