Trilobite, meaning "three lobes", occupied different levels of the food web including predator, scavenger, and prey. Trilobites molted their exoskeleton much like lobsters of today and are one of the first animals known to have the sense of vision. Trilobites vary widely in size and shape. They can be so small that they need to be viewed with a microscope. They can also be quite large. Isotelus rex could grow up to two feet long. They are typically found by splitting sheets of shale and hard limestone deposits.